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HomeMy WebLinkAbout2024/02/20 - Stormwater Management Report - - STORMWATER MANAGEMENT REPORT Corner Development 18 1 Afft Ic PrIUj %:::'1i t at Mcrrimailcic College pf(KK%N) IIIIIIIIIIIIIII NNNnnnl¢ A� �,�ry��m1Y )' 1 imjjjjjj�I 6wiz,,I�������uq� ,) <e .......... el""It' PREPARED FOR Greystar Development East, LLC 1 Federal Street, Suite 1804 Boston, MA 02210 Merrimack College 315 Turnpike Street North Andover, MA 01845 978.837.5000 PREPARED BY q;Mvh�b 101 Walnut Street PO Box 9151 Watertown, MA 02471 August 1 7, 2,02,3 Septei,rilo&r-' 15, 2,0 2,3�.............� [��ev I f,e b a iiry 2,0, 2,024............. ItRev2, Table of Contents Checklist for Stormwater Report...................................................................................................4 StormwaterReport Narrative.........................................................................................................5 ProjectDescription............................................................................................................................................................5 SiteDescription...................................................................................................................................................................5 ExistingDrainage Conditions........................................................................................................................................6 ProposedDrainage Conditions....................................................................................................................................7 RegulatoryCompliance.................................................................................................................13 Massachusetts Department of Environmental Protection (DEP)—Stormwater Management Standards............................................................................................................................................................................13 Standard 1: No New Untreated Discharges or Erosion to Wetlands............................................13 Standard 2: Peak Rate Attenuation............................................................................................................13 Standard3: Stormwater Recharge.............................................................................................................14 Standard4:Water Quality.............................................................................................................................15 Standard 5: Land Uses with Higher Potential Pollutant Loads (LUHPPLs).................................15 Standard6: Critical Areas..............................................................................................................................15 Standard 7: Redevelopments and Other Projects Subject to the Standards only to the MaximumExtent Practicable........................................................................................................................15 Standard 8: Construction Period Pollution Prevention and Erosion and Sedimentation Controls................................................................................................................................................................15 Standard 9: Operation and Maintenance Plan......................................................................................15 Standard 10: Prohibition of Illicit Discharges........................................................................................16 Appendices Appendix A: Standard 1 Computations and Supporting Information................................................A-1 Appendix B: Standard 2 Computations and Supporting Information................................................B-1 i Table of Contents AppendixC: Standard 3 Computations and Supporting Documentation........................................[-1 AppendixC, Standard 4 Computations and Supporting Information -----..C-1 AppendixE Standard 7 Supporting Information........................................................................................E-1 AppendixF: Standard 8 Supporting Information........................................................................................F-1 n Table ofContents List of Tables Table No. Description Page .......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... Table 1 Existing Conditions Hydrologic Data..........................................................................................6 Table 2 Proposed Conditions Hydrologic Data......................................................................................7 Table 4.1 Peak Discharge Rates (cfs*)..........................................................................................................14 Table 4.2 Stormwater Volume Analysis (cf)...............................................................................................14 Table 5 Summary of Recharge Calculations..........................................................................................14 iii Table of Contents Checklist for Stormwater Report 4 Checklist for 5mrmwater Report Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checkl'ist Stormwater Report A. Introduction Important:When A Stormwater Report must be submitted with the Notice of Intent permit application to document filling out forms compliance with the Stormwater Management Standards. The following checklist is NOT a substitute for on the computer, theStormwater Report ormwaer e (which sou provide more substantive and detailed information use only the tabp ( p ) but is offered key to move your here as a tool to help the applicant organize their Stormwater Management documentation for their cursor-do not Report and for the reviewer to assess this information in a consistent format. As noted in the Checklist, use the return the Stormwater Report must contain the engineering computations and supporting information set forth in key. Volume 3 of the Massachusetts Stormwater Handbook. The Stormwater Report must be prepared and certified by a Registered Professional Engineer(RPE) licensed in the Commonwealth. The Stormwater Report must include: • The Stormwater Checklist completed and stamped by a Registered Professional Engineer(see page 2)that certifies that the Stormwater Report contains all required submittals.' This Checklist is to be used as the cover for the completed Stormwater Report. • Applicant/Project Name Project Address • Name of Firm and Registered Professional Engineer that prepared the Report • Long-Term Pollution Prevention Plan required by Standards 4-6 • Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan required by Standard 82 • Operation and Maintenance Plan required by Standard 9 In addition to all plans and supporting information, the Stormwater Report must include a brief narrative describing stormwater management practices, including environmentally sensitive site design and LID techniques, along with a diagram depicting runoff through the proposed BMP treatment train. Plans are required to show existing and proposed conditions, identify all wetland resource areas, NRCS soil types, critical areas, Land Uses with Higher Potential Pollutant Loads (LUHPPL), and any areas on the site where infiltration rate is greater than 2.4 inches per hour. The Plans shall identify the drainage areas for both existing and proposed conditions at a scale that enables verification of supporting calculations. As noted in the Checklist, the Stormwater Management Report shall document compliance with each of the Stormwater Management Standards as provided in the Massachusetts Stormwater Handbook. The soils evaluation and calculations shall be done using the methodologies set forth in Volume 3 of the Massachusetts Stormwater Handbook. To ensure that the Stormwater Report is complete, applicants are required to fill in the Stormwater Report Checklist by checking the box to indicate that the specified information has been included in the Stormwater Report. If any of the information specified in the checklist has not been submitted, the applicant must provide an explanation. The completed Stormwater Report Checklist and Certification must be submitted with the Stormwater Report. .................................................................................................................................................................................................................................................... 1 The Stormwater Report may also include the Illicit Discharge Compliance Statement required by Standard 10. If not included in the Stormwater Report,the Illicit Discharge Compliance Statement must be submitted prior to the discharge of stormwater runoff to the post-construction best management practices. 2 For some complex projects, it may not be possible to include the Construction Period Erosion and Sedimentation Control Plan in the Stormwater Report. In that event,the issuing authority has the discretion to issue an Order of Conditions that approves the project and includes a condition requiring the proponent to submit the Construction Period Erosion and Sedimentation Control Plan before commencing any land disturbance activity on the site. swcheck.doc•04/01/08 Stormwater Report Checklist-Page 1 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report B. Stormwater Checklist and Certification The following checklist is intended to serve as a guide for applicants as to the elements that ordinarily need to be addressed in a complete Stormwater Report. The checklist is also intended to provide conservation commissions and other reviewing authorities with a summary of the components necessary for a comprehensive Stormwater Report that addresses the ten Stormwater Standards. Note: Because stormwater requirements vary from project to project, it is possible that a complete Stormwater Report may not include information on some of the subjects specified in the Checklist. If it is determined that a specific item does not apply to the project under review, please note that the item is not applicable (N.A.) and provide the reasons for that determination. A complete checklist must include the Certification set forth below signed by the Registered Professional Engineer who prepared the Stormwater Report. Registered Professional Engineer's Certification I have reviewed the Stormwater Report, including the soil evaluation, computations, Long-term Pollution Prevention Plan, the Construction Period Erosion and Sedimentation Control Plan (if included), the Long- term Post-Construction Operation and Maintenance Plan, the Illicit Discharge Compliance Statement(if included) and the plans showing the stormwater management system, and have determined that they have been prepared in accordance with the requirements of the Stormwater Management Standards as further elaborated by the Massachusetts Stormwater Handbook. I have also determined that the information presented in the Stormwater Checklist is accurate and that the information presented in the Stormwater Report accurately reflects conditions at the site as of the date of this permit application. Registered Professional Engineer Block and Signature Signature and Date Checklist Project Type: Is the application for new development, redevelopment, or a mix of new and redevelopment? E New development ❑ Redevelopment ❑ Mix of New Development and Redevelopment swcheck.doc•04/01/08 Stormwater Report Checklist•Page 2 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) LID Measures: Stormwater Standards require LID measures to be considered. Document what environmentally sensitive design and LID Techniques were considered during the planning and design of the project: M No disturbance to any Wetland Resource Areas ❑ Site Design Practices (e.g. clustered development, reduced frontage setbacks) ❑ Reduced Impervious Area (Redevelopment Only) ❑ Minimizing disturbance to existing trees and shrubs ❑ LID Site Design Credit Requested: ❑ Credit 1 ❑ Credit 2 ❑ Credit 3 ❑ Use of"country drainage"versus curb and gutter conveyance and pipe ❑ Bioretention Cells (includes Rain Gardens) ❑ Constructed Stormwater Wetlands (includes Gravel Wetlands designs) ❑ Treebox Filter ❑ Water Quality Swale ❑ Grass Channel ❑ Green Roof ❑ Other(describe): Standard 1: No New Untreated Discharges � No new untreated discharges � Outlets have been designed so there is no erosion or scour to wetlands and waters of the Commonwealth � Supporting calculations specified in Volume 3 of the Massachusetts Stormwater Handbook included. swcheck.doc•04/01/08 Stormwater Report Checklist•Page 3 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checkl'ist Stormwater Report Checklist (continued) Standard 2: Peak Rate Attenuation ❑ Standard 2 waiver requested because the project is located in land subject to coastal storm flowage and stormwater discharge is to a wetland subject to coastal flooding. ❑ Evaluation provided to determine whether off-site flooding increases during the 100-year 24-hour storm. ® Calculations provided to show that post-development peak discharge rates do not exceed pre- development rates for the 2-year and 10-year 24-hour storms. If evaluation shows that off-site flooding increases during the 100-year 24-hour storm, calculations are also provided to show that post-development peak discharge rates do not exceed pre-development rates for the 100-year 24- hour storm. Standard 3: Recharge ® Soil Analysis provided. ® Required Recharge Volume calculation provided. ❑ Required Recharge volume reduced through use of the LID site Design Credits. ® Sizing the infiltration, BMPs is based on the following method: Check the method used. E Static ❑ Simple Dynamic ❑ Dynamic Field' ❑ Runoff from all impervious areas at the site discharging to the infiltration BMP. ® Runoff from all impervious areas at the site is not discharging to the infiltration BMP and calculations are provided showing that the drainage area contributing runoff to the infiltration BMPs is sufficient to generate the required recharge volume. ® Recharge BMPs have been sized to infiltrate the Required Recharge Volume. ❑ Recharge BMPs have been sized to infiltrate the Required Recharge Volume only to the maximum extent practicable for the following reason: ❑ Site is comprised solely of C and D soils and/or bedrock at the land surface ❑ M.G.L. c. 21 E sites pursuant to 310 CMR 40.0000 ❑ Solid Waste Landfill pursuant to 310 CMR 19.000 ❑ Project is otherwise subject to Stormwater Management Standards only to the maximum extent practicable. ® Calculations showing that the infiltration BMPs will drain in 72 hours are provided. ❑ Property includes a M.G.L. c. 21 E site or a solid waste landfill and a mounding analysis is included. .................................................................................................................................................................................................................................................... 1 80%TSS removal is required prior to discharge to infiltration BMP if Dynamic Field method is used. swcheck.doc•04/01/08 Stormwater Report Checklist-Page 4 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checkl'ist Stormwater Report Checklist (continued) Standard 3: Recharge (continued) ❑ The infiltration BMP is used to attenuate peak flows during storms greater than or equal to the 10- year 24-hour storm and separation to seasonal high groundwater is less than 4 feet and a mounding analysis is provided. ❑ Documentation is provided showing that infiltration BMPs do not adversely impact nearby wetland resource areas. Standard 4: Water Quality The Long-Term Pollution Prevention Plan typically includes the following: • Good housekeeping practices; • Provisions for storing materials and waste products inside or under cover; • Vehicle washing controls; • Requirements for routine inspections and maintenance of stormwater BMPs; • Spill prevention and response plans; • Provisions for maintenance of lawns, gardens, and other landscaped areas; Requirements for storage and use of fertilizers, herbicides, and pesticides; • Pet waste management provisions; • Provisions for operation and management of septic systems; • Provisions for solid waste management; • Snow disposal and plowing plans relative to Wetland Resource Areas; • Winter Road Salt and/or Sand Use and Storage restrictions; • Street sweeping schedules; • Provisions for prevention of illicit discharges to the stormwater management system; • Documentation that Stormwater BMPs are designed to provide for shutdown and containment in the event of a spill or discharges to or near critical areas or from LUHPPL; • Training for staff or personnel involved with implementing Long-Term Pollution Prevention Plan; • List of Emergency contacts for implementing Long-Term Pollution Prevention Plan. ® A Long-Term Pollution Prevention Plan is attached to Stormwater Report and is included as an attachment to the Wetlands Notice of Intent. ❑ Treatment BMPs subject to the 44% TSS removal pretreatment requirement and the one inch rule for calculating the water quality volume are included, and discharge: ❑ is within the Zone II or Interim Wellhead Protection Area ❑ is near or to other critical areas ❑ is within soils with a rapid infiltration rate (greater than 2.4 inches per hour) ❑ involves runoff from land uses with higher potential pollutant loads. ❑ The Required Water Quality Volume is reduced through use of the LID site Design Credits. ® Calculations documenting that the treatment train meets the 80% TSS removal requirement and, if applicable, the 44% TSS removal pretreatment requirement, are provided. swcheck.doc•04/01/08 Stormwater Report Checklist-Page 5 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) Standard 4: Water Quality(continued) � The BMP is sized (and calculations provided) based on: M The '/2"or 1° Water Quality Volume or ❑ The equivalent flow rate associated with the Water Quality Volume and documentation is provided showing that the BMP treats the required water quality volume. � The applicant proposes to use proprietary BMPs, and documentation supporting use of proprietary BMP and proposed TSS removal rate is provided. This documentation may be in the form of the propriety BMP checklist found in Volume 2, Chapter 4 of the Massachusetts Stormwater Handbook and submitting copies of the TARP Report, STEP Report, and/or other third party studies verifying performance of the proprietary BMPs. ❑ A TMDL exists that indicates a need to reduce pollutants other than TSS and documentation showing that the BMPs selected are consistent with the TMDL is provided. Standard 5: Land Uses With Higher Potential Pollutant Loads (LUHPPLs) ❑ The NPDES Multi-Sector General Permit covers the land use and the Stormwater Pollution Prevention Plan (SWPPP) has been included with the Stormwater Report. � The NPDES Multi-Sector General Permit covers the land use and the SWPPP will be submitted prior to the discharge of stormwater to the post-construction stormwater BMPs. ❑ The NPDES Multi-Sector General Permit does not cover the land use. ❑ LUHPPLs are located at the site and industry specific source control and pollution prevention measures have been proposed to reduce or eliminate the exposure of LUHPPLs to rain, snow, snow melt and runoff, and been included in the long term Pollution Prevention Plan. ❑ All exposure has been eliminated. ❑ All exposure has not been eliminated and all BMPs selected are on MassDEP LUHPPL list. ❑ The LUHPPL has the potential to generate runoff with moderate to higher concentrations of oil and grease (e.g. all parking lots with >1000 vehicle trips per day)and the treatment train includes an oil grit separator, a filtering bioretention area, a sand filter or equivalent. Standard 6: Critical Areas ❑ The discharge is near or to a critical area and the treatment train includes only BMPs that MassDEP has approved for stormwater discharges to or near that particular class of critical area. ❑ Critical areas and BMPs are identified in the Stormwater Report. swcheck.doc•04/01/08 Stormwater Report Checklist•Page 6 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) Standard 7: Redevelopments and Other Projects Subject to the Standards only to the maximum extent practicable ❑ The project is subject to the Stormwater Management Standards only to the maximum Extent Practicable as a: ❑ Limited Project ❑ Small Residential Projects: 5-9 single family houses or 5-9 units in amulti-family development provided there is no discharge that may potentially affect a critical area. ❑ Small Residential Projects: 2-4 single family houses or 2-4 units in amulti-family development with a discharge to a critical area ❑ Marina and/or boatyard provided the hull painting, service and maintenance areas are protected from exposure to rain, snow, snow melt and runoff ❑ Bike Path and/or Foot Path ❑ Redevelopment Project ❑ Redevelopment portion of mix of new and redevelopment. ❑ Certain standards are not fully met(Standard No. 1, 8, 9, and 10 must always be fully met)and an explanation of why these standards are not met is contained in the Stormwater Report. ❑ The project involves redevelopment and a description of all measures that have been taken to improve existing conditions is provided in the Stormwater Report. The redevelopment checklist found in Volume 2 Chapter 3 of the Massachusetts Stormwater Handbook may be used to document that the proposed stormwater management system (a)complies with Standards 2, 3 and the pretreatment and structural BMP requirements of Standards 4-6 to the maximum extent practicable and (b) improves existing conditions. Standard 8: Construction Period Pollution Prevention and Erosion and Sedimentation Control A Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan must include the following information: • Narrative; • Construction Period Operation and Maintenance Plan; • Names of Persons or Entity Responsible for Plan Compliance; • Construction Period Pollution Prevention Measures; • Erosion and Sedimentation Control Plan Drawings; • Detail drawings and specifications for erosion control BMPs, including sizing calculations; • Vegetation Planning; • Site Development Plan; • Construction Sequencing Plan; • Sequencing of Erosion and Sedimentation Controls; • Operation and Maintenance of Erosion and Sedimentation Controls; • Inspection Schedule; • Maintenance Schedule; • Inspection and Maintenance Log Form. ❑ A Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan containing the information set forth above has been included in the Stormwater Report. swcheck.doc•04/01/08 Stormwater Report Checklist•Page 7 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) Standard 8: Construction Period Pollution Prevention and Erosion and Sedimentation Control (continued) ❑ The project is highly complex and information is included in the Stormwater Report that explains why it is not possible to submit the Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan with the application. A Construction Period Pollution Prevention and Erosion and Sedimentation Control has not been included in the Stormwater Report but will be submitted before land disturbance begins. ❑ The project is not covered by a NPDES Construction General Permit. ❑ The project is covered by a NPDES Construction General Permit and a copy of the SWPPP is in the Stormwater Report. � The project is covered by a NPDES Construction General Permit but no SWPPP been submitted. The SWPPP will be submitted BEFORE land disturbance begins. Standard 9: Operation and Maintenance Plan � The Post Construction Operation and Maintenance Plan is included in the Stormwater Report and includes the following information: � Name of the stormwater management system owners; � Party responsible for operation and maintenance; � Schedule for implementation of routine and non-routine maintenance tasks; � Plan showing the location of all stormwater BMPs maintenance access areas; ❑ Description and delineation of public safety features; ❑ Estimated operation and maintenance budget; and E Operation and Maintenance Log Form. ❑ The responsible party is not the owner of the parcel where the BMP is located and the Stormwater Report includes the following submissions: El A copy of the legal instrument(deed, homeowner's association, utility trust or other legal entity) that establishes the terms of and legal responsibility for the operation and maintenance of the project site stormwater BMPs; ❑ A plan and easement deed that allows site access for the legal entity to operate and maintain BMP functions. Standard 10: Prohibition of Illicit Discharges � The Long-Term Pollution Prevention Plan includes measures to prevent illicit discharges; � An Illicit Discharge Compliance Statement is attached; ❑ NO Illicit Discharge Compliance Statement is attached but will be submitted prior to the discharge of any stormwater to post-construction BMPs. swcheck.doc•04/01/08 Stormwater Report Checklist•Page 8 of 8 I Stormwater Report Narrat I ive This Stormwater Report has been prepared to demonstrate compliance with the Massachusetts Stormwater Management Standards in accordance with the Massachusetts Wetlands Protection Act Regulations (310 CMR 10.00) and Water Quality Certification Regulations (314 CMR 9.00). This report also demonstrates compliance with the North Andover's Chapter 250 Stormwater Management and Erosion Control regulations for stormwater design and mitigation. �00 �� qiiljeclllt The Applicant, Merrimack College (owner) and Greystar Development East, LLC (developer), are proposing to construct two (2) buildings with student residential and academic space (the Project). The Project will entail the construction of one 77,600 square foot building situated along Turnpike Street, and one 62,000 square foot building situated along Andover Street. The Project will also include improvements to a portion of the existing Medina Drive, enhancement of the pedestrian and view corridors between Route 114 and the Collegiate Church of Christ the Teacher, utility infrastructure, a stormwater management plan and associated landscaping. The project is not considered a Land Use with Higher Potential Pollutant Loads (LUHPPL). S���111111te uumuu puu uuu uuum Iu The Project Site is located on an approximately 4-acre portion of the Merrimack College campus (the Site) at 315 Turnpike Street in North Andover, Massachusetts. The Site is bounded by Turnpike Street/Route 114 to the northeast, Andover Street to the northwest, and Flaherty Road and Medina Drive to the south.The Site lies outside of any Wetland Resource Areas and their associated 100-foot buffer zones. The Site falls entirely within the Town of North Andover municipal boundary and lies within the surface watershed of the Shawsheen River. The existing Site is predominantly lawn with an existing one-way campus site drive and associated head-in parking spaces.At the center of the Site is a statue of Christ the Teacher,with connecting walkways and views between the Andover Street/Route 114 intersection and the front entry of the Collegiate Church of Christ the Teacher. Refer to Figure 1, Site Locus Map. According to the National Resources Conservation Service (NRCS), surface soils on the Site include woodbridge fine sandy loam and are classified as Hydrologic Soil Group (HSG) C/D. 5 Stormwater Report Narrative Based on the soil evaluation prepared by GeoEngineers and included in Appendix C, the design infiltration rates should be based on the receiving layer for future stormwater management areas, based on the soils consisting of Sandy Loam as defined by the USDA classification system and the corresponding infiltration rate of 0.52 inches/hr.With that, the Site is not considered to be within an area of rapid infiltration (soils with a saturated hydraulic conductivity greater than 2.4 inches per hour). According to the most recent FEMA Flood Insurance Rate Mapping, the Site is located in an area of minimal flood hazard (Zone X), refer to Appendix Figure 2— FEMA Firmette. IN uuuumuuuuu uuu uuum i„mi uumoll uu I,u i ii i,,, uuu uuum Under existing conditions, the Site is a largely undeveloped lawn area gently sloping to the North Figure 3 illustrates the existing drainage patterns on the Site. Currently, the Site is divided into two (2) drainage areas as stormwater runoff flows to one Design Point, which have been identified as DP-1.A third drainage area (EX-3) includes the off-site area of Route 114 and Andover Street that also drains to DP-1. Table 1 below provides a summary of the existing conditions hydrologic data. Table 1 Existing Conditions Hydrologic Data Time of Design Area Curve Concentration Drainage Area Discharge Location Point (Acres) Number (min) EX-1 Existing closed DP-1 2.9 76 6.6 drainage system at Andover Street EX-2 Existing closed DP-1 4.9 83 7.1 drainage system at Andover Street EX-3 Existing closed DP-1 0.8 95 6 drainage system at Andover Street 6 Stormwater Report Narrative i uuumuuu I uu liuumim uu uuum e C o d 11111it"I Figure 4 illustrates the proposed "post construction" drainage conditions for the project.As shown, the Site will be divided into nine drainage areas that discharge treated stormwater to the one (1) existing Design Point (DP-1).An unchanged portion of the Merrimack College campus that flows to DP-1 is represented by PR-20.The existing drainage area, PR-30, that includes the area of Route 114 and Andover Street that also drains to DP-1 is also unchanged in the proposed drainage conditions and is defined as PR-30. Table 2 below provides a summary of the proposed conditions hydrologic data. Table 2 Proposed Conditions Hydrologic Data Time of Design Area Curve Concentration Drainage Area Discharge Location Point (Acres) Number (min) PR-11 Existing closed DP-1 0.5 85 6 drainage system at Andover Street PR-12 Existing closed DP-1 0.8 86 6 drainage system at Andover Street PR-13 Existing closed DP-1 0.9 76 6 drainage system at Andover Street PR-14 Existing closed DP-1 0.8 85 6 drainage system at Andover Street PR-15 Existing closed DP-1 0.9 76 6 drainage system at Andover Street PR-16 Existing closed DP-1 0.3 98 6 drainage system at Andover Street PR-17 Existing closed DP-1 0.2 98 6 drainage system at Andover Street PR-18 Existing closed DP-1 0.2 98 6 drainage system at Andover Street PR-19 Existing closed DP-1 0.2 98 6 drainage system at Andover Street PR-20 Existing closed DP-1 3.0 86 6 drainage system at Andover Street PR-30 (EX-3) Existing closed DP-1 0.8 95 6 drainage system at Andover Street 7 Stormwater Report Narrative The site design integrates a comprehensive stormwater management system that has been developed in accordance with the Massachusetts Stormwater Handbook and the North Andover Stormwater Management and Erosion Control Bylaw.The proposed stormwater management system has been designed to meet the 0.5-inch Water Quality Volume treatment requirement but treats an excess of one inch over the site. 8 Stormwater Report Narrative Figure 1 Site Locus Map 9 Stormwater Report Narrative \\vhb.com\gbl\proj\Wat-LD\11625.34 Greystar P3 Development\cad\Id\Eng\Stormwater\Site Locus\1162534-Site Locus.dwg '�Ovhb� r, A eY r � , e � „ { u r r f , d roe z r P F r � A �s , a wl U s 9 „ a f y „ i i i e v a P i n y r w� I I i it V,. r, I I tl I 114 lr,� Y U / � r da lYry l r „ � S u, i Y " t 7, r ' 1 r, ry, rP`I ^e I ' 7 If o, I' I W,P ,r if r M u�i�V k I w I ur I Y I r N A M., I p 3� 1 i e � f P r 1 r y I � I r. i r, I n„ 1 l' Y a l U 7, v r il! Ir I. y� ' V 2 I" I Vr�r�fr. I�ffR iW r 'tare f h J, , o � r I , i V 4 � � I , q F u, r , ui k r , I r 1 J / a y r a rrI � o n a li p � r I Site Locus Map Figure 1 Corner Development 0 500 1000 2000 Feet at Merrimack College January2024 North Andover, MA 01845 Figure 2 FEMA Firmette 10 Stormwater Report Narrative Figure 2 NationalFIRMette � Le end 7107'48"W 42040'35"N SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT _NMiMMII - Flood Elevation F ) Without Ease E E - With BF€or Depth Zone AE AO,AH,v,A n SPECIAL FLOOD \ HAZARD AREAS� Regulatory Floodw y Y e a \\ \ " .2%Annual Chance Flood Hazard,Areas \ of \ 1%annual chance flood with average � depth less than one foot or with drainage o._e._ areas O less an one square tulle � Future Conditions 1%Annual ZoneX a\\\\\\\\\ \ \\\\ \\ \ \\ Chance Flood Hazard IN WIN \ \ \mawo- y yAre with ReducedFlo Risk due to l yy ._ M. o� Levee. Notes. one od \\ e ee See OTHER AREAS OF \ � \ - FLOOD HAZARD jk o° Area with Flood Risk due to Levee o e D .e AreaNO SCREEN o inima Flood Hazard X \ Effective L4M Rs OTHER AREAS Area of Undetermined Flood Hazard Zone - GENERAL -®-- Channel,Culvert,or Storm Sewer _ \\ STRUCTURES 1 1 i 1 1 i 1 Levee,Dike,or Floodwall \� _ 9 8 la Cross Sections with 1 Annual Chance y yyy vv � y 17.5 Water Surface Elevation 1 \ V 4 ORHAZARu, \ a - - Coastal ransect �'' \ \�6 \ Elevation Line F } \\\ \ \\ \ Limit of Study - Jurisdiction Boundary Coastal Transect Baseline 3 OTHER Profile Baseline FEATURES Hydrographic Feature u I \_�11 - _ � Digital Data Available \� No Digital Data Available SITEMAP PANEL Unmapped ~ \`\ 50076 . � ap The pin displayed on the map is an approximate Dint selected by the user and does not represent an authoritative property location. S a complies t s standards p t e se p This map milli with FEMAr h u f digital flood maps if it is not void as described below. \- The basemap shown complies with FEMA s basemap accuracy standards \\ - hazard information is derived directly from the authoritative NFHL web services provided by FEMA.This map Was exported On 6/13/12023 at 230 PM and does not \\ \ \\ reflect changes Or amendments subsequent t0 this date and time.The NFHL and effective information may change or 4 become superseded by new data overtime. \\ \ This map image is void if the one or more of the following map Ad - t elements do not appear:basemap imagery,flood zone labels, r - - s r, ail c e,community MOLL legend, tale bar,m creation date, ommuni identifiers, FIRM panel number,and FIRM effective date.Map images for 11111111111117- Feet 1 7107'11"W 42040'9"N unmapped and unmodernized areas cannot be used for 0 250 500 1,000 1,500 2,000 regulatory purposes. 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I\'7..­.`"I 1�., I"7''.",, �",�.-'",­I'�-\1111�.��-"",I.,�l,"���',..'�_"1' \',_,­..1 I',,��1',,I�-.­",I-.\. " .., lI,'1'1',,-l1,.il� 1_,.,"�"� �"-.�,1-1l'_"",,.�l\_l.-1",\�,�\1..",,.,I\\�l.­z'7'."".1 \."�,'I,:."�_�"\.,F"_�,, ,"� r , \FFE-22 2 - ,,, o,, s _ . a �'.... - :, c,.. _ z N _ DP 1 ti R 1 b ...� �,, �, n,, LINETYPES ,,. . �_ ti _: .; � . . . F y .,..� ,.,. CLOSED DRAINAGEROPosEo R-19 , _, BWILDINi 2 . ,.. R 3 ` �, \ DRAINAGE AREA SYSTEM OUTFACE \ _ _� _--_ ,, zzo.oa?".o - ;:. R Is._,,ouECE _ ;4 _ BOUNDARY N �,>, .\: �. :., ,... a s -. - .v .a...: _ .. s - - �� NCENTRATION <.. TIME OF CO ,.. FLOW LINE -' x ,._ , .' _, R-2 e ;... z '. , 0 c ,, N.. .,. .. \. „ z :, >, z, SOIL TYPE BOUNDARY a �4 _ �, e .� ,,° ,: .., ,r, ....o ,. ._ .. '�r a _ r. :;� .. _r. ... ,. ------. s 7 >, .............. — \, 100 BUFFER ZONE t _ ''^a�_ ,.., , e �. _ , .... ,. "k, OV_ WETLAND B NDARY ,..;. I. \ ._. \ \ 220 4 2 9 .:...,. :...e. - :.,:x, `. .... ,. .. ,. , � .... 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SANDY LOAM 0 TO 8 , - ,.,, , .. ::: , ,� �..t, , , , , ., ., \...... , f , _. �� 311B �� _ , T L PE ERY ', = PERCEN S O S V .. �� ' � �, �. _ , _. ,, ,. _ _ .�. , v x ,, STONY 2 - 9.. _: ,. , R,,,_ ;., : � N O, .,. „ 1 _ ,t_ ... �. ,:,: , ,; , _. , , ,. ,,,, ,� ,. ;, �.�...0_.­",,�,,'.,.�ll.,�_I g...11 II.�..'k1". ,11\.,1,I��.\l.""i,1_I��0,".,.R."--1,., _,\.,"""i-�.I,.',-_�'�.I.­.1��.t. _­l,,1...I,,,..-­,""-I .—,I�',­-.�,,C�,",,._­I,\1."l",�.I'_I 1","II�1.,, �l...,,,­",1,,,,., ,: _ - ,. , . ,, ,> :' � , ,„ - � ., t .: t �. ...•,�. ,,,„, ., , <' - , ,, ,....,t. ,: ,. ., V " .,..,,, ,s, ..,' \ a „ ""l :, ,,,,, c,,, , ., r .G , , ..,,,. - ..p ,3 .,: ., .. I I FI,L.I,, ,.. :NEPRI�S4,_k C:, 3 _.,..,. ... .,.. T M/�.F 2 R .... .� ,, , ., ,� �. �:� \ .< .,. , .. .,„ G n , .„ .. E,7:K�....FFE I� \: N "- VhbPropsed Drainage Conditions Figure 4 IIIIIIIIIIIIIIIIIIIIIIIIII Corner Development Project at 0 50 100 200Feet Merrimack College 08/17/2023 North Andover,MA REV1 -09/15/2023 REV2-02/20/2024 This page intentionally left blank. 13 Stormwater Report Narrative I w uuuuuu uuuuuuuum uuum °ui i i I i uuuumuum uuuuuuuumuuuuuuuuu uuu uuum I I m uuu uuum I i I i P uuu uuum muuu imuuuuuunn uuuuum uuuummuuu IIN Illumu umm Regulatory Compliance �������\Aassac��������liusell'Illt'll'Its o"I"IF uuu uuum um As demonstrated below, the proposed Project fully complies with the DEP Stormwater Management Standards. S II III New II II °°°° °°°° Dilsdharges III II o s IIIII o n In d s The Project has been designed to comply with Standard 1. The Best Management Practices (BMPs) included in the proposed stormwater management system have been designed in accordance with the Massachusetts Stormwater Handbook. Supporting information and computations demonstrating that no new untreated discharges will result from the Project are presented through compliance with Standards 4 through 6. All proposed Project stormwater outlets and conveyances have been designed to not cause erosion or scour to wetlands or receiving waters.The proposed project will discharge reduced and treated Stormwater flows to the existing piping system. Computations and supporting information for the sizing and selection of materials used to protect from scour and erosion are included in Appendix A. S tandar te t II iii o II The Project has been designed to comply with Standard 2. The rainfall-runoff response of the Site under existing and proposed conditions was analyzed for storm events with recurrence intervals of 2, 10, 25 and 100 years. The results of the analysis, as summarized in Tables 4.1 and 4.2 below, indicate that there is no increase in peak discharge rates or runoff volumes between the existing and proposed conditions for each of these storm events. Closed drainage and subsurface stormwater management systems have been designed to fully accommodate the 25-year storm event, and there will be no expected ponding from the 100- year storm event. Computations and supporting information regarding the hydrologic modeling are included in Appendix B. 14 Regulatory Compliance Table 4.1 Peak Discharge Rates (cfs*) Design Point 2-year 10-year 25-year 100-year DP-1 Existing 14.7 30.0 39.9 55.3 Proposed 10.8 25.4 35.1 52.8 Design Point 2-year 10-year 25-year 100-year DP-1 Existing 48,010 97,260 129,910 182,050 Proposed 43,280 94,540 128,010 181,070 SIIIII IIIII �I�I�IppRecharge ww : II ter ii The Project has been designed to comply with Standard 3. In accordance with the Stormwater Handbook, the Required Recharge Volume for the Project is 1,322 cubic feet. Recharge of stormwater has been provided through the use of subsurface infiltration systems, which have been sized using the Static method. Each infiltration BMP has been designed to drain completely within 72 hours.Table 5 below provides a summary of the proposed infiltration BMPs utilized for the Project. Table 5 Summary of Recharge Calculations Bottom of Bottom of Lowest System Provided Recharge System Area System/Stone Outlet Invert Volume Infiltration BMP (square feet) Elevation (cubic feet) Subsurface Infiltration 11488 223.6 224.4 666 System A Subsurface Infiltration 1,829 217.0 218.3 1,583 System B Subsurface Infiltration 3,028 212.5 215.6 7,305 System C Total Required Recharge 1,322 Total Provided Recharge 9,554 Soil evaluation (including Geotechnical Report), computations, and supporting information are included in Appendix C. 15 Regulatory Compliance S°'tandard nn : Wa°'te il°' „ The Project has been designed to comply with Standard 4 and 250-23(B) of the North Andover Stormwater Management and Erosion Control Regulations. The proposed stormwater management system implements a treatment train of BMPs that has been designed to provide a minimum 90%Total Suspended Solids (TSS) removal and 60%Total Phosphorus (TP) removal of stormwater runoff from all proposed impervious surfaces.Water quality treatment is provided via deep-sump catch basins, structural water quality units for pretreatment, and subsurface infiltration chambers. Computations and supporting information are included in Appendix D.The Long-Term Pollution Prevention Plan is included under separate cover as part of the O&M Plan. S"'tandar ndIIIII IIIII IIF en il ao u ta I t ��...........oads .U��I s) The Project is not considered a LU H PPL. S"'tandard 6.- Cril"' IIIII IIF°°° The Project will not discharge stormwater near or to a critical area. S ta n d a men ts and 0 t h e Pro S"'tandards aI "'to the "'ten"' Ira c"'""'il c a b��e The Project is considered new development and has been designed to comply with all ten of the Stormwater Management Standards. Refer directly to each Standard for applicable computations and supporting information demonstrating compliance with each. S°'tandard 8: Cons°'truc°' IIIII II °°I °°°°IIF IIIII °° °''IIIII II ,), reven°''IIIII n and Erosi�on a I il m e I °'t a til II II trols IF The Project will disturb approximately four(4) acres of land and is therefore required to obtain coverage under the Environmental Protection Agency(EPA) National Pollutant Discharge Elimination System (NPDES) Construction General Permit.As required under this permit, a Stormwater Pollution Prevention Plan (SWPPP) will be developed and submitted before land disturbance begins. Recommended construction period pollution prevention and erosion and sedimentation controls to be finalized in the SWPPP are included in Appendix F. S°'tandard 9,-, Opera t IIIII 11 IIMai�hn°'t e I a n c°°°° °° II In compliance with Standard 9, a Post Construction Stormwater Operation and Maintenance (O&M) Plan has been developed for the Project. The O&M Plan is included under separate cover, including the Long Term Pollution Prevention Plan. 16 Regulatory Compliance Snitandard 10: nni IIIII IIIII nit i��o n o nif ������iii IIIII ni ��',',,')iisdharges The site was previously undeveloped and no sanitary sewer or storm drainage infrastructure is known to exist on the majority of the site.The design plans submitted with this report have been designed in full compliance with current standards.The Long-Term Pollution Prevention Plan includes measures to prevent illicit discharges. A signed Illicit discharge statement is included in Appendix F. 17 Regulatory Compliance Appendix A: Standard 1 Computations and Supporting Information > Pipe Sizing Calculations A-1 Appendix A: Standard 1 Computations and Supporting Information This page intentionally left blank. A-2 Appendix A: Standard 1 Computations and Supporting Information S"���, IIIIVi uum pug i������i g C a c u pm uuu uuum IW The closed drainage system was designed for the 25-year storm event, in accordance with the North Andover's stormwater management and erosion control regulations. Drainage pipes were sized using StormCAD, a HEC-22 based program. A-3 Appendix A: Standard 1 Computations and Supporting Information y O Stormcad Conduit Output Table - Hydraulic Pipe Analysis 1;20-0Vhb Project Corner Development at Project# 11625.34 Merrimack College Calculated by N DS/S M Date 2/1/2024 Checked by JWK Date 2/1/2024 Upstream Upstream Time of Manning's Capacity Velocity Rim Hydraulic Rim Hydraulic Invert Invert Start Node Stop Node System CA Intensity Pipe Size Material Slope Length Flow Grade Line Grade Line Inlet Area Inlet C Conc. (Design) (Average) (Upper) (Lower) Out (Upper) (Lower) In - (acres) - (acres) (min) (in/hr) (in) - - (ft/ft) (ft) (cfs) (cfs) (ft/s) (ft) (ft) (ft) (ft) (ft) (ft) A101 A102 0.308 0 0.164 5 7.931 12 HDPE 0.012 0.024 70.1 1.31 6.01 6.13 229.6 227.48 227.3 225.62 227 225.3 A103 A102 0.175 0 0.085 5 7.931 12 HDPE 0.012 0.005 40.9 0.68 2.7 2.86 227.3 225.05 227.3 225.04 224.7 224.5 A107 SYS A IN (N/A) (N/A) 0.263 5 7.756 12 HDPE 0.012 0.02 5 2.05 5.46 6.46 227.9 224.81 227.9 224.6 224.2 224.1 BLDG 1 A105 0.23 0.9 0.207 5 7.931 12 HDPE 0.012 0.02 10 1.65 5.46 6.09 228 225.15 226.4 224.82 224.6 224.4 A102 A107 (N/A) (N/A) 0.263 5 7.83 12 HDPE 0.012 0.005 38 2.07 2.8 3.9 227.3 225.04 227.9 224.82 224.4 224.2 A105 SYS A IN (N/A) (N/A) 0.207 5 7.927 12 HDPE 0.012 0.018 5.5 1.65 5.2 5.87 226.4 224.85 227.9 224.65 224.3 224.2 SYS A OUT A106 (N/A) (N/A) 0 5 7.931 12 HDPE 0.012 0.01 20.9 3.1 3.78 5.37 227.9 225.16 227.6 224.89 224.4 224.2 A106 B107 (N/A) (N/A) 0 5 7.931 12 HDPE 0.012 0.01 108.3 3.1 3.89 5.5 227.6 222.96 225.3 221.77 222.2 221.1 A108 A102 0.043 0 0.013 5 7.931 12 HDPE 0.012 0.011 26.1 0.11 4.14 2.25 228.1 226.23 227.3 225.91 226.1 225.8 B117 B118 0.196 0 0.122 5 7.495 12 HDPE 0.012 0.011 37.3 0.92 4 4.14 225.9 223.8 226.3 223.33 223.4 223 B105 B118 0.625 0 0.327 5 7.931 12 HDPE 0.012 0.012 16.8 2.61 4.21 5.65 225.2 223.29 226.3 222.99 222.6 222.4 B107 B111 (N/A) (N/A) 0.243 5 7.917 18 HDPE 0.012 0.01 91.7 5.04 11.28 6.2 225.3 220.46 226.1 219.71 219.6 218.7 B118 B111 (N/A) (N/A) 0.449 5 7.426 18 HDPE 0.012 0.011 81.3 3.36 11.98 5.82 226.3 223 226.1 221.94 222.3 221.4 BLDG-1 B107 0.27 0.9 0.243 5 7.931 12 HDPE 0.012 0.017 18.2 1.94 4.96 5.93 224 220.59 225.3 220.46 220 219.7 B111 B102 (N/A) (N/A) 0.692 5 7.319 18 HDPE 0.012 0.01 82 8.21 11.24 6.94 226.1 219.71 223.5 218.75 218.6 217.8 B103 B104 (N/A) (N/A) 0 5 7.931 18 HDPE 0.012 0.021 53.4 9.5 16.33 9.59 223.5 214.19 213.1 212.76 213 211.9 BLDG-2 B102 0.19 0.9 0.171 5 7.931 12 HDPE 0.012 0.01 40 1.37 3.86 4.49 224 220.49 223.5 220.01 220 219.6 B102 SYS B IN (N/A) (N/A) 0.863 5 7.228 18 HDPE 0.012 0.01 10 9.39 11.38 7.19 223.5 218.88 223.5 218.69 217.7 217.6 SYS B OUT B103 (N/A) (N/A) 0 5 7.931 18 HDPE 0.012 0.02 10 9.5 16.09 9.48 227.7 218.69 223.5 218.29 217.5 217.3 B104 D101 (N/A) (N/A) 0 5 7.931 18 HDPE 0.012 0.008 159.6 9.5 9.87 6.36 213.1 212.99 214.5 211.8 211.8 210.6 C110 C111 (N/A) (N/A) 0.526 5 7.41 12 HDPE 0.012 0.011 45.7 3.93 4.04 5.85 221.3 216.34 220 215.8 215.5 215 C108 C111 0.059 0 0.019 5 7.931 12 HDPE 0.012 0.012 24.1 0.15 4.31 2.57 219.5 217.66 220 217.33 217.5 217.2 C111 SYS C IN (N/A) (N/A) 0.545 5 7.35 12 HDPE 0.012 0.02 5 4.03 5.46 7.6 220 215.75 218 215.54 214.9 214.8 BLDG-2 C113 0.16 0.9 0.144 5 7.931 12 HDPE 0.012 0.013 23 1.15 4.41 4.72 220 216.56 222 216.59 216 215.7 SYS C OUT Cl 12 (N/A) (N/A) 0 5 7.931 18 HDPE 0.012 0.01 10 3.6 11.38 5.71 215.5 213.72 219.2 213.52 213 212.9 Cl 12 D101 (N/A) (N/A) 0 5 7.931 18 HD[E 0.012 0.008 59.3 3.6 10.45 5.37 219.2 212.72 214.5 212.11 212 211.5 D101 D102 (N/A) (N/A) 0 5 7.931 24 HDPE 0.012 0.017 72.3 13.1 31.57 9.58 214.5 211.8 215.8 210.23 210.5 209.3 D102 D103 (N/A) (N/A) 0 5 7.931 24 HDPE 0.012 0.01 9.6 13.1 25.03 8.06 215.8 210.4 212.79 210.16 209.1 209 C101 C102 0.286 0 0.075 5 7.931 12 HDPE 0.012 0.01 149.8 0.6 3.86 3.57 226.5 224.82 226.5 223.27 224.5 223 C102 C103 0.124 0 0.108 5 7.618 12 HDPE 0.012 0.014 14.3 0.83 4.56 4.41 226.5 223.28 226.5 223 222.9 222.7 C103 C109 0.042 0 0.12 5 7.593 12 HDPE 0.012 0.024 46.6 0.92 5.93 5.48 226.5 223 223.5 221.77 222.6 221.5 C104 C105 0.145 0 0.159 5 7.464 12 HDPE 0.012 0.009 110.9 1.2 3.66 4.17 222.5 220.86 222.5 219.79 220.4 219.4 C105 C107 0.078 0 0.181 5 7.26 12 HDPE 0.012 0.019 69.1 1.33 5.29 5.6 222.5 219.29 219.5 217.84 218.8 217.5 C107 C106 0.241 0 0.239 5 7.165 12 HDPE 0.012 0.011 17.5 1.73 4.13 5.02 219.5 217.96 220.3 217.66 217.4 217.2 C109 C104 (N/A) (N/A) 0.12 5 7.528 12 HDPE 0.012 0.021 43.5 0.91 5.55 5.21 223.5 221.8 222.5 220.77 221.4 220.5 C113 C110 (N/A) (N/A) 0.381 5 7.473 12 HDPE 0.012 0.011 45.8 2.87 4.03 5.57 222 216.59 221.3 216.34 215.6 215.1 \\vhb\gbl\prof\wat-LD\11625.34 Greystar P3 Development\ssheets\Stormwater\11625.34-Stormcad Conduit Output Table 1 of 2 y O Stormcad Conduit Output Table - Hydraulic Pipe Analysis 1;20-0Vhb Project Corner Development at Project# 11625.34 Merrimack College Calculated by N DS/S M Date 2/1/2024 Checked by JWK Date 2/1/2024 Upstream Upstream Time of Manning's Capacity Velocity Rim Hydraulic Rim Hydraulic Invert Invert Start Node Stop Node System CA Intensity Pipe Size Material Slope Length Flow Grade Line Grade Line Inlet Area Inlet C Conc. (Design) (Average) (Upper) (Lower) Out (Upper) (Lower) In (acres) - (acres) (min) (in/hr) (in) - - (ft/ft) (ft) (cfs) (cfs) (ft/s) (ft) (ft) (ft) (ft) (ft) (ft) C114 C113 (N/A) (N/A) 0.237 5 7.569 12 HDPE 0.012 0.011 63.2 1.81 4.06 5.02 222.5 217.37 222 216.57 216.8 216.1 C115 C114 0.044 0 0.01 5 7.931 12 HDPE 0.012 0.01 39 0.08 3.91 1.97 219.5 217.61 222.5 217.37 217.5 217.1 C116 C114 0.154 0 0.118 5 7.931 12 HDPE 0.012 0.01 29 0.95 3.93 4.12 222.5 220.51 222.5 220.13 220.1 219.8 C117 C118 0.187 0 0.106 5 7.931 12 HDPE 0.012 0.01 29 0.85 3.93 3.99 222.5 220.49 222.9 220.12 220.1 219.8 C118 C110 (N/A) (N/A) 0.145 5 7.81 12 HDPE 0.012 0.011 92 1.14 4.02 4.41 222.9 218.45 221.3 217.36 218 217 C119 C118 0.075 0 0.039 5 7.931 12 HDPE 0.012 0.011 52.3 0.31 4.14 3.09 223.4 218.93 222.9 218.45 218.7 218.1 C120 C114 (N/A) (N/A) 0.028 5 7.804 12 HDPE 0.012 0.011 43.7 0.22 4.13 2.8 220.2 217.59 222.5 217.37 217.4 216.9 C121 C123 0.136 0 0.063 5 7.931 12 HDPE 0.012 0.01 59.9 0.5 3.86 3.4 223 221.29 223.4 220.64 221 220.4 C122 C123 0.076 0 0.017 5 7.931 12 HDPE 0.012 0.009 64.5 0.14 3.72 2.26 223 221.15 223.4 220.63 221 220.4 C123 C114 (N/A) (N/A) 1 0.08 1 5 7.721 1 12 1 HDPE 1 0.012 1 0.011 1 73.7 1 0.63 1 4.02 1 3.72 1 223.4 1 220.63 222.5 1 219.77 1 220.3 1 219.5 C106 SYS C IN (N/A) (N/A) 1 0.239 1 5 7.139 12 HDPE 0.012 0.02 15 1.72 5.46 6.15 220.3 217.66 217.8 217.21 217.1 216.8 \\vhb\gbl\prof\wat-LD\11625.34 Greystar P3 Development\ssheets\Stormwater\11625.34-Stormcad Conduit Output Table 2 of 2 Appendix B: Standard 2 Computations and Supporting Information The rainfall-runoff response of the Site under existing and proposed conditions was evaluated for storm events with recurrence intervals of 2, 10, 25 and 100-years. Rainfall volumes used for this analysis were based on the Natural Resources Conservation Service (NRCS)Type III, 24-hour storm and NOAA Atlas 14 precipitation depths for the site:3.16, 5.01, 6.16, and 7.94 inches, respectively. Runoff coefficients for the pre- and post-development conditions, as previously shown in Tables 2 and 3 respectively, were determined using NRCS Technical Release 55 (TR-55) methodology as provided in HydroCAD. Drainage areas used in the analyses were described in previous sections and shown on Figures 2 and 3.The HydroCAD model is based on the NRCS Technical Release 20 (TR-20) Model for Project Formulation Hydrology. > HydroCAD Analysis: Existing Conditions > HydroCAD Analysis: Proposed Conditions B-1 Appendix B:Standard 2 Computations and Supporting Information uuuuu°uum I uuumuuu i' um � mm�oi uuuumuuuuu uuu uuum �,,, uuu umuu°loom 6-2 Appendix 6:Standard 2 Computations and Supporting Information EX-1 Rt 114 and Andover St Corner DP-1 " EX-2 Andover Street System Medina Drive, Church, Main Entrance EX-3 Outside Project Site - Andover/Elm St SubC2f Reach /Po\ndLinkRouting Diagram for 11625.34-EX Subcat Reach Link Prepared by VHB, Inc, Printed 9/15/2023 HytlroGAD@ 10.203c sln 01038 02023 HytlroCAD Software Solutions LLC 11625.34 - EX Prepared by VH B, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 2 Rainfall Events Listing Event# Event Storm Type Curve Mode Duration B/B Depth AMC Name (hours) (inches) 1 2-Year Type III 24-hr Default 24.00 1 3.16 2 2 10-Year Type III 24-hr Default 24.00 1 5.01 2 3 25-Year Type III 24-hr Default 24.00 1 6.16 2 4 100-Year Type III 24-hr Default 24.00 1 7.94 2 11625.34 - EX Prepared by VH B, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 3 Area Listing (all nodes) Area CN Description (sq-ft) (subcatchment-numbers) 2567630 74 >75% Grass cover, Good, HSG C (EX-1, EX-2, EX-3) 91,670 98 Paved parking (EX-1, EX-2, EX-3) 297220 98 Roof (EX-2) 3775520 82 TOTAL AREA 2 IIIIIIIIIIIYea r S torm t .................... IIIIIIIII III Iii I ii 6-3 Appendix 6:Standard 2 Computations and Supporting Information 11625.34 - EX Type/1/ 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 4 Time span=0.00-30.00 hrs, dt=0.01 hrs, 3001 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentEX-1: Rt 114 and Andover Runoff Area=125,650 sf 6.33% Impervious Runoff Depth=1.12" Flow Length=488' Tc=6.6 min CN=76 Runoff=3.6 cfs 11,772 cf SubcatchmentEX-2: Medina Drive, Runoff Area=215,120 sf 37.51% Impervious Runoff Depth=1.58" Flow Length=465' Tc=7.1 min CN=83 Runoff=8.8 cfs 28,260 cf SubcatchmentEX-3: Outside Project Site- Runoff Area=36,750 sf 87.73% Impervious Runoff Depth=2.61" Tc=6.0 min CN=95 Runoff=2.4 cfs 7,980 cf Link DP-1:AndoverStreet System Inflow=14.7 cfs 48,012 cf Primary=14.7 cfs 48,012 cf Total Runoff Area = 377,520 sf Runoff Volume = 48,012 cf Average Runoff Depth = 1.53" 67.98% Pervious = 256,630 sf 32.02% Impervious = 120,890 sf 11625.34 - EX Type 111 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment EX-1 : Rt 114 and Andover St Corner Runoff = 3.6 cfs @ 12.10 hrs, Volume= 11,772 cf, Depth= 1.12" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 1177700 74 >75% Grass cover, Good, HSG C 0 98 Roof 7,950 98 Paved parking 125,650 76 Weighted Average 117700 93.67% Pervious Area 71950 6.33% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 4.3 50 0.0400 0.19 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.4 90 0.0500 3.60 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 62 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 1.3 250 0.0400 3.22 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 36 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 6.6 488 Total 11625.34 - EX Type 111 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 6 Subcatchment EX-1: Rt 114 and Andover St Corner Hydrograph 4 El Runoff 3.6 cfs Type III 24-hr 2-Year Rainfall=3.16" 3 Runoff Area=125,650 sf Runoff Volume=11,772 cf Runoff Depth=1.12" 3 2 / o Flow Length=488' Tc=6.6 m i n CN=76 0 �JIF]11[71IF71IF71jr7ll7]1171IF71IF71IF-7111 U U U U U U U U U U U U U U U U U U U U U U U711F 1111 '111 711-711`711711PI1`711`7111 U U U U U U U U U U U U U U U U U U U U U U U7r7llr7ll7��711771jr7llr7ll7��71171j U U U U U U U U U U U YJ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 7 Summary for Subcatchment EX-2: Medina Drive, Church, Main Entrance Runoff = 8.8 cfs @ 12.10 hrs, Volume= 28,260 cf, Depth= 1.58" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 1347420 74 >75% Grass cover, Good, HSG C 291220 98 Roof 511480 98 Paved parking 2157120 83 Weighted Average 134,420 62.49% Pervious Area 80,700 37.51% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 3.9 50 0.0500 0.21 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.1 28 0.0500 3.60 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 1.0 100 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 70 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.8 132 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.9 85 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 7.1 465 Total 11625.34 - EX Type 111 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 8 Subcatchment EX-2: Medina Drive, Church, Main Entrance Hydrograph El Runoff 9 8.8 cfs T ype 11124-hr 8- 2-Year Rainfall=3.16" 7 Runoff Area=215,120 sf Runoff Volume=28,260 cf Runoff Depth=1.58 5 Flow Length=465' 4 Tc=7.1 min 3 r� CN=83 2- //. /r / r i 0 1111 U U U i.,cr:,%a ,a"o", a.,".;rr.,/ ".,%"".%'111,.,'.,. '111 '111 '111 '111 '111 '111 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 9 Summary for Subcatchment EX-3: Outside Project Site - Andover/Elm St Runoff = 2.4 cfs @ 12.08 hrs, Volume= 7,980 cf, Depth= 2.61" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 4,510 74 >75% Grass cover, Good, HSG C 0 98 Roof 321240 98 Paved parking 361750 95 Weighted Average 4,510 12.27% Pervious Area 321240 87.73% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment EX-3: Outside Project Site - Andover/Elm St Hydrograph El Runoff 2.4 cfs Type III 24=hr 2-Year Rainfall=3.16" 2 / Runoff Area=36,750 sf Runoff Volume=7,980 d Runoff Depth=2.61 0 Tc=6,0 min CN=95 rill i: 0- F7117117]FJJF711711 171IF-7117[71IF7117FFT-V7FFTrTTTT-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 10 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 32.02% Impervious, Inflow Depth = 1.53" for 2-Year event Inflow = 14.7 cfs @ 12.10 hrs, Volume= 48,012 cf Primary = 14.7 cfs @ 12.10 hrs, Volume= 48,012 cf, Atten= 0%, Lag= 0.0 min Routed to nonexistent node DP-2 Primary outflow = Inflow, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Link DP-1: Andover Street System Hydrograph Inflow - - - - - - -14. E Primary 16 7 cfs 15 14.7 cfs Inflow Area=377,520 sf 13 12 11 10 1 / o uL 7 6 i 5 4 3 , r 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) IIIIIIIIII IIIIIIIIII il ii 10........ ��� IIIIIII ��� IIIIIIIIIIIIIIIIIIII IIIII ���IIIYea S (IIIIIIIIII IIIIIIIIIII I 6-4 Appendix 6:Standard 2 Computations and Supporting Information 11625.34 - EX Type III 24-hr 10-Year Rainfal1=5.01 if Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 11 Time span=0.00-30.00 hrs, dt=0.01 hrs, 3001 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentEX-1: Rt 114 and Andover Runoff Area=125,650 sf 6.33% Impervious Runoff Depth=2.54" Flow Length=488' Tc=6.6 min CN=76 Runoff=8.4 cfs 26,635 cf SubcatchmentEX-2: Medina Drive, Runoff Area=215,120 sf 37.51% Impervious Runoff Depth=3.18" Flow Length=465' Tc=7.1 min CN=83 Runoff=17.7 cfs 57,063 cf SubcatchmentEX-3: Outside Project Site- Runoff Area=36,750 sf 87.73% Impervious Runoff Depth=4.43" Tc=6.0 min CN=95 Runoff=4.0 cfs 13,565 cf Link DP-1:AndoverStreet System Inflow=30.0 cfs 97,264 cf Primary=30.0 cfs 97,264 cf Total Runoff Area = 377,520 sf Runoff Volume = 97,264 cf Average Runoff Depth = 3.09" 67.98% Pervious = 256,630 sf 32.02% Impervious = 120,890 sf 11625.34 - EX Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 12 Summary for Subcatchment EX-1 : Rt 114 and Andover St Corner Runoff = 8.4 cfs @ 12.10 hrs, Volume= 26,635 cf, Depth= 2.54" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 117,700 74 >75% Grass cover, Good, HSG C 0 98 Roof 7,950 98 Paved parking 125,650 76 Weighted Average 117700 93.67% Pervious Area 7,950 6.33% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 4.3 50 0.0400 0.19 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.4 90 0.0500 3.60 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 62 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 1.3 250 0.0400 3.22 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 36 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 6.6 488 Total 11625.34 - EX Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 13 Subcatchment EX-1: Rt 114 and Andover St Corner Hydrograph -- - - - - - - - - - - - - - - - El Runoff 9 8.4 cfs Type III 24-hr 10-Year Rainfall=5.01"' 7 / Runoff Area=125,650 sf 6 % Runoff Volume=26,635 cf 5 % Runoff Depth=2.54" 3 Flow Length=488' 4 Tc=6.6 m i n 3 CN=76 2 e.; 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 14 Summary for Subcatchment EX-2: Medina Drive, Church, Main Entrance Runoff = 17.7 cfs @ 12.10 hrs, Volume= 57,063 cf, Depth= 3.18" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 1347420 74 >75% Grass cover, Good, HSG C 297220 98 Roof 517480 98 Paved parking 2157120 83 Weighted Average 1347420 62.49% Pervious Area 807700 37.51% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 3.9 50 0.0500 0.21 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.1 28 0.0500 3.60 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 1.0 100 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 70 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.8 132 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.9 85 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 7.1 465 Total 11625.34 - EX Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 15 Subcatchment EX-2: Medina Drive, Church, Main Entrance Hydrograph 19 Runoff 18 17.7 cfs 17 Type 11124-hr 16 j 1 0 Year Rainfall=5.01 15 14 Runoff Area=215,120 sf 13° 12 Runoff Volume=57,063 cf Runoff Depth=3.18" ,, , Flow Length=465' UL Tc=7.1 min 7 CN=83 5 4 3 U U U /�i i, / / //i�,'i�r � f i c r.,.,/.,,,,is, rr.,,�-.,�%-./��.,. ,,0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 16 Summary for Subcatchment EX-3: Outside Project Site - Andover/Elm St Runoff = 4.0 cfs @ 12.08 hrs, Volume= 13,565 cf, Depth= 4.43" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 4,510 74 >75% Grass cover, Good, HSG C 0 98 Roof 321240 98 Paved parking 361750 95 Weighted Average 4,510 12.27% Pervious Area 321240 87.73% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment EX-3: Outside Project Site - Andover/Elm St Hydrograph El Runoff 4.0 cfs 4 Type III 24-hr 10-Year Rainfall=5.01" % Runoff Area=36,750 sf 3 Runoff Volume=13,565 cf Runoff Depth=4.43" 0 Tc=6.0 m i n 2 CN=95 Yll 0 7. U U U U U U U U U U U U M M'Ili 1111 1111 1111 1111 1111 U lug 1111 111111 1111 Ili 11 111 11 11 111111 11 11 11 Ul' 'U U9"I'll"11111111"I'll"uu Uu uu uU uu uu U 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 17 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 32.02% Impervious, Inflow Depth = 3.09" for 10-Year event Inflow = 30.0 cfs @ 12.10 hrs, Volume= 97,264 cf Primary = 30.0 cfs @ 12.10 hrs, Volume= 97,264 cf, Atten= 0%, Lag= 0.0 min Routed to nonexistent node DP-2 Primary outflow = Inflow, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Link DP-1: Andover Street System Hydrograph Inflow 32 �,30.0 cfs El Prima ry 30 30.0 cfs Inflow Area=377,520 sf j 26 24 22 / 18 3 16 o UL 14r, 12 101 r r� r 2 r r /r 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) I IIryµII�II�IpII,1"11"� IIIIIIIIII IIIIIIIIII � IIIryµIIIIIII�IIIII1"11"�� �........ ���` II IIIIIRR ��� IIIIIIIIIIIIIIIIIM IIIIIPR IIIII III IIIII IIIIIIII�lln II Yea S IIIIIIIIIII IIIIIIIIIII I 6-5 Appendix 6:Standard 2 Computations and Supporting Information 11625.34 - EX Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 18 Time span=0.00-30.00 hrs, dt=0.01 hrs, 3001 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentEX-1: Rt 114 and Andover Runoff Area=125,650 sf 6.33% Impervious Runoff Depth=3.52" Flow Length=488' Tc=6.6 min CN=76 Runoff=11.7 cfs 36,842 cf SubcatchmentEX-2: Medina Drive, Runoff Area=215,120 sf 37.51% Impervious Runoff Depth=4.24" Flow Length=465' Tc=7.1 min CN=83 Runoff=23.3 cfs 76,011 cf SubcatchmentEX-3: Outside Project Site- Runoff Area=36,750 sf 87.73% Impervious Runoff Depth=5.57" Tc=6.0 min CN=95 Runoff=5.0 cfs 17,060 cf Link DP-1:AndoverStreet System Inflow=39.9 cfs 129,913 cf Primary=39.9 cfs 129,913 cf Total Runoff Area = 377,520 sf Runoff Volume = 129,913 cf Average Runoff Depth = 4.13" 67.98% Pervious = 256,630 sf 32.02% Impervious = 120,890 sf 11625.34 - EX Type/1/ 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 19 Summary for Subcatchment EX-1 : Rt 114 and Andover St Corner Runoff = 11.7 cfs @ 12.10 hrs, Volume= 36,842 cf, Depth= 3.52" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 117,700 74 >75% Grass cover, Good, HSG C 0 98 Roof 7,950 98 Paved parking 125,650 76 Weighted Average 117700 93.67% Pervious Area 7,950 6.33% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 4.3 50 0.0400 0.19 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.4 90 0.0500 3.60 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 62 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 1.3 250 0.0400 3.22 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 36 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 6.6 488 Total 11625.34 - EX Type/1/ 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 20 Subcatchment EX-1: Rt 114 and Andover St Corner Hydrograph 13, El Runoff 12 11.7 cfs Type 11124-hr 11 25-Year Rainfall=6.16" 10 9 Runoff Area=125,650 sf 8 % Runoff Volume=36,842 cf � 7 Runoff Depth=3.52" 0 6,' Flow Length=488' 5 Tc=6.6 m i n 4 '''' CN=76 3 %r/ 0 / ,ic 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 21 Summary for Subcatchment EX-2: Medina Drive, Church, Main Entrance Runoff = 23.3 cfs @ 12.10 hrs, Volume= 767011 cf, Depth= 4.24" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 1347420 74 >75% Grass cover, Good, HSG C 297220 98 Roof 517480 98 Paved parking 2157120 83 Weighted Average 1347420 62.49% Pervious Area 807700 37.51% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 3.9 50 0.0500 0.21 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.1 28 0.0500 3.60 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 1.0 100 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 70 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.8 132 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.9 85 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 7.1 465 Total 11625.34 - EX Type/1/ 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 22 Subcatchment EX-2: Medina Drive, Church, Main Entrance Hydrograph 26 El Runoff 25 24 23.3 cfs 23 Type III 24-hr 22 21 .� 25-Year Rainfall=6.16" 20 18 Runoff Area=215,120 sf 191 17 - - - - 16 j Runoff Volume=76,011 cf 15 14 ,, Runoff Depth=4.24" 13 ' 0 12 Flow Length=465' 10 ,''' Tc=7.1 min CN-83 7 ,. 4° 3 1 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 23 Summary for Subcatchment EX-3: Outside Project Site - Andover/Elm St Runoff = 5.0 cfs @ 12.08 hrs, Volume= 17,060 cf, Depth= 5.57" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 4,510 74 >75% Grass cover, Good, HSG C 0 98 Roof 321240 98 Paved parking 361750 95 Weighted Average 4,510 12.27% Pervious Area 321240 87.73% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment EX-3: Outside Project Site - Andover/Elm St Hydrograph Runoff 5.0 cfs 5 Type 11124-hr 25-Year Rainfall=6.16" Runoff Area=36,750 sf Runoff Volume=17,060 cf � 3 Runoff Depth=5.57" 0 Tc=6.0 rn i n 2 CN=95 0 Awn 0 zo/wnzz// wV/ v ,�x 0 U i��U I--TT-TV-TT-TT-TT-P 9 T7117[711711F7117117 U U U U U U U U U U U U-FFYT-FF T T T F TT UTT FIFIF 11 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 24 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 32.02% Impervious, Inflow Depth = 4.13" for 25-Year event Inflow = 39.9 cfs @ 12.10 hrs, Volume= 129,913 cf Primary = 39.9 cfs @ 12.10 hrs, Volume= 129,913 cf, Atten= 0%, Lag= 0.0 min Routed to nonexistent node DP-2 Primary outflow = Inflow, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Link DP-1: Andover Street System Hydrograph Inflow 44 39.9 cfs / Primary 42 39.9 cfs Inflow Area=377,520 sf 40 38 � 34 _ - 32 30 28 3 22 I 20 18 16 ' 14 12, 10' 8 6" 4 � � r� 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) �I�I��,,��gg IryIII �I�I��,,gq IIIIIIIIII IIIIIIIIII � � 100 IIIIIIII III II IIIIIRR III IIIIIIIIIIIIIIIIIM IIIIIPR i III iI III y IIIYea III S III (IIIIIIIIII IIIIIIIIIII II III IIIIIIIIII 6-6 Appendix 6:Standard 2 Computations and Supporting Information 11625.34 - EX Type 111 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 25 Time span=0.00-30.00 hrs, dt=0.01 hrs, 3001 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentEX-1: Rt 114 and Andover Runoff Area=125,650 sf 6.33% Impervious Runoff Depth=5.10" Flow Length=488' Tc=6.6 min CN=76 Runoff=16.8 cfs 53,436 cf SubcatchmentEX-2: Medina Drive, Runoff Area=215,120 sf 37.51% Impervious Runoff Depth=5.92" Flow Length=465' Tc=7.1 min CN=83 Runoff=32.1 cfs 106,128 cf SubcatchmentEX-3: Outside Project Site- Runoff Area=36,750 sf 87.73% Impervious Runoff Depth=7.34" Tc=6.0 min CN=95 Runoff=6.5 cfs 22,484 cf Link DP-1:AndoverStreet System Inflow=55.3 cfs 182,048 cf Primary=55.3 cfs 182,048 cf Total Runoff Area = 377,520 sf Runoff Volume = 182,048 cf Average Runoff Depth = 5.79" 67.98% Pervious = 256,630 sf 32.02% Impervious = 120,890 sf 11625.34 - EX Type 111 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 26 Summary for Subcatchment EX-1 : Rt 114 and Andover St Corner Runoff = 16.8 cfs @ 12.09 hrs, Volume= 53,436 cf, Depth= 5.10" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 117,700 74 >75% Grass cover, Good, HSG C 0 98 Roof 7,950 98 Paved parking 125,650 76 Weighted Average 117700 93.67% Pervious Area 7,950 6.33% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 4.3 50 0.0400 0.19 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.4 90 0.0500 3.60 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 62 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 1.3 250 0.0400 3.22 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 36 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 6.6 488 Total 11625.34 - EX Type 111 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 27 Subcatchment EX-1: Rt 114 and Andover St Corner Hydrograph El Runoff 16.8 cfs 17 , Type 11124-hr i 16 15 100-Year Rainfall=7.94" 14 13° Runoff Area=125,650 sf 12 / Runoff Volume=53,436 d Runoff 10 Depth=5.10" 9 Flow Length=488' 8 7' Tc=6.6 min 6 � CN=76 5 4 2 i r r/;,',,,i�cr��/,,,�ia, rr„/�-�,��,-�%ur,,,�,�?r,%/;,',%„ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 28 Summary for Subcatchment EX-2: Medina Drive, Church, Main Entrance Runoff = 32.1 cfs @ 12.10 hrs, Volume= 106,128 cf, Depth= 5.92" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 1347420 74 >75% Grass cover, Good, HSG C 297220 98 Roof 517480 98 Paved parking 2157120 83 Weighted Average 1347420 62.49% Pervious Area 807700 37.51% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 3.9 50 0.0500 0.21 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.1 28 0.0500 3.60 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 1.0 100 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 70 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.8 132 0.0300 2.79 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.9 85 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 7.1 465 Total 11625.34 - EX Type 111 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 29 Subcatchment EX-2: Medina Drive, Church, Main Entrance Hydrograph El Runoff 34 32.1 cfs 32 l j Type III 24-hr 30 � 28 100-Year Rainfall=7.94" /° Runoff Area=215,120 sf 26 ��% Runoff Volume=106,128 d 22° Runoff Depth=5.92" 20 � Flow Len18 gth=465' 16 � 0 14 Tc=7.1 m i n 12 ,r CN=83 10 8 ig ,%/. =191 0 s 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 30 Summary for Subcatchment EX-3: Outside Project Site - Andover/Elm St Runoff = 6.5 cfs @ 12.08 hrs, Volume= 22,484 cf, Depth= 7.34" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 4,510 74 >75% Grass cover, Good, HSG C 0 98 Roof 321240 98 Paved parking 361750 95 Weighted Average 4,510 12.27% Pervious Area 321240 87.73% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment EX-3: Outside Project Site - Andover/Elm St Hydrograph 1- - - - - - - - - - - - - - - - E Runoff 7 6.5 cfs Type III 24-hr 100-Year Rainfall=7.94" 5 % Runoff Area=36 750 sf Runoff Volume=22,484 cf 4-Runoff Depth=7.34" 0 Tc=6.0 m i n 3 CN=95 r K/6 //, 0 /-"„-ir,//r„-ion , 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - EX Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 31 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 32.02% Impervious, Inflow Depth = 5.79" for 100-Year event Inflow = 55.3 cfs @ 12.10 hrs, Volume= 182,048 cf Primary = 55.3 cfs @ 12.10 hrs, Volume= 182,048 cf, Atten= 0%, Lag= 0.0 min Routed to nonexistent node DP-2 Primary outflow = Inflow, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Link DP-1: Andover Street System Hydrograph Inflow 60 55.3 cfs El Primary 55.3 cf, Inflow Area=377,520 sf „ j 45 � 40 ,� 35 C 25 UL 20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) uuuuumuuu uuumuuu um ull I ° P,,,uuuo uuu uumi'lllllu� I uuml I I V iIIIIIIV� uumullllll VI uuuuuuuuu II B-7 Appendix B:Standard 2 Computations and Supporting Information PR-11 PR-11 P 1 tPR-17 StormTrap ST2 Single BLDG 1-EAST SIDE 20 PR-12 PR-12 P2 PR-19 StormTrap ST2 Singl BLDG 2-SOUTH SIDE 4-0 PR-16 DP-1 BLDG 1-WEST SIDE Andover Street PR-18 DG 2-NORTH SIDE P3 PR-13 StormTrap ST2 Sing PR-13 4-6 tPR-14 PR-15 PR-14 PR-15 PR-20 PR-20 tPR-J30 Outside Project Site- Andover/Elm St S4ca Reach Pond Link Routing Diagram for 11625.34-PR Prepared by VHB, Inc, Printed 2/19/2024 HydroCAD®10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC 11625.34 - PR Prepared by VH B, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 2 Rainfall Events Listing Event# Event Storm Type Curve Mode Duration B/B Depth AMC Name (hours) (inches) 1 2-Year Type III 24-hr Default 24.00 1 3.16 2 2 10-Year Type III 24-hr Default 24.00 1 5.01 2 3 25-Year Type III 24-hr Default 24.00 1 6.16 2 4 100-Year Type III 24-hr Default 24.00 1 7.94 2 11625.34 - PR Prepared by VH B, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 3 Area Listing (all nodes) Area CN Description (sq-ft) (subcatchment-numbers) 1931170 74 >75% Grass cover, Good, HSG C (PR-111 PR-12, PR-13, PR-14, PR-157 PR-20, PR-30) 117,860 98 Paved parking (PR-11, PR-12, PR-13, PR-14, PR-15, PR-20, PR-30) 667490 98 Roof (PR-12, PR-16, PR-17, PR-18, PR-19, PR-20) 3775520 86 TOTAL AREA 2 II IIIIIIIIIYea r S torm t .................... �IIlroposed 6-8 Appendix 6:Standard 2 Computations and Supporting Information 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 4 Time span=0.00-30.00 hrs, dt=0.01 hrs, 3001 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentPR-11: PR-11 Runoff Area=22,900 sf 44.28% Impervious Runoff Depth=1.72" Flow Length=167' Tc=6.0 min CN=85 Runoff=1.1 cfs 3,289 cf SubcatchmentPR-12: PR-12 Runoff Area=36,390 sf 48.26% Impervious Runoff Depth=1.80" Tc=6.0 min CN=86 Runoff=1.8 cfs 5,460 cf SubcatchmentPR-13: PR-13 Runoff Area=39,890 sf 8.77% Impervious Runoff Depth=1.12" Tc=6.0 min CN=76 Runoff=1.2 cfs 3,737 cf SubcatchmentPR-14: PR-14 Runoff Area=34,140 sf 46.87% Impervious Runoff Depth=1.72" Tc=6.0 min CN=85 Runoff=1.6 cfs 4,903 cf SubcatchmentPR-15: PR-15 Runoff Area=38,790 sf 8.53% Impervious Runoff Depth=1.12" Tc=6.0 min CN=76 Runoff=1.1 cfs 3,634 cf SubcatchmentPR-16: BLDG 1 -WEST Runoff Area=11,820 sf 100.00% Impervious Runoff Depth=2.93" Tc=6.0 min CN=98 Runoff=0.8 cfs 2,884 cf SubcatchmentPR-17: BLDG 1 - EAST Runoff Area=10,110 sf 100.00% Impervious Runoff Depth=2.93" Tc=6.0 min CN=98 Runoff=0.7 cfs 2,467 cf SubcatchmentPR-18: BLDG 2 - NORTH Runoff Area=6,990 sf 100.00% Impervious Runoff Depth=2.93" Tc=6.0 min CN=98 Runoff=0.5 cfs 1,705 cf SubcatchmentPR-19: BLDG 2 -SOUTH Runoff Area=8,350 sf 100.00% Impervious Runoff Depth=2.93" Tc=6.0 min CN=98 Runoff=0.6 cfs 2,037 cf SubcatchmentPR-20: PR-20 Runoff Area=131,390 sf 48.96% Impervious Runoff Depth=1.80" Tc=6.0 min CN=86 Runoff=6.4 cfs 19,713 cf SubcatchmentPR-30: Outside Project Site Runoff Area=36,750 sf 87.73% Impervious Runoff Depth=2.61" Tc=6.0 min CN=95 Runoff=2.4 cfs 7,980 cf Pond P1: StormTrap ST2 Single 2-0 Peak EIev=225.05' Storage=1,466 cf Inflow=1.8 cfs 5,756 cf Discarded=0.0 cfs 1,555 cf Primary=1.2 cfs 3,889 cf Outflow=1.2 cfs 5,444 cf Pond P2: StormTrap ST2 Single 4-0 Peak EIev=220.36' Storage=4,721 cf Inflow=4.2 cfs 14,270 cf Discarded=0.0 cfs 1,994 cf Primary=2.1 cfs 11,073 cf Outflow=2.2 cfs 13,066 cf Pond P3: StormTrap ST2 Single 4-6 Peak EIev=215.70' Storage=7,564 cf Inflow=3.2 cfs 10,346 cf Discarded=0.0 cfs 2,836 cf Primary=0.1 cfs 880 cf Outflow=0.1 cfs 3,717 cf Link DP-1:AndoverStreet System Inflow=10.8 cfs 43,280 cf Primary=10.8 cfs 43,280 cf Total Runoff Area = 377,520 sf Runoff Volume = 57,809 cf Average Runoff Depth = 1.84" 51.17% Pervious = 193,170 sf 48.83% Impervious = 184,350 sf 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment PR-11: PR-11 Runoff = 1.1 cfs @ 12.09 hrs, Volume= 3,289 cf, Depth= 1.72" Routed to Pond P1 : StormTrap ST2 Single 2-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 121760 74 >75% Grass cover, Good, HSG C 0 98 Roof 101140 98 Paved parking 22,900 85 Weighted Average 121760 55.72% Pervious Area 101140 44.28% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 3.6 50 0.0600 0.23 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.2 20 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 62 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.2 35 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 4.4 167 Total, Increased to minimum Tc = 6.0 min 11625.34 - PR Type 111 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 6 Subcatchment PR-11: PR-11 Hydrograph El Runoff 1.1 cfs 1 Type III 24=hr 2-Year Rainfall=3.16" Runoff Area=22,900 Sf Runoff Volume=3,289 cf Runoff Depth=1,72" 0 Flow Length=167' Tc=6,0 min CN=85 / 0 i„ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 7 Summary for Subcatchment PR-12: PR-12 Runoff = 1.8 cfs @ 12.09 hrs, Volume= 5,460 cf, Depth= 1.80" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 181830 74 >75% Grass cover, Good, HSG C 3,680 98 Roof 131880 98 Paved parking 361390 86 Weighted Average 18,830 51.74% Pervious Area 171560 48.26% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-12: PR-12 Hydrograph El Runoff 1.8 cfs Type III 24=hr 2-Year Rainfall=3.16" Runoff Area=36,390 sf Runoff Volume=5,460 d Runoff Depth=1.80 0 Tc=6,0 min CN=86 r i %i," // i„ M U U U U U U U U U U M M 1111 1111 1111 1111 1111 1111 U U U U U U U U U U U U U U U U U U U U U TIT974"IIFIIF-]Il�IIFIIFIIIFlI 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 8 Summary for Subcatchment PR-13: PR-13 Runoff = 1.2 cfs @ 12.09 hrs, Volume= 3,737 cf, Depth= 1.12" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 361390 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,500 98 Paved parking 391890 76 Weighted Average 36,390 91.23% Pervious Area 3500 8.77% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-13: PR-13 Hydrograph Runoff 1.2 cfs Type III 24=hr 2-Year Rainfall�3.16" 1 Runoff Area=39,890 sf %! Runoff Volume=3,737 d Runoff Depth=1.12" 0 Tc=6,0 min CN=76 / r rr r 0 % c, %,'o'„ ,,,c, %'/ /',%,✓r,,,,i, ,,,,!/i,' „/,'„/ i�-,u, 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 9 Summary for Subcatchment PR-14: PR-14 Runoff = 1.6 cfs @ 12.09 hrs, Volume= 4,903 cf, Depth= 1.72" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 181140 74 >75% Grass cover, Good, HSG C 0 98 Roof 161000 98 Paved parking 341140 85 Weighted Average 18,140 53.13% Pervious Area 161000 46.87% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-14: PR-14 Hydrograph El Runoff 1.6 cfs Type III 24=hr 2-Year Rainfall=3.16" Runoff Area=34 140 sf Runoff Volume=4,903 d Runoff Depth=1,72" ,0 Tc=6,0 min CN=85 F13-11FIF-liml I r %�," //,,.i�. „"it i;c/',%;"i Ui,r,,,,,, „/ M M 1111 1111 1111 1111 ill 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 10 Summary for Subcatchment PR-15: PR-15 Runoff = 1.1 cfs @ 12.09 hrs, Volume= 3,634 cf, Depth= 1.12" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 351480 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,310 98 Paved parking 381790 76 Weighted Average 35,480 91.47% Pervious Area 3,310 8.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-15: PR-15 Hydrograph LEI Runoff 1.1 cfs Type III 24=hr 1 / 2-Year Rainfall=3.16" j Runoff Area=38,790 sf Runoff Volume=3,634 d Runoff Depth=1.12" 0 Tc=6,0 min CN=76 i 01, 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 11 Summary for Subcatchment PR-16: BLDG 1 - WEST SIDE Runoff = 0.8 cfs @ 12.08 hrs, Volume= 2,884 cf, Depth= 2.93" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 111820 98 Roof 0 98 Paved parking 111820 98 Weighted Average 11,820 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-16: BLDG 1 - WEST SIDE Hydrograph 0.9 El Runoff 0.85 0.8 cfs 0.8Type III 24=hr � 0.75 � 2=Year Rainfall=3.16" 0.7 0.65 Runoff Area=11,820 sf Runoff Volume=2,884 d 0.55 0.5 % Runoff Depth=2,93" 3 0.45 i Tc=6.0 min � 0.4 0.35 CN=98 0.2 0.15 i 0.1 0.05 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 12 Summary for Subcatchment PR-17: BLDG 1 - EAST SIDE Runoff = 0.7 cfs @ 12.08 hrs, Volume= 2,467 cf, Depth= 2.93" Routed to Pond P1 : StormTrap ST2 Single 2-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 101110 98 Roof 0 98 Paved parking 101110 98 Weighted Average 10,110 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-17: BLDG 1 - EAST SIDE Hydrograph El Runoff 0.75 0.7 cfs 0.7 % Type III 24=hr 0.65 2-Year Rainfall=3.16" 0.6 Runoff Area sf j 0.5 �� Runoff Volume=2,467 d 0.45 Runoff Depth=2,93" 0.4 _ ,: 0.35 % Tc=6.0 min �' 0.3 CN=98 0.25 0.2 j 0.15 r 0.1 0.05 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 13 Summary for Subcatchment PR-18: BLDG 2 - NORTH SIDE Runoff = 0.5 cfs @ 12.08 hrs, Volume= 1,705 cf, Depth= 2.93" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 6,990 98 Roof 0 98 Paved parking 6,990 98 Weighted Average 6,990 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-18: BLDG 2 - NORTH SIDE Hydrograph 0.55 El Runoff 0.5 cfs 0.5 / Type III 24=hr 2-Year Rainfall=3.16" % Runoff Area=6,990 sf 0.35 Runoff Volume=1 705 d 0.3 Runoff Depth=2,93" 0.25 Tc=6.0 min CN=98 0.15 0.1 0.05 01 % 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 14 Summary for Subcatchment PR-19: BLDG 2 - SOUTH SIDE Runoff = 0.6 cfs @ 12.08 hrs, Volume= 2,037 cf, Depth= 2.93" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 8,350 98 Roof 0 98 Paved parking 8,350 98 Weighted Average 8,350 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-19: BLDG 2 - SOUTH SIDE Hydrograph 0.65 El Runoff 0.6 0.6 cfs Type III 24=hr 0.55 0.5 2-Year Rainfall=3.16" Runoff Area 8,350 sf 0.4 41 Runoff Volume=2,037 cf 0.35 Runoff Depth=2,93" 0.3 UL Tc=6.0 min 0.25 CN=98 0.2 0.15 0.1 0.05 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 15 Summary for Subcatchment PR-20: PR-20 Runoff = 6.4 cfs @ 12.09 hrs, Volume= 19,713 cf, Depth= 1.80" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 671060 74 >75% Grass cover, Good, HSG C 251540 98 Roof 381790 98 Paved parking 131,390 86 Weighted Average 67,060 51.04% Pervious Area 641330 48.96% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-20: PR-20 Hydrograph 7 0 Runoff 6.4 cfs Type III 24-hr 6 2-Year Rainfall=3.16" 5 % Runoff Area=131,390 sf Runoff Volume=19,713 cf 4 Runoff Depth=1.80" 3 o Tc=6.0 min CN=86 r /, i', %"" i' r 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 16 Summary for Subcatchment PR-30: Outside Project Site - Andover/Elm St Runoff = 2.4 cfs @ 12.08 hrs, Volume= 7,980 cf, Depth= 2.61" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 2-Year Rainfall=3.16" Area (sf) CN Description 4,510 74 >75% Grass cover, Good, HSG C 0 98 Roof 321240 98 Paved parking 361750 95 Weighted Average 4,510 12.27% Pervious Area 321240 87.73% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-30: Outside Project Site - Andover/Elm St Hydrograph El Runoff 2.4 cfs Type III 24=hr 2-Year Rainfall=3.16" Runoff Area=36,750 sf Runoff Volume=7,980 d Runoff Depth=2.61'' 0 Tc=6,0 min CN=95 i r �ir a a sir„"a'%rr,%✓ „/,,,,, ,,, ! a/�, „,,",,,%,,,,,,i",/„',a,/i 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 17 Summary for Pond P1: StormTrap ST2 Single 2-0 Inflow Area = 33,010 sf, 61.35% Impervious, Inflow Depth = 2.09" for 2-Year event Inflow = 1.8 cfs @ 12.09 hrs, Volume= 5,756 cf Outflow = 1.2 cfs @ 12.17 hrs, Volume= 5,444 cf, Atten= 30%, Lag= 4.8 min Discarded = 0.0 cfs @ 8.47 hrs, Volume= 1,555 cf Primary = 1.2 cfs @ 12.17 hrs, Volume= 3,889 cf Routed to Pond P2 : StormTrap ST2 Single 4-0 Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 225.05'@ 12.17 hrs Surf.Area= 1,488 sf Storage= 1,466 cf Plug-Flow detention time= 121.6 min calculated for 5,443 cf(95% of inflow) Center-of-Mass det. time= 91.6 min ( 888.2 - 796.7 ) Volume Invert Avail.Storage Storage Description #1 A 223.60' 450 cf 32.27'W x 46.10'L x 3.00'H Field A 4,463 cf Overall - 3,338 cf Embedded = 1,126 cf x 40.0% Voids #2A 224.10' 2,316 cf StormTrap ST2 SingleTrap 2-Ox 4 Inside #1 Inside= 101.7"W x 24.0"H => 15.05 sf x 15.40'L = 231.7 cf Outside= 101.7"W x 30.0"H => 21.20 sf x 15.401 = 326.4 cf 4 Chambers in 2 Rows 16.96' x 30.79' Core + 6.66' Border= 30.27' x 44.10' System #3 224.20' 35 cf 4.00'D x 2.80'H Vertical Cone/CylindeFimpervious #4 227.00' 90 cf Custom Stage Data (Prismatic)Listed below(Recalc) 2,892 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 227.00 110 0 0 227.50 250 90 90 Device Routing Invert Outlet Devices #1 Discarded 223.60' 0.520 in/hr Exfiltration over Surface area #2 Primary 224.40' 12.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 224.40'/224.30' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 0.79 sf Discarded OutFlow Max=0.0 cfs @ 8.47 hrs HW=223.64' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=1.2 cfs @ 12.17 hrs HW=225.05' (FreeDischarge) L2=Culvert (Barrel Controls 1.2 cfs @ 3.21 fps) 11625.34 - PR Type 11124-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 18 Pond P1: StormTrap ST2 Single 2-0 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrap 2-0(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 24.0"H => 15.05 sf x 15.401 = 231.7 cf Outside= 101.7"W x 30.0"H => 2120 sf x 15.401 = 326.4 cf 2 ChamberslRow x 15.40' Long = 30.79' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 46.10' Base Length 2 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 32.27' Base Width 6.0" Stone Base + 30.0" Chamber Height= 3.00' Field Height 4 Chambers x 231.7 cf+ 1,389.8 cf Border= 2,316.5 cf Chamber Storage 4 Chambers x 326.4 cf+ 2,032.2 cf Border= 3,337.7 cf Displacement 4,463.5 cf Field- 3,337.7 cf Chambers = 1,125.8 cf Stone x 40.0%Voids = 450.3 cf Stone Storage Chamber Storage + Stone Storage= 2,766.8 cf = 0.064 of Overall Storage Efficiency = 62.0 Overall System Size =46.10'x 32.27'x 3.00' 4 Chambers(plus border) 165.3 cy Field 41.7 cy Stone 11625.34 - PR Type H/ 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 19 Pond Pl: StormTrap ST2 Single 2-0 Hydrograph M Inflow 1.8 cfs """���Outflow Inflow Area=33 El ,010 Sf Discarded 0 Primary Peak Elev=225.05' Stograe=1,466 cf 1.2 cfs 1.2 cfs o UL mmmm 0 1111 U7F-F-U-TV-U7FU-]FU-F U U U U U U U U U U U U WT�1jr7ll7llpllr7llF71jr7ll7llpllr7llF 1111 U U U U U U U U U U U U U U U U U U U U U U U U U U U iiir7MT��Fiir7iir7iir7ii7��Fiir7iI 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 20 Summary for Pond P2: StormTrap ST2 Single 4-0 Inflow Area = 89,570 sf, 64.73% Impervious, Inflow Depth = 1.91" for 2-Year event Inflow = 4.2 cfs @ 12.10 hrs, Volume= 14,270 cf Outflow = 2.2 cfs @ 12.33 hrs, Volume= 13,066 cf, Atten= 48%, Lag= 13.8 min Discarded = 0.0 cfs @ 7.34 hrs, Volume= 1,994 cf Primary = 2.1 cfs @ 12.33 hrs, Volume= 11,073 cf Routed to Link DP-1 : Andover Street System Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 220.36'@ 12.33 hrs Surf.Area= 1,829 sf Storage= 4,721 cf Plug-Flow detention time= 116.1 min calculated for 13,062 cf(92% of inflow) Center-of-Mass det. time= 75.4 min ( 873.4 - 798.0 ) Volume Invert Avail.Storage Storage Description #1 A 217.00' 721 cf 23.79'W x 76.90'L x 5.00'H Field A 9,147 cf Overall - 7,344 cf Embedded = 1,803 cf x 40.0% Voids #2A 217.50' 5,720 cf StormTrap ST2 SingleTrap 4-Ox 4 Inside #1 Inside= 101.7"W x 48.0"H => 30.55 sf x 15.40'L = 470.3 cf Outside= 101.7"W x 54.0"H => 38.16 sf x 15.401 = 587.4 cf 8.48' x 61.58' Core + 6.66' Border = 21.79' x 74.90' System #3 217.50' 75 cf 4.00'D x 6.00'H Vertical Cone/CylindeFImpervious #4 223.50' 222 cf Custom Stage Data (Prismatic)Listed below(Recalc) 6,738 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum-Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 223.50 110 0 0 223.90 11000 222 222 Device Routing Invert Outlet Devices #1 Discarded 217.00' 0.520 in/hr Exfiltration over Surface area #2 Primary 217.50' 18.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 217.50'/217.30' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 1.77 sf #3 Device 2 218.30' 6.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 2 220.20' 4.0' long x 2.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) Discarded OutFlow Max=0.0 cfs @ 7.34 hrs HW=217.07' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=2.1 cfs @ 12.33 hrs HW=220.36' (Free Discharge) L2=Culvert (Passes 2.1 cfs of 12.4 cfs, potential flow) 3=Orifice/Grate (Orifice Controls 1.3 cfs @ 6.48 fps) 4=Sharp-Crested Rectangular Weir(Weir Controls 0.9 cfs @ 1.32 fps) 11625.34 - PR Type 11124-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 21 Pond P2: StormTrap ST2 Single 4-0 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrap 4-0(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 48.0"H => 30.55 sf x 15.401 = 470.3 cf Outside= 101.7"W x 54.0"H => 38.16 sf x 15.401 = 587.4 cf 4 Chambers/Row x 15.40' Long = 61.58' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 76.90' Base Length 1 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 23.79' Base Width 6.0" Stone Base + 54.0" Chamber Height= 5.00' Field Height 4 Chambers x 470.3 cf+ 3,838.5 cf Border= 5,719.E cf Chamber Storage 4 Chambers x 587.4 cf+ 4,994.7 cf Border= 7,344.5 cf Displacement 9,147.4 cf Field- 7,344.5 cf Chambers = 1,802.9 cf Stone x 40.0%Voids = 721.2 cf Stone Storage Chamber Storage + Stone Storage= 6,440.7 cf = 0.148 of Overall Storage Efficiency = 70.4 Overall System Size = 76.90'x 23.79'x 5.00' 4 Chambers(plus border) 338.8 cy Field 66.8 cy Stone 11625.34 - PR Type 111 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 22 Pond P2: StormTrap ST2 Single 4-0 Hydrograph Inflow 4.2 cfs aull Outflow Inflow Area=89,570 Sf Discarded 0 Primary Peak Elev=220.36' 4 Storage=4,721 cf 3 2.2 cfs t� 2.1 cfs O � 2 1 � 1 e m 0.0 cfs 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 23 Summary for Pond P3: StormTrap ST2 Single 4-6 Inflow Area = 81,020 sf, 32.70% Impervious, Inflow Depth = 1.53" for 2-Year event Inflow = 3.2 cfs @ 12.09 hrs, Volume= 10,346 cf Outflow = 0.1 cfs @ 17.40 hrs, Volume= 3,717 cf, Atten= 97%, Lag= 318.8 min Discarded = 0.0 cfs @ 10.18 hrs, Volume= 2,836 cf Primary = 0.1 cfs @ 17.40 hrs, Volume= 880 cf Routed to Link DP-1 : Andover Street System Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 215.70'@ 17.40 hrs Surf.Area= 3,028 sf Storage= 7,564 cf Plug-Flow detention time=457.5 min calculated for 3,715 cf(36% of inflow) Center-of-Mass det. time= 321.6 min ( 1,147.4 - 825.8 ) Volume Invert Avail.Storage Storage Description #1 A 212.50' 1,040 cf 49.23'W x 61.50'L x 5.50'H Field A 16,652 cf Overall - 14,051 cf Embedded = 2,601 cf x 40.0% Voids #2A 213.00' 11,204 cf StormTrap ST2 SingleTrap 4-6x 12 Inside #1 Inside= 101.7"W x 54.0"H => 34.42 sf x 15.40'L = 529.9 cf Outside= 101.7"W x 60.0"H => 42.40 sf x 15.401 = 652.7 cf 12 Chambers in 4 Rows 33.92' x 46.19' Core + 6.66' Border = 47.23' x 59.50' System #3 216.00' 48 cf 4.00'D x 3.80'H Vertical Cone/Cylinder #4 219.80' 90 cf Custom Stage Data (Prismatic)Listed below(Recalc) 12,382 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum-Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 219.80 50 0 0 221.00 100 90 90 Device Routing Invert Outlet Devices #1 Discarded 212.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 213.00' 18.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 213.00'/212.80' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 1.77 sf #3 Device 2 215.60' 12.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 2 217.00' 4.0' long x 2.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) Discarded OutFlow Max=0.0 cfs @ 10.18 hrs HW=212.59' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=0.0 cfs @ 17.40 hrs HW=215.70' (Free Discharge) L2=Culvert (Passes 0.0 cfs of 11.9 cfs, potential flow) 3=Orifice/Grate (Orifice Controls 0.0 cfs @ 1.08 fps) 4=Sharp-Crested Rectangular Weir( Controls 0.0 cfs) 11625.34 - PR Type 11124-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 24 Pond P3: StormTrap ST2 Single 4-6 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrep 4-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 54.0"H => 34.42 sf x 15.401 = 529.9 cf Outside= 101.7"W x 60.0"H => 42.40 sf x 15.401 = 652.7 cf 3 Chambers/Row x 15.40' Long =46.19' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 61.50' Base Length 4 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 49.23' Base Width 6.0" Stone Base + 60.0" Chamber Height= 5.50' Field Height 12 Chambers x 529.9 cf+ 4,844.5 cf Border= 11,203.8 cf Chamber Storage 12 Chambers x 652.7 cf+ 6,218.0 cf Border= 14,050.7 cf Displacement 16,651.8 cf Field - 14,050.7 cf Chambers= 2,601.1 cf Stone x 40.0% Voids = 1,040.4 cf Stone Storage Chamber Storage + Stone Storage= 12,244.2 cf= 0.281 of Overall Storage Efficiency = 73.5 Overall System Size = 61.50'x 49.23'x 5.50' 12 Chambers(plus border) 616.7 cy Field 96.3 cy Stone 11625.34 - PR Type H/ 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 25 Pond P3: StormTrap ST2 Single 4-6 Hydrograph M Inflow 3.2 cfs Outflow Inflow Area=81 El 020 sf Discarded , 0 Primary Peak Elev=215.70' 3,, Storag a=7 564 cf 2-, 0 0.1 Cfs CS 0 1111 U U v U U U U U U U u FFFFWT-TTV-W--TTT-FT�JIF711711plIF71IF71IF711711plIF71IF711 ��71IF71jr7ll[71171171jr7llF711[711711711 F]JJPJJ�11�11�11[]Jj 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 26 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 48.83% Impervious, Inflow Depth = 1.38" for 2-Year event Inflow = 10.8 cfs @ 12.09 hrs, Volume= 43,280 cf Primary = 10.8 cfs @ 12.09 hrs, Volume= 43,280 cf, Atten= 0%, Lag= 0.0 min Routed to nonexistent node DP-2 Primary outflow = Inflow, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Link DP-1: Andover Street System Hydrograph Inflow 12 _ _ 10.8 Cfs - - - - - - - - - El Primary 11 l 10.$Ofs Inflow Area=377,520 sf 10 9 8 o UL 5 / i i rid j 1 i � � 0 l/U U;,'l//",'�,�a'i,//�%u",,,,! a//',/," 'III 'III ,�c,,,,,,,,/,,,,/ U U 'III 'III 'III 'III'III 'III 'III 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) IIIIIIIIII 10........Yea r ��� II IIIII� ��� IIIIIIIIIIIIIIIIIIII IIIII S IIIIIIIIIII II 6-9 Appendix 6:Standard 2 Computations and Supporting Information 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 27 Time span=0.00-30.00 hrs, dt=0.01 hrs, 3001 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentPR-11: PR-11 Runoff Area=22,900 sf 44.28% Impervious Runoff Depth=3.38" Flow Length=167' Tc=6.0 min CN=85 Runoff=2.1 cfs 6,445 cf SubcatchmentPR-12: PR-12 Runoff Area=36,390 sf 48.26% Impervious Runoff Depth=3.48" Tc=6.0 min CN=86 Runoff=3.4 cfs 10,542 cf SubcatchmentPR-13: PR-13 Runoff Area=39,890 sf 8.77% Impervious Runoff Depth=2.54" Tc=6.0 min CN=76 Runoff=2.7 cfs 8,456 cf SubcatchmentPR-14: PR-14 Runoff Area=34,140 sf 46.87% Impervious Runoff Depth=3.38" Tc=6.0 min CN=85 Runoff=3.1 cfs 9,608 cf SubcatchmentPR-15: PR-15 Runoff Area=38,790 sf 8.53% Impervious Runoff Depth=2.54" Tc=6.0 min CN=76 Runoff=2.7 cfs 8,223 cf SubcatchmentPR-16: BLDG 1 -WEST Runoff Area=11,820 sf 100.00% Impervious Runoff Depth=4.77" Tc=6.0 min CN=98 Runoff=1.3 cfs 4,702 cf SubcatchmentPR-17: BLDG 1 - EAST Runoff Area=10,110 sf 100.00% Impervious Runoff Depth=4.77" Tc=6.0 min CN=98 Runoff=1.1 cfs 4,021 cf SubcatchmentPR-18: BLDG 2 - NORTH Runoff Area=6,990 sf 100.00% Impervious Runoff Depth=4.77" Tc=6.0 min CN=98 Runoff=0.8 cfs 2,780 cf SubcatchmentPR-19: BLDG 2 -SOUTH Runoff Area=8,350 sf 100.00% Impervious Runoff Depth=4.77" Tc=6.0 min CN=98 Runoff=0.9 cfs 3,321 cf SubcatchmentPR-20: PR-20 Runoff Area=131,390 sf 48.96% Impervious Runoff Depth=3.48" Tc=6.0 min CN=86 Runoff=12.1 cfs 38,063 cf SubcatchmentPR-30: Outside Project Site Runoff Area=36,750 sf 87.73% Impervious Runoff Depth=4.43" Tc=6.0 min CN=95 Runoff=4.0 cfs 13,565 cf Pond P1: StormTrap ST2 Single 2-0 Peak Elev=225.42' Storage=1,925 cf Inflow=3.2 cfs 10,466 cf Discarded=0.0 cfs 1,684 cf Primary=2.4 cfs 8,442 cf Outflow=2.5 cfs 10,126 cf Pond P2: StormTrap ST2 Single 4-0 Peak EIev=220.80' Storage=5,385 cf Inflow=7.8 cfs 27,006 cf Discarded=0.0 cfs 2,143 cf Primary=7.3 cfs 23,621 cf Outflow=7.3 cfs 25,764 cf Pond P3: StormTrap ST2 Single 4-6 Peak EIev=216.37' Storage=9,297 cf Inflow=6.6 cfs 20,845 cf Discarded=0.0 cfs 3,080 cf Primary=1.9 cfs 11,064 cf Outflow=2.0 cfs 14,144 cf Link DP-1:AndoverStreet System Inflow=25.4 cfs 94,536 cf Primary=25.4 cfs 94,536 cf Total Runoff Area = 377,520 sf Runoff Volume = 109,727 cf Average Runoff Depth = 3.49" 51.17% Pervious = 193,170 sf 48.83% Impervious = 184,350 sf 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 28 Summary for Subcatchment PR-11: PR-11 Runoff = 2.1 cfs @ 12.09 hrs, Volume= 6,445 cf, Depth= 3.38" Routed to Pond P1 : StormTrap ST2 Single 2-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 121760 74 >75% Grass cover, Good, HSG C 0 98 Roof 101140 98 Paved parking 22,900 85 Weighted Average 121760 55.72% Pervious Area 101140 44.28% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 3.6 50 0.0600 0.23 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.2 20 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 62 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.2 35 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 4.4 167 Total, Increased to minimum Tc = 6.0 min 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 29 Subcatchment PR-11: PR-11 Hydrograph El Runoff 2.1 cfs Type III 24-hr 1 0-Year Rainfall=5.01" j Runoff Area=22,900 Sf Runoff Volume=6,445 cf Runoff Depth=3.38" o Flow Length=167' Tc=6,0 min CN=85 .... .................. o-e/ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 30 Summary for Subcatchment PR-12: PR-12 Runoff = 3.4 cfs @ 12.09 hrs, Volume= 10,542 cf, Depth= 3.48" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 181830 74 >75% Grass cover, Good, HSG C 3,680 98 Roof 131880 98 Paved parking 361390 86 Weighted Average 18,830 51.74% Pervious Area 171560 48.26% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-12: PR-12 Hydrograph El Runoff 3.4 cfs Type III 24-hr 3 / 10-Year Rainfall=5.01" Runoff Area=36,390 sf Runoff Volume=10,542 cf U 2 % Runoff Depth=3.48" Tc=6.0 m i n CN=86 0144 U U U U U U U U U U U U U U U M M 1111 1111 1111 1111 111111111111 111111111111 U U U U I U U U U U U U U U U U T TTTT"I I I 1 11 11 1111 11 11 11 11 r??M?TMrF?T7U 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 31 Summary for Subcatchment PR-1 3: PR-13 Runoff = 2.7 cfs @ 12.09 hrs, Volume= 8,456 cf, Depth= 2.54" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 361390 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,500 98 Paved parking 391890 76 Weighted Average 36,390 91.23% Pervious Area 3500 8.77% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-13: PR-13 Hydrograph 3 El Runoff 2.7 cfs / Type III 24=hr 1 0-Year Rainfall=5.01"IN .. Runoff Area=39,890 sf 2 Runoff Volume=8,456 d Runoff Depth=2,54" 0 Tc=6,0 min CN=76 F� ......I'll, i /�U U' j o1111 1111/ / ' /O ur%/ it lF U U U U M M 1111 1111 1111 1111 U U U U U U U U U U U U U U U U U U U U U U U U U U 9 9 1111 1111 111171IF71IF71IF711 U U 9 1111 1111 1111 11711­71171171 U U U U U FT7FT-FT7FF-FFTT-"U y7FFTJ�p 1111 1111 1111 1111 1111 1111 U U U U U U U U U U U U U 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 32 Summary for Subcatchment PR-14: PR-14 Runoff = 3.1 cfs @ 12.09 hrs, Volume= 9,608 cf, Depth= 3.38" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 181140 74 >75% Grass cover, Good, HSG C 0 98 Roof 161000 98 Paved parking 341140 85 Weighted Average 18,140 53.13% Pervious Area 161000 46.87% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-14: PR-14 Hydrograph Runoff 3.1 cfs 3 ,,. TYp e III 24=hr j 1 0-Year Rainfall=5.01'' Runoff Area=34,140 sf .. j 2 Runoff Volume=9,608 d Runoff Depth=3.38" 0 3 Tc=6,0 min CN=85 1 r rr; / 0 // ou- / „-ur,%%u.- 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 33 Summary for Subcatchment PR-15: PR-15 Runoff = 2.7 cfs @ 12.09 hrs, Volume= 8,223 cf, Depth= 2.54" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 351480 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,310 98 Paved parking 381790 76 Weighted Average 35,480 91.47% Pervious Area 3,310 8.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-15: PR-15 Hydrograph LEI Runoff 2.7 cfs Type III 24=hr 1 0-Year Rainfall=5.01.. % Runoff Area=38,790 sf Runoff Volume=8,223 d Runoff Depth=2.54" 0 Tc=6,0 min CN=76 1 0 �z/?. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 34 Summary for Subcatchment PR-16: BLDG 1 - WEST SIDE Runoff = 1.3 cfs @ 12.08 hrs, Volume= 4,702 cf, Depth= 4.77" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 111820 98 Roof 0 98 Paved parking 111820 98 Weighted Average 11,820 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-16: BLDG 1 - WEST SIDE Hydrograph I El Runoff 1.3 cfs Type III 24=hr 1 0-Year Rainfall=5.01 % Runoff Area=1 1 sf Runoff Volume=4,702 d Runoff Depth=4,77" 0 Tc=6,0 min CN=98 PT, i �/ � /�. �// o/✓/ .,...% U U III U U U U 011 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 35 Summary for Subcatchment PR-17: BLDG 1 - EAST SIDE Runoff = 1.1 cfs @ 12.08 hrs, Volume= 4,021 cf, Depth= 4.77" Routed to Pond P1 : StormTrap ST2 Single 2-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 101110 98 Roof 0 98 Paved parking 101110 98 Weighted Average 10,110 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-17: BLDG 1 - EAST SIDE Hydrograph I El Runoff 1.1 cfs Type III 24=hr 1 1 0-Year Rainfall=5.01 Runoff Area=10,110 sf Runoff Volume=4,021 d Runoff Depth=4,77" 0 Tc=6,0 min CN=98 011 UU14i U U U U U �/ i,. /�. �//,i/��o/,ri;o-./✓/ U U U M 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 36 Summary for Subcatchment PR-18: BLDG 2 - NORTH SIDE Runoff = 0.8 cfs @ 12.08 hrs, Volume= 2,780 cf, Depth= 4.77" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 6,990 98 Roof 0 98 Paved parking 6,990 98 Weighted Average 6,990 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-18: BLDG 2 - NORTH SIDE Hydrograph 0.85 El Runoff 0.8 0.8 cfs Type III 24=hr 0.75 - 1 0-Year Rainfall=5.01 0.65 Runoff Area 6,990 sf 0.6 0.55 .� Runoff Volume=2 780 d 0.5 0.45 ! Runoff Depth=4,77" 0.4 UL Tc=6.0 min - ,� 0.35 CN=98 0.25 0.15 0.1PQ 0.05 , 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 37 Summary for Subcatchment PR-19: BLDG 2 - SOUTH SIDE Runoff = 0.9 cfs @ 12.08 hrs, Volume= 3,321 cf, Depth= 4.77" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 8,350 98 Roof 0 98 Paved parking 8,350 98 Weighted Average 8,350 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-19: BLDG 2 - SOUTH SIDE Hydrograph E Runoff 1 0.9 cfs Type III 24=hr 1 0-Year Rainfall=5.01 % Runoff Area=8,350 sf Runoff Volume=3,321 d Runoff Depth=4,77" 0 Tc=6,0 min CN=98 i / i,. > r',/ �;j � is r'%- �i/ U U U U U U U M /��o/,ri;o-./✓/ .,...%/,f .,//.,. �,�.,,///'.%,,i/c,,,,,/c.ra%.,.//:, U-11ru U M M M M U M U M M U U U U M U M M M M U,M M M M U U M M U M M M M U U U U U U U U U U U U M M 01 UU"NUjjUUUU 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 38 Summary for Subcatchment PR-20: PR-20 Runoff = 12.1 cfs @ 12.09 hrs, Volume= 38,063 cf, Depth= 3.48" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 677060 74 >75% Grass cover, Good, HSG C 251540 98 Roof 381790 98 Paved parking 1317390 86 Weighted Average 677060 51.04% Pervious Area 641330 48.96% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-20: PR-20 Hydrograph - - - - - - - - - - - - - - - - El Runoff 13 12.1 cfs 12 ! Type III 24-hr 1 0-Year Rainfall=5.01 10 ON, Runoff Area=131,390f s Runoff Volume=38,063 cf Runoff Depth=3.48" 7 o 9: 6 Tc=6.0 m i n CN=86 4 �, 3 2 , 1 ' =1111U 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 39 Summary for Subcatchment PR-30: Outside Project Site - Andover/Elm St Runoff = 4.0 cfs @ 12.08 hrs, Volume= 13,565 cf, Depth= 4.43" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 10-Year Rainfall=5.01" Area (sf) CN Description 4,510 74 >75% Grass cover, Good, HSG C 0 98 Roof 321240 98 Paved parking 361750 95 Weighted Average 4,510 12.27% Pervious Area 321240 87.73% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-30: Outside Project Site - Andover/Elm St Hydrograph El Runoff 4.0 cfs 4 / Type III 24-hr j 10-Year Rainfall=5.01" Runoff Area=36,750 sf 3 Runoff Volume=13,565 cf Runoff Depth=4.43" 0 Tc=6.0 m i n 2, i CN=95 0 , 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 40 Summary for Pond P1: StormTrap ST2 Single 2-0 Inflow Area = 33,010 sf, 61.35% Impervious, Inflow Depth = 3.80" for 10-Year event Inflow = 3.2 cfs @ 12.09 hrs, Volume= 10,466 cf Outflow = 2.5 cfs @ 12.15 hrs, Volume= 10,126 cf, Atten= 23%, Lag= 3.9 min Discarded = 0.0 cfs @ 6.54 hrs, Volume= 1,684 cf Primary = 2.4 cfs @ 12.15 hrs, Volume= 8,442 cf Routed to Pond P2 : StormTrap ST2 Single 4-0 Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 225.42'@ 12.15 hrs Surf.Area= 1,488 sf Storage= 1,925 cf Plug-Flow detention time=79.4 min calculated for 10,126 cf(97% of inflow) Center-of-Mass det. time= 59.9 min ( 844.5 - 784.6 ) Volume Invert Avail.Storage Storage Description #1 A 223.60' 450 cf 32.27'W x 46.10'L x 3.00'H Field A 4,463 cf Overall - 3,338 cf Embedded = 1,126 cf x 40.0% Voids #2A 224.10' 2,316 cf StormTrap ST2 SingleTrap 2-Ox 4 Inside #1 Inside= 101.7"W x 24.0"H => 15.05 sf x 15.40'L = 231.7 cf Outside= 101.7"W x 30.0"H => 21.20 sf x 15.401 = 326.4 cf 4 Chambers in 2 Rows 16.96' x 30.79' Core + 6.66' Border= 30.27' x 44.10' System #3 224.20' 35 cf 4.00'D x 2.80'H Vertical Cone/CylindeFimpervious #4 227.00' 90 cf Custom Stage Data (Prismatic)Listed below(Recalc) 2,892 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 227.00 110 0 0 227.50 250 90 90 Device Routing Invert Outlet Devices #1 Discarded 223.60' 0.520 in/hr Exfiltration over Surface area #2 Primary 224.40' 12.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 224.40'/224.30' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 0.79 sf Discarded OutFlow Max=0.0 cfs @ 6.54 hrs HW=223.64' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=2.4 cfs @ 12.15 hrs HW=225.42' (FreeDischarge) L2=Culvert (Barrel Controls 2.4 cfs @ 3.78 fps) 11625.34 - PR Type III 24-hr 10-Year Rainfal1=5.01„ Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 41 Pond P1: StormTrap ST2 Single 2-0 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrap 2-0(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 24.0"H => 15.05 sf x 15.401 = 231.7 cf Outside= 101.7"W x 30.0"H => 2120 sf x 15.401 = 326.4 cf 2 ChamberslRow x 15.40' Long = 30.79' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 46.10' Base Length 2 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 32.27' Base Width 6.0" Stone Base + 30.0" Chamber Height= 3.00' Field Height 4 Chambers x 231.7 cf+ 1,389.8 cf Border= 2,316.5 cf Chamber Storage 4 Chambers x 326.4 cf+ 2,032.2 cf Border= 3,337.7 cf Displacement 4,463.5 cf Field- 3,337.7 cf Chambers = 1,125.8 cf Stone x 40.0%Voids = 450.3 cf Stone Storage Chamber Storage + Stone Storage= 2,766.8 cf = 0.064 of Overall Storage Efficiency = 62.0 Overall System Size =46.10'x 32.27'x 3.00' 4 Chambers(plus border) 165.3 cy Field 41.7 cy Stone 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 42 Pond P1: StormTrap ST2 Single 2-0 Hydrograph Inflow 3.2 cfs aull Outflow Infl ow Area=33010 Sf Primary ar Disc, y � Primary ded Peak Elev=225.42' 3 2.5cfs Storae=1 925 cf g 2.4 cfs � i i to 2 O � r 1 mmm 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfall=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 43 Summary for Pond P2: StormTrap ST2 Single 4-0 Inflow Area = 89,570 sf, 64.73% Impervious, Inflow Depth = 3.62" for 10-Year event Inflow = 7.8 cfs @ 12.10 hrs, Volume= 27,006 cf Outflow = 7.3 cfs @ 12.13 hrs, Volume= 25,764 cf, Atten= 6%, Lag= 2.0 min Discarded = 0.0 cfs @ 4.83 hrs, Volume= 2,143 cf Primary = 7.3 cfs @ 12.13 hrs, Volume= 23,621 cf Routed to Link DP-1 : Andover Street System Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 220.80'@ 12.13 hrs Surf.Area= 1,829 sf Storage= 5,385 cf Plug-Flow detention time=77.3 min calculated for 25,756 cf(95% of inflow) Center-of-Mass det. time= 51.7 min ( 841.4 - 789.6 ) Volume Invert Avail.Storage Storage Description #1 A 217.00' 721 cf 23.79'W x 76.90'L x 5.00'H Field A 9,147 cf Overall - 7,344 cf Embedded = 1,803 cf x 40.0% Voids #2A 217.50' 5,720 cf StormTrap ST2 SingleTrap 4-Ox 4 Inside #1 Inside= 101.7"W x 48.0"H => 30.55 sf x 15.40'L = 470.3 cf Outside= 101.7"W x 54.0"H => 38.16 sf x 15.401 = 587.4 cf 8.48' x 61.58' Core + 6.66' Border = 21.79' x 74.90' System #3 217.50' 75 cf 4.00'D x 6.00'H Vertical Cone/CylindeFImpervious #4 223.50' 222 cf Custom Stage Data (Prismatic)Listed below(Recalc) 6,738 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum-Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 223.50 110 0 0 223.90 11000 222 222 Device Routing Invert Outlet Devices #1 Discarded 217.00' 0.520 in/hr Exfiltration over Surface area #2 Primary 217.50' 18.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 217.50'/217.30' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 1.77 sf #3 Device 2 218.30' 6.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 2 220.20' 4.0' long x 2.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) Discarded OutFlow Max=0.0 cfs @ 4.83 hrs HW=217.07' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=7.3 cfs @ 12.13 hrs HW=220.80' (Free Discharge) L2=Culvert (Passes 7.3 cfs of 13.6 cfs potential flow) 3=Orifice/Grate (Orifice Controls 1.4 cfs @ 7.22 fps) 4=Sharp-Crested Rectangular Weir(Weir Controls 5.9 cfs @ 2.53 fps) 11625.34 - PR Type III 24-hr 10-Year Rainfall=5.01„ Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 44 Pond P2: StormTrap ST2 Single 4-0 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrap 4-0(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 48.0"H => 30.55 sf x 15.401 = 470.3 cf Outside= 101.7"W x 54.0"H => 38.16 sf x 15.401 = 587.4 cf 4 Chambers/Row x 15.40' Long = 61.58' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 76.90' Base Length 1 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 23.79' Base Width 6.0" Stone Base + 54.0" Chamber Height= 5.00' Field Height 4 Chambers x 470.3 cf+ 3,838.5 cf Border= 5,719.E cf Chamber Storage 4 Chambers x 587.4 cf+ 4,994.7 cf Border= 7,344.5 cf Displacement 9,147.4 cf Field- 7,344.5 cf Chambers = 1,802.9 cf Stone x 40.0%Voids = 721.2 cf Stone Storage Chamber Storage + Stone Storage= 6,440.7 cf = 0.148 of Overall Storage Efficiency = 70.4 Overall System Size = 76.90'x 23.79'x 5.00' 4 Chambers(plus border) 338.8 cy Field 66.8 cy Stone 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 45 Pond P2: StormTrap ST2 Single 4-0 Hydrograph Inflow 7.8 cfs aull Outflow Inflow Area=89,570 Sf Discarded 7.3 cfs / Primary 8 Peak Elev=220.80' 7.3 cfs Storage=5,385 cf lo- 5 01000 4 2 '%„�� 1 Ad 0.0 cfs 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfall=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 46 Summary for Pond P3: StormTrap ST2 Single 4-6 Inflow Area = 81,020 sf, 32.70% Impervious, Inflow Depth = 3.09" for 10-Year event Inflow = 6.6 cfs @ 12.09 hrs, Volume= 20,845 cf Outflow = 2.0 cfs @ 12.43 hrs, Volume= 14,144 cf, Atten= 70%, Lag= 20.5 min Discarded = 0.0 cfs @ 12.21 hrs, Volume= 3,080 cf Primary = 1.9 cfs @ 12.43 hrs, Volume= 11,064 cf Routed to Link DP-1 : Andover Street System Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 216.37'@ 12.43 hrs Surf.Area= 3,040 sf Storage= 9,297 cf Plug-Flow detention time=223.7 min calculated for 14,144 cf(68% of inflow) Center-of-Mass det. time= 124.5 min ( 934.0 - 809.6 ) Volume Invert Avail.Storage Storage Description #1 A 212.50' 1,040 cf 49.23'W x 61.50'L x 5.50'H Field A 16,652 cf Overall - 14,051 cf Embedded = 2,601 cf x 40.0% Voids #2A 213.00' 11,204 cf StormTrap ST2 SingleTrap 4-6x 12 Inside #1 Inside= 101.7"W x 54.0"H => 34.42 sf x 15.40'L = 529.9 cf Outside= 101.7"W x 60.0"H => 42.40 sf x 15.401 = 652.7 cf 12 Chambers in 4 Rows 33.92' x 46.19' Core + 6.66' Border = 47.23' x 59.50' System #3 216.00' 48 cf 4.00'D x 3.80'H Vertical Cone/Cylinder #4 219.80' 90 cf Custom Stage Data (Prismatic)Listed below(Recalc) 12,382 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum-Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 219.80 50 0 0 221.00 100 90 90 Device Routing Invert Outlet Devices #1 Discarded 212.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 213.00' 18.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 213.00'/212.80' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 1.77 sf #3 Device 2 215.60' 12.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 2 217.00' 4.0' long x 2.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) Discarded OutFlow Max=0.0 cfs @ 12.21 hrs HW=216.03' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=1.9 cfs @ 12.43 hrs HW=216.37' (Free Discharge) L2=Culvert (Passes 1.9 cfs of 13.8 cfs potential flow) 3=Orifice/Grate (Orifice Controls 1.9 cfs @ 2.99 fps) 4=Sharp-Crested Rectangular Weir( Controls 0.0 cfs) 11625.34 - PR Type III 24-hr 10-Year Rainfall=5.01„ Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 47 Pond P3: StormTrap ST2 Single 4-6 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrep 4-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 54.0"H => 34.42 sf x 15.401 = 529.9 cf Outside= 101.7"W x 60.0"H => 42.40 sf x 15.401 = 652.7 cf 3 Chambers/Row x 15.40' Long =46.19' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 61.50' Base Length 4 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 49.23' Base Width 6.0" Stone Base + 60.0" Chamber Height= 5.50' Field Height 12 Chambers x 529.9 cf+ 4,844.5 cf Border= 11,203.8 cf Chamber Storage 12 Chambers x 652.7 cf+ 6,218.0 cf Border= 14,050.7 cf Displacement 16,651.8 cf Field - 14,050.7 cf Chambers= 2,601.1 cf Stone x 40.0% Voids = 1,040.4 cf Stone Storage Chamber Storage + Stone Storage= 12,244.2 cf= 0.281 of Overall Storage Efficiency = 73.5 Overall System Size = 61.50'x 49.23'x 5.50' 12 Chambers(plus border) 616.7 cy Field 96.3 cy Stone 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 48 Pond P3: StormTrap ST2 Single 4-6 Hydrograph Inflow 6.6 cfs Outflow Inflow Area=81 020 sf Discarded , Primary 7 Peak Elev=216.37' 6 Storage=9,297 cf 5 4 3 _o 3 2.o cfs 1.9 cfs 2 1 mmmm % / r 0 ii , a %; r /� sir UUUUUU UUUUUUUUUU UUUUUUUUUU i 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type 111 24-hr 10-Year Rainfal1=5.01" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 49 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 48.83% Impervious, Inflow Depth = 3.00" for 10-Year event Inflow = 25.4 cfs @ 12.10 hrs, Volume= 94,536 cf Primary = 25.4 cfs @ 12.10 hrs, Volume= 94,536 cf, Atten= 0%, Lag= 0.0 min Routed to nonexistent node DP-2 Primary outflow = Inflow, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Link DP-1: Andover Street System Hydrograph Inflow 28 25.4 cfs El Primary 26 25.4 cfs Inflow Area=377,520 sf 22 20 18, o uL 12 � 10 r 8 2 0 1 U U U UU U�a'i,//%u-,,,, a//',/,. o'1,,,, ,/„ A 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 25...........Yea r S torm t ................. )roposed 6-10 Appendix B:Standard 2 Computations and Supporting Information 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 50 Time span=0.00-30.00 hrs, dt=0.01 hrs, 3001 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentPR-11: PR-11 Runoff Area=22,900 sf 44.28% Impervious Runoff Depth=4.45" Flow Length=167' Tc=6.0 min CN=85 Runoff=2.7 cfs 8,499 cf SubcatchmentPR-12: PR-12 Runoff Area=36,390 sf 48.26% Impervious Runoff Depth=4.56" Tc=6.0 min CN=86 Runoff=4.4 cfs 13,833 cf SubcatchmentPR-13: PR-13 Runoff Area=39,890 sf 8.77% Impervious Runoff Depth=3.52" Tc=6.0 min CN=76 Runoff=3.8 cfs 11,696 cf SubcatchmentPR-14: PR-14 Runoff Area=34,140 sf 46.87% Impervious Runoff Depth=4.45" Tc=6.0 min CN=85 Runoff=4.0 cfs 12,671 cf SubcatchmentPR-15: PR-15 Runoff Area=38,790 sf 8.53% Impervious Runoff Depth=3.52" Tc=6.0 min CN=76 Runoff=3.7 cfs 11,374 cf SubcatchmentPR-16: BLDG 1 -WEST Runoff Area=11,820 sf 100.00% Impervious Runoff Depth=5.92" Tc=6.0 min CN=98 Runoff=1.6 cfs 5,833 cf SubcatchmentPR-17: BLDG 1 - EAST Runoff Area=10,110 sf 100.00% Impervious Runoff Depth=5.92" Tc=6.0 min CN=98 Runoff=1.4 cfs 4,989 cf SubcatchmentPR-18: BLDG 2 - NORTH Runoff Area=6,990 sf 100.00% Impervious Runoff Depth=5.92" Tc=6.0 min CN=98 Runoff=1.0 cfs 3,449 cf SubcatchmentPR-19: BLDG 2 -SOUTH Runoff Area=8,350 sf 100.00% Impervious Runoff Depth=5.92" Tc=6.0 min CN=98 Runoff=1.2 cfs 4,121 cf SubcatchmentPR-20: PR-20 Runoff Area=131,390 sf 48.96% Impervious Runoff Depth=4.56" Tc=6.0 min CN=86 Runoff=15.7 cfs 49,946 cf SubcatchmentPR-30: Outside Project Site Runoff Area=36,750 sf 87.73% Impervious Runoff Depth=5.57" Tc=6.0 min CN=95 Runoff=5.0 cfs 17,060 cf Pond P1: StormTrap ST2 Single 2-0 Peak Elev=225.64' Storage=2,197 cf Inflow=4.1 cfs 13,488 cf Discarded=0.0 cfs 1,740 cf Primary=3.1 cfs 11,400 cf Outflow=3.1 cfs 13,140 cf Pond P2: StormTrap ST2 Single 4-0 Peak EIev=220.94' Storage=5,601 cf Inflow=9.9 cfs 35,186 cf Discarded=0.0 cfs 2,194 cf Primary=9.5 cfs 31,738 cf Outflow=9.5 cfs 33,932 cf Pond P3: StormTrap ST2 Single 4-6 Peak EIev=216.99' Storage=10,907 cf Inflow=8.8 cfs 27,816 cf Discarded=0.0 cfs 3,197 cf Primary=3.6 cfs 17,890 cf Outflow=3.6 cfs 21,087 cf Link DP-1:AndoverStreet System Inflow=35.1 cfs 128,008 cf Primary=35.1 cfs 128,008 cf Total Runoff Area = 377,520 sf Runoff Volume = 143,471 cf Average Runoff Depth = 4.56" 51.17% Pervious = 193,170 sf 48.83% Impervious = 184,350 sf 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 51 Summary for Subcatchment PR-11: PR-11 Runoff = 2.7 cfs @ 12.09 hrs, Volume= 8,499 cf, Depth= 4.45" Routed to Pond P1 : StormTrap ST2 Single 2-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 121760 74 >75% Grass cover, Good, HSG C 0 98 Roof 101140 98 Paved parking 22,900 85 Weighted Average 121760 55.72% Pervious Area 101140 44.28% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 3.6 50 0.0600 0.23 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.2 20 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 62 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.2 35 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 4.4 167 Total, Increased to minimum Tc = 6.0 min 11625.34 - PR Type/1/ 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 52 Subcatchment PR-11: PR-11 Hydrograph 3 El Runoff 2.7 cfs Type III 24=hr I 25=Year Rainfall=6.16" Runoff Area=22,900 Sf 2 Runoff Volume=8,499 cf Runoff Depth=4,45" 0 Flow Length=167' , r Tc=6,0 min- i CN=85 O 0 / 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 53 Summary for Subcatchment PR-12: PR-12 Runoff = 4.4 cfs @ 12.09 hrs, Volume= 13,833 cf, Depth= 4.56" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 181830 74 >75% Grass cover, Good, HSG C 3,680 98 Roof 131880 98 Paved parking 361390 86 Weighted Average 18,830 51.74% Pervious Area 171560 48.26% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-12: PR-12 Hydrograph Runoff 4.4 cfs % Type III 24-hr 4 25-Year Rainfall=6.16" Runoff Area=36,390 sf 3 / Runoff Volume=13,833 cf Runoff Depth=4.56" 0 Tc=6.0 m i n 2r� CN=86 O �i 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 54 Summary for Subcatchment PR-13: PR-13 Runoff = 3.8 cfs @ 12.09 hrs, Volume= 11,696 cf, Depth= 3.52" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 361390 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,500 98 Paved parking 391890 76 Weighted Average 36,390 91.23% Pervious Area 3500 8.77% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-13: PR-13 Hydrograph - - - - - - - - - - - - El Runoff 4 3.8 cfs Type III 24-hr 25-Year Rainfall=6.16" 3 Runoff Area=39,890 sf j Runoff Volume=11,696 cf Runoff Depth=3.52" 0 2 Tc=6.0 rn i n CN=76 j 0 i;a,/ //„ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 55 Summary for Subcatchment PR-14: PR-14 Runoff = 4.0 cfs @ 12.09 hrs, Volume= 12,671 cf, Depth= 4.45" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 181140 74 >75% Grass cover, Good, HSG C 0 98 Roof 161000 98 Paved parking 341140 85 Weighted Average 18,140 53.13% Pervious Area 161000 46.87% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-14: PR-14 Hydrograph El Runoff 4.0 cfs 4 Type III 24-hr 25-Year Rainfall=6.16" Runoff Area=34,140 sf 3 Runoff Volume=12,671 cf Runoff Depth=4.45" !% Tc=6.0 m i n 2 y ,. CN=85 r� 0 U r r r 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 56 Summary for Subcatchment PR-15: PR-15 Runoff = 3.7 cfs @ 12.09 hrs, Volume= 11,374 cf, Depth= 3.52" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 351480 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,310 98 Paved parking 381790 76 Weighted Average 35,480 91.47% Pervious Area 3,310 8.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-15: PR-15 Hydrograph 4 El Runoff 3.7 cfs Type III 24-hr 251-Year Rainfall=6.16"' 3 Runoff Area=38,790 sf Runoff Volume=11,374 cf Runoff Depth=3.52" 2 Tc=6.0 rn i n f CN=76 it /r r 01 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 57 Summary for Subcatchment PR-16: BLDG 1 - WEST SIDE Runoff = 1.6 cfs @ 12.08 hrs, Volume= 5,833 cf, Depth= 5.92" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 111820 98 Roof 0 98 Paved parking 111820 98 Weighted Average 11,820 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-16: BLDG 1 - WEST SIDE Hydrograph El Runoff 1.6 cfs Type III 24=hr 25=Year Rainfall=6.16" % Runoff Area=1 1 sf NMI' Runoff Volume=5,833 d Runoff Depth=5,92" 0 Tc=6,0 min CN=98 i i i 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 58 Summary for Subcatchment PR-17: BLDG 1 - EAST SIDE Runoff = 1.4 cfs @ 12.08 hrs, Volume= 4,989 cf, Depth= 5.92" Routed to Pond P1 : StormTrap ST2 Single 2-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 101110 98 Roof 0 98 Paved parking 101110 98 Weighted Average 10,110 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-17: BLDG 1 - EAST SIDE Hydrograph El Runoff 1.4 cfs Type III 24=hr 25=Year Rainfall=6.16" % Runoff Area=10,110 sf 1 Runoff Volume=4,989 d %-woo Runoff Depth=5,92" 3: Tc=6,0 min CN=98 i i i// �/%-„ r' r, 011 U U'U U U U U U U U M M U M U U M U M M M 9 U U U U U U U U 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 59 Summary for Subcatchment PR-18: BLDG 2 - NORTH SIDE Runoff = 1.0 cfs @ 12.08 hrs, Volume= 3,449 cf, Depth= 5.92" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 6,990 98 Roof 0 98 Paved parking 6,990 98 Weighted Average 6,990 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-18: BLDG 2 - NORTH SIDE Hydrograph El Runoff 1 1.0 cfs Type III 24=hr 25=Year Rainfall=6.16" / Runoff Area=6,990 sf Runoff Volume=3,449 d Runoff Depth=5,92" 0 Tc=6,0 min CN=98 U U U U i i / 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 60 Summary for Subcatchment PR-19: BLDG 2 - SOUTH SIDE Runoff = 1.2 cfs @ 12.08 hrs, Volume= 4,121 cf, Depth= 5.92" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 8,350 98 Roof 0 98 Paved parking 8,350 98 Weighted Average 8,350 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-19: BLDG 2 - SOUTH SIDE Hydrograph I El Runoff 1.2 cfs Type III 24=hr 1 25=Year Rainfall=6.16" % Runoff Area=8,350 sf Runoff Volume=4,121 d Runoff Depth=5,92" 0 Tc=6,0 min CN=98 U U U U i i / 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 61 Summary for Subcatchment PR-20: PR-20 Runoff = 15.7 cfs @ 12.09 hrs, Volume= 49,946 cf, Depth= 4.56" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 677060 74 >75% Grass cover, Good, HSG C 251540 98 Roof 381790 98 Paved parking 1317390 86 Weighted Average 677060 51.04% Pervious Area 641330 48.96% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-20: PR-20 Hydrograph 17 El Runoff 15.7 cfs 16 Type III 24-hr 15, 25-Year Rainfall=6.16" 13 - Runoff Area=131,390 sf 12 � Runoff Volume=49,946 cf Runoff Depth=4.56" 0 8 Tc=6.0 m i n LUL CN=86 4 3 „r 2 1 IF 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 62 Summary for Subcatchment PR-30: Outside Project Site - Andover/Elm St Runoff = 5.0 cfs @ 12.08 hrs, Volume= 17,060 cf, Depth= 5.57" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 25-Year Rainfall=6.16" Area (sf) CN Description 4,510 74 >75% Grass cover, Good, HSG C 0 98 Roof 321240 98 Paved parking 361750 95 Weighted Average 4,510 12.27% Pervious Area 321240 87.73% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-30: Outside Project Site - Andover/Elm St Hydrograph El Runoff 5.0 cfs 5 / Type III 24-hr 25-Year Rainfall=6.16" 4 % Runoff Area=36,750 sf Runoff Volume=17,060 cf %U 3 Runoff Depth=5.57" 0 Tc=6.0 m i n CN=95 i 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 63 Summary for Pond P1: StormTrap ST2 Single 2-0 Inflow Area = 33,010 sf, 61.35% Impervious, Inflow Depth = 4.90" for 25-Year event Inflow = 4.1 cfs @ 12.08 hrs, Volume= 13,488 cf Outflow = 3.1 cfs @ 12.15 hrs, Volume= 13,140 cf, Atten= 24%, Lag= 4.0 min Discarded = 0.0 cfs @ 5.42 hrs, Volume= 1,740 cf Primary = 3.1 cfs @ 12.15 hrs, Volume= 11,400 cf Routed to Pond P2 : StormTrap ST2 Single 4-0 Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 225.64'@ 12.15 hrs Surf.Area= 1,488 sf Storage= 2,197 cf Plug-Flow detention time=66.9 min calculated for 13,136 cf(97% of inflow) Center-of-Mass det. time= 51.2 min ( 830.5 - 779.4 ) Volume Invert Avail.Storage Storage Description #1 A 223.60' 450 cf 32.27'W x 46.10'L x 3.00'H Field A 4,463 cf Overall - 3,338 cf Embedded = 1,126 cf x 40.0% Voids #2A 224.10' 2,316 cf StormTrap ST2 SingleTrap 2-Ox 4 Inside #1 Inside= 101.7"W x 24.0"H => 15.05 sf x 15.40'L = 231.7 cf Outside= 101.7"W x 30.0"H => 21.20 sf x 15.401 = 326.4 cf 4 Chambers in 2 Rows 16.96' x 30.79' Core + 6.66' Border= 30.27' x 44.10' System #3 224.20' 35 cf 4.00'D x 2.80'H Vertical Cone/CylindeFimpervious #4 227.00' 90 cf Custom Stage Data (Prismatic)Listed below(Recalc) 2,892 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 227.00 110 0 0 227.50 250 90 90 Device Routing Invert Outlet Devices #1 Discarded 223.60' 0.520 in/hr Exfiltration over Surface area #2 Primary 224.40' 12.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 224.40'/224.30' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 0.79 sf Discarded OutFlow Max=0.0 cfs @ 5.42 hrs HW=223.64' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=3.1 cfs @ 12.15 hrs HW=225.64' (Free Discharge) L2=Culvert (Barrel Controls 3.1 cfs @ 4.05 fps) 11625.34 - PR Type 11124-hr 25-Year Rainfall=6.16„ Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 64 Pond P1: StormTrap ST2 Single 2-0 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrap 2-0(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 24.0"H => 15.05 sf x 15.401 = 231.7 cf Outside= 101.7"W x 30.0"H => 2120 sf x 15.401 = 326.4 cf 2 ChamberslRow x 15.40' Long = 30.79' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 46.10' Base Length 2 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 32.27' Base Width 6.0" Stone Base + 30.0" Chamber Height= 3.00' Field Height 4 Chambers x 231.7 cf+ 1,389.8 cf Border= 2,316.5 cf Chamber Storage 4 Chambers x 326.4 cf+ 2,032.2 cf Border= 3,337.7 cf Displacement 4,463.5 cf Field- 3,337.7 cf Chambers = 1,125.8 cf Stone x 40.0%Voids = 450.3 cf Stone Storage Chamber Storage + Stone Storage= 2,766.8 cf = 0.064 of Overall Storage Efficiency = 62.0 Overall System Size =46.10'x 32.27'x 3.00' 4 Chambers(plus border) 165.3 cy Field 41.7 cy Stone 11625.34 - PR Type/1/ 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 65 Pond P1: StormTrap ST2 Single 2-0 Hydrograph EM Inflow 4.1 cfs outflow Infl ow Area=33010 sf Primary ar Disc, y � Primary ded Peak Elev=225.64' 4 3.1 cfs Storage=2,197 cf 3.1 cfs 3 ' v O 2 1 ,r / 0 > 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 66 Summary for Pond P2: StormTrap ST2 Single 4-0 Inflow Area = 89,570 sf, 64.73% Impervious, Inflow Depth = 4.71" for 25-Year event Inflow = 9.9 cfs @ 12.09 hrs, Volume= 35,186 cf Outflow = 9.5 cfs @ 12.12 hrs, Volume= 33,932 cf, Atten= 4%, Lag= 1.6 min Discarded = 0.0 cfs @ 3.76 hrs, Volume= 2,194 cf Primary = 9.5 cfs @ 12.12 hrs, Volume= 31,738 cf Routed to Link DP-1 : Andover Street System Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 220.94'@ 12.12 hrs Surf.Area= 1,829 sf Storage= 5,601 cf Plug-Flow detention time=66.2 min calculated for 33,920 cf(96% of inflow) Center-of-Mass det. time=45.5 min ( 830.7 - 785.2 ) Volume Invert Avail.Storage Storage Description #1 A 217.00' 721 cf 23.79'W x 76.90'L x 5.00'H Field A 9,147 cf Overall - 7,344 cf Embedded = 1,803 cf x 40.0% Voids #2A 217.50' 5,720 cf StormTrap ST2 SingleTrap 4-Ox 4 Inside #1 Inside= 101.7"W x 48.0"H => 30.55 sf x 15.40'L = 470.3 cf Outside= 101.7"W x 54.0"H => 38.16 sf x 15.401 = 587.4 cf 8.48' x 61.58' Core + 6.66' Border = 21.79' x 74.90' System #3 217.50' 75 cf 4.00'D x 6.00'H Vertical Cone/CylindeFImpervious #4 223.50' 222 cf Custom Stage Data (Prismatic)Listed below(Recalc) 6,738 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum-Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 223.50 110 0 0 223.90 11000 222 222 Device Routing Invert Outlet Devices #1 Discarded 217.00' 0.520 in/hr Exfiltration over Surface area #2 Primary 217.50' 18.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 217.50'/217.30' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 1.77 sf #3 Device 2 218.30' 6.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 2 220.20' 4.0' long x 2.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) Discarded OutFlow Max=0.0 cfs @ 3.76 hrs HW=217.07' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=9.5 cfs @ 12.12 hrs HW=220.94' (Free Discharge) L2=Culvert (Passes 9.5 cfs of 14.0 cfs, potential flow) 3=Orifice/Grate (Orifice Controls 1.5 cfs @ 7.44 fps) 4=Sharp-Crested Rectangular Weir(Weir Controls 8.0 cfs @ 2.81 fps) 11625.34 - PR Type 11124-hr 25-Year Rainfall=6.16„ Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 67 Pond P2: StormTrap ST2 Single 4-0 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrap 4-0(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 48.0"H => 30.55 sf x 15.401 = 470.3 cf Outside= 101.7"W x 54.0"H => 38.16 sf x 15.401 = 587.4 cf 4 Chambers/Row x 15.40' Long = 61.58' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 76.90' Base Length 1 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 23.79' Base Width 6.0" Stone Base + 54.0" Chamber Height= 5.00' Field Height 4 Chambers x 470.3 cf+ 3,838.5 cf Border= 5,719.E cf Chamber Storage 4 Chambers x 587.4 cf+ 4,994.7 cf Border= 7,344.5 cf Displacement 9,147.4 cf Field- 7,344.5 cf Chambers = 1,802.9 cf Stone x 40.0%Voids = 721.2 cf Stone Storage Chamber Storage + Stone Storage= 6,440.7 cf = 0.148 of Overall Storage Efficiency = 70.4 Overall System Size = 76.90'x 23.79'x 5.00' 4 Chambers(plus border) 338.8 cy Field 66.8 cy Stone 11625.34 - PR Type/1/ 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 68 Pond P2: StormTrap ST2 Single 4-0 Hydrograph EM Inflow 9.9 cfs outflow Discarded 1 1 °° 9.5 cfs Inflow Area=89,570 sf Primary 10 9.57s Peak Elev=220.94' 9 / Storage=5,601 cf o LL i 4 2 0 i s r %' 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 69 Summary for Pond P3: StormTrap ST2 Single 4-6 Inflow Area = 81,020 sf, 32.70% Impervious, Inflow Depth = 4.12" for 25-Year event Inflow = 8.8 cfs @ 12.09 hrs, Volume= 27,816 cf Outflow = 3.6 cfs @ 12.31 hrs, Volume= 21,087 cf, Atten= 59%, Lag= 13.2 min Discarded = 0.0 cfs @ 12.07 hrs, Volume= 3,197 cf Primary = 3.6 cfs @ 12.31 hrs, Volume= 17,890 cf Routed to Link DP-1 : Andover Street System Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 216.99'@ 12.31 hrs Surf.Area= 3,040 sf Storage= 10,907 cf Plug-Flow detention time= 178.8 min calculated for 21,080 cf(76% of inflow) Center-of-Mass det. time= 93.5 min ( 896.1 - 802.6 ) Volume Invert Avail.Storage Storage Description #1 A 212.50' 1,040 cf 49.23'W x 61.50'L x 5.50'H Field A 16,652 cf Overall - 14,051 cf Embedded = 2,601 cf x 40.0% Voids #2A 213.00' 11,204 cf StormTrap ST2 SingleTrap 4-6x 12 Inside #1 Inside= 101.7"W x 54.0"H => 34.42 sf x 15.40'L = 529.9 cf Outside= 101.7"W x 60.0"H => 42.40 sf x 15.401 = 652.7 cf 12 Chambers in 4 Rows 33.92' x 46.19' Core + 6.66' Border = 47.23' x 59.50' System #3 216.00' 48 cf 4.00'D x 3.80'H Vertical Cone/Cylinder #4 219.80' 90 cf Custom Stage Data (Prismatic)Listed below(Recalc) 12,382 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum-Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 219.80 50 0 0 221.00 100 90 90 Device Routing Invert Outlet Devices #1 Discarded 212.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 213.00' 18.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 213.00'/212.80' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 1.77 sf #3 Device 2 215.60' 12.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 2 217.00' 4.0' long x 2.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) Discarded OutFlow Max=0.0 cfs @ 12.07 hrs HW=216.03' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=3.6 cfs @ 12.31 hrs HW=216.99' (Free Discharge) L2=Culvert (Passes 3.6 cfs of 15.3 cfs, potential flow) 3=Orifice/Grate (Orifice Controls 3.6 cfs @ 4.55 fps) 4=Sharp-Crested Rectangular Weir( Controls 0.0 cfs) 11625.34 - PR Type 11124-hr 25-Year Rainfall=6.16„ Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 70 Pond P3: StormTrap ST2 Single 4-6 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrep 4-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 54.0"H => 34.42 sf x 15.401 = 529.9 cf Outside= 101.7"W x 60.0"H => 42.40 sf x 15.401 = 652.7 cf 3 Chambers/Row x 15.40' Long =46.19' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 61.50' Base Length 4 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 49.23' Base Width 6.0" Stone Base + 60.0" Chamber Height= 5.50' Field Height 12 Chambers x 529.9 cf+ 4,844.5 cf Border= 11,203.8 cf Chamber Storage 12 Chambers x 652.7 cf+ 6,218.0 cf Border= 14,050.7 cf Displacement 16,651.8 cf Field - 14,050.7 cf Chambers= 2,601.1 cf Stone x 40.0% Voids = 1,040.4 cf Stone Storage Chamber Storage + Stone Storage= 12,244.2 cf= 0.281 of Overall Storage Efficiency = 73.5 Overall System Size = 61.50'x 49.23'x 5.50' 12 Chambers(plus border) 616.7 cy Field 96.3 cy Stone 11625.34 - PR Type/1/ 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 71 Pond P3: StormTrap ST2 Single 4-6 Hydrograph EM Inflow 8.8 cfs 11 outflow Inflow Area=81 020 Sf Discarded � Primary 9 Peak Elev=216.99' 8,1 Storage=1 0 cf 7 6 c.� 5 3.6 cfs � 4 3.6 cfs 3 2 r r 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 72 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 48.83% Impervious, Inflow Depth = 4.07" for 25-Year event Inflow = 35.1 cfs @ 12.10 hrs, Volume= 128,008 cf Primary = 35.1 cfs @ 12.10 hrs, Volume= 128,008 cf, Atten= 0%, Lag= 0.0 min Routed to nonexistent node DP-2 Primary outflow = Inflow, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Link DP-1: Andover Street System Hydrograph El Inflow 35.1 cfs El Prima 38ry 36 35.E cfs Inflow Area=377,520 sf 34 32" 30 28. 26 24 22 � , �-- 20 _ 0 18 UL 16 14 12 1 0 8 4 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) �I�I��,,��gg IryIII �I�I��,,gq IIIIIIIIII ���� 100 IIIIIIII III II IIIIIRR III IIIIIIIIIIIIIIIIIM IIIII III IIIYea III S III IIIIIIIIIII III II B-11 Appendix B:Standard 2 Computations and Supporting Information 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 73 Time span=0.00-30.00 hrs, dt=0.01 hrs, 3001 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method SubcatchmentPR-11: PR-11 Runoff Area=22,900 sf 44.28% Impervious Runoff Depth=6.16" Flow Length=167' Tc=6.0 min CN=85 Runoff=3.7 cfs 11,746 cf SubcatchmentPR-12: PR-12 Runoff Area=36,390 sf 48.26% Impervious Runoff Depth=6.27" Tc=6.0 min CN=86 Runoff=5.9 cfs 19,024 cf SubcatchmentPR-13: PR-13 Runoff Area=39,890 sf 8.77% Impervious Runoff Depth=5.10" Tc=6.0 min CN=76 Runoff=5.4 cfs 16,964 cf SubcatchmentPR-14: PR-14 Runoff Area=34,140 sf 46.87% Impervious Runoff Depth=6.16" Tc=6.0 min CN=85 Runoff=5.5 cfs 17,512 cf SubcatchmentPR-15: PR-15 Runoff Area=38,790 sf 8.53% Impervious Runoff Depth=5.10" Tc=6.0 min CN=76 Runoff=5.3 cfs 16,497 cf SubcatchmentPR-16: BLDG 1 -WEST Runoff Area=11,820 sf 100.00% Impervious Runoff Depth=7.70" Tc=6.0 min CN=98 Runoff=2.1 cfs 7,585 cf SubcatchmentPR-17: BLDG 1 - EAST Runoff Area=10,110 sf 100.00% Impervious Runoff Depth=7.70" Tc=6.0 min CN=98 Runoff=1.8 cfs 6,487 cf SubcatchmentPR-18: BLDG 2 - NORTH Runoff Area=6,990 sf 100.00% Impervious Runoff Depth=7.70" Tc=6.0 min CN=98 Runoff=1.3 cfs 4,485 cf SubcatchmentPR-19: BLDG 2 -SOUTH Runoff Area=8,350 sf 100.00% Impervious Runoff Depth=7.70" Tc=6.0 min CN=98 Runoff=1.5 cfs 5,358 cf SubcatchmentPR-20: PR-20 Runoff Area=131,390 sf 48.96% Impervious Runoff Depth=6.27" Tc=6.0 min CN=86 Runoff=21.3 cfs 68,687 cf SubcatchmentPR-30: Outside Project Site Runoff Area=36,750 sf 87.73% Impervious Runoff Depth=7.34" Tc=6.0 min CN=95 Runoff=6.5 cfs 22,484 cf Pond P1: StormTrapST2 Single 2-0 Peak EIev=226.02' Storage=2,656 cf Inflow=5.5 cfs 18,234 cf Discarded=0.0 cfs 1,797 cf Primary=4.0 cfs 16,080 cf Outflow=4.0 cfs 17,877 cf Pond P2: StormTrapST2 Single 4-0 Peak EIev=221.13' Storage=5,883 cf Inflow=13.1 cfs 48,047 cf Discarded=0.0 cfs 2,243 cf Primary=12.6 cfs 44,537 cf Outflow=12.7 cfs 46,780 cf Pond P3: StormTrapST2 Single 4-6 Peak EIev=217.66' Storage=12,235 cf Inflow=12.2 cfs 38,962 cf Discarded=0.0 cfs 3,341 cf Primary=11.5 cfs 28,869 cf Outflow=11.5 cfs 327210 cf Link DP-1:AndoverStreet System Inflow=52.8 cfs 181,073 cf Primary=52.8 cfs 181,073 cf Total Runoff Area = 377,520 sf Runoff Volume = 196,829 cf Average Runoff Depth = 6.26" 51.17% Pervious = 193,170 sf 48.83% Impervious = 184,350 sf 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 74 Summary for Subcatchment PR-11: PR-11 Runoff = 3.7 cfs @ 12.09 hrs, Volume= 11,746 cf, Depth= 6.16" Routed to Pond P1 : StormTrap ST2 Single 2-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 121760 74 >75% Grass cover, Good, HSG C 0 98 Roof 101140 98 Paved parking 22,900 85 Weighted Average 121760 55.72% Pervious Area 101140 44.28% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 3.6 50 0.0600 0.23 Sheet Flow, Grass: Short n= 0.150 P2= 3.16" 0.2 20 0.0100 1.61 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.4 62 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.2 35 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 4.4 167 Total, Increased to minimum Tc = 6.0 min 11625.34 - PR Type 111 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 75 Subcatchment PR-11: PR-11 Hydrograph 4 Runoff 3.7 cfs Type III 24-hr 100-Year Rainfall=7.94" 3 % Runoff Area=22,900 Sf Runoff Volume=11,746 d j Runoff Depth=6.16" 3 2 Flow Length=167' Tc=6.0 m i n CN=85 0 -�Fu U U U U U U U U U U U U U U U U U U U U U U 1111 1111'111'111'111 1111'111'111'111'111 U U U U U U U U U U U U U U OFrF?99Ml9MR011171IF71jr7llF71jr7ll7]���JIF71jr7llF711FU U U U U U U U U U U U U U U U U U U U U U U 1111 1111 1111'111'111'111'111 1111'111'111'111 U 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 76 Summary for Subcatchment PR-12: PR-12 Runoff = 5.9 cfs @ 12.08 hrs, Volume= 19,024 cf, Depth= 6.27" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 181830 74 >75% Grass cover, Good, HSG C 3,680 98 Roof 131880 98 Paved parking 361390 86 Weighted Average 18,830 51.74% Pervious Area 171560 48.26% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-12: PR-12 Hydrograph El Runoff 6 5.9 cfs Type III 24-hr - - / 100-Year Rainfall-7.94" Runoff Area=36,390 sf 4 Runoff Volume=19,024 cf Runoff Depth=6.27" 3 3 Tc=6.0 m i n UL CN=86 i 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 77 Summary for Subcatchment PR-13: PR-13 Runoff = 5.4 cfs @ 12.09 hrs, Volume= 16,964 cf, Depth= 5.10" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 361390 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,500 98 Paved parking 391890 76 Weighted Average 36,390 91.23% Pervious Area 3500 8.77% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-13: PR-13 Hydrograph 6 El Runoff 5.4 cfs Type III 24-hr j 100-Year Rainfall=7.94" Runoff Area=39,890f s / Runoff Volume=16,964 cf Runoff Depth=5.1 0 Tc=6.0 m i n CN=76 2 r� r 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 78 Summary for Subcatchment PR-14: PR-14 Runoff = 5.5 cfs @ 12.09 hrs, Volume= 17,512 cf, Depth= 6.16" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 181140 74 >75% Grass cover, Good, HSG C 0 98 Roof 161000 98 Paved parking 341140 85 Weighted Average 18,140 53.13% Pervious Area 161000 46.87% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-14: PR-14 Hydrograph 6 El Runoff 5.5 cfs Type III 24-hr 100-Year Rainfall=7.94" % Runoff Area=34,140 sf 4 % Runoff Volume=17,512 cf Runoff Depth=6.16" 3 3 Tc=6.0 m i n CN=85 2 i �i /0' 0 U%��„-ur,%%c-„��ii;u,%;�c,i;�„��,,,,,,,,%,,,,�c�r,��„r�,„-ii „�/'„%'„%,/�'o'„-ur,%c��� U U U U 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 79 Summary for Subcatchment PR-15: PR-15 Runoff = 5.3 cfs @ 12.09 hrs, Volume= 16,497 cf, Depth= 5.10" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 351480 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,310 98 Paved parking 381790 76 Weighted Average 35,480 91.47% Pervious Area 3,310 8.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-15: PR-15 Hydrograph LEI Runoff 5.3 cfs Type III 24-hr j 100-Year Rainfall=7.94" Runoff Area=38,790 sf 4 Runoff Volume=16,497 cf %Qo '% Runoff Depth=5.1 0 3 i 3 ; 0 Tc=6.0 m i n CN=76 i i �,� ;,r r i„�a'%o�/�/a�/�/�„�,,�,,,%,,,ice ,�,.'o��,,, 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 80 Summary for Subcatchment PR-16: BLDG 1 - WEST SIDE Runoff = 2.1 cfs @ 12.08 hrs, Volume= 7,585 cf, Depth= 7.70" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 111820 98 Roof 0 98 Paved parking 111820 98 Weighted Average 11,820 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-16: BLDG 1 - WEST SIDE Hydrograph El Runoff 2.1 cfs 2 Type III 24=hr 100=Year Rainfall=7.94" Runoff Area=1 1 sf Runoff Volume=7,585 d Runoff Depth=7,70" o � - - - - - -- Tc=6.0 min CN=98 I wftnj., jj jj r 5U U U U U U U U U U U U M U U U M M U M M M M U U U U U U U U U U U U M M M U M M M M U M M 9 9 U 9 9 9 9 U 9 9 9 U U U U U U U U U U U U U 9 9 9 U 9 9 9 9 U 9 9 TT-TV77r77F779-rl7l7r7rl-rl7l'117rl7I 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 81 Summary for Subcatchment PR-17: BLDG 1 - EAST SIDE Runoff = 1.8 cfs @ 12.08 hrs, Volume= 6,487 cf, Depth= 7.70" Routed to Pond P1 : StormTrap ST2 Single 2-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 101110 98 Roof 0 98 Paved parking 101110 98 Weighted Average 10,110 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-17: BLDG 1 - EAST SIDE Hydrograph 2 El Runoff 1.8 cfs Type III 24=hr 100=Year Rainfall=7.94" Runoff Area=10,110 sf Runoff Volume=6,487 d Runoff Depth=7,70" o Tc=6,0 min CN=98 K/z/ r 0' 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 82 Summary for Subcatchment PR-18: BLDG 2 - NORTH SIDE Runoff = 1.3 cfs @ 12.08 hrs, Volume= 4,485 cf, Depth= 7.70" Routed to Pond P3 : StormTrap ST2 Single 4-6 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 6,990 98 Roof 0 98 Paved parking 6,990 98 Weighted Average 6,990 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-18: BLDG 2 - NORTH SIDE Hydrograph El Runoff 1.3 cfs Type III 24=hr 100=Year Rainfall=7.94" / Runoff Area=6,990 sf Runoff Volume=4,485 d Runoff Depth=7,70" 0 UL Tc=6,0 min CN=98 i /-// Mw/ �- 011 U U U U U U U U U U U U M U U M U M M U U U U U U U U U U U U U M M U M M M M U M M M M U U U M U M M U U U U U U U U U U U U M M M U M M M M U M M M M U U M U M M U� 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 83 Summary for Subcatchment PR-19: BLDG 2 - SOUTH SIDE Runoff = 1.5 cfs @ 12.08 hrs, Volume= 5,358 cf, Depth= 7.70" Routed to Pond P2 : StormTrap ST2 Single 4-0 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 0 74 >75% Grass cover, Good, HSG C 8,350 98 Roof 0 98 Paved parking 8,350 98 Weighted Average 8,350 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-19: BLDG 2 - SOUTH SIDE Hydrograph El Runoff 1.5 cfs Type III 24=hr 100=Year Rainfall=7.94" / Runoff Area=8,350 sf Runoff Volume=5,358 d Runoff Depth=7,70" 0 Tc=6,0 min CN=98 r 0M U M U U M U M M M M U U U U U U U U U U U U U M M U M M M M U,M M M M U U U M M U M M M M U U U U U U U U U U U U U M M M U M M 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 84 Summary for Subcatchment PR-20: PR-20 Runoff = 21.3 cfs @ 12.08 hrs, Volume= 68,687 cf, Depth= 6.27" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 677060 74 >75% Grass cover, Good, HSG C 251540 98 Roof 381790 98 Paved parking 1317390 86 Weighted Average 677060 51.04% Pervious Area 641330 48.96% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PR-20: PR-20 Hydrograph 23 1 El Runoff 22 21.3 cfs 2 Type III 24=hr 1 20,11 19 - - - - - - - - 100-Year Rainfall=7.94"- 18 17 / / Runoff Area=131,390 sf 15 / Runoff Volume=68,687 d .� 14 ,� 13 �,/ Runoff Depth=6.27" 3 12 Oil , Tc=6.0 min1 01' - - - - - CN=86 7 E. 6 - 5' 4 a'r,-rr 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 85 Summary for Subcatchment PR-30: Outside Project Site - Andover/Elm St Runoff = 6.5 cfs @ 12.08 hrs, Volume= 22,484 cf, Depth= 7.34" Routed to Link DP-1 : Andover Street System Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Type III 24-hr 100-Year Rainfall=7.94" Area (sf) CN Description 4,510 74 >75% Grass cover, Good, HSG C 0 98 Roof 321240 98 Paved parking 361750 95 Weighted Average 4,510 12.27% Pervious Area 321240 87.73% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, 5.0 0 Total, Increased to minimum Tc = 6.0 min Subcatchment PR-30: Outside Project Site - Andover/Elm St Hydrograph -- - - - - - - - - - - - - - - - E Runoff 7 6.5 cfs Type III 24-hr 100-Year Rainfall=7.94" Runoff Area=36 750 sf i Runoff Volume=22,484 cf 4 Runoff Depth=7.34" 0 Tc=6.0 min- 3 cN=95 01 i j, 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 86 Summary for Pond P1: StormTrap ST2 Single 2-0 Inflow Area = 33,010 sf, 61.35% Impervious, Inflow Depth = 6.63" for 100-Year event Inflow = 5.5 cfs @ 12.08 hrs, Volume= 18,234 cf Outflow = 4.0 cfs @ 12.16 hrs, Volume= 17,877 cf, Atten= 27%, Lag= 4.3 min Discarded = 0.0 cfs @ 3.90 hrs, Volume= 1,797 cf Primary = 4.0 cfs @ 12.16 hrs, Volume= 16,080 cf Routed to Pond P2 : StormTrap ST2 Single 4-0 Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 226.02'@ 12.16 hrs Surf.Area= 1,488 sf Storage= 2,656 cf Plug-Flow detention time=55.1 min calculated for 17,871 cf(98% of inflow) Center-of-Mass det. time=43.0 min ( 816.1 - 773.1 ) Volume Invert Avail.Storage Storage Description #1 A 223.60' 450 cf 32.27'W x 46.10'L x 3.00'H Field A 4,463 cf Overall - 3,338 cf Embedded = 1,126 cf x 40.0% Voids #2A 224.10' 2,316 cf StormTrap ST2 SingleTrap 2-Ox 4 Inside #1 Inside= 101.7"W x 24.0"H => 15.05 sf x 15.40'L = 231.7 cf Outside= 101.7"W x 30.0"H => 21.20 sf x 15.401 = 326.4 cf 4 Chambers in 2 Rows 16.96' x 30.79' Core + 6.66' Border= 30.27' x 44.10' System #3 224.20' 35 cf 4.00'D x 2.80'H Vertical Cone/CylindeFimpervious #4 227.00' 90 cf Custom Stage Data (Prismatic)Listed below(Recalc) 2,892 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 227.00 110 0 0 227.50 250 90 90 Device Routing Invert Outlet Devices #1 Discarded 223.60' 0.520 in/hr Exfiltration over Surface area #2 Primary 224.40' 12.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 224.40'/224.30' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 0.79 sf Discarded OutFlow Max=0.0 cfs @ 3.90 hrs HW=223.64' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=4.0 cfs @ 12.16 hrs HW=226.01' (FreeDischarge) L2=Culvert (Inlet Controls 4.0 cfs @ 5.08 fps) 11625.34 - PR Type 11124-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 87 Pond P1: StormTrap ST2 Single 2-0 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrap 2-0(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 24.0"H => 15.05 sf x 15.401 = 231.7 cf Outside= 101.7"W x 30.0"H => 2120 sf x 15.401 = 326.4 cf 2 ChamberslRow x 15.40' Long = 30.79' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 46.10' Base Length 2 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 32.27' Base Width 6.0" Stone Base + 30.0" Chamber Height= 3.00' Field Height 4 Chambers x 231.7 cf+ 1,389.8 cf Border= 2,316.5 cf Chamber Storage 4 Chambers x 326.4 cf+ 2,032.2 cf Border= 3,337.7 cf Displacement 4,463.5 cf Field- 3,337.7 cf Chambers = 1,125.8 cf Stone x 40.0%Voids = 450.3 cf Stone Storage Chamber Storage + Stone Storage= 2,766.8 cf = 0.064 of Overall Storage Efficiency = 62.0 Overall System Size =46.10'x 32.27'x 3.00' 4 Chambers(plus border) 165.3 cy Field 41.7 cy Stone 11625.34 - PR Type 111 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 88 Pond P1: StormTrap ST2 Single 2-0 Hydrograph EM Inflow 5.5 cfs 11 outflow Dided r Inflow Area=33,010 sf Pri a ymary Peak Elev=226.02' 5 4. Storage=2,656 cf 0 cfs 4.0 cfs 4 t� 3 r j mmmmm 0.0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 89 Summary for Pond P2: StormTrap ST2 Single 4-0 Inflow Area = 89,570 sf, 64.73% Impervious, Inflow Depth = 6.44" for 100-Year event Inflow = 13.1 cfs @ 12.09 hrs, Volume= 48,047 cf Outflow = 12.7 cfs @ 12.12 hrs, Volume= 46,780 cf, Atten= 3%, Lag= 1.4 min Discarded = 0.0 cfs @ 2.72 hrs, Volume= 2,243 cf Primary = 12.6 cfs @ 12.12 hrs, Volume= 44,537 cf Routed to Link DP-1 : Andover Street System Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 221.13'@ 12.12 hrs Surf.Area= 1,829 sf Storage= 5,883 cf Plug-Flow detention time=55.7 min calculated for 46,780 cf(97% of inflow) Center-of-Mass det. time= 39.7 min ( 819.0 - 779.3 ) Volume Invert Avail.Storage Storage Description #1 A 217.00' 721 cf 23.79'W x 76.90'L x 5.00'H Field A 9,147 cf Overall - 7,344 cf Embedded = 1,803 cf x 40.0% Voids #2A 217.50' 5,720 cf StormTrap ST2 SingleTrap 4-Ox 4 Inside #1 Inside= 101.7"W x 48.0"H => 30.55 sf x 15.40'L = 470.3 cf Outside= 101.7"W x 54.0"H => 38.16 sf x 15.401 = 587.4 cf 8.48' x 61.58' Core + 6.66' Border = 21.79' x 74.90' System #3 217.50' 75 cf 4.00'D x 6.00'H Vertical Cone/CylindeFImpervious #4 223.50' 222 cf Custom Stage Data (Prismatic)Listed below(Recalc) 6,738 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum-Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 223.50 110 0 0 223.90 11000 222 222 Device Routing Invert Outlet Devices #1 Discarded 217.00' 0.520 in/hr Exfiltration over Surface area #2 Primary 217.50' 18.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 217.50'/217.30' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 1.77 sf #3 Device 2 218.30' 6.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 2 220.20' 4.0' long x 2.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) Discarded OutFlow Max=0.0 cfs @ 2.72 hrs HW=217.07' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=12.6 cfs @ 12.12 hrs HW=221.13' (Free Discharge) L2=Culvert (Passes 12.6 cfs of 14.4 cfs potential flow) 3=Orifice/Grate (Orifice Controls 1.5 cfs @ 7.73 fps) 4=Sharp-Crested Rectangular Weir(Weir Controls 11.1 cfs @ 3.15 fps) 11625.34 - PR Type 11124-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 90 Pond P2: StormTrap ST2 Single 4-0 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrap 4-0(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 48.0"H => 30.55 sf x 15.401 = 470.3 cf Outside= 101.7"W x 54.0"H => 38.16 sf x 15.401 = 587.4 cf 4 Chambers/Row x 15.40' Long = 61.58' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 76.90' Base Length 1 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 23.79' Base Width 6.0" Stone Base + 54.0" Chamber Height= 5.00' Field Height 4 Chambers x 470.3 cf+ 3,838.5 cf Border= 5,719.E cf Chamber Storage 4 Chambers x 587.4 cf+ 4,994.7 cf Border= 7,344.5 cf Displacement 9,147.4 cf Field- 7,344.5 cf Chambers = 1,802.9 cf Stone x 40.0%Voids = 721.2 cf Stone Storage Chamber Storage + Stone Storage= 6,440.7 cf = 0.148 of Overall Storage Efficiency = 70.4 Overall System Size = 76.90'x 23.79'x 5.00' 4 Chambers(plus border) 338.8 cy Field 66.8 cy Stone 11625.34 - PR Type 111 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 91 Pond P2: StormTrap ST2 Single 4-0 Hydrograph Inflow 13.1 cfs Outflow El Discarded 12.7 cfs Inflow Area=89,570 sf 0 Primary 14 13 12.6 cfs_ Peak Elev=221 .13' 12 Storage=5,883 cf 10 �, 9 f' 5 4 2 a 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 92 Summary for Pond P3: StormTrap ST2 Single 4-6 Inflow Area = 81,020 sf, 32.70% Impervious, Inflow Depth = 5.77" for 100-Year event Inflow = 12.2 cfs @ 12.09 hrs, Volume= 38,962 cf Outflow = 11.5 cfs @ 12.13 hrs, Volume= 32,210 cf, Atten= 5%, Lag= 2.7 min Discarded = 0.0 cfs @ 11.90 hrs, Volume= 3,341 cf Primary = 11.5 cfs @ 12.13 hrs, Volume= 28,869 cf Routed to Link DP-1 : Andover Street System Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 217.66'@ 12.13 hrs Surf.Area= 3,040 sf Storage= 12,235 cf Plug-Flow detention time= 142.1 min calculated for 32,199 cf(83% of inflow) Center-of-Mass det. time= 71.9 min ( 866.3 - 794.4 ) Volume Invert Avail.Storage Storage Description #1 A 212.50' 1,040 cf 49.23'W x 61.50'L x 5.50'H Field A 16,652 cf Overall - 14,051 cf Embedded = 2,601 cf x 40.0% Voids #2A 213.00' 11,204 cf StormTrap ST2 SingleTrap 4-6x 12 Inside #1 Inside= 101.7"W x 54.0"H => 34.42 sf x 15.40'L = 529.9 cf Outside= 101.7"W x 60.0"H => 42.40 sf x 15.401 = 652.7 cf 12 Chambers in 4 Rows 33.92' x 46.19' Core + 6.66' Border = 47.23' x 59.50' System #3 216.00' 48 cf 4.00'D x 3.80'H Vertical Cone/Cylinder #4 219.80' 90 cf Custom Stage Data (Prismatic)Listed below(Recalc) 12,382 cf Total Available Storage Storage Group A created with Chamber Wizard Elevation Surf.Area Inc.Store Cum-Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 219.80 50 0 0 221.00 100 90 90 Device Routing Invert Outlet Devices #1 Discarded 212.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 213.00' 18.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 213.00'/212.80' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 1.77 sf #3 Device 2 215.60' 12.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 2 217.00' 4.0' long x 2.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) Discarded OutFlow Max=0.0 cfs @ 11.90 hrs HW=216.04' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=11.5 cfs @ 12.13 hrs HW=217.66' (Free Discharge) L2=Culvert (Passes 11.5 cfs of 16.8 cfs potential flow) 3=Orifice/Grate (Orifice Controls 4.7 cfs @ 6.01 fps) 4=Sharp-Crested Rectangular Weir(Weir Controls 6.7 cfs @ 2.65 fps) 11625.34 - PR Type 11124-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2119/2024 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 93 Pond P3: StormTrap ST2 Single 4-6 - Chamber Wizard Field A Chamber Model=StormTrap ST2 SingleTrep 4-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 54.0"H => 34.42 sf x 15.401 = 529.9 cf Outside= 101.7"W x 60.0"H => 42.40 sf x 15.401 = 652.7 cf 3 Chambers/Row x 15.40' Long =46.19' Row Length +79.9" Border x 2 +1 2.0" End Stone x 2 = 61.50' Base Length 4 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 49.23' Base Width 6.0" Stone Base + 60.0" Chamber Height= 5.50' Field Height 12 Chambers x 529.9 cf+ 4,844.5 cf Border= 11,203.8 cf Chamber Storage 12 Chambers x 652.7 cf+ 6,218.0 cf Border= 14,050.7 cf Displacement 16,651.8 cf Field - 14,050.7 cf Chambers= 2,601.1 cf Stone x 40.0% Voids = 1,040.4 cf Stone Storage Chamber Storage + Stone Storage= 12,244.2 cf= 0.281 of Overall Storage Efficiency = 73.5 Overall System Size = 61.50'x 49.23'x 5.50' 12 Chambers(plus border) 616.7 cy Field 96.3 cy Stone 11625.34 - PR Type 111 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 94 Pond P3: StormTrap ST2 Single 4-6 Hydrograph EM Inflow 12.2 cfs Outflow Discarded 13 11.5 cfs Inflow Area=81,020 sf Primary 12 11.5 cfs Peak Elev=217.66' 11 Storage=12,235 cf 10`�� 9 i / 8 7 3 00° i „ i / �/, / r � 'r - r' U U U U U U U U U U U U U U U U U U U U U U U 1111 1111 1111'ill'ill'ill'ill 1111'ill'ill'ill'ill U U I U U I U U U U U U U U U VROX09? 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) 11625.34 - PR Type /// 24-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 95 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 48.83% Impervious, Inflow Depth = 5.76" for 100-Year event Inflow = 52.8 cfs @ 12.13 hrs, Volume= 181,073 cf Primary = 52.8 cfs @ 12.13 hrs, Volume= 181,073 cf, Atten= 0%, Lag= 0.0 min Routed to nonexistent node DP-2 Primary outflow = Inflow, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Link DP-1: Andover Street System Hydrograph Inflow 52.8 cfs El Prima ry 55 l 52.8 cfs Inflow Area=377,520 sf 45 40 .. 35 30 - - - - - - - - - o 25 15 10 % 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Time (hours) This page intentionally left blank. 6-12 Appendix 6:Standard 2 Computations and Supporting Information Appendix C: Standard 3 Computations and Supporting Documentation > Soil Evaluation in accordance with Volume 3, Chapter 1 of the Handbook > Recharge Volume Calculations and Drawdown Analysis > HydroCAD Staged Storage Areas C-1 Appendix C:Standard 3 Computations and Supporting Documentation +�u� uuuuuuuuuu +dui uuuumuuuuu um uuu umuu um d A um ����Ys S C-2 Appendix C:Standard 3 Computations and Supporting Documentation Hydrologic Soil Group—Essex County, Massachusetts, Northern Part 00 Ln Ln ° ° 325300 325400 325500 325600 325700 325800 325900 326000 326100 326200 326300 326400 326500 420 40'28"N I _ 420 40'28"N ® • cv y • s `� CO � \a Soil M1ap may no=t b� valid at this scale=. � �� 420 39'59"N —. a v I 420 39'59"N 3252M 325300 325400 325500 325600 325700 325800 325900 326000 326100 326200 326300 326400 326500 CO Ln Ln Map Scale:1:6,280 if printed on A landscape(11"x 8.5")sheet. Meters °� N 0 50 100 200 300 Feet 0 300 600 1200 1800 Map projection:Web Mercator Comer coordinates:WGS84 Edge tics:UTM Zone 19N WGS84 usDA Natural Resources Web Soil Survey 5/25/2023 Conservation Service National Cooperative Soil Survey Page 1 of 4 Hydrologic Soil Group—Essex County, Massachusetts, Northern Part MAP LEGEND MAP INFORMATION Area of Interest(AOI) 13 C The soil surveys that comprise your AOI were mapped at .................................. Area of Interest(AOI) 1:15,800. 13 C/D Soils 13 D Warning:Soil Map may not be valid at this scale. Soil Rating Polygons A Not rated or not available Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil A/D Water Features line placement.The maps do not show the small areas of B Streams and Canals contrasting soils that could have been shown at a more detailed scale. Transportation ® B/D Rails Please rely on the bar scale on each map sheet for map 0 C Interstate Highways measurements. 0 C/D us Routes Source of Map: Natural Resources Conservation Service �� Web Soil Survey URL: 0 D Major Roads Coordinate System: Web Mercator(EPSG:3857) Not rated or not available Local Roads Maps from the Web Soil Survey are based on the Web Mercator Soil Rating Lines Background projection,which preserves direction and shape but distorts A distance and area.A projection that preserves area,such as the Aerial Photography Albers equal-area conic projection,should be used if more A/D accurate calculations of distance or area are required. B This product is generated from the USDA-NRCS certified data as B/D of the version date(s)listed below. C Soil Survey Area: Essex County, Massachusetts, Northern Part Survey Area Data: Version 18,Sep 9,2022 C/D Soil map units are labeled(as space allows)for map scales D 1:50,000 or larger. Not rated or not available Date(s)aerial images were photographed: May 22,2022—Jun Soil Rating Points 5,2022 13 q The orthophoto or other base map on which the soil lines were 13 compiled and digitized probably differs from the background A/D compiled displayed on these maps.As a result,some minor B shifting of map unit boundaries may be evident. ® B/D usDA Natural Resources Web Soil Survey 5/25/2023 Conservation Service National Cooperative Soil Survey Page 2 of 4 Hydrologic Soil Group—Essex County, Massachusetts, Northern Part Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 70A Ridgebury fine sandy D 36.2 18.2% loam,0 to 3 percent slopes 72A Whitman fine sandy D 29.0 14.6% loam,0 to 3 percent slopes 305B Paxton fine sandy loam, C 0.0 0.0% 3 to 8 percent slopes 310A Woodbridge fine sandy C/D 78.3 39.3% loam,0 to 3 percent slopes 310B Woodbridge fine sandy C/D 20.2 10.2% loam,3 to 8 percent slopes 311 B Woodbridge fine sandy C/D 23.6 11.9% loam,0 to 8 percent slopes,very stony 405B Charlton fine sandy B 1.7 0.8% loam,3 to 8 percent slopes 651 Udorthents,smoothed A 5.5 2.8% 715B Ridgebury and Leicester D 4.5 2.3% fine sandy loams,3 to 8 percent slopes, extremely stony Totals for Area of Interest 199.2 100.0% USDA Natural Resources Web Soil Survey 5/25/2023 Conservation Service National Cooperative Soil Survey Page 3 of 4 Hydrologic Soil Group—Essex County, Massachusetts, Northern Part Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential)when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential)when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff:None Specified Tie-break Rule: Higher usDA Natural Resources Web Soil Survey 5/25/2023 Conservation Service National Cooperative Soil Survey Page 4 of 4 0000000 IIIIII G o000000i e o n g i n e e rs U SA Memorandum (S 239 Causeway Street,Suite 400,Boston,Massachusetts 02114 www.geoengineers.com To: Chistina Audet, Jacob Hawes, and Ryan Souls - Greystar Development East, LLC cc: Jeffrey Koetteritz, PE ~ VHB From: Amy Blomeke, PE and Stan Sadkowski, PE - GeoEngineers USA, PC w Date: July 27, 2023 File: 20449-009-00 Subject: Stormwater Evaluation Memorandum Merrimack College - Residential Project North Andover, Massachusetts GeoEngineers USA, PC(GeoEngineers) is pleased to provide this memorandum to Greystar Development East, LLC (client) to convey stormwater design considerations for the proposed residential project at Merrimack College in North Andover, Massachusetts(the Site),as shown on Figure 1.This memorandum transmits recent subsurface information collected at the Site to help inform stormwater management design bythe project team. This memorandum is subject to the limitations attached herein. PROJECT UNDERSTANDING The Site consists of approximately 4 acres of landscaped land and associated drive isles located in the northern edge of the Merrimack College campus, between Elm Street, Flaherty Street and MA Rt. 125. We understand the project includes the construction of two student residential dormitories(approximately 800 total units).The buildings will be constructed at-grade, with four levels of wood-framed construction. Concept plans are in progress and proposed stormwater management areas are currently being evaluated (partly based on the information contained herein). We understand stormwater is anticipated to be managed by a combination of surface infiltration basins and below grade detention basins. SUBSURFACE EXPLORATION PROGRAMS GeoEngineers performed a subsurface exploration program consisting of test pits and borings within and adjacent to the proposed building footprints and land areas designed for potential stormwater management areas.Test pits were located within proposed stormwater management areas under advice from VHB, Inc. (VHB) of Watertown, Massachusetts. Borings were located within the proposed building footprints to evaluate subsurface conditions for the future buildings. Historical test pits were performed by others for alternate site concepts.The subsurface investigations are summarized below.The approximate locations of the explorations are shown on Figure 1, Exploration Location Plan. Logs of the subsurface explorations are provided in Attachment A and laboratory data reports are provided in Attachment B. Disclaimer:Any electronic form,facsimile or hard copy of the original document(email,text,table,and/or figure),if provided,and any attachments are only a copy of the original document.The original document is stored by GeoEngineers USA,PC and will serve as the official document of record. Memorandum to Greystar Development East, LLC July 27, 2023 Page 2 St oiiinin� a teiiir est III,,,,,GeoEngineers observed 5 test pits to evaluate the subsurface conditions, measure the depth to groundwater, depth to a restrictive layer (if present), suitability of subsurface soils to receive stormwater, and identify evidence of estimated seasonal high groundwater(ESHGW)at the anticipated stormwater management areas. The test pit program was completed on June 19, 20237 by Machine Time, LLC (Machine Time)of Hudson, New Hampshire using a Bobcat E50 excavator.The test pits (designated as TP-A through TP-C,TP-E, and TP-F)were excavated to depths between approximately 9 and 10 feet below existing ground surface (bgs). The test pits were observed by a Massachusetts Licensed Soil Evaluator from GeoEngineers who examined and classified the soils encountered using the United States Department of Agriculture (USDA)soil classification system and the Unified Soil Classification System (USCS), obtained representative soil samples, observed groundwater conditions(if present),and prepared a detailed log of the explorations.Attachment A includes logs prepared by GeoEngineers using the USDA and USCS classification systems. The USDA logs are typically used by the stormwater management designers, whereas the USCS logs are typically more informative to sitework contractors. M� � IIIII��iiiii�liiiii IIIIIIIIIIII oirliiIiiings I ,,,, GeoEngineers performed 9 geotechnical test borings to evaluate the subsurface conditions and measure depth to groundwater within proposed building areas. The boring program was completed between June 21 and 23, 20237 by SoilX Corporation, LLC (SoilX) of Leominster, Massachusetts using an ATV-mounted drill rig. The test borings (designated as GEO-1W through GEO-9)were drilled to depths of approximately 27 feet bgs. Three test borings designated as GEO-1W, GEO-4W, and GEO-8(W) were completed as 2-inch diameter groundwater monitoring wells. The soil borings were observed by a representative of GeoEngineers who examined and classified the soils, obtained representative soil samples, observed groundwater conditions, and prepared a detailed log of the explorations. Soils encountered in the borings were visually classified in general accordance with the USCS classification system described in Figure A-1. A key to the boring log symbols is also presented in Figure A-1. Standard Penetration Test(SPT) N-values' were documented and soil samples were generally obtained continuously to a depth of about 8 feet and every 5 feet thereafter. Soil classifications, N-values, and other field observations were recorded on our field logs. a VHB and UTS of Massachusetts Inc.(UTS) performed 7 test pits as part of the parking lot C and northern campus projects, respectively. VHB completed 6 test pits (designated as TP-1 Lot C through TP-3 Lot C, TP-4A Lot C, TP-4B Lot C, and TP-5 Lot C)which were excavated to depths between approximately 4.3 and 12.5 feet bgs on June 23, 2022. UTS completed 1 test pit(designated as TP-1 North Campus) which was excavated to a depth of 9 feet bgs on July 2, 2014. ' The Standard Penetration Test (SPT) is an in-situ testing technique used to infer soil density and consistency. The SPT N-value is defined as the number of blows required to drive a 2-inch-diameter split-barrel sampler 12 inches after an initial penetration of 6-inches using a 140-pound hammer falling freely from 30 inches in accordance with ASTM D1586, Standard Penetration Test. Memorandum to Greystar Development East, LLC July 27, 2023 Page 3 IIIII�iiiii�liiiii IIIIIII IIIIIII.......... iiiiri dIIIIII,,,,,s liiiiis byIIIIIIIUIIIIIIII iiiii liiiii iiiii�a iiiii ° Three soil samples from the stormwater test pits performed by GeoEngineers were submitted to Thielsch Engineering of Cranston, Rhode Island for grain-size with hydrometer testing to confirm USDA textural classifications. Representative samples included the following: TP-A(3 to 4 feet bgs) -the sample is classified as loamy sand and is representative of the onsite glacial till corresponding to Hydrologic Soil Group(HSG)A. TP-C (2 to 3 feet bgs) - the sample is classified as sandy loam and is representative of the onsite granular fill corresponding to HSG B. TP-F(1.75 to 9.5 feet bgs) - the sample is classified as sandy loam and is representative of the onsite glacial till corresponding to HSG B. The samples were selected to represent potential receiving layers in areas of the Site that are anticipated to receive stormwater. Results of the laboratory analysis are provided herein as Attachment B. SUBSURFACE CONDITIONS In general, the soil conditions observed by GeoEngineers at the Site consist of topsoil, underlain by subsoil overlying a natural, dense glacial till deposit underlain by probable bedrock. Isolated layers of fill ranging in thickness from approximately 1 to 4 feet thick consisting of re-worked glacial till were observed at TP-C, TP-E and GEO-5. An approximately 2-foot-thick layer of buried topsoil and subsoil was observed at TP-C. Shallow refusal on probable bedrock was observed by VHB at test pits TP-4A Lot C and TP-413 Lot C. Refer to the groundwater table below for our observations of the depth to groundwater and depth to estimated seasonal high groundwater observed in the recent explorations by GeoEngineers and historical test pits by others. STORMWATER MANAGEMENT DESIGN RECOMMENDATIONS Based on the subsurface conditions observed in the test pit excavations and soil borings, it is our opinion that the natural, inorganic,granular soil is suitable to serve as the receiving layer for future stormwater management areas. The design infiltration rates should be based on the receiving layer soils consisting of Sandy Loam as defined by the USDA classification system and the corresponding infiltration rates for Hydrologic Soils Group (HSG) B. Infiltration rates for HSG B range from 0.52 to 1.02 inches/hr. Given the bottom of basin will be constructed with the receiving layer consisting of glacial till, we recommend using the low end of the range for design purposes. The table below summarizes the observations by GeoEngineers regarding groundwater and/or evidence of ESHGW(i.e.soil mottling, redoximorphic features) in the test pits. Depth to groundwater in test borings is also noted; however, seasonal high groundwater estimates are not applicable for the wells. The ESHGW on the historical test pit logs by others is also listed in the table below. We recommend that the bottom of basin(s)for the stormwater management areas consider the information herein. Memorandum to Greystar Development East, LLC July 27, 2023 Page 4 Exploration Location Exploration Approximate Depth to Depth to Estimated Seasonal by GeoEngineers Location by Others Standing Groundwater(ft) High Groundwater(ft) G EO-01W -- 10.0 N/A G EO-04W -- 8.0 N/A G EO-08W -- 6.5 N/A TP-A -- 9.0 5.5 TP-B -- 8.5 2.0 TP-C -- 8.5 5.4 TP-E -- 8.3 3.5 TP-F -- 8.0 2.5 -- TP#1 Lot C Not observed 3.5 -- TP#2 Lot C Not observed 3.0 -- TP#3 Lot C Not observed 3.5 -- TP#4A Lot C Not observed 4.5 -- TP#4B Lot C Not observed 4.0 -- TP#5 Lot C Not observed 3.0 LIMITATIONS We have prepared this preliminary design memorandum for the exclusive use of Greystar Development East, LLC and their authorized agents for the Merrimack College residential project in North Andover, Massachusetts. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this memorandum was prepared. No warranty or other conditions, express or implied,should be understood. Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments should be considered a copy of the original document. The original document is stored by GeoEngineers USA, PC. and will serve as the official document of record. Please refer to Attachment C, "Design Memorandum Limitations and Guidelines for Use" for additional information pertaining to use of this memorandum. ACB-® : Attachments: Figure 1. Exploration Location Plan Attachment A.Subsurface Exploration Logs Attachment B. Laboratory Data Report Attachment C. Design Memorandum Limitations and Guidelines for Use All Legend GE0-01 Test Boring by GeoEngineers,June 2023 load "W"Denoted Well Installed Op F TP-A Stormwater Test Pit by GeoEngineers,June 2023 TP-1 Lot A Test Pit by Others TP-1 North Campus GEO-08(W) TP-E y GEO-09 Proposed Building 2 0 G EO-07 m m TP-B LO N prove Notes: o Medina N 1. The locations of all features shown are approximate. 0 2. This drawing is for information purposes.It is intended to assist in showing features discussed in an attached document.GeoEngineers USA,P.C.cannot $ / guarantee the accuracy and content of electronic files.The master file is stored w TP-2 Lot C GEO-03 GEO-06 by GeoEngineers USA,P.C.and will serve as the official record of this �J �✓i communication. 0 No GEO-05 Source(s): Base map from VHB 3 TP-F - Proposed site features from Cube3 w TP-C TP-A- Projection:MA State Plane,Mainland Zone,NAD83,US Foot TP-3 Lot C- N O U- O O O O O 0 TP-4A Lot C TP-4B Lot C TP-1 Lot C o Proposed Building 1 +V GEO-04(W) GEO-02 GEO-01(W) TP-5 Lot C - 60 0 60 0 Feet 0 i Exploration Location Plan .o z Merrimack College a Turnpike street North Andover,Massachusetts,Essex County V -n airs USA N N n -�i ee beol. R Figure 1 0 ATTACH M ENT A Subsurface Exploration Logs Deep Observation Hole Site Location: North Andover, MA Date: 6/19/23 G-eoEngineers USA(9 1 Site Address: Merrimack College-Residential Project Time: 8:55 AM Project No.: 20449-009-00 Weather: 60's Cloudy Test Pit I D: TP-A Logged by: F.Ali Ground Surface Elev. (ft.): 216 +/- Massachusetts Licensed Soil Evaluator#: SE14747 Soil Matrix Coarse Fragments(% Soil Depth Soil Horizon Redoximorphic Features Soil Texture Soil Color by Volume) Consistence Other (inches) or Layer (MRCS) Structure (Moist) Depth (in) Color Percent Gravel Cobbles (Moist) 0 - 12 Ap 10YR 2/2 Sandy loam Granular Friable 12 - 18 Bw 10 YR 5/6 Sandy loam <5 <5 Massive Friable 18 - 114 Cd 5Y 5/3 66 7.5 YR 5/8 >5 Loamy sand 15-30 10-15 Massive V. Firm Test Pit Termination Depth(in.): 114 Reason for Termination: Excavator Reach Groundwater Observations: In Situ Testing: Depth to water weeping from pit face(in.): 66 Percolation Test: NT Depth (in.): NA Depth to standing water in hole(in.): 108 Stabilization Time: 45 Minutes Permeameter Test: NT Depth (in.): NA Depth to estimated seasonal high 66 Basis for ESHGW: Seepage Falling Head Test: NT Depth (in.): NA groundwater[ESHGW] (in.): Other Test: NT Depth (in.): NA Additional Notes: NT= not tested NA= not applicable GeoEngineers USA,PC Deep Observation Hole Site Location: North Andover, MA Date: 6/19/23 • G-eoEngineers us„ Site Address: Merrimack College-Residential Project Time: 10:50 AM Project No.: 20449-009-00 Weather: 60's Cloudy Test Pit ID: TP-B Logged by: F.Ali Ground Surface Elev. (ft.): 216.5 +/- Massachusetts Licensed Soil Evaluator#: SE14747 Soil Matrix Coarse Fragments(% Soil Depth Soil Horizon Redoximorphic Features Soil Texture Soil Color by Volume) Consistence Other (inches) or Layer (NRCS) Structure (Moist) Depth (in) Color Percent Gravel Cobbles (Moist) 0 - 6 Ap 10YR 2/2 Sandy loam Granular Friable 6 - 18 B 10YR 5/6 Sandy loam Massive Friable 18 - 108 Cd 5Y 5/3 24 7.5 YR 5/8 >5 Sandy loam 15-20 10-15 Massive V. Firm Test Pit Termination Depth(in.): 108 Reason for Termination: Excavator Reach Groundwater Observations: In-Situ Testing: Depth to water weeping from pit face(in.): 48 Percolation Test: NT Depth (in.): NA Depth to standing water in hole(in.): 102 Stabilization Time: 45 Minutes Permeameter Test: NT Depth (in.): NA Depth to estimated seasonal high 24 Basis for ESHGW: Redox Falling Head Test: NT Depth (in.): NA groundwater[ESHGW] (in.): Other Test: NT Depth (in.): NA Additional Notes: NT= not tested NA= not applicable GeoEngineers USA,PC Deep Observation Hole Site Location: North Andover, MA Date: 6/19/23 S USA Site Address: Merrimack College-Residential Project Time: 2:30 PM G- eoEnglltineer Project No.: 20449-009-00 Weather: 60's Cloudy Test Pit I D: TP-C Logged by: F.Ali Ground Surface Elev. (ft.): 227 +/- Massachusetts Licensed Soil Evaluator#: SE14747 Soil Matrix Coarse Fragments(% Soil Depth Soil Horizon Redoximorphic Features Soil Texture Soil Color by Volume) Consistence Other (inches) or Layer (MRCS) Structure (Moist) Depth (in) Color Percent Gravel Cobbles (Moist) 0 - 36 Fill 10YR 2/2 Sandy loam Massive Friable 10YR 4 4 36 - 48 Apb 10YR 2/2 Sandy loam Granular V. Friable 48 - 60 Bw 10YR 5/6 Sandy loam Massive Friable 60 - 78 Cd1 5Y 5/3 65 7.5YR 5/8 >5 Sandy loam 20-30 20-25 Massive Firm 78 - 102 Cd2 5Y 6/3 5-15 Loamy sand 20-30 20-25 Massive Firm 102 - 120 Cd3 5Y 5/3 15-20 Sandy loam 20-30 20-25 Massive V. Firm Test Pit Termination Depth(in.): 120 Reason for Termination: Excavator Reach Groundwater Observations: In Situ Testing: Depth to water weeping from pit face(in.): 96 Percolation Test: NT Depth (in.): NA Depth to standing water in hole(in.): 102 Stabilization Time: 30 Minutes Permeameter Test: NT Depth (in.): NA Depth to estimated seasonal high 65 Basis for ESHGW: Redox Falling Head Test: NT Depth (in.): NA groundwater[ESHGW] (in.): Other Test: NT Depth (in.): NA Additional Notes: NT= not tested NA= not applicable GeoEngineers USA,PC Deep Observation Hole Site Location: North Andover, MA Date: 6/19/23 G-eoEngineers USA Site Address: Merrimack College-Residential Project Time: 11:55 AM Project No.: 20449-009-00 Weather: 60's Cloudy Test Pit I D: TP-E Logged by: F.Ali Ground Surface Elev. (ft.): 212 +/- Massachusetts Licensed Soil Evaluator#: SE14747 Soil Matrix Coarse Fragments(% Soil Depth Soil Horizon Redoximorphic Features Soil Texture Soil Color by Volume) Consistence Other (inches) or Layer (MRCS) Structure (Moist) Depth (in) Color Percent Gravel Cobbles (Moist) 0 - 42 Fill 10YR 2/2 Sandy loam 10-15 <5 Massive Friable 10YR 4 4 42 - 120 Cd 5Y 5/3 42 7.5YR 5/8 >5 Sandy loam 10-15 <5 Massive Firm 1 Test Pit Termination Depth(in.): 120 Reason for Termination: Excavator Reach/ Excessive Caving Groundwater Observations: In Situ Testing: Depth to water weeping from pit face(in.): 48 Percolation Test: NT Depth (in.): NA Depth to standing water in hole(in.): 100 Stabilization Time: 40 Minutes Permeameter Test: NT Depth (in.): NA Depth to estimated seasonal high 42 Basis for ESHGW: Redox Falling Head Test: NT Depth (in.): NA groundwater[ESHGW] (in.): Other Test: NT Depth (in.): NA Additional Notes: 1. Excessive caving at approximately 4.5 feet below ground surface. NT= not tested NA= not applicable GeoEngineers USA,PC Deep Observation Hole Site Location: North Andover, MA Date: 6/19/23 S USA Site Address: Merrimack College-Residential Project Time: 1:35 PM G- eoEnglltineer Project No.: 20449-009-00 Weather: 60's Cloudy Test Pit I D: TP-F Logged by: F.Ali Ground Surface Elev. (ft.): 220.5 +/- Massachusetts Licensed Soil Evaluator#: SE14747 Soil Matrix Coarse Fragments(% Soil Depth Soil Horizon Redoximorphic Features Soil Texture Soil Color by Volume) Consistence Other (inches) or Layer (MRCS) Structure (Moist) Depth (in) Color Percent Gravel Cobbles (Moist) 0 - 9 Ap 10YR 2/2 Sandy loam Granular V. Friable 9 - 21 Bw 10YR 5/6 Sandy loam Massive Friable 21 - 114 Cd 5Y 5/3 30 7.5YR 5/8 >5 Sandy loam 15 5-10 Massive Firm 1 Test Pit Termination Depth(in.): 114 Reason for Termination: Excavator Reach Groundwater Observations: In Situ Testing: Depth to water weeping from pit face(in.): 78 Percolation Test: NT Depth (in.): NA Depth to standing water in hole(in.): 96 Stabilization Time: 30 Minutes Permeameter Test: NT Depth (in.): NA Depth to estimated seasonal high Falling Head Test: NT Depth (in.): NA groundwater[ESHGW] (in.): 30 Basis for ESHGW: RedoxOther Test: NT Depth (in.): NA Additional Notes: 1. Caving at approximately 4 below ground surface. NT= not tested NA= not applicable GeoEngineers USA,PC SOIL CLASSIFICATION CHART ADDITIONAL MATERIAL SYMBOLS MAJOR DIVISIONS SYMBOLS TYPICAL SYMBOLS TYPICAL GRAPH LETTER DESCRIPTIONS GRAPH LETTER DESCRIPTIONS CLEAN GRAVELS o()0 o GW WELL-GRADED GRAVELS,GRAVEL- GRAVEL SAND MIXTURES AC Asphalt Concrete AND o 0 GRAVELLY (LITTLE OR NO FINES) O O POORLY-GRADED GRAVELS, SOILS O 0 GP GRAVEL-SAND MIXTURES 0 0 C olCC Cement Concrete COARSE GM SILTY GRAVELS,GRAVEL-SAND- GRAVELS WITH SILT MIXTURES GRAINED MORE THAN 50% FINES Crushed Rock/ SOILS OF COARSE CR FRACTION RETAINED Quarry Spalls ON NO.4 SIEVE (APPRECIABLE AMOUNT CLAYEY GRAVELS,GRAVEL-SAND- OF FINES) No GC CLAY MIXTURES ���i 0 00000000004 _ \\//_ SOD Sod/Forest Duff °0 0 WELL-GRADED SANDS,GRAVELLY 0 0 °CLEAN SANDS SW SANDS° ° ° ° ° 0 0 0 0 0 VA A A"A'VA A A MORE THAN 50% SAND °o°o°o°o°o RETAINED ON AND (LITTLE OR NO FINES) AAAAAAAAAAAAAAAAAA TS Topsoil A A A A A A A A A A A A A A NO.200 SIEVE SANDY SP POORLY-GRADED SANDS,GRAVELLY A A A A A A A A A AA A A SAND AAAAAAAAAAAAAAAAAA SOILS MORE THAN 50% SANDS WITH SM SILTY SANDS,SAND-SILT MIXTURES OF COARSE FINES Groundwater Contact FRACTION PASSING ON NO.4 SIEVE (APPRECIABLE AMOUNT @C CLAYEY SANDS,SAND-CLAY Measured groundwater level in exploration, OF FINES) �7Lr MIXTURES _ well,or piezometer INORGANIC SILTS,ROCK FLOUR, ML CLAYEY SILTS WITH SLIGHT PLASTICITY Measured free product in well or piezometer INORGANIC CLAYS OF LOW TO SILTS AND MEDIUM PLASTICITY,GRAVELLY FINE LESS THAN 50 CLAYS LIQUID LIMIT CL CLAYS,SANDY CLAYS,SILTY CLAYS, Graphic Log Contact GRAINED LEAN CLAYS SOILS OL ORGANIC SILTS AND ORGANIC SILTY Distinct contact between soil strata CLAYS OF LOW PLASTICITY Approximate contact between soil strata MORE THAN 50% INORGANIC SILTS,MICACEOUS OR PASSING MH DIATOMACEOUS SILTYSOILS NO.200SIEVE Material Description Contact SILTS AND CLAYS LIQUID LIMIT GREATER CI„I INORGANIC CLAYS OF HIGH Contact between geologic units THAN 50 PLASTICITY ORGANIC CLAYS AND SILTS OF ____ Contact between soil of the same geologic OH MEDIUM TO HIGH PLASTICITY unit HIGHLY ORGANIC SOILS PT PEAT,HUMUS,SWAMP SOILS WITH HIGH ORGANIC CONTENTS Laboratory/ Field Tests %F NOTE: Multiple symbols are used to indicate borderline or dual soil classifications Percent fines /oG Percent gravel AL Atterberg limits Sampler Symbol Descriptions CA Chemical analysis CP Laboratory compaction test ® 2.4-inch I.D.split barrel/Dames&Moore(D&M) CS Consolidation test DD Dry density ® Standard Penetration Test(SPT) DS Direct shear Shelby HA Hydrometer analysis ■ Y tube MC Moisture content ® Piston MD Moisture content and dry density Mohs Mohs hardness scale F] Direct-Push OC Organic content PM Permeability or hydraulic conductivity m Bulk or grab PI Plasticity index PL Point load test IF5Continuous Coring PP Pocket penetrometer SA Sieve analysis Blowcount is recorded for driven samplers as the number of TX Triaxial compression blows required to advance sampler 12 inches(or distance noted). UC Unconfined compression See exploration log for hammer weight and drop. UU Unconsolidated undrained triaxial compression VS Vane shear "P"indicates sampler pushed using the weight of the drill rig. Sheen Classification "WOH"indicates sampler pushed using the weight of the NS No Visible Sheen hammer. SS Slight Sheen MS Moderate Sheen HS Heavy Sheen NOTE:The reader must refer to the discussion in the report text and the logs of explorations for a proper understanding of subsurface conditions. Descriptions on the logs apply only at the specific exploration locations and at the time the explorations were made;they are not warranted to be representative of subsurface conditions at other locations or times. Key to Exploration Logs GeoEngineers USA Figure A-1 Rev 03/2023 Date Total Logged By SPD Excavator See"Remarks"section for groundwater observed Excavated 6/19/2023 Depth(ft) 9'5 Checked By ACB Equipment Bobcat E501/3 C.Y.bucket See"Remarks"section for caving observed Surface Elevation(ft) 216 Easting(X) 756779 Coordinate System MA State Plane North L cal Datum NAVD88 Northing(Y) 3070364 Horizontal Datum NAD83(feet) SAMPLE 4-1 °' EE 0- rZ MATERIAL 0 z DESCRIPTION Q O U Q� U c6 Q > 0- v u C6 O Q w o Notes """"""" TS Dark brown silty fine to medium sand with organic matter(roots) """"""" PID=ND " """"""A"" (moist)(topsoil) """ """"""" """"""" A.A."" PID=ND SM Light brown silty fine to medium sand with gravel and organic matter (roots)(moist)(subsoil) SM PID=ND Light brown silty fine to medium sand with gravel,occasional cobbles ti 2 (moist to wet)(glacial till) 1 4 N 5 Caving observed at approximately 5 feet below ground surface Groundwater seepage observed at approximately 0 51/2 feet below ground surface 6- 7- 8- 9 Standing groundwater observed at approximately 9 feet below ground surface w Terminated at approximately 91/2 feet below ground surface due to �' excavator reach U) w LO w m J ❑ H �I LL Q ZD O W a J T J m ❑ d O O O O O O O N H Notes:See Figure A 1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 1/2 foot. Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0 N Log of Test Pit TP-A N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-2 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Date 6 19 2023 Total 9 Logged By SPD Excavator See"Remarks"section for groundwater observed Excavated Depth(ft) Checked By ACB Equipment Bobcat E501/3 C.Y.bucket See"Remarks"section for caving observed Surface Elevation(ft) 216.5 Easting(X) 756768 Coordinate System MA State Plane North L cal Datum NAVD88 Northing(Y) 3070200 Horizontal Datum NAD83(feet) SAMPLE 4-1 °' EE 0- rZ MATERIAL 0 z DESCRIPTION Q O U Q� U c6 Q > 0- v u C6 O Q w o Notes ^^^°^°^^^^^^^^ TS Dark brown silty fine to medium sand with organic matter(roots) ^^^^^^^ PID=ND ^^^^^^^ (moist)(topsoil) PID=ND SM Light brown silty fine to medium sand with gravel and organic matter (trace roots)(moist)(subsoil) PID=ND SM Light brown-gray silty fine to medium sand with gravel and occasional 2 cobbles(moist to wet)(glacial till) Redoxi morph ic features at approximately 2 feet below ground surface 3 4 Groundwater seepage and caving observed at approximately 4 feet below ground surface 5 6 7 Boulder observed at approximately 71/2 feet below ground surface 8 Standing groundwater observed at approximately 81/2 feet below ground surface 9 Test pit terminated at approximately 9 feet below ground surface due to excavator reach z w Ld w LO w m J ❑ H �I LL Q ZD O W a J T J m ❑ d O O O O O O O N H Notes:See Figure A 1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 1/2 foot. Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0 N Log of Test Pit TP-B N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-3 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Date 6/19/2023 Total 10 Logged By SPD Excavator See"Remarks"section for groundwater observed Excavated Depth(ft) Checked By ACB Equipment Bobcat E501/3 C.Y.bucket Caving not observed Surface Elevation(ft) 227 Easting(X) 756997 Coordinate System MA State Plane North L cal Datum NAVD88 Northing(Y) 3070117 Horizontal Datum NAD83(feet) SAMPLE 4-1 E MATERIAL 0 z DESCRIPTION Q O U Q� U c6 Q > 0- v u (10O Q w o Notes "^"^"^" TS Dark brown silty fine to medium sand with organic matter(roots,wood "^"^^^^ PID=ND " ^^"^"^"^^^^^ chips)(moist)(topsoil/fill) ^ V "^"^"^" 1 "^"^"^" "^"^"^" "^"^"^" "^"^"^" "^"^"^" A^A^"^A "^"^"^" "^"^"^" �✓✓ -- ------------------------ PID ND 2 1 SP-SM Light brown fine to medium sand with silt,gravel and occasional organic matter(roots)(moist)(fill) PID=ND TS Dark brown silty fine to medium sand with organic matter(roots) "^"^"^" "^"^"^A (moist)(buried topsoil) """" ^^^"""" PID=ND SM Light brown silty fine to medium sand with gravel and organic matter (roots)(moist)(buried subsoil) 5 PID=ND sM Gray silty fine to medium sand with gravel(moist)(glacial till) Redoxi morph ic features at approximately 5.4 feet below ground surface N 6 SP-SM Gray fine to medium sand with silt,gravel and cobbles(moist)(glacial PID=ND till) ° g Groundwater seepage observed at approximately 8 feet below ground surface PID=ND SM Graysilt fine to medium sand with ravel wet (glacial till Standing groundwater observed at approximately y g (wet)(g ) 8/2 feet below ground surface `L g z Ld 10 Test pit terminated at approximately 10 feet below ground surface due w to excavator reach LO w m J ❑ H �I LL Q ZD O Ld a J T J m ❑ d O O O O O O O N H Notes:See Figure A 1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 1/2 foot. Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0 N Log of Test Pit TP-C N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-4 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Date 6/19/2023 Total 10 Logged By SPD Excavator See"Remarks"section for groundwater observed Excavated Depth(ft) Checked By ACB Equipment Bobcat E501/3 C.Y.bucket See"Remarks"section for caving observed Surface Elevation(ft) 212 Easting(X) 756819 Coordinate System MA State Plane North L cal Datum NAVD88 Northing(Y) 3070062 Horizontal Datum NAD83(feet) SAMPLE 4-1 °' EE 0- rZ MATERIAL 0 z DESCRIPTION Q O U Q� U c6 Q > 0- v u (10O Q w o Notes " ^^^ TS Dark brown silty fine to medium sand with organic matter(roots) """^ ^"^"^"^ (moist)(topsoil/fill) PID=ND SP-SM PID=ND �N Brown fine to medium sand with silt and organic matter(roots)(moist) `L 1 (fill) PID=ND SM Dark brown silty fine to medium sand with organic matter(roots) (moist)(fill) tiro 2- 3- PID=ND Redoximorphic features observed at 31h feet below SM Gray silty fine to medium sand with gravel,occasional cobbles(moist ground surface and continued through to 10 feet to wet)(glacial till) below ground surface 4 Groundwater seepage observed at approximately 4 feet;excessive caving observed from 4 to 5 feet below ground surface 5- 6- 7- 8— Standing groundwater observed at approximately 8.3 feet below ground surface �00 9 z Ld 10 a Test pit terminated at approximately 10 feet below ground surface due w to excavator reach and repeated collapse LO w m J 0 ❑ H �I LL Q ZD 0 Ld a J T J m ❑ d O O O O O O O N H Notes:See Figure A 1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 1/2 foot. Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0 N Log of Test Pit TP-E N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-5 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Date Total Logged By SPD Excavator See"Remarks"section for groundwater observed Excavated 6/19/2023 Depth(ft) 9'5 Checked By ACB Equipment Bobcat E501/3 C.Y.bucket See"Remarks"section for caving observed Surface Elevation(ft) 220.5 Easting(X) 756636 Coordinate System MA State Plane North L cal Datum NAVD88 Northing(Y) 3070127 Horizontal Datum NAD83(feet) SAMPLE 4-1 °' EE 0- rZ MATERIAL 0 z DESCRIPTION Q O U Q� U c6 Q > 0- v u C6 O Q w o Notes ^^^°^°^^^^^^^^ TS Dark brown silty fine to medium sand with organic matter(roots) ^^^^^^^ PID=ND ti� ^^^^^^^ (moist)(topsoil) PID=ND SM Light brown silty fine to medium sand with gravel and organic matter (roots)(moist)(subsoil) 9, SM Gray silty fine to medium sand with gravel and occasional cobbles PID=ND 2 1 (moist to wet)(glacial till) 3 4 Caving observed at approximately 4 feet below ground surface 10 5- 6- Groundwater seepage observed at approximately 61/2 feet below ground surface 7 8 Standing groundwater observed at approximately 8 feet below ground surface 9 w Test pit terminated at approximately 91/2 feet below ground surface �' due to excavator reach U) w LO w m J 0 ❑ H �I LL Q V) ZD O W a J T J m ❑ d O O O O O O O N H Notes:See Figure A 1 for explanation of symbols. The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 1/2 foot. Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0 N Log of Test Pit TP-F N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-6 ❑ Project Number: 20449-009-00 Sheet 1 of 1 SOIL CLASSIFICATION CHART ADDITIONAL MATERIAL SYMBOLS MAJOR DIVISIONS SYMBOLS TYPICAL SYMBOLS TYPICAL GRAPH LETTER DESCRIPTIONS GRAPH LETTER DESCRIPTIONS CLEAN GRAVELS o()0 o GW WELL-GRADED GRAVELS,GRAVEL- GRAVEL SAND MIXTURES AC Asphalt Concrete AND o 0 GRAVELLY (LITTLE OR NO FINES) O O POORLY-GRADED GRAVELS, SOILS O 0 GP GRAVEL-SAND MIXTURES 0 0 C olCC Cement Concrete COARSE GM SILTY GRAVELS,GRAVEL-SAND- GRAVELS WITH SILT MIXTURES GRAINED MORE THAN 50% FINES Crushed Rock/ SOILS OF COARSE CR FRACTION RETAINED Quarry Spalls ON NO.4 SIEVE (APPRECIABLE AMOUNT CLAYEY GRAVELS,GRAVEL-SAND- OF FINES) No GC CLAY MIXTURES ���i 0 00000000004 _ \\//_ SOD Sod/Forest Duff °0 0 WELL-GRADED SANDS,GRAVELLY 0 0 °CLEAN SANDS SW SANDS° ° ° ° ° 0 0 0 0 0 VA A A"A'VA A A MORE THAN 50% SAND °o°o°o°o°o RETAINED ON AND (LITTLE OR NO FINES) AAAAAAAAAAAAAAAAAA TS Topsoil A A A A A A A A A A A A A A NO.200 SIEVE SANDY SP POORLY-GRADED SANDS,GRAVELLY A A A A A A A A A AA A A SAND AAAAAAAAAAAAAAAAAA SOILS MORE THAN 50% SANDS WITH SM SILTY SANDS,SAND-SILT MIXTURES OF COARSE FINES Groundwater Contact FRACTION PASSING ON NO.4 SIEVE (APPRECIABLE AMOUNT @C CLAYEY SANDS,SAND-CLAY Measured groundwater level in exploration, OF FINES) �7Lr MIXTURES _ well,or piezometer INORGANIC SILTS,ROCK FLOUR, ML CLAYEY SILTS WITH SLIGHT PLASTICITY Measured free product in well or piezometer INORGANIC CLAYS OF LOW TO SILTS AND MEDIUM PLASTICITY,GRAVELLY FINE LESS THAN 50 CLAYS LIQUID LIMIT CL CLAYS,SANDY CLAYS,SILTY CLAYS, Graphic Log Contact GRAINED LEAN CLAYS SOILS OL ORGANIC SILTS AND ORGANIC SILTY Distinct contact between soil strata CLAYS OF LOW PLASTICITY Approximate contact between soil strata MORE THAN 50% INORGANIC SILTS,MICACEOUS OR PASSING MH DIATOMACEOUS SILTYSOILS NO.200SIEVE Material Description Contact SILTS AND CLAYS LIQUID LIMIT GREATER CI„I INORGANIC CLAYS OF HIGH Contact between geologic units THAN 50 PLASTICITY ORGANIC CLAYS AND SILTS OF ____ Contact between soil of the same geologic OH MEDIUM TO HIGH PLASTICITY unit HIGHLY ORGANIC SOILS PT PEAT,HUMUS,SWAMP SOILS WITH HIGH ORGANIC CONTENTS Laboratory/ Field Tests %F NOTE: Multiple symbols are used to indicate borderline or dual soil classifications Percent fines /oG Percent gravel AL Atterberg limits Sampler Symbol Descriptions CA Chemical analysis CP Laboratory compaction test ® 2.4-inch I.D.split barrel/Dames&Moore(D&M) CS Consolidation test DD Dry density ® Standard Penetration Test(SPT) DS Direct shear Shelby HA Hydrometer analysis ■ Y tube MC Moisture content ® Piston MD Moisture content and dry density Mohs Mohs hardness scale F] Direct-Push OC Organic content PM Permeability or hydraulic conductivity m Bulk or grab PI Plasticity index PL Point load test IF5Continuous Coring PP Pocket penetrometer SA Sieve analysis Blowcount is recorded for driven samplers as the number of TX Triaxial compression blows required to advance sampler 12 inches(or distance noted). UC Unconfined compression See exploration log for hammer weight and drop. UU Unconsolidated undrained triaxial compression VS Vane shear "P"indicates sampler pushed using the weight of the drill rig. Sheen Classification "WOH"indicates sampler pushed using the weight of the NS No Visible Sheen hammer. SS Slight Sheen MS Moderate Sheen HS Heavy Sheen NOTE:The reader must refer to the discussion in the report text and the logs of explorations for a proper understanding of subsurface conditions. Descriptions on the logs apply only at the specific exploration locations and at the time the explorations were made;they are not warranted to be representative of subsurface conditions at other locations or times. Key to Exploration Logs GeoEngineers USA Figure A-1 Rev 03/2023 Start End Total 27 Logged By ERH Drilling Drilled 6/22/2023 6/22/2023 Depth(ft) Checked By ACB Driller Soil X Corp. Metho Hollow-stem Auger Hammer Autohammer Drilling B57 Mobile Drill ATV Rig Data 140(Ibs)/30(in)Drop Equipment A 2-in well was installed on 6/22/2023 to a depth of 16 ft. Surface Elevation(ft) 222 Top of Casing 222.00 Vertical Datum NAVD88 Elevation(ft) Groundwater Depth to Easting(X) 756888 Horizontal MA State Plane North Date Measured Water ft Elevation(ft) Northing(Y) 3070336 Datum NAD83(feet) 6/22/2023 10.00 212.00 Notes: FIELD DATA WELL LOG 4-1 2 � W 0 MATERIAL �> o c0 M > O }' Steel surface o _� � 0 0 DESCRIPTION Q� monument > �� �� O }, Q N O > Q O U }' (6 O (n N (6 Q w of m U Cn > 0 0 U (n > 0 24 15 S-1 """"" TS Dark brown silty fine sand with roots and organic Concrete surface """" matter(medium dense,moist)(topsoil) 1� .�� .�� seal SM Brown silty fine sand with roots(medium dense, ' rP moist)(subsoil) ND ' 24 13 S-2 . Sand backfill ND •' 2-inch Schedule 40 SM Brown silty fine to medium sand with gravel '. '• PVC well casing (medium dense,moist)(glacial till) ND 4' '•' 24 22 S-3 Becomes I ight brown °T; (,„;iN "' Bentonite seal 5' 24 57 S-4 Becomes very dense ND 6 10 T 24 36 S 5 ND '. '. Becomes dense Filter sand backfill 2-inch Schedule 40 p PVC screen, 0.010-inch slot width 15 24 38 S-6 ND :. 16LU J J JI z w z w 20 20 26 S-7 Becomes medium dense ND LO w oo Native o' �11 CO Q' 0 w 25 24 55 S-8 Becomes very denseco ND oh Boring terminated at approximately 27 feet,no 27 refusal encountered 0 0 0 0 0 N H z Note:See Figure A 1 for explanation of symbols. 0 Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0MIN N Log of Monitoring Well GEO-01(W) N Project: Merrimack College-Residential Project All GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-2 0 Project Number: 20449-009-00 Sheet 1 of 1 Start End Total Logged By ERH Drilling Drilled 6/21/2023 6/21/2023 Depth(ft) 27 Checked By ACB Driller Soil X Corp. Method Hollow-stem Auger Surface Elevation(ft) 226 Hammer Autohammer Drilling B57 Mobile Drill ATV Rig Vertical Datum NAVD88 Data 140(Ibs)/30(in)Drop Equipment Easting(X) 757002 System MA State Plane North See"Remarks"section for groundwater observed Northing(Y) 3070223 Datum NAD83(feet) Notes: FIELD DATA Q z o MATERIAL E REMARKS 0 DESCRIPTION (� � %—. Q� > v � c�1 0 % (n CL D C co O Q w of m U (n 0 C3 U cn _> 0 24 11 S-1 ND TS Dark brown silty fine sand with roots and organic h SM matter(medium dense,moist)(topsoil) Brown silty fine to medium sand with trace roots 24 19 s 2 (medium dense,moist)(subsoil) ND SM Gray silty fine to medium sand with trace gravel ND 24 33 S 3 (medium dense,moist)(glacial till) 5 Becomes dense ND rVo 24 76 SA ND Becomes very dense 10 24 32 S 5 ND Groundwater observed at approximately Becomes dense,wet 10 feet below ground surface during drilling 15 19 49 S-6 ND c� 0 zi ❑ 0 JI z w z & 20 24 48 S-7 ND z 0 ZD c� m J ❑I H �I LL QI 0 W 25 24 73 S-8 ND o Becomes very dense �o co Boring terminated at approximately 27 feet,no refusal encountered 0 0 0 0 0 N H z Note:See Figure A 1 for explanation of symbols. 0 Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0MIN N Log of Boring GEa02 N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-3 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Start End Total Logged By ERH Drilling Drilled 6/21/2023 6/21/2023 Depth(ft) 27 Checked By ACB Driller Soil X Corp. Method Hollow-stem Auger Surface Elevation(ft) 223 Hammer Autohammer Drilling B57 Mobile Drill ATV Rig Vertical Datum NAVD88 Data 140(Ibs)/30(in)Drop Equipment Easting(X) 756901 System MA State Plane North See"Remarks"section for groundwater observed Northing(Y) 3070164 Datum NAD83(feet) Notes: FIELD DATA Q z o MATERIAL E REMARKS 7 0 DESCRIPTION Q� (� � %-. > v �CL D C cn 1 0 (n co O Q w of m U (n C3 C3 U cn _> 0 18 6 S 1ND ^^^ TS Dark brown silty fine to medium sand with roots and A^AA organic matter(loose,moist)(topsoil) ND SM Brown silty fine to medium sand with trace roots and 24 28 s 2 organic matter(loose,moist)(subsoil) ND SM Gray silty fine to medium sand with trace gravel (medium dense,moist)(glacial till) 24 40 S-3 ND Becomes dense 5 24 25 SA N D Becomes medium dense,moist to wet h Groundwater observed at approximately 71/2 feet below ground surface during drilling 10 24 37 S 5 ND Becomes dense �yo 15 24 66 S-6 Becomes very dense ND 0 z i ❑ a � Q �O J' H z w z & 20 16 59 S-7 ND w LO w c� m J 0 o of 0,0 L' Q ZD 0 Ld 25 24 51 S-8 ND J co i J Boring terminated at approximately 27 feet,no refusal encountered 0 0 0 0 0 N H z Note:See Figure A 1 for explanation of symbols. 0 Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0MIN N Log of Boring GEa03 N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-4 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Start End Total 27 Logged By ERH Drilling Drilled 6/21/2023 6/21/2023 Depth(ft) Checked By ACB Driller Soil X Corp. Metho Hollow-stem Auger Hammer Autohammer Drilling B57 Mobile Drill ATV Rig Data 140(Ibs)/30(in)Drop Equipment A 2-in well was installed on 6/21/2023 to a depth of 25 ft. Surface Elevation(ft) 230 Top of Casing 230.00 Vertical Datum NAVD88 Elevation(ft) Groundwater Depth to Easting(X) 757123 Horizontal MA State Plane North Date Measured Water ft Elevation(ft) Northing(Y) 3070100 Datum NAD83(feet) 6/21/2023 8.00 222.00 Notes: FIELD DATA WELL LOG 4-1 2 � W 0 MATERIAL �> o c0 M > O }' Steel surface o _� _J U 0 DESCRIPTION monument > �� �� O }, Q N O > Q O U }' (6 O (n N (6 Q w of m U Cn > 0 0 U (n > 0 AAAAAAA 24 19 S 1 A A A A TS Dark brown silty fine sand with roots and organic 0 5, ,� ,• Concrete surface matter(medium dense,moist)(topsoil) ND seal SM Brown silty fine to medium sand with trace gravel •' Sand backfill SP-SM and trace roots(medium dense,moist)(subsoil) ND 2' ; •' 24 48 S-2 ',,, l` Light brown fine to medium sand with silt and 2-inch Schedule 40 gravel(dense,moist)(glacial till) PVC well casing ;„ ''n,,i:,,, Bentonite seal ''�', 111,11 24 25 Becomes medium dense 5 ND 4 5' 24 44 S 4 Becomes dense ND ND . 24 59 S-5 Becomes very dense and wet 10 ND 24 85 S-6 <0 15 N D ' 24 56 S-7 2-inch Schedule 40 • PVC screen, '. 0.010-inch slot width • Filter sand backfill J J LJ ' z • Lu z . z `t'�� 20 ND •' '' w 24 76 S-8 L LU m . J LLI Q 25 ND 25' 24 72 S-9 J Native co 27' Boring terminated at approximately 27 feet,no refusal encountered 0 O 0 0 0 N H z Note:See Figure A 1 for explanation of symbols. Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0MIN N Log of Monitoring Well GEQ04(W) N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-5 0 Project Number: 20449-009-00 Sheet 1 of 1 Start End Total Logged By ERH Drilling Drilled 6/21/2023 6/21/2023 Depth(ft) 27 Checked By ACB Driller Soil X Corp. Method Hollow-stem Auger Surface Elevation(ft) 227.5 Hammer Autohammer Drilling B57 Mobile Drill ATV Rig Vertical Datum NAVD88 Data 140(Ibs)/30(in)Drop Equipment Easting(X) 757041 System MA State Plane North See"Remarks"section for groundwater observed Northing(Y) 3070032 Datum NAD83(feet) Notes: FIELD DATA Q z o MATERIAL E REMARKS 7 0 DESCRIPTION Q� (� � %—. > v �CL D C cn 1 w of 00 U (n 0 0 U a => 0 20 18 S 1 TS Dark brown silty fine to medium sand with roots and SM organic matter(medium dense,moist)(topsoil) ND Brown silty fine to medium sand with trace organic 24 29 S-2 SM matter(medium dense,moist)(subsoil) ND Brown silty fine to medium sand with gravel(medium dense,moist)(fill/till) 24 18 S-3 N D 5 SM Light brown silty fine to medium sand with gravel ND (medium dense,moist)(glacial till) 4 50/4 SA ND Becomes very dense Groundwater observed at approximately 81/2 feet below ground surface during drilling 10 24 48 S-5 Becomes gray,dense ND 15 24 52 S-6 Becomes very dense ND c� 0 z ❑ ti z a J H z w z & 20 24 70 S-7 ND z w LO w c� m ❑11 Q1 0 ZD 0 w 25 24 97 S-8 ND J co i J Boring terminated at approximately 27 feet,no refusal encountered 0 0 0 0 0 0 N H z Note:See Figure A 1 for explanation of symbols. Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0MIN N Log of Boring GEa05 N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-6 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Start End Total Logged By SPD/ERH Drilling Drilled 6/22/2023 6/22/2023 Depth(ft) 27 Checked By ACB Driller Soil X Corp. Method Hollow-stem Auger Surface Elevation(ft) 215 Hammer Autohammer Drilling B57 Mobile Drill ATV Rig Vertical Datum NAVD88 Data 140(Ibs)/30(in)Drop Equipment Easting(X) 756745 System MA State Plane North See"Remarks"section for groundwater observed Northing(Y) 3070318 Datum NAD83(feet) Notes: FIELD DATA Q z o MATERIAL E REMARKS 7 0 DESCRIPTION Q� (� � %—. > v �CL D C cn 1 0 (n (o O Q w of 00 U (n 0 0 U a => 0 22 15 S-1 TS Dark brown silty fine sand with roots(medium dense, SM moist)(topsoil) ND Brown silty fine sand with trace roots(medium dense, 18 32 S-2 SP-SM moist)(subsoil) ND Light brown fine to medium sand with silt and gravel (medium dense,moist)(glacial till) Becomes dense 14 18 S-3 ND o Becomes medium dense and moist to wet 5 Groundwater observed at approximately -X 23 20 S 4 ND 51/2 feet below ground surface during drilling Becomes wet 10 ND 23 34 S 5 Becomes dense 1 ND 5 18 48 S-6 c� 0 z i ❑ 0 z JI Q H z w z CP ti z 20 18 70 S-7 Becomes very dense ND w LO w m J ❑ H LLI Q � O � `�� 25 ND 18 61 S-8 co T J Boring terminated at approximately 27 feet,no refusal encountered 0 O 0 0 0 N H z Note:See Figure A 1 for explanation of symbols. Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0MIN N Log of Boring GEa06 N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-7 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Start End Total Logged By SPD/ERH Drilling Drilled 6/22/2023 6/22/2023 Depth(ft) 27 Checked By ACB Driller Soil X Corp. Method Hollow-stem Auger Surface Elevation(ft) 214.5 Hammer Autohammer Drilling B57 Mobile Drill ATV Rig Vertical Datum NAVD88 Data 140(Ibs)/30(in)Drop Equipment Easting(X) 756726 System MA State Plane North See"Remarks"section for groundwater observed Northing(Y) 3070178 Datum NAD83(feet) Notes: FIELD DATA Q z o MATERIAL E REMARKS 0 DESCRIPTION (� � %—. Q� > v � c�1 0 D C(n (� O Q w of 00 U (n 0 C3 U (n => 0 14 7 S-1 AAAAA A A A TS Dark brown silty fine sand with roots and organic SM matter(loose,moist)(topsoil) ND Brown silty fine to medium sand with trace roots and 18 14 s 2 SM organic matter(loose,moist)(subsoil) ND Light brown silty fine to medium sand with gravel (loose,moist)(glacial till) Becomes medium dense O ND 20 11 S 3 Becomes moist to wet 5 20 26 S 4 ND Groundwater observed at approximately Becomes wet 6 feet below ground surface during drilling 10 15 42 S-5 Becomes dense ND boo 15 22 76 S-6 Becomes very dense ND c� 0 z 0 Z JI Q LJ �co Z & 20 24 60 S-7 ND Z LO LU m J 0 ❑I H C01I LL Q O ZD O ^� Ld Y 25 24 76 S-8 ND J co T J Boring terminated at approximately 27 feet,no refusal encountered 0 0 0 0 0 N H z Note:See Figure A 1 for explanation of symbols. 0 Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0MIN N Log of Boring GEa07 N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-8 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Start End Total 27 Logged By SPD/ERH Drilling Drilled 6/22/2023 6/22/2023 Depth(ft) Checked By ACB Driller Soil X Corp. Metho Hollow-stem Auger Hammer Autohammer Drilling B57 Mobile Drill ATV Rig Data 140(Ibs)/30(in)Drop Equipment A 2-in well was installed on 6/22/2023 to a depth of 12 ft. Surface Elevation(ft) 213 Top of Casing 213.00 Vertical Datum NAVD88 Elevation(ft) Groundwater Depth to Easting(X) 756661 Horizontal MA State Plane North Date Measured Water ft Elevation(ft) Northing(Y) 3070164 Datum NAD83(feet) 6/22/2023 6.50 206.50 Notes: FIELD DATA WELL LOG 4-1 2 � W 0 MATERIAL �> o c0 M > O }' U Steel surface o _� � U DESCRIPTION Q� monument > �� O }, Q N O > Q O U }' (6 O (n N (6 Q w of m U Cn > 0 0 U (n => 0 14 20 s 1 A A A A A ATS Dark brown fine sand with roots(medium dense, ,� , Concrete surface moist)(topsoil) 0.5 °s „u seal SM Light brown fine to medium sand with gravel and ND 1' Bentonite seal ..N, .. • 2-inch Schedule 40 19 20 S 2 organic matter(medium dense,moist)(subsoil) ND 2' •: PVC well casing SM Gray silty fine to medium sand with gravel(medium dense,moist)(glacial till) 8 24 S-3 ND . 5 •. 8 19 S 4 1: Becomes moist to wet ND - Filter sand backfill 2-inch Schedule 40 PVC screen, 0.010-inch slot width 10 19 27 S-5 With more silt ND 12' boo 15 17 55 S-6 Becomes very dense ND J J 3: Nco J H z Lu z Native z 20 18 77 S 7 ND w LO LU c� m J o of LL QI ZD 0 25 24 34 S-8 ND Becomes dense J i m ❑ Boring terminated at approximately 27 feet,no 27 refusal encountered 0 0 0 0 0 N H z Note:See Figure A 1 for explanation of symbols. 0 Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0MIN N Log of Monitoring Well GEQ08(W) N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-9 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Start End Total Logged By ERH Drilling Drilled 6/23/2023 6/23/2023 Depth(ft) 27 Checked By ACB Driller Soil X Corp. Method Hollow-stem Auger Surface Elevation(ft) 219 Hammer Autohammer Drilling B57 Mobile Drill ATV Rig Vertical Datum NAVD88 Data 140(Ibs)/30(in)Drop Equipment Easting(X) 756783 System MA State Plane North See"Remarks"section for groundwater observed Northing(Y) 3070095 Datum NAD83(feet) Notes: FIELD DATA Q z o MATERIAL E REMARKS 0 DESCRIPTION (� � %-. Q� > v � c�1 0 D C(n co O Q w of m U (n 0 0 U cn _> ND 12 18 S-1 TS Dark brown silty fine sand with roots and organic AAAAAAA SP-SM matter(medium dense,moist)(topsoil) ND Light brown fine sand with silt and gravel(medium dense,moist)(glacial till) ND s 2 7 14 SM ----- ----------- Becomes silty sand 2yh 15 19 S-3 N D 5 22 22 SA ND Groundwater observed at approximately Becomes wet 6 feet below ground surface during drilling �yo 10 18 21 S-5 ND 15 20 120 S 6 Becomes gray and very dense ND c� 0 z i ❑ a ❑ z z w z > 20 15 111 S-7 ND w LO w c� m J ❑ H �I LL CVJ QI ZD 0 25 20 82 S-8 ND J co i J Boring terminated at approximately 27 feet,no refusal encountered 0 0 0 0 0 N H z Note:See Figure A 1 for explanation of symbols. 0 Coordinates Data Source:Horizontal approximated based on the ground survey by VHB,Inc.dated June 8,2023(the Survey).Vertical approximated based on the Survey. 0MIN N Log of Boring GEa09 N Project: Merrimack College-Residential Project GeolEngineuti r's Project Location: North Andover, Massachusetts Figure A-10 ❑ Project Number: 20449-009-00 Sheet 1 of 1 Location Address or Lot No. Merrimack College On-site Review Deep Hole Number TP#1 Date 6/23/2022 Time 10:00 Weather 70 deg/sunny Location(identify on site plan) See plan Land Use Open field Slope(%) 1-5% Surface Stones N/A Vegetation grass DEEP OBSERVATION HOLE LOG* Depth from Soil Soil Texture Soil Color Soil Other Surface Horizon (USDA) (Munsell) Mottling (Structure,Stones,Boulders,Consistency,%gravel) 0-12" A topsoil - - 12"-124" B/C sandy loam - 42" 10%gravel,5%cobbles/stones.Firm,silty nodules throughout(1-4"in size).All nodules had redox flecks throughout.Layer seemed siltier with depth Depth to Bedrock: N/A Depth to Groundwater: Standing Water in the Hole: N/A Weeping from Pit Face: 108" Estimated Seasonal High Ground Water: 42" Vanasse Hangen Brustlin 101 Walnut Street Watertown,,MA 02471 617- 24-1770 Location Address or Lot No. Merrimack College On-site Review Deep Hole Number TP#2 Date 6/23/2022 Time 10:50 Weather 70 deg/sunny Location(identify on site plan) See plan Land Use Open field Slope(%) 1-5% Surface Stones N/A Vegetation grass DEEP OBSERVATION HOLE LOG* Depth from Soil Soil Texture Soil Color Soil Other Surface Horizon (USDA) (Munsell) Mottling (Structure,Stones,Boulders,Consistency,%gravel) 0-40" A topsoil - - sandy loam texture 40"-84" B/C sandy loam - 36" 10%gravel,5%cobbles/stones.Firm,silty nodules throughout(1-4"in size).All nodules had redox flecks throughout.Layer seemed siltier with depth Depth to Bedrock: N/A Depth to Groundwater: Standing Water in the Hole: N/A Weeping from Pit Face: N/A Estimated Seasonal High Ground Water: 36" Vanasse Hangen Brustlin 101 Walnut Street Watertown,,MA 02471 617- 24-1770 Location Address or Lot No. Merrimack College On-site Review Deep Hole Number TP#3 Date 6/23/2022 Time 9:00 Weather 70 deg/sunny Location(identify on site plan) See plan Land Use Open field Slope(%) 1-5% Surface Stones N/A Vegetation grass DEEP OBSERVATION HOLE LOG* Depth from Soil Soil Texture Soil Color Soil Other Surface Horizon (USDA) (Munsell) Mottling (Structure,Stones,Boulders,Consistency,%gravel) 0-8" A topsoil - - 8"-24" B loamy sand - - 24"-150" C sandy loam - 42" 10%gravel,5%cobbles/stones.Firm,silty nodules throughout(1-4"in size).All nodules had redox flecks throughout.Layer seemed siltier with depth Depth to Bedrock: N/A Depth to Groundwater: Standing Water in the Hole: N/A Weeping from Pit Face: 108" Estimated Seasonal High Ground Water: 42" Vanasse Hangen Brustlin 101 Walnut Street Watertown,,MA 02471 617-9 4-1770 Location Address or Lot No. Merrimack College On-site Review Deep Hole Number TP#4A Date 6/23/2022 Time 7:30 Weather 70 deg/sunny Location(identify on site plan) See plan Land Use Open field Slope(%) 1-5% Surface Stones N/A Vegetation grass DEEP OBSERVATION,HOLE LOG Depth from Soil Soil Texture Soil Color Soil Other Surface Horizon (USDA) (Munsell) Mottling (Structure,Stones,Boulders,Consistency,%gravel) 0-12" A topsoil - - 12"-20" B loamy sand - - 20"-60" C loamy sand - 54" 5-10%gravel,trace cobbles/stones 60"-72" Ledge rock - - weathered ledge or bedrock,able to rip away top 6-12"of this layer. Depth to Bedrock: 6-7 ft Depth to Groundwater: Standing Water in the Hole: N/A Weeping from Pit Face: N/A Estimated Seasonal High Ground Water: 54" Vanasse Hangen Brustlin 101 Walnut Street Watertown,,MA 02471 617- 4-1770 Location Address or Lot No. Merrimack College On-site Review Deep Hole Number TP#413 Date 6/23/2022 Time 8:30 Weather 70 deg/sunny Location(identify on site plan) See plan Land Use Open field Slope(%) 1-5% Surface Stones N/A Vegetation grass DEEP OBSERVATION,HOLE LOG Depth from Soil Soil Texture Soil Color Soil Other Surface Horizon (USDA) (Munsell) Mottling (Structure,Stones,Boulders,Consistency,%gravel) 0-12" A topsoil - - 12"-18" B loamy sand - - 18"-52" C loamy sand - 48" 10%gravel,trace cobbles/stones 52" Ledge rock - - similarly rippable to TP#4A. Depth to Bedrock: 52" Depth to Groundwater: Standing Water in the Hole: N/A Weeping from Pit Face: N/A Estimated Seasonal High Ground Water: 48" Vanasse Hangen Brustlin 101 Walnut Street Watertown,,MA 02471 617- 4-1770 Location Address or Lot No. Merrimack College On-site Review Deep Hole Number TP#5 Date 6/23/2022 Time 11:30 Weather 70 deg/sunny Location(identify on site plan) See plan Land Use Open field Slope(%) 1-5% Surface Stones N/A Vegetation grass DEEP OBSERVATION HOLE LOG* Depth from Soil Soil Texture Soil Color Soil Other Surface Horizon (USDA) (Munsell) Mottling (Structure,Stones,Boulders,Consistency,%gravel) 0-12" A topsoil - - 12"-48" B loamy sand - - 48"-102" C sandy loam - 36" 15%gravel, 15%cobbles/stones(up to 18"long).Pockets of very sandy material.Stopped digging due to excessive rocks/boulder Depth to Bedrock: N/A Depth to Groundwater: Standing Water in the Hole: N/A Weeping from Pit Face: N/A Estimated Seasonal High Ground Water: 36" Vanasse Hangen Brustlin 101 Walnut Street Watertown,,MA 02471 617-924-1770 TEST PIT FIELD LOG PROJECT: Merrimac College TEST PIT NO.: 1 =huft"IM, Student Residences LOCATION: See Sketch *nw cmftwim Testmq%*W LOCATION. No. Andover, MA SURFACE EL.. ENGINEER: L. Crabtree EXCAVATION EQUIPMENT GROUNDWATER Contractor: Merrimac College OBSERVATION WEATHER: Clear 80's Operator: John DATE DEPTH (in.) TIME Make: John Deere Model: 310 7/2 N/A DATE: July 2, 2014 Capacity: Reach: Upon completion of test pit STRATUM EXCAV. BOULDER DEPTH CHANGE SOIL DESCRIPTION EFFORT COUNT NOTES (FT) (FT) QTY/ LASS 1 Dark Brown Loamy silty sand, E little gravel (Fill) 2 E 3 M 4 3.5' M Brown F-M Sand, some silt, some 5 ravel (Fill) M g 6 M 7 6.5' Dark Brown Fine Sand and silt M (topsoil) 8 7.5' M Grey F-M Sand, some silt, little 9 ravel M g 10 End @ 9, 11 12 13 14 Remarks: TEST PIT LEGEND: PROPORTIONS ABBREVIATIONS EXCAVATION DIMENSIONS BOULDER COUNT USED F—Fine EFFORT SIZE RANGE LETTER TRACE 0-10% M—Medium E—Easy L(FT) CLASSIFICATION DESIGNATION LITTLE 10-20% C—Coarse M—Moderate 6"— 18" A SOME 20-35% F/M—Fine D—Difficult W(FT) 18"—36" B AND 35-50% to Medium 36"and larger C F/C—Fine to Coarse VW ....._.... _ _ a _-#-VW AS� Ak WON wog f aj- W#3- 'ine ell F a a g ATTACHMENT B Laboratory Data Report 195 Frances Avenue Client Information: Project Information: Cranston RI,02910 GeoEngineers,USA PC Merrimack College Th*lelsch Phone:(401)-467-6454 Boston,MA North Andover,MA Fax: 401 -467-2398 Project Manager: Am Blomeke Project Number: 20449-009-00 ( ) J 9 Y J DIVISION C ETHE RISE GROUP cts.th=e ch.com Assigned By: Amy Blomeke Summary Page: 1 of 1 Let's Build a Solid Foundation Collected By: Client Report Date: 06.29.23 LABORATORY TESTING DATA SHEET, Report No.: 7423-F-13028 Identification Tests Proctor/CBR/Permeability Tests As Rcvd 9d 9d Test Target CBR CBR Laboratory Log Sample Depth Laboratory Moisture LL PL Gravel Sand Fines Org. pH MAX c MAX c Dry unit Moisture Test Setup Permeability Source @ @ and No. (ft) No. Content % % % % % % W°pt Wopt M wt.(pcf) Content as%of „ „ cm/sec % (%) (Corr.) 0.1 0.2 Soil Description Proctor D2216 I D4318 D6913 j D2974j D4792 D1557 Test Pit TP-F 1.75-9.5 23-S-B438 9.1 48.0 42.9 Brown silty clayey sand// Sandy Loam Test Pit TP-A 3-4 23-S-B439 7.8 58.7 33.5 Light Brown silty clayey sand Loamy Sand Test Pit TP-C 2-3 23-S-B440 4.9 54.4 40.7 Light Brown silty clayey sand Sandy Loam _ rt Date Received: 06.23.23 Reviewed By: P. Date Reviewed: 06.30.23 This report only relates to items inspect and/or tested.No warranty,expressed or implied,is made. This report shall not be reproduced,except in full,without prior written approval from the Agency,as defined in ASTM E329. N ra E N N E Particle Size Distribution Report 0 C) C) 0 C: 0 C 0 0 0 0 Tt C -0 lD M N r-I r-I � � M �k N 100 N v 90 a--' it it it it it ca 80 O Z 70 a-J LC 60 +- w L z LL z 50 CD w v („) � � it it it it it w cn CL 40 N E 30 O a--+ N W 20 10 O 0 v 100 10 1 0.1 0.01 0.001 L Ln GRAIN SIZE-mm. Gravel %Sand %Fines a) %+3" a) Coarse Fine Coarse Medium Fine Silt Clay .J 0.0 0.0 9.1 4.9 13.1 30.0 39.6 3.3 O a) SIEVE SIZE PERCENT SPEC.* PASS? Soil Description v OR DIAMETER FINER PERCENT (X=NO) Brown silty clayey sand av 3/4" 100.0 1/2" 97.9 3/8" 97.6 #4 86.0. #10 86 Atterberg Limits #20 79.3 PL= NP LL= NV P1= NP o #40 72.9 Coefficients +� #60 65.4 a) #100 55.6 D90= 4.2015 D85= 1.7215 D60= 0.1878 -0 #200 42.9 D50= 0.1069 D30= 0.0526 D 15= 0.0118 v 0.0468 mm. 26.6 D10= 0.0055 Cu= 34.08 CC= 2.67 0.0338 mm. 23.0 0.0242 mm. 21.2 Classification 0.0129 mm. 15.8 USCS= SM AASHTO= A-4(0) 0.0093 mm. 13.1 0.0066 mm. 11.3 Remarks > 0.00 m. 8.8 Sample visually classified as plastic.Sample rolled to 1/4" 0.0034 34 mm. 5.4 p �' p p v 0.0014 mm. 2.5 x v v (no specification provided) L ° Source of Sample:Test Pit Depth: 1.75-9.5' Sample Number:TP-F Date: 06.29.23 �a N Client: GeoEngineers,USA PC Thielsch Engineering Inc. QJ Project: Merrimack College Q) North Andover,MA v Cranston, RI Project No: 20449-009-00 Figure 23-S-B438 Tested By:SF Checked By:Andrew Vanasse N r6 E N d USDA Soil Classification 0 100 0 4.1 N N O 90 ti X 4.1 }' o 80ra i i ra O z 70 N 60 a--' i V 0 ro Q 50 IC i to saIII °Ill •C: 40 lic a''ly o0 N ._ (� cl 7'Z [ilk)a tSi'it w �IVi� 0 30 N c a°'!Ip"ipai a-J V Z C6 O 20 to MM t 0 oi''\ i i�any h o Iola iil'rIlu!''' saml 5'iIIII't cn sand 0 0 do H moo 00 co o (50 so Io 10 1?0 Percent Sand 0 a SOIL DATA Source Sample Depth Percentages From Material Passing a#10 Sieve Classification No. Sand Silt Clay E • Test Pit TP-F 1.75-9.5' 64.8 31.4 3.8 Sandy loam 0 0 a� U N +J 0 N N N �N U X O i 0 zt N N Thielsch Engineering Inc. Client: GeoEngineers,USA PC Project: Merrimack College °1 North Andover,MA N v Cranston, RI Project No.: 20449-009-00 Figure 23-S-B438 Checked By:AV N ra E N N E Particle Size Distribution Report 0 C) C) 0 C: 0 C 0 0 0 0 Tt C -0 lD M N r-I r-I � � M �k N 100 N v 90 a--' it it it it it ca 80 O lks Z 70 a-J LC 60 +- w L z LL z 50 CD w v („) � � it it it it it w cn 40 N E 30 O a--+ N 20 10 O 0 v 100 10 1 0.1 0.01 0.001 L Ln GRAIN SIZE-mm. Gravel %Sand %Fines a) %+3" a) Coarse Fine Coarse Medium Fine Silt Clay .J 0.0 0.0 7.8 4.8 18.1 35.8 31.3 2.2 O a) SIEVE SIZE PERCENT SPEC.* PASS? Soil Description v OR DIAMETER FINER PERCENT (X=NO) Light Brown silty clayey sand av 3/4" 100.0 1/2" 97.8 3/8" 97.0 #4 .2 87 #10 87.4 Atterberg Limits #20 78.2 PL= NP LL= NV P1= NP o #40 69.3 Coefficients +-� #60 59.7 a) #100 48.4 D90= 3.0796 D85= 1.5484 D60= 0.2535 -0 #200 33.5 D50= 0.1610 D30= 0.0674 D 15= 0.0163 v 0.0489 mm. 19.5 D10= 0.0090 Cu= 28.30 CC= 2.00 0.0350 mm. 17.7 0.0250 mm. 15.9 Classification 0.0130 mm. 14.0 USCS= SM AASHTO= A-2-4(0) 0.0094 mm. 10.4 0.0067 mm. 7.8 Remarks > 0.0048 mm. 6.1 0.0034 mm. 3.6 Sample visually classified as plastic.Sample rolled to 1/4" v 0.0014 mm. 1.6 x v v (no specification provided) L ° Source of Sample:Test Pit Depth:3-4' Sample Number:TP-A Date: 06.29.23 N Client: GeoEngineers,USA PC Thielsch Engineering Inc. QJ Project: Merrimack College Q) North Andover,MA v Cranston, RI Project No: 20449-009-00 Figure 23-S-B439 Tested By:SF Checked By:Andrew Vanasse N r6 E N d USDA Soil Classification 0 100 0 4.1 N N O 90 ti X 4.1 }' o 80ra i i ra O z 70 N 60 a--' i V 0 ro Q 50 IC i to saIII °Ill •C: 40 lic a''ly o0 N ._ (� cl 7'Z [ilk)a tSi'it w �IVi� 0 30 N c a°'!Ip"ipai a-J V Z C6 O 20 to MM t 0 oi''\ i i�any h o Iola iil'rIlu!''' saml 5'iIIII't cn sand 0 0 do H moo 00 co o (50 so Io 10 1?0 Percent Sand 0 a SOIL DATA Source Sample Depth Percentages From Material Passing a#10 Sieve Classification No. Sand Silt Clay E • Test Pit TP-A 3-4' 75.6 21.9 2.5 Loamy sand 0 0 a� U N +J 0 N N N �N U X O i 0 zt N N Thielsch Engineering Inc. Client: GeoEngineers,USA PC Project: Merrimack College °1 North Andover,MA N v Cranston, RI Project No.: 20449-009-00 Figure 23-S-B439 Checked By:AV N ra E N N E Particle Size Distribution Report ° � C* 0 0 0 0 0 0 Tt 0 v a \ r-I N M It � r-I r-I N � lD M N r-I r-I � � M �k N 100 N v 90 a--' it it it it it ca 80 O Z 70 a-J Ln N �C 4- 60 w L z LL z 50 CD w v (.,) � � it it it it it w cn CL 40 N E 30 O a--+ N 20 10 O 0 v 100 10 1 0.1 0.01 0.001 L Ln GRAIN SIZE-mm. Gravel %Sand %Fines a) %+3" a) Coarse Fine Coarse Medium Fine Silt Clay .J 0.0 0.0 4.9 5.1 15.2 34.1 38.0 2.7 O a) SIEVE SIZE PERCENT SPEC.* PASS? Soil Description v OR DIAMETER FINER PERCENT (X=NO) Light Brown silty clayey sand av 1/2" 100.0 3/8" 99.4 #4 95.1 #10 83.1. #20 83 Atterberg Limits #40 74.8 P L= NP L L= NV P 1= NP o #60 66.8 Coefficients +-� #100 55.8 #200 40.7 D90= 1.9930 D85= 1.0402 D60= 0.1809 .0 0.0473 ram. 21.7 D50= 0.1111 D30= 0.0586 D15= 0.0259 v 0.0342 mm. 18.5 D10= 0.0121 Cu= 14.96 CC= 1.57 0.0249 mm. 14.6 0.0132 mm. 10.6 Classification v o.0094 mm. 8.2 USCS= SM AASHTO= A-4(0) 0.0067 mm. 6.7 v 0.0048 mm. 6.1 Remarks > 0.0034 ram. . 0.0014 mm. 1.4 Sample visually classified as plastic.Sample rolled to 1/4" x v v (no specification provided) L ° Source of Sample:Test Pit Depth:2-3' Sample Number:TP-C Date: 06.29.23 N Client: GeoEngineers,USA PC Thielsch Engineering Inc. QJ Project: Merrimack College Q) North Andover,MA v Cranston, RI Project No: 20449-009-00 Figure 23-S-B440 Tested By:SF Checked By:Andrew Vanasse N r6 E N d USDA Soil Classification 0 100 0 4.1 N N O 90 ti X 4.1 }' o 80ra i i ra O z 70 N 60 a--' i V 0 ro Q 50 IC i to saIII °Ill •C: 40 lic a''ly o0 N ._ (� cl 7'Z [ilk)a tSi'it w �IVi� 0 30 N c a°'!Ip"ipai a-J V Z C6 O 20 to MM t 0 oi''\ i i�any h o Iola iil'rIlu!''' saml 5'iIIII't cn sand 0 0 do H moo 00 co o (50 so Io 10 1?0 Percent Sand 0 a SOIL DATA Source Sample Depth Percentages From Material Passing a#10 Sieve Classification No. Sand Silt Clay E • Test Pit TP-C 2-3' 71.7 25.3 3.0 Sandy loam 0 0 a� U N +J 0 N N N �N U X O i 0 zt N N Thielsch Engineering Inc. Client: GeoEngineers,USA PC Project: Merrimack College °1 North Andover,MA N v Cranston, RI Project No.: 20449-009-00 Figure 23-S-B440 Checked By:AV ATTACHMENT C Design Memorandum Limitations and Guidelines for Use Merrimack College Massachusetts -Residential Project North Andover, ATTACHMENT C DESIGN MEMORANDUM LIMITATIONS AND GUIDELINES FOR USEJ- This attachment provides information to help you manage your risks with respect to the use of this memorandum. f iiiiii IIIIIII 'iiiiiii iiiiir,iii��sIW , I It is important to recognize that the geoscience practices (geotechnical engineering, geology and environmental science) rely on professional judgment and opinion to a greater extent than other engineering and natural science disciplines, where more precise and/or readily observable data may exist. To help clients better understand how this difference pertains to our services, GeoEngineers includes the following explanatory "limitations" provisions in its reports. Please confer with GeoEngineers if you need to know more how these "Design Memorandum Limitations and Guidelines for Use" apply to your project or site. Diu uuim ��� n� �� �� �����,. � ���� ����,,uum uum � IIII�r Y �� ���i�l I r IIIIIII IIIIIII Y"� II�r,w, III IIii Y" ��iiiiii�l IIIIIII iiiiii� IIIIIIIIt This memorandum has been prepared for Greystar Development East, LLC and for the Project(s) specifically identified in the memorandum. The information contained herein is not applicable to other sites or projects. GeoEngineers structures its services to meet the specific needs of its clients. No party other than the party to whom this memorandum is addressed may rely on the product of our services unless we agree to such reliance in advance and in writing. Within the limitations of the agreed scope of services for the Project, and its schedule and budget, our services have been executed in accordance with our Agreement with Greystar Development East, LLC dated June 15, 2023 and generally accepted geotechnical practices in this area at the time this memorandum was prepared. We do not authorize, and will not be responsible for, the use of this memorandum for any purposes or projects other than those identified in the memorandum. u iiiiiiriiiiii iiiiii uiiiiiii iiiiii l iiiii iiiiii iiiiii iiiiii l iiiil Based iiii iiiiii l IIIIIII e�t ufiiiiii If n w IIIIIII iiiiiii a iiiiiir This memorandum has been prepared for Greystar Development East, LLC. GeoEngineers considered a number of unique, project-specific factors when establishing the scope of services for this project and memorandum. Unless GeoEngineers specifically indicates otherwise, it is important not to rely on this memorandum if it was: Not prepared for you, Not prepared for your project, Not prepared for the specific site explored, or Completed before important project changes were made. 1 Developed based on material provided by ASFE,Professional Firms Practicing in the Geosciences;www.asfe.org. nnnnnrta n gIIq�n e e p �����((" '.,. i�lagM„� uw G �" ���u ����� nnnni Merrimack College Massachusetts -Residential Project North Andover, For example, changes that can affect the applicability of this memorandum include those that affect: IIIIIIIIIIIIIIIIIIIIIIII The function of the proposed structure; IIIIIIIIIIIIIIIIIIIIIIII Elevation, configuration, location, orientation or weight of the proposed structure; IIIIIIIIIIIIIIIIIIIIIIII Composition of the design team; or IIIIIIIIIIIIIIIIIIIIIIII Project ownership. If changes occur after the date of this memorandum, GeoEngineers cannot be responsible for any consequences of such changes in relation to this memorandum unless we have been given the opportunity to review our interpretations and recommendations. Based on that review, we can provide written modifications or confirmation, as appropriate. R IIIIII�'i IIIIIII IIIIII IIIIII I IIIIII I IIIIII�'I° CulnceIIIrIiis AIIIr o�t( IIIIII Unless environmental services were specifically included in our scope of services, this memorandum does not provide any environmental findings, conclusions, or recommendations, including but not limited to,the likelihood of encountering underground storage tanks or regulated contaminants. S o I °14 o Illlr Illln 11a Ill This geotechnical or geologic memorandum is based on conditions that existed at the time the study was performed. The findings and conclusions of this memorandum may be affected by the passage of time, by man-made events such as construction on or adjacent to the site, new information or technology that becomes available subsequent to the memorandum date, or by natural events such as floods, earthquakes, slope instability or groundwater fluctuations. If more than a few months have passed since issuance of our memorandum or work product, or if any of the described events may have occurred, please contact GeoEngineers before applying this memorandum for its intended purpose so that we may evaluate whether changed conditions affect the continued reliability or applicability of our conclusions and recommendations. ���Illlll l IIIIIII IIIIn IIIIIII IIIIII� IIIIIII Illlllf IIIIII °°" IIIIII� °° W IIIIIII Illlllf m IIIIIII IIIIII�'I IIIIIII IIIIII�'I "` Our interpretations of subsurface conditions are based on field observations from widely spaced sampling locations at the site. Site exploration identifies the specific subsurface conditions only at those points where subsurface tests are conducted or samples are taken. GeoEngineers reviewed field and laboratory data and then applied its professional judgment to render an informed opinion about subsurface conditions at other locations. Actual subsurface conditions may differ, sometimes significantly, from the opinions presented in this memorandum. Our memorandum, conclusions and interpretations are not a warranty of the actual subsurface conditions. °�� �� Illlli�' ''����������i��� � � ��°°�f'iiiiiii Illlli��l IIIIII�IIIII��IIIII�� IIIIII� Illlli � Illlli� l '°��°° °w�� IIIIII�IIIII��IIIII��IIIIII�IIIII�II�� IIIIII °�f'iiiiiii IIIIIII°°°14 ����� �° f °°°°°°"'iiiiiiillllll �We have developed the following recommendations based on data gathered from subsurface investigation(s). These investigations sample just a small percentage of a site to create a snapshot of the subsurface conditions elsewhere on the site. Such sampling on its own cannot provide a complete and accurate view of subsurface conditions for the entire site. Therefore, the recommendations included in this memorandum are preliminary and should not be considered final. GeoEngineers' recommendations can be finalized only by observing actual subsurface conditions revealed during construction. G e onnnnnrta �n e e rs (E) ,n gIIq �������" a IIIG [IleIII..),20449 . 009 0 Merrimack College Massachusetts -Residential Project North Andover, GeoEngineers cannot assume responsibility or liability for the recommendations in this memorandum if we do not perform construction observation. We recommend that you allow sufficient monitoring, testing and consultation during construction by GeoEngineers to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes if the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork activities are completed in accordance with our recommendations. Retaining GeoEngineers for construction observation for this project is the most effective means of managing the risks associated with unanticipated conditions. If another party performs field observation and confirms our expectations, the other party must take full responsibility for both the observations and recommendations. Please note, however, that another party would lack our project-specific knowledge and resources. B � °,° iiiiiii 'iiiiiii IIIIIII° m IIIIIII IIIIIII°° °,'iiiiiii IIIIIIr I Misinterpretation of this memorandum by members of the design team or by contractors can result in costly problems. GeoEngineers can help reduce the risks of misinterpretation by conferring with appropriate members of the design team after submitting the memorandum, reviewing pertinent elements of the design team's plans and specifications, participating in pre-bid and preconstruction conferences, and providing construction observation. um w � I uuuuuuu � uuuuuu im i"" IIIIIII IIIIIII' � Geotechnical engineers and geologists prepare final boring and testing logs based upon their interpretation of field logs and laboratory data. The logs included in a geotechnical engineering or geologic memorandum should never be redrawn for inclusion in architectural or other design drawings. Photographic or electronic reproduction is acceptable, but separating logs from the memorandum can create a risk of misinterpretation. Giii °IIIIIIf'I°fIIIIIII f IIIIIII ° IIIIII Ii�mIIIIIi IIIIIII�i IIIII IIIIII III IIIIIII�W °"' ���'�' 'IIIIIII ICI�� IIIIIII ' IIIIIII To help reduce the risk of problems associated with unanticipated subsurface conditions, GeoEngineers recommends giving contractors the complete stormwater evaluation memorandum, including these "Desing Memorandum Limitations and Guidelines for Use." When providing the memorandum, you should preface it with a clearly written letter of transmittal that: IIIIIIIIIIIIIIIIIIIIIIII Advises contractors that the memorandum was not prepared for purposes of bid development and that its accuracy is limited; and IIIIIIIIIIIIIIIIIIIIIIII Encourages contractors to confer with GeoEngineers and/or to conduct additional study to obtain the specific types of information they need or prefer. (IIIIIII°f IIIIII ° IIIIIII° s IIIIIIII 'iiiiiii °°°° ° °f IIIIIII °°"'f" III iiiiiii IIIIIII IIIIIII I IIIIIII °°f IIIIIII ° 'iiiiiii IIIIIII IIIIIII ��,°f�,�����°�f IIIIIII ° I IIIIIII IIIIIII°° I°° Our geotechnical recommendations are not intended to direct the contractor's procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to on-site personnel and adjacent properties. �n e e rs (E) � (III n g q Ili °. e ����������� ills III ), 0 00 Merrimack College Massachusetts -Residential Project North Andover, ����� mil �� � ������� � � � ������������� ������� ����� � � � � �� �� � ���� ���IIIIII I IIIIIII � ��IIIIIII �� IIIIIIr I IIIIII IIIIIII IIIIII IIIIII IIIIIII IIIIII I w IIIII IIIII IIIIIII �o [ u u B IIIIII I°f IIIII IIIIII II The equipment, techniques and personnel used to perform an environmental study differ significantly from those used to perform a geotechnical or geologic study and vice versa. For that reason, a geotechnical engineering or geologic memorandum does not usually relate any environmental findings, conclusions or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Similarly, environmental memoranda are not used to address geotechnical or geologic concerns regarding a specific project. 1������ ll�f "Its GeoEngineers' Scope of Work specifically excludes the investigation, detection, prevention or assessment of the presence of Biological Pollutants. Accordingly, this memorandum does not include any interpretations, recommendations, findings or conclusions regarding the detecting, assessing, preventing or abating of Biological Pollutants, and no conclusions or inferences should be drawn regarding Biological Pollutants as they may relate to this project. The term "Biological Pollutants" includes, but is not limited to, molds,fungi, spores, bacteria and viruses, and/or any of their byproducts. A Client that desires these specialized services is advised to obtain them from a consultant who offers services in this specialized field. Illllli" IIIIIII IIIIIII �'lllllll"' "IIIIII�"I I°°°�IIIIIII" 'IIIIIII � by GeoEngineers has relied upon certain data or information provided or compiled by others in the performance of our services. Although we use sources that we reasonably believe to be trustworthy, GeoEngineers cannot warrant or guarantee the accuracy or completeness of information provided or compiled by others. nnnnnrta IIq p ���������" ' i�lag,, M�„� uw Al, e n g [Ile III )20449 009..00 u a���1111111111111J dmi m VuV6���u���llnes uuuuuuu IW Iuu i i C-3 Appendix C:Standard 3 Computations and Supporting Documentation 0 hb: Recharge Calculations Project Corner Development at Merrimack Project# 11625.34 College, North Andover, MA Calculated by SM Date 2/19/2024 Checked by J K REQUIRED RECHARGE VOLUME Hydrologic Area Inches of Runoff Volume Soil Group (HSG) (ft2) (in) (ft) A 0 0.60 0 B 0 0.35 0 C 63,460 0.25 11322 D 0 0.10 0 TOTAL 1,322 CAPTURE AREA ADJUSTMENT Required Recharge Volume (ft) 11322 Total Site Net Impervious Area (ft) 63,460 Total Site Impervious Area Draining to Recharge Facilities (ft2) 84,470 Capture Area Adjustment Factor 0.75 Adjusted Required Recharge Volume (ft) N/A PROVIDED RECHARGE VOLUME SYSTEM A: Stormtrap SingleTrap (2.0'H) Volumes provided below the lowest outlet at elevation: 224.4 Provided Volume: Bottom Area Volume (ft) (ft) 1,488 666 Drawdown: (Vlnfiltration/ABottom)/Rawl's Rate Rawls Recharge Rate: 0.52 (in/hr) Drawdown Time: 10.33 (hours) 11625.34-Recharge&Drawdown Calculations.xlsx 1 of 4 0 hb: Recharge Calculations Project Corner Development at Merrimack Project# 11625.34 College, North Andover, MA Calculated by SM Date 2/19/2024 Checked by J K SYSTEM B: StormTrap SingleTrap (4.0'H) Volumes provided below the lowest outlet at elevation: 218.3 Provided Volume: Bottom Area Volume (ft) (ft) 11829 1,583 Drawdown: (VI nfiltration/ABottom)/Raw I's Rate Rawls Recharge Rate: 0.52 (in/hr) Drawdown Time: 20 (hours) SYSTEM C: StormTrap SingleTrap (451-1) Volumes provided below the lowest outlet at elevation: 215.6 Provided Volume: Bottom Area Volume (ft) (ft) 31028 71F305 Drawdown: (Vlnfiltration/ABottom)/Rawl's Rate Rawls Recharge Rate: 0.52 (in/hr) Drawdown Time: 56 (hours) RECHARGE VOLUME SUMMARY Required Recharge Volume: 11322 (ft) Total Recharge Volume Provided: 91F554 (ft) 11625.34-Recharge&Drawdown Calculations.xlsx 2 of 4 uuuuuum yd CA 111 11S111111111,11taged A���omeas Sllllllta���o-age I C-4 Appendix C:Standard 3 Computations and Supporting Documentation 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond P1: StormTrap ST2 Single 2-0 SYS A Elevation Surface Storage Elevation Surface Storage (feet) (sq-ft) (cubic-feet) (feet) (sq-ft) (cubic-feet) 223.60 13488 0 226.20 1,488 2,768 223.65 13488 30 226.25 1,488 2,771 223.70 13488 60 226.30 1,488 2,775 223.75 13488 89 226.35 1,488 2,779 223.80 13488 119 226.40 1,488 23782 223.85 13488 149 226.45 1,488 23786 223.90 1,488 179 226.50 1,488 2,790 223.95 1,488 208 226.55 1,488 2,793 224.00 1,488 238 226.60 1,488 2,797 224.05 1,488 268 226.65 1,488 2,798 224.10 1,488 298 226.70 1,488 2,798 224.15 13488 359 226.75 1,488 2,799 224.20 13488 419 226.80 1,488 2,799 224.25 13488 481 226.85 1,488 2,800 224.30 13488 543 226.90 1,488 23801 224.35 13488 604 226.95 1,488 23801 224.40 17488 666 227.00 1,598 2,802 224.45 1,488 727 227.05 1,612 2,808 224.50 1,488 789 227.10 1,626 2,814 224.55 1,488 851 227.15 1,640 2,822 224.60 1,488 912 227.20 1,654 2,830 224.65 13488 974 227.25 1,668 2,838 224.70 13488 1,035 227.30 1,682 2,848 224.75 13488 11097 227.35 1,696 2,858 224.80 13488 1,159 227.40 1,710 2,868 224.85 13488 1,220 227.45 1,724 23880 224.90 13488 1,282 227.50 11738 29892 224.95 1,488 1,343 225.00 1,488 1,405 225.05 1,488 11467 225.10 1,488 11528 225.15 1,488 1590 225.20 13488 1,651 225.25 13488 1,713 225.30 13488 11775 225.35 13488 1,836 225.40 13488 1,898 225.45 1,488 1,959 225.50 1,488 2,021 225.55 1,488 2,083 225.60 1,488 21144 225.65 1,488 2,206 225.70 1,488 2,267 225.75 13488 2,329 225.80 13488 21391 225.85 13488 2,452 225.90 13488 2,514 225.95 13488 2,575 226.00 1,488 2,637 226.05 1,488 2,699 226.10 1,488 21760 226.15 1,488 21764 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond P2: StormTrap ST2 Single 4-0 SYS B Elevation Surface Storage Elevation Surface Storage (feet) (sq-ft) (cubic-feet) (feet) (sq-ft) (cubic-feet) 217.00 13829 0 222.20 1,829 6500 217.10 13829 73 222.30 1,829 6501 217.20 13829 146 222.40 1,829 6502 217.30 13829 220 222.50 1,829 6,504 217.40 13829 293 222.60 1,829 63505 217.50 13829 366 222.70 1,829 63506 217.60 1,829 518 222.80 1,829 6507 217.70 1,829 670 222.90 1,829 6509 217.80 1,829 822 223.00 1,829 6510 217.90 1,829 974 223.10 1,829 6511 218.00 1,829 1,127 223.20 1,829 6512 218.10 13829 1,279 223.30 1,829 6514 218.20 13829 1,431 223.40 1,829 6515 218.30 17829 1,583 223.50 1,939 6,516 218.40 13829 1,735 223.60 2,162 63538 218.50 13829 1,887 223.70 2,384 63583 218.60 1,829 2,039 223.80 2,607 6,649 218.70 1,829 2,192 223.90 29829 69738 218.80 1,829 2,344 218.90 1,829 21496 219.00 1,829 2,648 219.10 13829 2,800 219.20 13829 2,952 219.30 13829 31104 219.40 13829 3,257 219.50 13829 3,409 219.60 13829 3,561 219.70 1,829 3,713 219.80 1,829 3,865 219.90 1,829 41017 220.00 1,829 41169 220.10 1,829 4,322 220.20 13829 4,474 220.30 13829 4,626 220.40 13829 41778 220.50 13829 4,930 220.60 13829 5,082 220.70 1,829 5,234 220.80 1,829 5,387 220.90 1,829 5539 221.00 1,829 51691 221.10 1,829 5,843 221.20 1,829 5,995 221.30 13829 6,147 221.40 13829 61299 221.50 13829 6,452 221.60 13829 6,461 221.70 13829 6,470 221.80 1,829 6,479 221.90 1,829 6,488 222.00 1,829 61497 222.10 1,829 61499 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 2/19/2024 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond P3: StormTrap ST2 Single 4-6 SYS C Elevation Surface Storage Elevation Surface Storage (feet) (sq-ft) (cubic-feet) (feet) (sq-ft) (cubic-feet) 212.50 33028 0 217.70 3,040 127239 212.60 33028 121 217.80 3,040 127249 212.70 33028 242 217.90 3,040 127259 212.80 33028 363 218.00 3,040 127269 212.90 33028 484 218.10 3,040 121271 213.00 33028 606 218.20 3,040 121272 213.10 3,028 863 218.30 3,040 127273 213.20 3,028 1,121 218.40 3,040 127274 213.30 3,028 11379 218.50 3,040 127276 213.40 3,028 11636 218.60 3,040 127277 213.50 3,028 1,894 218.70 3,040 127278 213.60 33028 2,152 218.80 3,040 127279 213.70 33028 2,409 218.90 3,040 127281 213.80 33028 21667 219.00 3,040 127282 213.90 33028 2,925 219.10 3,040 121283 214.00 33028 3,182 219.20 3,040 121284 214.10 3,028 3,440 219.30 3,040 127286 214.20 3,028 3,698 219.40 3,040 127287 214.30 3,028 3,955 219.50 3,040 127288 214.40 3,028 41213 219.60 3,040 127289 214.50 3,028 4,471 219.70 3,040 127291 214.60 33028 4,728 219.80 3,090 127292 214.70 33028 4,986 219.90 3,094 127297 214.80 33028 51244 220.00 3,098 127303 214.90 33028 5,501 220.10 3,103 127309 215.00 33028 5,759 220.20 3,107 12,315 215.10 33028 6,017 220.30 3,111 12,322 215.20 3,028 6,274 220.40 3,115 127329 215.30 3,028 6,532 220.50 3,119 127337 215.40 3,028 61790 220.60 3,123 127345 215.50 3,028 71047 220.70 3,128 127354 215.60 37028 7,305 220.80 3,132 127363 215.70 33028 7563 220.90 3,136 127372 215.80 33028 7,820 221.00 31140 12,382 215.90 33028 81078 216.00 33040 8,336 216.10 33040 8,595 216.20 3,040 8,854 216.30 3,040 9,112 216.40 3,040 9,371 216.50 3,040 91630 216.60 3,040 9,889 216.70 3,040 10,148 216.80 33040 10,407 216.90 33040 10,666 217.00 33040 10,925 217.10 33040 11,184 217.20 33040 11,443 217.30 3,040 11,702 217.40 3,040 11,961 217.50 3,040 12,220 217.60 3,040 121230 Appendix D: Standard 4 Computations and Supporting Information > Water Quality Volume Calculations > TSS Removal Worksheets > Phosphorous Removal Worksheets D-1 Appendix D:Standard 4 Computations and Supporting Information IWa�te��� I umi um e C c u a Is D-2 Appendix D:Standard 4 Computations and Supporting Information 0 hb Water Quality Volume Calculations Project Corner Development at Merrimack College Project# 11625.34 North Andover, MA Calculated by SM/NDS Date 2/19/2024 Checked by J K Date Infiltration Systems Runoff from subcatchment area PR-1 1, PR-12, PR-13, PR-14, PR-16, PR-17, PR-18, and PR-19 Water Quality Storm Runoff Depth (in) 0.5 Total Impervious Area (ft2) 84,470 BASIN WQV: Required Volume: Runoff Depth to be Treated Required Volume (in) (ft) 0.5 31520 Provided Volume: Total Storage Capacity (ft3) System A- StormTrap SingleTrap (2.0'H) 666 System B - StormTrap SingleTrap (4.0'H) 11583 System C - StormTrap SingleTrap (4.5'H) 71305 Total 91554 11625.34-Water Quality Volume Calculations.xlsx 1 of 1 mu n uu � lipum uuuuuum uumuuu uuu uuum mi N D-3 Appendix D:Standard 4 Computations and Supporting Information Of- V11b VH B, Inc.. Corner Development at 101 Walnut Street Project Name: Merrimack College Sheet: 1 of 1 Post Office Box 9151 Project Number: 11625.34 Date: 19-Feb-2024 Watertown, MA 02471 Location: North Andover, MA Computed by: SM P 617.924.1770 Discharge Point: DP-1 Checked by: JK Drainage Area(s): PR-11 to PR-14 and PR-16 to PR-19 A B C D E B"M P TSS, Removal Rate. Startrn TS,S" Load*, mount Removed Remaining Load. (C*D) C E WQV 50% 1.00 0.50 0.50 Subsurface Infiltration 80% 0.50 0.40 0.10 Structure 0% 0.10 0.00 0.10 0% 0.10 0.00 0.10 0% 0.10 0.00 0.10 * BMP and TSS Removal Rate Values from the MassDEP Stormwater Handbook Vol. 1. Treatment Train **Equals remaining load from previous BMP(E) 90% TSS Removal = 11625.34-TSS Removal Calculations.xlsx I I IIIIVu°' uuu uuum m �I uuumuum o uuuo D-4 Appendix D:Standard 4 Computations and Supporting Information z Site Summary hb Project Corner Development Project at Merrimack College Project# 11625.34 � p J 9 � Calculated by SM Date 2/19/2024 Checked by J K Date Area to Treatment Impervious Area to P Load Removed Average Area Treatment Category Category( ) Treatement Category P Load of Impervious Area(Ib/yr) (Ib/ r) Weighted P Reduction g Yac Y(ac) (%) Structural BMPs 3.9 1.9 4.5 4.0 81% Impervious Area Disconnection - - - - Porous Pavement(w/underdrain) - - - - Untreated 0.9 0.1 0.2 0 0% TOTAL 1 4.8 2.0 4.7 4.0 78% Untreated Area Calculations %0 I lAib Project Corner Development Project at Merrimack College Project# 11625.34 Calculated by SM Date 2/19/2024 Checked by J K Date User Inputs Load Calculations z z Impervious TP Loading P Load of Impervious Area Untreated Area ID Impervious Area(ft) Pervious Area(ft) Land Use Rate(Ib/ac/yr) (Ib/yr) PR-15 3,310 35,480 Multi-Family and High Density Residential 2.3 0.2 11625.34-BMP WQ Credit Calculator.xlsm Structural BMP Calculations m'-wvhb Project Corner Development at Merrimack College Project# 11625.34 North Andover,MA Calculated by SM Date 2/19/2024 Checked by JK Date Water Quality Results User Inputs Phosphorus BMP Design Impervious Pervious Catchment Runoff Depth Impervious P Impervious P Pervious P Pervious P Total P Load P Load BMP ID BMP Type BMP Soil Type Storage Catchment Catchment Catchment Prima Land Use Prima from Impervious EPA Water Quality Curve Loading Rate Load to BMP Loading Rate Load to BMP to BMP P Removal Reduction Yp YP g a z z Primary Primary P Y g g Credit(%) Volume(ft) Area(ft) Area(ft) HSG Area(in) (lb/ac/yr) (lb/yr) (lb/ac/yr) (lb/yr) (lb/yr) (lb/yr) System A Subsurface Infiltration System Loam(0.52 in/hr) 666 20,250 12,760 Multi-Family and High Density Residenti HSG C 0.4 Infiltration Trench 2.3 1.1 0.2 0.1 1.1 67% 0.8 System B Subsurface Infiltration System Loam(0.52 in/hr) 1,583 37,730 18,830 Multi-Family and High Density Residentil HSG C 0.5 Infiltration Trench i 2.3 1 2.0 1 0.2 1 0.1 1 2.1 1 75% 1 1.6 System C Subsurface Infiltration System Loam(0.52 in/hr) 7,305 26,490 54,530 Multi-Family and High Density Residentil HSG C 1 3.3 1 Infiltration Trench 1 2.3 1 1.4 1 0.2 1 0.3 1 1.7 1 99% 1 1.7 Appendix E: Standard 8 Supporting Information > List of recommended Construction Period BMPs > Recommended construction period maintenance checklist E-1 Appendix E:Standard 8 Supporting Information uuu umuu°Illlui uuu°u uumm i uuuouo uuuuVullll muuuuu m mli mm mm� m E-2 Appendix E: Standard 8 Supporting Information J'�vhb Recommended Construction Period Pollution Prevention and Erosion and Sedimentation Controls The following erosion and sedimentation controls are for use during the earthwork and construction phases of the project.The following controls are provided as recommendations for the site contractor and do not constitute or replace the final Stormwater Pollution Prevention Plan that must be fully implemented by the Contractor and Owner in compliance with EPA NPDES regulations. Compost-Filled Siltsock Barriers Compost-Filled Siltsock barriers will be placed to trap sediment transported by runoff before it reaches the drainage system or leaves the construction site.Where necessary or where shown on the plans,two rows of siltsocks may be used to provide enhanced protection for erosion-prone areas. Silt Fencing In areas where high runoff velocities or high sediment loads are expected, siltsock or straw bale barriers will be backed up with silt fencing.This semi-permeable barrier made of a synthetic porous fabric will provide additional protection.The silt fences and siltsock barrier will be replaced as determined by periodic field inspections. Catch Basin Protection Newly constructed and existing catch basins will be protected with straw bale barriers (where appropriate) or silt sacks throughout construction. 000 Construction Exits Temporary crushed-stone construction exits will be constructed.A cross slope will be placed in the entrance to direct runoff to a protected catch basin inlet or settling area. If deemed necessary after construction begins, a wash pad may be included to wash off vehicle wheels before leaving the project site. Diversion Channels Diversion channels will be used to collect runoff from construction areas and discharge to either sedimentation basins or protected catch basin inlets. Temporary Sediment Basins Temporary sediment basins will be designed either as excavations or bermed stormwater detention structures (depending on grading) that will retain runoff for a sufficient period of time to allow suspended soil particles to settle out prior to discharge.These temporary basins will be located based on construction needs as determined by the contractor and outlet devices will be designed to control velocity and sediment. Points of discharge from sediment basins will be stabilized to minimize erosion. Vegetative Slope Stabilization Stabilization of open soil surfaces will be implemented within 14 days after grading or construction activities have temporarily or permanently ceased, unless there is sufficient snow cover to prohibit implementation.Vegetative slope stabilization will be used to minimize erosion on slopes of 3:1 or flatter.Annual grasses, such as annual rye, will be used to ensure rapid germination and production of root mass. Permanent stabilization will be completed with the planting of perennial grasses or legumes. Establishment of temporary and permanent vegetative cover may be established by hydro-seeding or sodding.A suitable topsoil, good seedbed preparation, and adequate lime, fertilizer and water will be provided for effective establishment of these vegetative stabilization methods. Mulch will also be used after permanent seeding to protect soil from the impact of falling rain and to increase the capacity of the soil to absorb water. Erosion control blankets shall be used in all areas where slopes exceed 3:1. Street Sweeping Street sweeping of site and adjacent roadways will be completed throughout construction as necessary. I� Maintenance > The contractor or subcontractor will be responsible for implementing each control shown on the Sedimentation and Erosion Control Plan. In accordance with EPA regulations, the contractor must sign a copy of a certification to verify that a plan has been prepared and that permit regulations are understood. > The on-site contractor will inspect all sediment and erosion control structures periodically in accordance with the compliance path chosen during the NPDES CGP Notice of Intent (NOI) process. Records of the inspections will be prepared and maintained on-site by the contractor. > Sediment shall be removed from behind barriers if buildup exceeds half the bale height. > Damaged or deteriorated items will be repaired immediately after identification. > The underside of straw bales should be kept in close contact with the earth and reset as necessary. > Sediment that is collected in structures shall be disposed of properly and covered if stored on-site. > Erosion control structures shall remain in place until all disturbed earth has been securely stabilized.After removal of structures, disturbed areas shall be regraded and stabilized as necessary. uluum uuuuu ,�� uuuuumuu� I II II umi Ipw uullluum umuu uuuuuuum u� IIIII II uuu uuum E-3 Appendix E: Standard 8 Supporting Information CanstructIIIII ° r IIIII °°°° Mai�hntenance/ IIIIICheck��hilst Corner Development Project at Merrimack College- North Andover, MA Cleaning or Best Repair Needed Date of Management Inspection Date Inspector Minimum Maintenance ❑Yes/No Cleaning Performed Practice Frequency Inspected Initials and Key Items to Check (List Items) or Repair by: Erosion Weekly and Sediment build up, broken Control after any bales or stakes Barrier/ rainfall Silt Fencing Construction Weekly and Filled voids,runoff/sediments Exits after any into street rainfall Catch Basin Weekly and Clogged or sediment build- Protection after any up at surface or in basin rainfall Diversion Weekly and Maintained,moved as Channels after any necessary to correct locations, rainfall Check for erosion or breakout Temporary Weekly and Cracking,erosion, breakout, Sedimentation after any sediment buildup, Basins rainfall contaminants Stormwater Control Manager: Appendix F: Standard 10 Supporting Information > Illicit Discharge Statement F-1 Appendix F: Standard 10 Supporting Information c t Discharge Sta�tement 'The design plans submitted with this report have been designed so that the components included therein are in compliance with the current Ma DEP and municipal standards as noted. The Project site was previously undeveloped with no known illicit connections associated with the sanitary sewer or storm drainage infrastructure. Measures to prevent illicit discharges are included in the Construction Period and Long-Term Pollution Prevention Plans included in the Storm water Report. The Owner, Merrimack College, understands that no illicit discharges are allowed into the stormwater system .......... . .... ........... ................. ry —.......... ,-'rf 4)657 ............... .............................. ............................. .................... ............... Avhb.,c=gtA*rcjXWat-LM1 1625.34 Greystar P3 DeveloprnentAReports\StcrmwateMp,pencfices �AWenclix F-Standard 10 Computations and Supporting InformationTl-Illicit Discharge StatemenLdoc