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Home My WebLink About2023/09/15 - Stormwater Management Report - - STORMWATER MANAGEMENT REPORT Corner Development 111 JOWAk III I A#W& ig Priujq::,ct alt I\At: rrima �lcic College 3 ,5 11111111111111ru Slllt�� 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 101 Walnut Street PO Box 9151 Watertown, MA 02471 A u g tjii st 1 7, 20 23 S e pt e ir-n b e iir 15, 2 0 2,3 III„�Z ev 1 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 1 Checklist for Stormwater Report Appendix C: Standard 3 Computations and Supporting Documentation.........................................C-1 Appendix D: Standard 4 Computations and Supporting Information...............................................D-1 Appendix E: Standard 7 Supporting Information.......................................................................................E-1 Appendix F: Standard 8 Supporting Information.......................................................................................F-1 2 Checklist for Stormwater Report 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 3 Checklist for Stormwater Report '00rhb. Checklist for Stormwater Report 4 Checklist for Stormwa[er 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 Checkl'ist 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 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 h LOV E CIVIL , 40,726 August 18, 2023 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 00 i Stormwater Report Narrative 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 �Mieclllt uumuuu uuu uuum ll 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 uuuum i puu 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. 5 Stormwater Report Narrative 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. 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. 0 m u ' IIIIIIII....II g e C 0 I i P ao uuu uuum VuuuVl 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 uV I I Ipl I uullllp � uuu uuulll Ipw I uuuuuuVl uuum II Figure 4 illustrates the proposed "post construction" drainage conditions for the project.As shown, the Site will be divided into five 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 0.9 85 6 drainage system at Andover Street PR-12 Existing closed DP-1 1.9 89 6 drainage system at Andover Street PR-13 Existing closed DP-1 1.0 76 6 drainage system at Andover Street PR-14 Existing closed DP-1 0.2 94 6 drainage system at Andover Street PR-15 Existing closed DP-1 0.7 77 6 drainage system at Andover Street PR-20 Existing closed DP-1 3.1 85 6 drainage system at Andover Street PR-30(EX-3) Existing closed DP-1 0.8 95 6 drainage system at Andover Street 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. 7 Stormwater Report Narrative Figure 1 Site Locus Map 8 Stormwater Report Narrative \\Vhb\gbl\prof\Wat-LD\11625.34 Greystar P3 Development\cad\Id\Eng\Stormwater\Site Locus\1162534-Site Locus.dwg r, '�Ovhb� A eYr, e I „ u � r f , d ro„ z P F r r A �s V% , y a wi U s 9 „ a f y „ r , i , i , e v a P I , i n y // 7l r w� 1 I Il U V,. i r i V o i r 'V ri r , I p Y r � U r y u � r r ,� or ' r r i � u r r 5 U f r v , {' r 5 I W i p r, 1' „ I ! 7 e, I „ , y g J 0 j1 �I d �II Aij r If J fii Y J �I G 1 u P I I 1 f I i f ry i 0 r l r r e �J y � i f I i �iUFn J 1 r 1 I 0 I, I I. x I, ff I V ti p � w C y. u Y v f, f , r r ; „ „ re P r „ Ip 1 r „ r . r r u y r r r v i X � o a y i I a � T r � r M ri i i Site Locus Map Figure 1 Corner Development 0 500 1000 2000 Feet at Merrimack College August 2023 g North Andover, MA 01845 Figure 2 FEMA Firmette 9 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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'�1.,I 1 4.��",%1.�, 1,1"..,�I,i,,�1 v�"-",I,I,�,1.,".,�,,�-1',I.%,�o.�1I�.,,,,,.I-�I 1,-I�I'.,I-,,.�,�I 1,\.� .,I\,...._'I'."%,,I�I1,.""�,;..�_'�",I,,..,I J'fl.A,,.;".,1.�'.'�_,�1 I.�"_"�,I,-.7-, ft,'-,"1�,'�,"-11�,x'1 1,��1w I",��I�!�I",�_1,I\\11 11'',",-tI,1"1 �I-k,"'-I 1W"'1-I,I,,"\N",Ml-,1 -,,,11�...�,,',I,,�I.,�,,1.II\\A�,.""-�.1�.:I�.z_�1\R1,_\#.i '�-...—,_�II,,lI...",-1"_lII I...1.,I-,"I.1��I,,.11111',%\'.1,111111 I,,1.I��,...I,I1I,"....,�,,""..�1��,.""..��,,',IA..I�,.".I.1.I,�.�� KERE�AK�.��EGE W.: FFE-zzo v� BOUNDARY :::-.'�,I",":::_-.'IW"I...\.,I".:..,"""-,I 1.'"''..,I-,%1,�.'I I�",.,..1I._.1,'`.II�\I,.1 x.\,.�II,..',��.\\I,,I\I_.,\II:.,".\I,.III\""_\I.."I",I�\l,,,".,',,,','�I."".,,\",.Sl��I,lI".:".,.I,",,l",X,.K�.','I",'\,,"1<-I�".\.,�"�`,�k,\.I.�'.,1K.,;:.I,.."'Y1,\1�I\,'.","1 I,Q..ST�1,,,%1 SI\.,\.",��.,�,1�\1�M1,.-<,"".,'1".�I,,,I��--4 ,l,`_�\",-i I1�-1II'1-,-1,",I�",,I`1,,'"I�"I\1I'�111�_'1I, iI,,',_,,1,I�,!-I",I,""I%tIv\�--I 1I."'1"�III,,.�1-I ",�,..,",,�",1,,,1,'ll,1",��''"'1.I,,I\,,'1",,1",.',1,\',1\,�1"�11",,,,,,,-""I-,,,,, ,-_,"�-11.-.1"_.I'.11_,'".1,I,.1.,�.".' t >. o _, ; �, _ NCENTRATION �. ,�---� --- --- . :�:. .,. �: - • ,. V ..:�� I ,, \ .. _ y, N FLOW L NE x �a �. r .. _ N, EEK.� v,' R2 z 0 a _ >,.< I.... \: .._N a,. bo .<: SOIL TYPE BOUNDARY \ �, ...... r ... �.,ic..t r .... , v,.., r.: . .. ...."" „. .� ...:.,. .., , ::. ,,. x. .,...... <. �E, �. �: 100 BUFFER ZONE F: �... . r,; .._ _ >.. ...,. , °' _� "... 11.: , , ........ \ .....\ \ €aT f ...., :...,y. .., .�< _ WETLAND BOUNDARY ,A _ �___ - 4 4-220 4 219 � *. ,. _ \ ., ,.K. ,N \ " - `: , l..<_ :: �... o. .. <. \� 4' , �_' .' - ., ., :_.. , s .:' ., \ , SCS SOIL CLASSIFICATIONS v_ _ ; z .............. s.,...lam .,.:. ..,. ..,.... ..;, , '.i - I.i�F :E .` a BOOK 77,PAGCS .0 ;..'I.. ..'..� :: .., - RIDGEBURY FINE SANDY .. �_ ., �, v., : ... �:, �,,: _. � �.. .. ., °' ,> LOAM 0 TO 3 PERCENT ,: , , ., 7�iI .. _ c #, LOPE.., �, , - :_ SS _ .; , ,: ,.. ,..... _.,.. N WOODBRIGDE FINE �, • R 1�R 8 TH \ ` - Na ) 1 NE _ ,. >: 311B , ANo ta,,,:, �, SANDY LOAM 0 TO 3 �;: o, 1 , _ 0 AnhE„B,I.,AFIA co , ., R A- ... PERCENT SLOPES ., , .. 70A , ._,. I_ �,a ..,., 0 v, - .. .,� �, - o6 , , , >.:> �. , _ .,. �.; SANDY LOAM 0 TO 8 ; � 10 ., ., ,.., .,.' ,...... .. , — ., ',, ...a,. PERCENT SLOPES - - �. ��m �.. , - .,.. ,` 5 _ . .„ .. 2 - - WOODBRIGDE FINE �,. - , - ,., - - - ,,,. _ - :.,. M,0 ,, - SANDY LOA TO 8 ... - , , _ ,. _ 311B , = T SLOPE VERY,:. „ I - RCEN S V , ... ,.. �... .. , A �..'� ,t y �. _y . �. STONY _ y r l,, s... 4) , N R,; , , O , ,_ ,._ .,,, .. ,, ,,,,... , „,._< `, ,, - ° �:°, ,, ,` ;: -, - ., : ;: , : , y �< :. I :: F ' :, _ �, , ,.� �.:. ,NEPRI�SA.h i-.,IIEt,L.I,.... y .. �.... �.. .; € T 2 =... MP 2 ...... .. ��.. ., ._ \ €.. .s� .,. .. r-i t .. ., ,. N 4x // \..i ,.� ._ Ntoffi Vhb,' Propsed Drainage Conditions Figure 4 IIIIIIIIIIIIIIIIIIIIIIIII(20 Corner Development Project at 0 50 100 200Feet Merrimack College 08/17/2023 North Andover,MA REW -09/15/2023 This page intentionally left blank. 12 Stormwater Report Narrative �Ida i qwdo Regulatory Compliance IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII,III I II � I I IIIIIIIIII IIuuuuuu� I � uum I �� \Aassac��liusell'Illt'll"lts IVuuuvuu IIIIIIIIVIII IIIIIIIIIIIIIIIIIIIII VVuvUUW uuunn I umul uuuuuuuuuuuuuuuuum ��\Aa ul IVVuuuVV uuu IIIIIIII (IIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIII IIIIIIIII VI V I As demonstrated below, the proposed Project fully complies with the DEP Stormwater Management Standards. tandard 1: No New UnIII ��'Diisdharges �III IIIII II IId 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. III III : �°� �Ia te A°It°tenua° IIIII 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 ponding from the 100-year storm event is limited to on-site locations in the immediate vicinity of the systems and causing no adverse impacts to down-gradient properties. 13 Regulatory Compliance Computations and supporting information regarding the hydrologic modeling are included in Appendix B. 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 11.2 25.4 36.1 53.4 Design Point 2-year 10-year 25-year 100-year DP-1 Existing 48,010 971260 129,910 182,050 Proposed 43,350 941270 1271710 180,730 S tandard 1, S tormwa te r ��Ie c h a rg e The Project has been designed to comply with Standard 3. In accordance with the Stormwater Handbook, the Required Recharge Volume for the Project is therefore 1,265 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 11463 223.6 224.4 649 System A Subsurface Infiltration 21482 216.5 218.5 3,629 System B Subsurface Infiltration 2,506 213.5 215.8 4,314 System C Total Provided Recharge 81592 Total Required Recharge 11265 Soil evaluation (including Geotechnical Report), computations, and supporting information are included in Appendix C. 14 Regulatory Compliance S°'tandard nn ® Wa°'t e il°' n 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, including the Long-Term Pollution Prevention Plan, are included in Appendix D. S"'tandard 5: andIIIII"'t h """"'I il g h e o"'ten"'t il" °? o u"'ta I "'t oads .U��I ��:)�� S) The Project is not considered a LUHPPL. S°' IIF IIFGrii�°' IIIII IIF°°°° The Project will not discharge stormwater near or to a critical area. S ta I IIF : °° men°'ts and IIF0 ts Subjec°'' °' °'the S°'tandards aI °'totheMaxiimum °°°°° °'ten°' °° ra c t 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 t ru c°'t il o °° e il t il o n reve 'IIIII n and Erosiion n d S e d il m e I °' ' t ii�o I II trd�s 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 'IIIII II IIMailn°'t e n 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 as part of the Long Term Pollution Prevention Plan. 15 Regulatory Compliance Snitandard ni IIIII IIIII nit IIIII o n o nif ��hiiIIIII 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. 16 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 uuuuuuu g C uuuuuuuuu u i i p uuu uuum lip ��a e S 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 NDS Date 9/15/2023 Checked by JWK Date 9/15/2023 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 0.297 0 0.092 5 7.94 12 HDPE 0.012 0.02 66.6 0.74 5.39 4.81 229.2 226.96 227.9 225.55 226.6 225.3 A103 A102 0.18 0 0.083 5 7.94 12 HDPE 0.012 0.006 51.7 0.66 2.94 3.02 227.4 225.14 227.9 224.9 224.8 224.5 A102 SYS A IN (N/A) (N/A) 0.175 5 7.809 12 HDPE 0.012 0.008 26.4 1.38 3.36 4.06 227.9 224.9 226.7 224.65 224.4 224.2 BLDG 1 A105 0.229 0.9 0.206 5 7.94 12 HDPE 0.012 0.01 30.1 1.65 3.86 4.72 226.7 225.55 227.1 225.16 225 224.7 A104 A105 0.146 0.125 0.018 5 7.94 12 HDPE 0.012 0.007 13.5 0.15 3.32 2.12 226.6 224.99 227.1 224.99 224.6 224.5 A105 SYS A IN (N/A) (N/A) 0.224 5 7.891 12 HDPE 0.012 0.005 39.9 1.78 2.73 3.71 227.1 224.99 226.7 224.77 224.4 224.2 SYS A OUT A106 (N/A) (N/A) 0 5 7.931 12 HDPE 0.012 0.01 10 3.4 3.86 5.55 226.7 225.19 227.6 225.04 224.4 224.3 A106 B107 (N/A) (N/A) 0 5 10.219 12 HDPE 0.012 0.014 85.9 3.4 4.56 6.37 227.6 224.99 225.8 223.64 224.2 223 B117 B107 0.212 0 0.054 5 7.647 12 HDPE 0.012 0.01 91 0.42 3.84 3.21 225.4 223.67 225.8 222.72 223.4 222.5 B105 B107 0.125 0.825 0.103 5 7.94 12 HDPE 0.012 0.035 28.7 0.82 7.22 6.11 225.4 223.18 225.8 222.03 222.8 221.8 B106 B107 0.14 0.125 0.018 5 7.94 12 HDPE 0.012 0.016 12.8 0.14 4.83 2.72 223 221.53 225.8 221.53 221 220.8 B107 B111 (N/A) (N/A) 0.175 5 7.429 18 HDPE 0.013 0.011 92.7 4.71 10.91 5.94 225.8 221.53 223.5 220.39 220.7 219.7 B-109 B111 0.207 0 0.078 5 7.94 12 HDPE 0.012 0.059 29.1 0.63 9.34 6.76 223.4 221.73 223.5 220.45 221.4 219.7 BLDG-1 B111 0.285 0.9 0.257 5 7.94 12 HDPE 0.012 0.011 94.3 2.05 3.98 5.1 227.7 221.01 223.5 220.45 220.4 219.4 B112 B115 0.255 0 0.132 5 7.94 12 HDPE 0.012 0.007 44.9 1.05 3.15 3.61 222.5 220.53 222.9 220.48 220.1 219.8 B113 B115 0.157 0 0.099 5 7.94 12 HDPE 0.012 0.01 29.3 0.79 3.9 3.9 222.5 220.47 222.9 220.48 220.1 219.8 B115 B111 (N/A) (N/A) 0.231 5 7.845 12 HDPE 0.012 0.01 29.3 1.83 3.9 4.89 222.9 220.48 223.5 220.45 219.7 219.4 B111 B103 (N/A) (N/A) 0.741 5 7.309 18 HDPE 0.013 0.011 38 8.86 10.77 6.81 223.5 220.45 223.5 219.94 219.3 218.9 B-101 B-102 0.133 0 0.079 5 7.94 12 HDPE 0.012 0.01 233.6 0.63 3.86 3.62 223.4 221.73 223.4 221.16 221.4 220.8 B-102 B103 0.115 0 0.149 5 7.813 12 HDPE 0.012 0.012 16.8 1.17 4.23 4.6 223.4 221.16 223.5 220.87 220.7 220.5 B103 B104 (N/A) (N/A) 0.889 5 7.266 18 HDPE 0.013 0.01 49.8 9.91 10.53 6.78 223.5 220.01 223.5 219.46 218.8 218.3 BLDG-2 B104 0.189 0.9 0.17 5 7.94 12 HDPE 0.012 0.007 15.1 1.36 3.14 1.73 220.3 219.49 223.5 219.47 218.3 218.2 B104 SYS B IN (N/A) (N/A) 1.06 5 7.21 18 HDPE 0.013 0.02 10 11.1 14.86 9.22 223.5 219.47 227.7 219.1 218.2 218 SYS B OUT B114 (N/A) (N/A) 0 5 7.931 24 HDPE 0.012 0.017 6.2 12.6 31.64 9.5 227.7 219.48 223.6 219.2 218.2 218.1 B114 C110 (N/A) (N/A) 0 5 10.228 24 HDPE 0.012 0.015 45.5 12.6 30.44 9.23 223.6 217.38 219.2 216.35 216.1 215.4 C110 Cl 12 (N/A) (N/A) 0 5 10.19 24 HDPE 0.012 0.01 59.8 12.6 24.54 7.86 219.2 213.98 219.8 213.38 212.7 212.1 C108 C111 0.039 0 0.008 5 7.94 12 HDPE 0.012 0.014 222.2 0.06 4.53 2.02 219.5 217.6 219.2 217.28 217.5 217.2 C111 SYS C IN (N/A) (N/A) 0.147 5 7.857 12 HDPE 0.012 0.01 9.9 1.17 3.87 4.31 219.2 216.56 227.7 216.39 216.1 216 BLDG-2 C111 0.155 0.9 0.14 5 7.94 12 HDPE 0.012 0.013 15.3 1.12 4.42 4.69 227.7 216.85 219.2 216.55 216.4 216.2 SYS C OUT Cl 12 (N/A) (N/A) 0 5 7.931 12 HDPE 0.012 0.02 5.9 2.1 5.46 6.5 227.7 216.42 219.8 216.21 215.8 215.7 Cl 12 D101 (N/A) (N/A) 0 5 10.131 24 HDPE 0.012 0.011 47.2 14.7 25.23 8.34 219.8 213.38 215.8 212.64 212 211.5 D101 D102 (N/A) (N/A) 0 5 10.088 24 HDPE 0.012 0.015 78 14.7 30.38 9.59 215.8 211.88 215.8 210.31 210.5 209.3 D102 EX1 (N/A) (N/A) 0 5 10.026 24 HDPE 0.012 0.01 9.6 14.7 24.98 8.27 215.8 210.48 212.79 210.24 209.1 209 C101 C102 0.223 0.125 0.046 5 7.94 12 HDPE 0.012 0.01 149.8 0.37 3.86 3.1 226.5 224.75 226.5 223.21 224.5 223 C102 C103 0.078 0 0.063 5 7.569 12 HDPE 0.012 0.014 14.3 0.48 4.56 3.78 226.5 223.19 226.5 222.92 222.9 222.7 C103 C104 0.024 0 0.07 5 7.54 12 HDPE 0.012 0.023 90.2 0.53 5.89 4.65 226.5 222.9 222.5 220.7 222.6 220.5 \\vh1b.corn\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 NDS Date 9/15/2023 Checked by JWK Date 9/15/2023 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) C104 C105 0.092 0 0.092 5 7.391 12 HDPE 0.012 0.009 110.9 0.68 3.66 3.57 222.5 220.75 222.5 219.69 220.4 219.4 C105 C106 0.048 0 0.104 5 7.153 12 HDPE 0.012 0.033 92.2 0.75 6.96 5.8 222.5 219.66 219.4 216.52 219.3 216.3 C107 C106 0.2 0 0.035 5 7.94 12 HDPE 0.012 0.016 31.5 0.28 4.86 3.36 218.8 217.02 219.4 216.62 216.8 216.3 C106 SYS C IN (N/A) (N/A) 0.139 5 7.031 12 HDPE 0.012 0.022 18 0.99 5.75 5.48 219.4 216.62 227.7 216.09 216.2 215.8 \\vh1b.corn\gbl\prof\Wat-LD\11625.34 Greystar P3 Development\ssheets\Stormwater\11625.34-Stormcad Conduit Output Table 2 of 2 Appendix 13: 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 > 100-Year Storm: Ponding Elevations B-1 Appendix B:Standard 2 Computations and Supporting Information uuuumuuuu uuuuuum i i uuuuuuuuum i uummm uuuumuum uuu uuum P lip uuu uuum 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 IIIIIIIIII.Yea r S torm t .................... IIIII:IIIII ii I ii B-3 Appendix B: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 ii ii 10 IIIIIIII �� IIIIIII �� IIIIIIIIIIIIIIIIIIII IIIII ��IIIYea S (IIIIIIIIII IIIIIIIIIII I B-4 Appendix B: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) III,, ��I��Iry�Iryrypp�I�I�I�I�� IIIIIIIIII III IIIIIIIIII ii ii IIIIIIIIRR IIIIIIIIII. IIIIIIII III' SIII IIIIIIIII�IIII IIIIIIII ................. IIIIIII�IIII III B-5 Appendix B: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) II�,�y �Ilrylrypllll� II�,�, IIIIIIIIII IIIIIIIIII � ii 100 IIIIIIII SIII IIIIIIIRR III IIIIIIIIIIIIIIIIIM IIIIIRR III III IIIYea III III (IIIIIIIIII IIIIIIIIIII II B-6 Appendix B: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) uuuuu°uuul � uuumuuu �I umumuu I P uuu uuum I II i�Vu Illllllm I III uuuummuu� VI 6-7 Appendix 6:Standard 2 Computations and Supporting Information A PR-11 StormTrap ST2 Single PR-11 20 47 /P\2 PR-12 StormTrap ST2 Single PR-12 3-6 PR-13 DP-1 PR-13 P3 Andover Street S StormTrap ST2 Single 3-6 P R-14 PR-14 PR-15 PR-15 P R-20 PR-20 PR-30 Outside Project Site - Andover/Elm St Subcat Reach Pond Link Routing Diagram for 11625.34-PR Prepared by VHB, Inc, Printed 9/15/2023 HydroCAD®10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC 11625.34 - PR 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 - PR 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) 1951920 74 >75% Grass cover, Good, HSG C (PR-111 PR-12, PR-13, PR-14, PR-157 PR-20, PR-30) 114,990 98 Paved parking (PR-11, PR-12, PR-13, PR-14, PR-15, PR-20, PR-30) 667610 98 Roof (PR-11, PR-12, PR-14, PR-20) 3775520 86 TOTAL AREA 2 IIIIIIIIIYea r S torm t .................... II I ed I B-8 Appendix B:Standard 2 Computations and Supporting Information 11625.34 - PR 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 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=38,490 sf 45.49% Impervious Runoff Depth=1.72" Flow Length=235' Tc=6.0 min CN=85 Runoff=1.8 cfs 5,528 cf SubcatchmentPR-12: PR-12 Runoff Area=82,880 sf 63.75% Impervious Runoff Depth=2.05" Tc=6.0 min CN=89 Runoff=4.5 cfs 14,125 cf SubcatchmentPR-13: PR-13 Runoff Area=41,950 sf 8.39% Impervious Runoff Depth=1.12" Tc=6.0 min CN=76 Runoff=1.2 cfs 3,930 cf SubcatchmentPR-14: PR-14 Runoff Area=8,480 sf 81.96% Impervious Runoff Depth=2.51" Tc=6.0 min CN=94 Runoff=0.5 cfs 1,770 cf SubcatchmentPR-15: PR-15 Runoff Area=32,680 sf 13.77% Impervious Runoff Depth=1.18" Tc=6.0 min CN=77 Runoff=1.0 cfs 3,223 cf SubcatchmentPR-20: PR-20 Runoff Area=136,290 sf 46.99% Impervious Runoff Depth=1.72" Tc=6.0 min CN=85 Runoff=6.3 cfs 19,575 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=225.03' Storage=1,403 cf Inflow=1.8 cfs 5,528 cf Discarded=0.0 cfs 1,326 cf Primary=1.2 cfs 3,894 cf Outflow=1.2 cfs 5,220 cf Pond P2: StormTrap ST2 Single 3-6 Peak EIev=219.31' Storage=5,332 cf Inflow=5.3 cfs 18,019 cf Discarded=0.0 cfs 2,380 cf Primary=3.3 cfs 12,566 cf Outflow=3.3 cfs 14,946 cf Pond P3: StormTrap ST2 Single 3-6 Peak EIev=215.71' Storage=4,126 cf Inflow=1.8 cfs 5,700 cf Discarded=0.0 cfs 2,247 cf Primary=0.0 cfs 0 cf Outflow=0.0 cfs 2,247 cf Link DP-1:AndoverStreet System Inflow=11.2 cfs 43,344 cf Primary=11.2 cfs 43,344 cf Total Runoff Area = 377,520 sf Runoff Volume = 56,131 cf Average Runoff Depth = 1.78" 51.90% Pervious = 195,920 sf 48.10% Impervious = 181,600 sf 11625.34 - PR 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 5 Summary for Subcatchment PR-11: PR-11 Runoff = 1.8 cfs @ 12.09 hrs, Volume= 5,528 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 201980 74 >75% Grass cover, Good, HSG C 9,960 98 Roof 7,550 98 Paved parking 381490 85 Weighted Average 20,980 54.51% Pervious Area 171510 45.49% 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" 0.6 70 0.0140 1.90 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 45 0.0400 3.22 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 35 0.0200 2.87 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.2 35 0.0200 2.87 Shallow Concentrated Flow, Paved Kv= 20.3 fps 4.8 235 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 6 Subcatchment PR-11: PR-11 Hydrograph 2 El Runoff 1.8 cfs % Type III 24=hr 2-Year Rainfall=3.16" Runoff Area=38,490 sf Runoff Volume=5,528 cf Runoff Depth=1,72" 0 i Flow Length=235' Tc=6,0 min CN=85 111,00, 0 t W// ,, 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 7 Summary for Subcatchment PR-12: PR-12 Runoff = 4.5 cfs @ 12.09 hrs, Volume= 14,125 cf, Depth= 2.05" Routed to Pond P2 : StormTrap ST2 Single 3-6 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 301040 74 >75% Grass cover, Good, HSG C 241340 98 Roof 281500 98 Paved parking 821880 89 Weighted Average 30,040 36.25% Pervious Area 521840 63.75% 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 5 0 Runoff 4.5 cfs Type III 24-hr 4 / 2-Year Rainfall=3.16" Runoff Area=82,880 sf Runoff Volume=14,125 cf 3 Runoff Depth=2.05" 0 Tc=6.0 m i n am: 2 CN=89 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 9/15/2023 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= 3,930 cf, Depth= 1.12" Routed to Pond P3 : StormTrap ST2 Single 3-6 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 381430 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,520 98 Paved parking 411950 76 Weighted Average 38,430 91.61% Pervious Area 3520 8.39% 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 1.2 cfs Type III 24=hr 2-Year Rainfall=3.16" 1 Runoff Area=41,950 sf %! Runoff Volume=3,930 cf Runoff Depth=1.12" ,� �' Tc=6,0 min CN=76 i�&z/mn/%//*/*�mo�/'*//ills mn ii 0 U U U U U U U U U U U U U U U U U U U U M M'ill 1111'ill'ill'ill'ill 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 M M'ill'ill 1111'ill'ill'ill'ill U U U U U U U U U U U 111�lrlr-ijj�r�irii U U U U U U U U 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 /// 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 PR-14: PR-14 Runoff = 0.5 cfs @ 12.08 hrs, Volume= 1,770 cf, Depth= 2.51" Routed to Pond P3 : StormTrap ST2 Single 3-6 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 1,530 74 >75% Grass cover, Good, HSG C 6,770 98 Roof 180 98 Paved parking 8480 94 Weighted Average 1,530 18.04% Pervious Area 6,950 81.96% 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 0.6 1 El Runoff 0.5 cfs 0.55 Type III 24=hr 2-Year Rainfall=3.16" 0.45 Runoff Area=8,480 sf 0.4 Runoff Volume=1,770 d 0.35 / Runoff Depth=2,51 0.3 Tc=6.0-rein 0.25 ! CN=94- 0.15 0.1 0.05 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 10 Summary for Subcatchment PR-15: PR-15 Runoff = 1.0 cfs @ 12.09 hrs, Volume= 3,223 cf, Depth= 1.18" 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 2-Year Rainfall=3.16" Area (sf) CN Description 281180 74 >75% Grass cover, Good, HSG C 0 98 Roof 4500 98 Paved parking 321680 77 Weighted Average 28,180 86.23% Pervious Area 4500 13.77% 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 1.0 cfs 1 / Type III 24=hr 2=Year Rainfall=3.16" Runoff Area=32,680 sf Runoff Volume=3,223 d Runoff Depth=1.18" 0 Tc=6,0 min CN=77 / 0loom=, 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 11 Summary for Subcatchment PR-20: PR-20 Runoff = 6.3 cfs @ 12.09 hrs, Volume= 19,575 cf, Depth= 1.72" 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 721250 74 >75% Grass cover, Good, HSG C 251540 98 Roof 381500 98 Paved parking 136,290 85 Weighted Average 721250 53.01% Pervious Area 641040 46.99% 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 1 El Runoff 6.3 cfs 6 Type III 24-hr % 2-Year Rainfall=3.16" 5 / Runoff Area=136,290 sf / Runoff Volume=19,575 cf 4 Runoff Depth=1.72" 0 Tc=6.0 min CN=85 0 U U U U U U U U U U U U U U U M M'111 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 U` 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 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 12 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 13 Summary for Pond P1: StormTrap ST2 Single 2-0 I nflow Area = 38,490 sf, 45.49% Impervious, Inflow Depth = 1.72" for 2-Year event Inflow = 1.8 cfs @ 12.09 hrs, Volume= 5,528 cf Outflow = 1.2 cfs @ 12.18 hrs, Volume= 5,220 cf, Atten= 34%, Lag= 5.6 min Discarded = 0.0 cfs @ 9.72 hrs, Volume= 1,326 cf Primary = 1.2 cfs @ 12.18 hrs, Volume= 3,894 cf Routed to Pond P2 : StormTrap ST2 Single 3-6 Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 225.03'@ 12.18 hrs Surf.Area= 1,463 sf Storage= 1,403 cf Plug-Flow detention time= 120.4 min calculated for 5,220 cf(94% of inflow) Center-of-Mass det. time= 90.3 min ( 917.0 - 826.7 ) Volume Invert Avail.Storage Storage Description #1 A 223.60' 459 cf 23.79'W x 61.50'L x 3.00'H Field A 4,390 cf Overall - 3,242 cf Embedded = 1,148 cf x 40.0% Voids #2A 224.10' 2,242 cf StormTrap ST2 SingleTrap 2-Ox 3 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 8.48' x 46.19' Core + 6.66' Border = 21.79' x 59.50' System #3 224.40' 28 cf 4.00'D x 2.20'H Vertical Cone/CylindeFimpervious #4 226.60' 54 cf Custom Stage Data (Prismatic)Listed below(Recalc) 2,783 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) 226.60 110 0 0 226.90 250 54 54 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 @ 9.72 hrs HW=223.63' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=1.2 cfs @ 12.18 hrs HW=225.03' (FreeDischarge) L2=Culvert (Barrel Controls 1.2 cfs @ 3.18 fps) 11625.34 - PR Type 11124-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 14 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 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 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 + 30.0" Chamber Height= 3.00' Field Height 3 Chambers x 231.7 cf+ 1547.2 cf Border= 2,242.3 cf Chamber Storage 3 Chambers x 326.4 cf+ 2,262.4 cf Border= 3,241.5 cf Displacement 4,389.E cf Field- 3,241.5 cf Chambers = 1,148.1 cf Stone x 40.0%Voids = 459.2 cf Stone Storage Chamber Storage + Stone Storage= 2,701.5 cf = 0.062 of Overall Storage Efficiency = 61.5 Overall System Size = 61.50'x 23.79'x 3.00' 3 Chambers(plus border) 162.E cy Field 42.5 cy Stone 11625.34 - PR 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 15 Pond P1: StormTrap ST2 Single 2-0 Hydrograph Inflow 1.8 cfs aull Outflow Inflow Area=38,490 Sf Discarded Primary Peak Elev=225.03' Storage=1,403 cf 1.2 cfs 1.2 cfs V 0 i 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 /// 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 16 Summary for Pond P2: StormTrap ST2 Single 3-6 Inflow Area = 121,370 sf, 57.96% Impervious, Inflow Depth = 1.78" for 2-Year event Inflow = 5.3 cfs @ 12.10 hrs, Volume= 187019 cf Outflow = 3.3 cfs @ 12.24 hrs, Volume= 14,946 cf, Atten= 37%, Lag= 8.6 min Discarded = 0.0 cfs @ 11.99 hrs, Volume= 2,380 cf Primary = 3.3 cfs @ 12.24 hrs, Volume= 12,566 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= 219.31'@ 12.24 hrs Surf.Area= 2,494 sf Storage= 5,332 cf Plug-Flow detention time= 144.9 min calculated for 14,941 cf(83% of inflow) Center-of-Mass det. time= 78.6 min ( 894.1 - 815.5 ) Volume Invert Avail.Storage Storage Description #1 A 216.50' 839 cf 32.27'W x 76.90'L x 4.50'H Field A 11,167 cf Overall - 9,069 cf Embedded = 2,098 cf x 40.0% Voids #2A 217.00' 7,000 cf StormTrap ST2 SingleTrap 3-6x 8 Inside #1 Inside= 101.7"W x 42.0"H => 26.77 sf x 15.40'L = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 522.2 cf 8 Chambers in 2 Rows 16.96' x 61.58' Core + 6.66' Border = 30.27' x 74.90' System #3 218.20' 54 cf 4.00'D x 4.30'H Vertical Cone/Cylinder #4 222.50' 2,138 cf Custom Stage Data (Prismatic)Listed below(Recalc) 10,031 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) 222.50 700 0 0 223.00 71850 2,138 27138 Device Routing Invert Outlet Devices #1 Discarded 216.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 218.20' 24.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 218.20'/218.10' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 3.14 sf #3 Device 2 220.00' 6.0' long x 3.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) 3.0' Crest Height #4 Device 2 218.50' 10.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #5 Device 2 218.50' 10.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads 11625.34 - PR Type H/ 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 17 Discarded Outf low Max=0.0 cfs @ 11.99 hrs HW=218.22' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=3.3 cfs @ 12.24 hrs HW=219.31' (Free Discharge) L2=Culvert (Passes 3.3 cfs of 4.9 cfs potential flow) 3=Sharp-Crested Rectangular Weir( Controls 0.0 cfs) 4=Orifice/Grate (Orifice Controls 1.7 cfs @ 3.07 fps) 5=0rifice/Grate (Orifice Controls 1.7 cfs @ 3.07 fps) 11625.34 - PR Type 11124-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 18 Pond P2: StormTrap ST2 Single 3-6 - Chamber Wizard Field A Chamber Model= StormTrapST2 SingleTrep 3-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 42.0"H => 26.77 sf x 15.401 = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 5222 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 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 +48.0" Chamber Height=4.50' Field Height 8 Chambers x 412.1 cf+ 3,703.3 cf Border= 7,000.4 cf Chamber Storage 8 Chambers x 522.2 cf+ 4,891.2 cf Border= 9,068.E cf Displacement 11,166.7 cf Field - 9,068.E cf Chambers= 2,098.1 cf Stone x 40.0%Voids = 839.2 cf Stone Storage Chamber Storage + Stone Storage= 7,839.E cf = 0.180 of Overall Storage Efficiency = 70.2 Overall System Size = 76.90'x 32.27'x 4.50' S Chambers(plus border) 413.E cy Field 77.7 cy Stone 11625.34 - PR 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 19 Pond P2: StormTrap ST2 Single 3-6 Hydrograph EM Inflow 5.3 cfs 11 outflow Inflow Area=121,370 sf EM Discarded Primary Peak Elev=219.31' 5 Storage=5,332 cf 3.3 cfs 3.3 cfs 3 3, o r1�'e ve 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 20 Summary for Pond P3: StormTrap ST2 Single 3-6 nflow Area = 50,430 sf, 20.76% Impervious, Inflow Depth = 1.36" for 2-Year event Inflow = 1.8 cfs @ 12.09 hrs, Volume= 5,700 cf Outflow = 0.0 cfs @ 10.91 hrs, Volume= 2,247 cf, Atten= 98%, Lag= 0.0 min Discarded = 0.0 cfs @ 10.91 hrs, Volume= 2,247 cf Primary = 0.0 cfs @ 0.00 hrs, Volume= 0 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= 215.71'@ 21.71 hrs Surf.Area= 2,506 sf Storage= 4,126 cf Plug-Flow detention time=474.3 min calculated for 2,246 cf(39% of inflow) Center-of-Mass det. time= 341.0 min ( 1,176.0 - 835.0 ) Volume Invert Avail.Storage Storage Description #1 A 213.50' 822 cf 40.75'W x 61.50'L x 4.50'H Field A 11,278 cf Overall - 9,222 cf Embedded = 2,055 cf x 40.0% Voids #2A 214.00' 7,134 cf StormTrap ST2 SingleTrap 3-6x 9 Inside #1 Inside= 101.7"W x 42.0"H => 26.77 sf x 15.40'L = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 522.2 cf 9 Chambers in 3 Rows 25.44' x 46.19' Core + 6.66' Border= 38.75' x 59.50' System #3 216.80' 25 cf 4.00'D x 2.00'H Vertical Cone/Cylinder #4 218.80' 38 cf Custom Stage Data (Prismatic)Listed below(Recalc) 8,018 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) 218.80 50 0 0 219.30 100 38 38 Device Routing Invert Outlet Devices #1 Discarded 213.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 215.80' 12.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 215.80'/215.70' S= 0.0100 '/' Cc= 0.900 n= 0.012, Flow Area= 0.79 sf Discarded OutFlow Max=0.0 cfs @ 10.91 hrs HW=213.56' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=0.0 cfs @ 0.00 hrs HW=213.50' (Free Discharge) L2=Culvert ( Controls 0.0 cfs) 11625.34 - PR Type 11124-hr 2-Year Rainfall=3.16" Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 21 Pond P3: StormTrap ST2 Single 3-6 - Chamber Wizard Field A Chamber Model= StormTrapST2 SingleTrap 3-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 42.0"H => 26.77 sf x 15.401 = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 5222 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 3 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 40.75' Base Width 6.0" Stone Base +48.0" Chamber Height=4.50' Field Height 9 Chambers x 412.1 cf+ 3,424.5 cf Border= 7,133.E cf Chamber Storage 9 Chambers x 522.2 cf+ 4,522.9 cf Border= 9,222.5 cf Displacement 11,277.E cf Field - 9,222.5 cf Chambers= 2,055.1 cf Stone x 40.0%Voids = 822.0 cf Stone Storage Chamber Storage + Stone Storage= 7,955.7 cf = 0.183 of Overall Storage Efficiency = 70.5 Overall System Size = 61.50'x 40.75'x 4.50' 9 Chambers(plus border) 417.7 cy Field 76.1 cy Stone 11625.34 - PR 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 22 Pond P3: StormTrap ST2 Single 3-6 Hydrograph Inflow 1.8 cfs aull Outflow Inflow Area=50 430 Sf Discarded � � Primary Peak Elev=215.71' Storage=4,126 cf 3 0 mmm Ii 0.0 cfs 0.0 cfs O 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 23 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 48.10% Impervious, Inflow Depth = 1.38" for 2-Year event Inflow = 11.2 cfs @ 12.11 hrs, Volume= 43,344 cf Primary = 11.2 cfs @ 12.11 hrs, Volume= 43,344 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 12 11.2 cfs El Primary 11.2 cfs Inflow Area=377,520 sf 11 � 10 9 , oUL 2 ,.//i'/� � %, /�� /fir �/ /u u u 0 / / i,a/' ,,,, u Uu uu u U U u U 1111 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) IIIIIIIIII ��)roposed 10 IIIIIIII Yea r III IIIIIII� III IIIIIIIIIIIIIIIIIIII� IIIIIIIIIII B-9 Appendix B:Standard 2 Computations and Supporting Information 11625.34 - PR 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 24 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=38,490 sf 45.49% Impervious Runoff Depth=3.38" Flow Length=235' Tc=6.0 min CN=85 Runoff=3.5 cfs 10,833 cf SubcatchmentPR-12: PR-12 Runoff Area=82,880 sf 63.75% Impervious Runoff Depth=3.78" Tc=6.0 min CN=89 Runoff=8.2 cfs 26,118 cf SubcatchmentPR-13: PR-13 Runoff Area=41,950 sf 8.39% Impervious Runoff Depth=2.54" Tc=6.0 min CN=76 Runoff=2.9 cfs 8,893 cf SubcatchmentPR-14: PR-14 Runoff Area=8,480 sf 81.96% Impervious Runoff Depth=4.32" Tc=6.0 min CN=94 Runoff=0.9 cfs 3,051 cf SubcatchmentPR-15: PR-15 Runoff Area=32,680 sf 13.77% Impervious Runoff Depth=2.63" Tc=6.0 min CN=77 Runoff=2.3 cfs 7,166 cf SubcatchmentPR-20: PR-20 Runoff Area=136,290 sf 46.99% Impervious Runoff Depth=3.38" Tc=6.0 min CN=85 Runoff=12.3 cfs 38,358 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=225.49' Storage=1,955 cf Inflow=3.5 cfs 10,833 cf Discarded=0.0 cfs 1,445 cf Primary=2.7 cfs 9,055 cf Outflow=2.7 cfs 10,499 cf Pond P2: StormTrap ST2 Single 3-6 Peak EIev=220.27' Storage=7,349 cf Inflow=10.5 cfs 35,172 cf Discarded=0.0 cfs 2,594 cf Primary=8.9 cfs 29,463 cf Outflow=8.9 cfs 32,057 cf Pond P3: StormTrap ST2 Single 3-6 Peak EIev=216.34' Storage=5,454 cf Inflow=3.8 cfs 11,944 cf Discarded=0.0 cfs 2,437 cf Primary=0.9 cfs 5,719 cf Outflow=0.9 cfs 8,156 cf Link DP-1:AndoverStreet System Inflow=25.4 cfs 94,271 cf Primary=25.4 cfs 94,271 cf Total Runoff Area = 377,520 sf Runoff Volume = 107,983 cf Average Runoff Depth = 3.43" 51.90% Pervious = 195,920 sf 48.10% Impervious = 181,600 sf 11625.34 - PR 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 25 Summary for Subcatchment PR-11: PR-11 Runoff = 3.5 cfs @ 12.09 hrs, Volume= 10,833 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 201980 74 >75% Grass cover, Good, HSG C 9,960 98 Roof 7,550 98 Paved parking 381490 85 Weighted Average 20,980 54.51% Pervious Area 171510 45.49% 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" 0.6 70 0.0140 1.90 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 45 0.0400 3.22 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 35 0.0200 2.87 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.2 35 0.0200 2.87 Shallow Concentrated Flow, Paved Kv= 20.3 fps 4.8 235 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 26 Subcatchment PR-11: PR-11 Hydrograph El Runoff 3.5 cfs Type III 24-hr 3 10-Year Rainfall=5.01" n ff Area=38,490 Ru o sf / Runoff Volume=10,833 cf Runoff Depth=3.38"2 Flow Length=235' ;r Tc=6.0 m i n CN=85 ,i uuuuuuuuuuuulllllllllillillillilljlllllllllillillilluuuuuuuuuuuu 0 144MIllo ��,-%ur,,,,' v 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 27 Summary for Subcatchment PR-12: PR-12 Runoff = 8.2 cfs @ 12.09 hrs, Volume= 26,118 cf, Depth= 3.78" Routed to Pond P2 : StormTrap ST2 Single 3-6 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 301040 74 >75% Grass cover, Good, HSG C 241340 98 Roof 281500 98 Paved parking 821880 89 Weighted Average 30,040 36.25% Pervious Area 521840 63.75% 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 9 0 Runoff 8.2 cfs 8 Type III 24-hr 10-Year Rainfall=5.01" 7 Runoff Area=82,880 sf Runoff Volume=26,118 cf 5 / Runoff Depth=3.78" C Tc=6.0 min IL 4 C N=89 1 0 UI , .,- 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 28 Summary for Subcatchment PR-1 3: PR-13 Runoff = 2.9 cfs @ 12.09 hrs, Volume= 8,893 cf, Depth= 2.54" Routed to Pond P3 : StormTrap ST2 Single 3-6 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 381430 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,520 98 Paved parking 411950 76 Weighted Average 38,430 91.61% Pervious Area 3520 8.39% 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 3 2.9 cfs / Type III 24=hr 1 0-Year Rainfall=5.01.. Runoff Area=41,950 sf 2 Runoff Volume=8,893 d Runoff Depth=2,54" 0 Tc=6,0 min CN=76 r; O ur%/u it i;a/'% c it lF U U U U M M '111 1111 1111 1111 1111 1111 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 29 Summary for Subcatchment PR-14: PR-14 Runoff = 0.9 cfs @ 12.08 hrs, Volume= 3,051 cf, Depth= 4.32" Routed to Pond P3 : StormTrap ST2 Single 3-6 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 1,530 74 >75% Grass cover, Good, HSG C 6,770 98 Roof 180 98 Paved parking 8480 94 Weighted Average 1,530 18.04% Pervious Area 6,950 81.96% 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 1 1 El Runoff 0.9 cfs Type III 24=hr 1 0-Year Rainfall=5.01 % Runoff Area=8,480 sf Runoff Volume=3,051 d Runoff Depth=4.32" 0 Tc=6,0 min CN=94 �� i, /,� / „ �i// i,, i,�, a,;,;:, ,�,�� „� ,j, /�/ /''wV/ v U U U U U U UNO k UU UU UU UU UU UU UU UU UU MM 11111111 11111111 11 11 11 11 111111 11 11 11 11 11 UU UU UU UU U U U U U U U U U U M 1111 1111 1111 1111 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 30 Summary for Subcatchment PR-15: PR-15 Runoff = 2.3 cfs @ 12.09 hrs, Volume= 7,166 cf, Depth= 2.63" 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 281180 74 >75% Grass cover, Good, HSG C 0 98 Roof 4500 98 Paved parking 321680 77 Weighted Average 28,180 86.23% Pervious Area 4500 13.77% 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 2.3 cfs Type III 24=hr 2 10-Year Rainfall=5.01" Runoff Area=32,680 sf Runoff Volume=7,166 d -- ! Runoff Depth=2.63" 0 Tc=6,0 min CN=77 0 U„;ra r„sir„ a"/rr„/ a U U U M 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 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 31 Summary for Subcatchment PR-20: PR-20 Runoff = 12.3 cfs @ 12.09 hrs, Volume= 38,358 cf, Depth= 3.38" 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 727250 74 >75% Grass cover, Good, HSG C 251540 98 Roof 381500 98 Paved parking 1367290 85 Weighted Average 727250 53.01% Pervious Area 641040 46.99% 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 12.3 cfs 12 ,! Type III 24-hr 11 10-Year Rainfall=5.01" 10 Runoff.Area=136,290 sf Runoff Volume=38,358 cf 8 y / Runoff Depth=3.38" 7 3 ;,/ Tc=6.0 m i n 9: 6 CN=85 2 00, /„ 0 i,,,,,,,0 111 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 - PR 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 32 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 33 Summary for Pond P1: StormTrap ST2 Single 2-0 Inflow Area = 38,490 sf, 45.49% Impervious, Inflow Depth = 3.38" for 10-Year event Inflow = 3.5 cfs @ 12.09 hrs, Volume= 10,833 cf Outflow = 2.7 cfs @ 12.15 hrs, Volume= 10,499 cf, Atten= 23%, Lag= 3.9 min Discarded = 0.0 cfs @ 7.97 hrs, Volume= 1,445 cf Primary = 2.7 cfs @ 12.15 hrs, Volume= 9,055 cf Routed to Pond P2 : StormTrap ST2 Single 3-6 Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 225.49'@ 12.15 hrs Surf.Area= 1,463 sf Storage= 1,955 cf Plug-Flow detention time=72.5 min calculated for 10,499 cf(97% of inflow) Center-of-Mass det. time= 54.5 min ( 862.0 - 807.5 ) Volume Invert Avail.Storage Storage Description #1 A 223.60' 459 cf 23.79'W x 61.50'L x 3.00'H Field A 4,390 cf Overall - 3,242 cf Embedded = 1,148 cf x 40.0% Voids #2A 224.10' 2,242 cf StormTrap ST2 SingleTrap 2-Ox 3 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 8.48' x 46.19' Core + 6.66' Border = 21.79' x 59.50' System #3 224.40' 28 cf 4.00'D x 2.20'H Vertical Cone/CylindeFimpervious #4 226.60' 54 cf Custom Stage Data (Prismatic)Listed below(Recalc) 2,783 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) 226.60 110 0 0 226.90 250 54 54 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 @ 7.97 hrs HW=223.63' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=2.7 cfs @ 12.15 hrs HW=225.49' (FreeDischarge) L2=Culvert (Barrel Controls 2.7 cfs @ 3.87 fps) 11625.34 - PR Type III 24-hr 10-Year Rainfall=5.01„ Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 34 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 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 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 + 30.0" Chamber Height= 3.00' Field Height 3 Chambers x 231.7 cf+ 1547.2 cf Border= 2,242.3 cf Chamber Storage 3 Chambers x 326.4 cf+ 2,262.4 cf Border= 3,241.5 cf Displacement 4,389.E cf Field- 3,241.5 cf Chambers = 1,148.1 cf Stone x 40.0%Voids = 459.2 cf Stone Storage Chamber Storage + Stone Storage= 2,701.5 cf = 0.062 of Overall Storage Efficiency = 61.5 Overall System Size = 61.50'x 23.79'x 3.00' 3 Chambers(plus border) 162.E cy Field 42.5 cy Stone 11625.34 - PR 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 35 Pond P1: StormTrap ST2 Single 2-0 Hydrograph Inflow 3.5 cfs aull Outflow Inflow Area=38,490 Sf Discarded Primary Peak Elev=225.49' 2.7 cfs Storage=1 955 cf 3 2.7 cfs i v 2 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 111 24-hr 10-Year Rainfall=5.01" Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 36 Summary for Pond P2: StormTrap ST2 Single 3-6 Inflow Area = 121,370 sf, 57.96% Impervious, Inflow Depth = 3.48" for 10-Year event Inflow = 10.5 cfs @ 12.09 hrs, Volume= 35,172 cf Outflow = 8.9 cfs @ 12.15 hrs, Volume= 32,057 cf, Atten= 15%, Lag= 3.4 min Discarded = 0.0 cfs @ 11.30 hrs, Volume= 2,594 cf Primary = 8.9 cfs @ 12.15 hrs, Volume= 29,463 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= 220.27'@ 12.15 hrs Surf.Area= 2,494 sf Storage= 7,349 cf Plug-Flow detention time=91.1 min calculated for 32,047 cf(91% of inflow) Center-of-Mass det. time=47.9 min ( 849.2 - 801.3 ) Volume Invert Avail.Storage Storage Description #1 A 216.50' 839 cf 32.27'W x 76.90'L x 4.50'H Field A 11,167 cf Overall - 9,069 cf Embedded = 2,098 cf x 40.0% Voids #2A 217.00' 7,000 cf StormTrap ST2 SingleTrap 3-6x 8 Inside #1 Inside= 101.7"W x 42.0"H => 26.77 sf x 15.40'L = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 522.2 cf 8 Chambers in 2 Rows 16.96' x 61.58' Core + 6.66' Border = 30.27' x 74.90' System #3 218.20' 54 cf 4.00'D x 4.30'H Vertical Cone/Cylinder #4 222.50' 2,138 cf Custom Stage Data (Prismatic)Listed below(Recalc) 10,031 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) 222.50 700 0 0 223.00 71850 2,138 27138 Device Routing Invert Outlet Devices #1 Discarded 216.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 218.20' 24.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 218.20'/218.10' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 3.14 sf #3 Device 2 220.00' 6.0' long x 3.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) 3.0' Crest Height #4 Device 2 218.50' 10.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #5 Device 2 218.50' 10.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads 11625.34 - PR Type III 24-hr 10-Year Rainfal1=5.01 If Prepared by VHB, Inc Printed 9/15/2023 HydroCADO 10.20-3c s/n 01038 O 2023 HydroCAD Software Solutions LLC Page 37 Discarded OutFlow Max=0.0 cfs @ 11.30 hrs HW=218.20' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=8.9 cfs @ 12.15 hrs HW=220.27' (Free Discharge) L2=Culvert (Passes 8.9 cfs of 13.3 cfs potential flow) 3=Sharp-Crested Rectangular Weir(Weir Controls 2.8 cfs @ 1.73 fps) =Orifice/Grate (Orifice Controls 3.1 cfs @ 5.61 fps) =Orifice/Grate (Orifice Controls 3.1 cfs @ 5.61 fps) 11625.34 - PR Type III 24-hr 10-Year Rainfall=5.01„ Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 38 Pond P2: StormTrap ST2 Single 3-6 - Chamber Wizard Field A Chamber Model= StormTrapST2 SingleTrep 3-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 42.0"H => 26.77 sf x 15.401 = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 5222 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 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 +48.0" Chamber Height=4.50' Field Height 8 Chambers x 412.1 cf+ 3,703.3 cf Border= 7,000.4 cf Chamber Storage 8 Chambers x 522.2 cf+ 4,891.2 cf Border= 9,068.E cf Displacement 11,166.7 cf Field - 9,068.E cf Chambers= 2,098.1 cf Stone x 40.0%Voids = 839.2 cf Stone Storage Chamber Storage + Stone Storage= 7,839.E cf = 0.180 of Overall Storage Efficiency = 70.2 Overall System Size = 76.90'x 32.27'x 4.50' S Chambers(plus border) 413.E cy Field 77.7 cy Stone 11625.34 - PR Type III 24-hr 10-Year Rainfa/1=5.01 Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 39 Pond P2: StormTrap ST2 Single 3-6 Hydrograph M Inflow 10.5 CfS Utflow I of ow Area=121 370 sf El Discarded Primary 11 18-9 CfS Peak E lev=220.27' 10, Storage=7,349 cf 7 6, 0 4 3,1 0 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 1111'111'111'111'111 1111'111'111'111'111 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 1111 1111'111 1111'111 1111'111'111 1111'111'111'111 U U U uv-FJF-U--u--TV-T-WT--TTIF U U U U U U 1111 1111 1111'111'111 1111'111'111'111'111 1111'111 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 1111 1111 1111'111'111'111 1111 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 40 Summary for Pond P3: StormTrap ST2 Single 3-6 Inflow Area = 50,430 sf, 20.76% Impervious, Inflow Depth = 2.84" for 10-Year event Inflow = 3.8 cfs @ 12.09 hrs, Volume= 11,944 cf Outflow = 0.9 cfs @ 12.50 hrs, Volume= 8,156 cf, Atten= 77%, Lag= 24.8 min Discarded = 0.0 cfs @ 9.27 hrs, Volume= 2,437 cf Primary = 0.9 cfs @ 12.50 hrs, Volume= 5,719 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= 216.34'@ 12.50 hrs Surf.Area= 2,506 sf Storage= 5,454 cf Plug-Flow detention time=245.1 min calculated for 8,156 cf(68% of inflow) Center-of-Mass det. time= 145.4 min ( 962.6 - 817.2 ) Volume Invert Avail.Storage Storage Description #1 A 213.50' 822 cf 40.75'W x 61.50'L x 4.50'H Field A 11,278 cf Overall - 9,222 cf Embedded = 2,055 cf x 40.0% Voids #2A 214.00' 7,134 cf StormTrap ST2 SingleTrap 3-6x 9 Inside #1 Inside= 101.7"W x 42.0"H => 26.77 sf x 15.40'L = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 522.2 cf 9 Chambers in 3 Rows 25.44' x 46.19' Core + 6.66' Border= 38.75' x 59.50' System #3 216.80' 25 cf 4.00'D x 2.00'H Vertical Cone/Cylinder #4 218.80' 38 cf Custom Stage Data (Prismatic)Listed below(Recalc) 8,018 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) 218.80 50 0 0 219.30 100 38 38 Device Routing Invert Outlet Devices #1 Discarded 213.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 215.80' 12.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 215.80'/215.70' S= 0.0100 '/' Cc= 0.900 n= 0.012, Flow Area= 0.79 sf Discarded OutFlow Max=0.0 cfs @ 9.27 hrs HW=213.56' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=0.9 cfs @ 12.50 hrs HW=216.34' (FreeDischarge) L2=Culvert (Barrel Controls 0.9 cfs @ 2.88 fps) 11625.34 - PR Type III 24-hr 10-Year Rainfall=5.01„ Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 41 Pond P3: StormTrap ST2 Single 3-6 - Chamber Wizard Field A Chamber Model= StormTrapST2 SingleTrap 3-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 42.0"H => 26.77 sf x 15.401 = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 5222 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 3 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 40.75' Base Width 6.0" Stone Base +48.0" Chamber Height=4.50' Field Height 9 Chambers x 412.1 cf+ 3,424.5 cf Border= 7,133.E cf Chamber Storage 9 Chambers x 522.2 cf+ 4,522.9 cf Border= 9,222.5 cf Displacement 11,277.E cf Field - 9,222.5 cf Chambers= 2,055.1 cf Stone x 40.0%Voids = 822.0 cf Stone Storage Chamber Storage + Stone Storage= 7,955.7 cf = 0.183 of Overall Storage Efficiency = 70.5 Overall System Size = 61.50'x 40.75'x 4.50' 9 Chambers(plus border) 417.7 cy Field 76.1 cy Stone 11625.34 - PR Type III 24-hr 10-Year Rainfa/1=5.01 Prepared by VHB, Inc Printed 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 42 Pond P3: StormTrap ST2 Single 3-6 Hydrograph M Inflow 3.8 cfs """��Outflow El fl I Inflow Area=50430 Sf Discarded , M 4 Primary Peak Elev=216.34' Storag a=5 454 cf 0 LL o. 0.9 CLmmm 0.0 CfS 0 11711-711-7111 1111'111'111'111'111 1111'111'111 U U U U U 'III'111 1111'111 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 1111 '111'111'111'111 1111 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 43 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 48.10% Impervious, Inflow Depth = 3.00" for 10-Year event Inflow = 25.4 cfs @ 12.11 hrs, Volume= 94,271 cf Primary = 25.4 cfs @ 12.11 hrs, Volume= 94,271 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 Primary 26 25.4 cfs Inflow Area=377,520 sf 24 ' 22 20 - - - - - 16 0 12 10 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��,��p, ��I�Iryry�Iryrypp�I�I�I�I�� II�,� IIIIIIIIII ��)roposed IIIIIIIII ��ry� SIII ��I�"�� IIIIIRR III IIIIIIIIIIIIIIIIIM II �� III III IIIIIIII� IIIIIIIIIII B-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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 44 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=38,490 sf 45.49% Impervious Runoff Depth=4.45" Flow Length=235' Tc=6.0 min CN=85 Runoff=4.5 cfs 14,285 cf SubcatchmentPR-12: PR-12 Runoff Area=82,880 sf 63.75% Impervious Runoff Depth=4.89" Tc=6.0 min CN=89 Runoff=10.5 cfs 33,777 cf SubcatchmentPR-13: PR-13 Runoff Area=41,950 sf 8.39% Impervious Runoff Depth=3.52" Tc=6.0 min CN=76 Runoff=4.0 cfs 12,300 cf SubcatchmentPR-14: PR-14 Runoff Area=8,480 sf 81.96% Impervious Runoff Depth=5.46" Tc=6.0 min CN=94 Runoff=1.1 cfs 3,855 cf SubcatchmentPR-15: PR-15 Runoff Area=32,680 sf 13.77% Impervious Runoff Depth=3.62" Tc=6.0 min CN=77 Runoff=3.2 cfs 9,856 cf SubcatchmentPR-20: PR-20 Runoff Area=136,290 sf 46.99% Impervious Runoff Depth=4.45" Tc=6.0 min CN=85 Runoff=16.0 cfs 50,582 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: StormTrapST2 Single 2-0 Peak Elev=225.77' Storage=2,289 cf Inflow=4.5 cfs 14,285 cf Discarded=0.0 cfs 1,501 cf Primary=3.4 cfs 12,443 cf Outflow=3.4 cfs 13,944 cf Pond P2: StormTrapST2 Single 3-6 Peak EIev=220.45' Storage=7,729 cf Inflow=13.4 cfs 46,220 cf Discarded=0.0 cfs 2,690 cf Primary=12.5 cfs 40,403 cf Outflow=12.6 cfs 43,093 cf Pond P3: StormTrapST2 Single 3-6 Peak EIev=216.72' Storage=6,267 cf Inflow=5.1 cfs 16,155 cf Discarded=0.0 cfs 2,529 cf Primary=2.0 cfs 9,815 cf Outflow=2.1 cfs 12,344 cf Link DP-1:AndoverStreet System Inflow=36.1 cfs 127,716 cf Primary=36.1 cfs 127,716 cf Total Runoff Area = 377,520 sf Runoff Volume = 141,716 cf Average Runoff Depth = 4.50" 51.90% Pervious = 195,920 sf 48.10% Impervious = 181,600 sf 11625.34 - PR 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 45 Summary for Subcatchment PR-11: PR-11 Runoff = 4.5 cfs @ 12.09 hrs, Volume= 14,285 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 201980 74 >75% Grass cover, Good, HSG C 9,960 98 Roof 7,550 98 Paved parking 381490 85 Weighted Average 20,980 54.51% Pervious Area 171510 45.49% 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" 0.6 70 0.0140 1.90 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 45 0.0400 3.22 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 35 0.0200 2.87 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.2 35 0.0200 2.87 Shallow Concentrated Flow, Paved Kv= 20.3 fps 4.8 235 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 46 Subcatchment PR-11: PR-11 Hydrograph 51 El Runoff 4.5 cfs Type III 24-hr 4 25-Year Rainfall=6.16" Runoff Area=38,490 sf % RunoffVolume=14,285 cf Runoff Depth=4.45" Flow Length=235' 2 Tc=6.0 m i n CN=85 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 47 Summary for Subcatchment PR-12: PR-12 Runoff = 10.5 cfs @ 12.08 hrs, Volume= 33,777 cf, Depth= 4.89" Routed to Pond P2 : StormTrap ST2 Single 3-6 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 307040 74 >75% Grass cover, Good, HSG C 241340 98 Roof 281500 98 Paved parking 827880 89 Weighted Average 307040 36.25% Pervious Area 521840 63.75% 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 11 10.5 cfs _ Type III 24-hr 10 9 25-Year Rainfall=6.16" Area=82,880Runoff sf Runoff Volume=33,777 cf Runoff Depth=4.89" LL 5 � Tc=6.0 min CN=89 4" 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 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 48 Summary for Subcatchment PR-13: PR-13 Runoff = 4.0 cfs @ 12.09 hrs, Volume= 12,300 cf, Depth= 3.52" Routed to Pond P3 : StormTrap ST2 Single 3-6 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 381430 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,520 98 Paved parking 411950 76 Weighted Average 38,430 91.61% Pervious Area 3520 8.39% 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 4.0 cfs 4 Type III 24-hr 25-Year Rainfall=6.16" Runoff Area=41,950 Sf 3 Runoff Volume=12,300 cf Runoff Depth=3.52" 0 2 Tc=6.0 m i n CN=76 51 0 U U U U U U U U U U U U U U U M M 1111 1111 1111 1111711711 1 U I I I I U I I I I U I I I I U M 1111 1111 1111 1111 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 49 Summary for Subcatchment PR-14: PR-14 Runoff = 1.1 cfs @ 12.08 hrs, Volume= 3,855 cf, Depth= 5.46" Routed to Pond P3 : StormTrap ST2 Single 3-6 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 1,530 74 >75% Grass cover, Good, HSG C 6,770 98 Roof 180 98 Paved parking 8480 94 Weighted Average 1,530 18.04% Pervious Area 6,950 81.96% 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 1.1 cfs Type III 24=hr 1 25=Year Rainfall=6.16" % Runoff Area=8,480 sf j Runoff Volume=3,855 d Runoff Depth=5,46" 0 Tc=6,0 min r r, CN=94 0 U U U 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--VV-Fv FV FVTF--y V-Fvy-rIIFIIF-]Il�IIFIIFIIFlI 11111FIF]11�11FAFII 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 50 Summary for Subcatchment PR-15: PR-15 Runoff = 3.2 cfs @ 12.09 hrs, Volume= 9,856 cf, Depth= 3.62" 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 281180 74 >75% Grass cover, Good, HSG C 0 98 Roof 4500 98 Paved parking 321680 77 Weighted Average 28,180 86.23% Pervious Area 4500 13.77% 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 3.2 cfs Type III 24=hr 3 25=Year Rainfall=6.16" Runoff Area=32,680 sf Runoff Volume=9,856 d 2 Runoff Depth=3.62" 0 Tc=6,0 min CN=77 1 j WIRES ','r %,, / /,/r„ a,is ''r a ,a„ r„ a'%rr,/,is/�,� /,,,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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 51 Summary for Subcatchment PR-20: PR-20 Runoff = 16.0 cfs @ 12.09 hrs, Volume= 50,582 cf, Depth= 4.45" 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 727250 74 >75% Grass cover, Good, HSG C 251540 98 Roof 381500 98 Paved parking 1367290 85 Weighted Average 727250 53.01% Pervious Area 641040 46.99% 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 - - - - - - - - - - - - - - - - - Runoff 17 16.0 cfs 16 Type III 24-hr 15,11 - - - - -' - - - - - -Y rRainfall=6.16"25 ea 13 Runoff Area=136,290 sf 12 Runoff Volume=50,582 cf 14 10 j Runoff Depth=4.45" 3 9 - - - - - - - - - - -0 8 Tc=6.0 m i n 7 i _ CN=85- 5 4 2 1 ill;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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 52 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 53 Summary for Pond P1: StormTrap ST2 Single 2-0 I nflow Area = 38,490 sf, 45.49% Impervious, Inflow Depth = 4.45" for 25-Year event Inflow = 4.5 cfs @ 12.09 hrs, Volume= 14,285 cf Outflow = 3.4 cfs @ 12.16 hrs, Volume= 13,944 cf, Atten= 25%, Lag= 4.2 min Discarded = 0.0 cfs @ 7.08 hrs, Volume= 1,501 cf Primary = 3.4 cfs @ 12.16 hrs, Volume= 12,443 cf Routed to Pond P2 : StormTrap ST2 Single 3-6 Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 225.77'@ 12.16 hrs Surf.Area= 1,463 sf Storage= 2,289 cf Plug-Flow detention time=59.9 min calculated for 13,940 cf(98% of inflow) Center-of-Mass det. time=45.7 min ( 845.4 - 799.7 ) Volume Invert Avail.Storage Storage Description #1 A 223.60' 459 cf 23.79'W x 61.50'L x 3.00'H Field A 4,390 cf Overall - 3,242 cf Embedded = 1,148 cf x 40.0% Voids #2A 224.10' 2,242 cf StormTrap ST2 SingleTrap 2-Ox 3 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 8.48' x 46.19' Core + 6.66' Border = 21.79' x 59.50' System #3 224.40' 28 cf 4.00'D x 2.20'H Vertical Cone/CylindeFimpervious #4 226.60' 54 cf Custom Stage Data (Prismatic)Listed below(Recalc) 2,783 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) 226.60 110 0 0 226.90 250 54 54 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 @ 7.08 hrs HW=223.63' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=3.4 cfs @ 12.16 hrs HW=225.77' (FreeDischarge) L2=Culvert (Barrel Controls 3.4 cfs @ 4.28 fps) 11625.34 - PR Type 11124-hr 25-Year Rainfall=6.16„ Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 54 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 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 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 + 30.0" Chamber Height= 3.00' Field Height 3 Chambers x 231.7 cf+ 1547.2 cf Border= 2,242.3 cf Chamber Storage 3 Chambers x 326.4 cf+ 2,262.4 cf Border= 3,241.5 cf Displacement 4,389.E cf Field- 3,241.5 cf Chambers = 1,148.1 cf Stone x 40.0%Voids = 459.2 cf Stone Storage Chamber Storage + Stone Storage= 2,701.5 cf = 0.062 of Overall Storage Efficiency = 61.5 Overall System Size = 61.50'x 23.79'x 3.00' 3 Chambers(plus border) 162.E cy Field 42.5 cy Stone 11625.34 - PR 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 55 Pond P1: StormTrap ST2 Single 2-0 Hydrograph Inflow 4.5 cfs aull Outflow Inflow Area=38,490 Sf Discarded 0 Primary Peak Elev=225.77' 4 3.4cfs Storage=2,289 cf 3.4 cfs 3 LL �' j r mm �% 0.0 cfs ri O 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 56 Summary for Pond P2: StormTrap ST2 Single 3-6 Inflow Area = 121,370 sf, 57.96% Impervious, Inflow Depth = 4.57" for 25-Year event Inflow = 13.4 cfs @ 12.09 hrs, Volume= 46,220 cf Outflow = 12.6 cfs @ 12.13 hrs, Volume= 43,093 cf, Atten= 7%, Lag= 2.1 min Discarded = 0.0 cfs @ 10.62 hrs, Volume= 2,690 cf Primary = 12.5 cfs @ 12.13 hrs, Volume= 40,403 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= 220.45'@ 12.13 hrs Surf.Area= 2,494 sf Storage= 7,729 cf Plug-Flow detention time=76.6 min calculated for 43,093 cf(93% of inflow) Center-of-Mass det. time=41.0 min ( 836.0 - 795.0 ) Volume Invert Avail.Storage Storage Description #1 A 216.50' 839 cf 32.27'W x 76.90'L x 4.50'H Field A 11,167 cf Overall - 9,069 cf Embedded = 2,098 cf x 40.0% Voids #2A 217.00' 7,000 cf StormTrap ST2 SingleTrap 3-6x 8 Inside #1 Inside= 101.7"W x 42.0"H => 26.77 sf x 15.40'L = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 522.2 cf 8 Chambers in 2 Rows 16.96' x 61.58' Core + 6.66' Border = 30.27' x 74.90' System #3 218.20' 54 cf 4.00'D x 4.30'H Vertical Cone/Cylinder #4 222.50' 2,138 cf Custom Stage Data (Prismatic)Listed below(Recalc) 10,031 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) 222.50 700 0 0 223.00 71850 2,138 27138 Device Routing Invert Outlet Devices #1 Discarded 216.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 218.20' 24.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 218.20'/218.10' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 3.14 sf #3 Device 2 220.00' 6.0' long x 3.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) 3.0' Crest Height #4 Device 2 218.50' 10.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #5 Device 2 218.50' 10.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads 11625.34 - PR Type 11124-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/15/2023 HydroCADO 10.20-3c s/n 01038 O 2023 HydroCAD Software Solutions LLC Page 57 Discarded OutFlow Max=0.0 cfs @ 10.62 hrs HW=218.21' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=12.5 cfs @ 12.13 hrs HW=220.45' (Free Discharge) L2=Culvert (Passes 12.5 cfs of 14.9 cfs potential flow) 3=Sharp-Crested Rectangular Weir(Weir Controls 6.0 cfs @ 2.24 fps) =Orifice/Grate (Orifice Controls 3.3 cfs @ 5.97 fps) =Orifice/Grate (Orifice Controls 3.3 cfs @ 5.97 fps) 11625.34 - PR Type 11124-hr 25-Year Rainfall=6.16„ Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 58 Pond P2: StormTrap ST2 Single 3-6 - Chamber Wizard Field A Chamber Model= StormTrapST2 SingleTrep 3-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 42.0"H => 26.77 sf x 15.401 = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 5222 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 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 +48.0" Chamber Height=4.50' Field Height 8 Chambers x 412.1 cf+ 3,703.3 cf Border= 7,000.4 cf Chamber Storage 8 Chambers x 522.2 cf+ 4,891.2 cf Border= 9,068.E cf Displacement 11,166.7 cf Field - 9,068.E cf Chambers= 2,098.1 cf Stone x 40.0%Voids = 839.2 cf Stone Storage Chamber Storage + Stone Storage= 7,839.E cf = 0.180 of Overall Storage Efficiency = 70.2 Overall System Size = 76.90'x 32.27'x 4.50' S Chambers(plus border) 413.E cy Field 77.7 cy Stone 11625.34 - PR 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 59 Pond P2: StormTrap ST2 Single 3-6 Hydrograph Inflow 13.4 cfs Outflow Inflow Area=121,370 Sf Discarded 15Primary 12.6 cfs 14 Peak Elev=220.45' 13 12.5 cfs Storage=7,729 cf 10 ` 8 o ; UL 5 0.0 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 60 Summary for Pond P3: StormTrap ST2 Single 3-6 nflow Area = 50,430 sf, 20.76% Impervious, Inflow Depth = 3.84" for 25-Year event Inflow = 5.1 cfs @ 12.09 hrs, Volume= 16,155 cf Outflow = 2.1 cfs @ 12.32 hrs, Volume= 12,344 cf, Atten= 60%, Lag= 14.0 min Discarded = 0.0 cfs @ 8.52 hrs, Volume= 2,529 cf Primary = 2.0 cfs @ 12.32 hrs, Volume= 9,815 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= 216.72'@ 12.32 hrs Surf.Area= 2,506 sf Storage= 6,267 cf Plug-Flow detention time= 190.0 min calculated for 12,344 cf(76% of inflow) Center-of-Mass det. time= 105.1 min ( 914.8 - 809.7 ) Volume Invert Avail.Storage Storage Description #1 A 213.50' 822 cf 40.75'W x 61.50'L x 4.50'H Field A 11,278 cf Overall - 9,222 cf Embedded = 2,055 cf x 40.0% Voids #2A 214.00' 7,134 cf StormTrap ST2 SingleTrap 3-6x 9 Inside #1 Inside= 101.7"W x 42.0"H => 26.77 sf x 15.40'L = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 522.2 cf 9 Chambers in 3 Rows 25.44' x 46.19' Core + 6.66' Border= 38.75' x 59.50' System #3 216.80' 25 cf 4.00'D x 2.00'H Vertical Cone/Cylinder #4 218.80' 38 cf Custom Stage Data (Prismatic)Listed below(Recalc) 8,018 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) 218.80 50 0 0 219.30 100 38 38 Device Routing Invert Outlet Devices #1 Discarded 213.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 215.80' 12.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 215.80'/215.70' S= 0.0100 '/' Cc= 0.900 n= 0.012, Flow Area= 0.79 sf Discarded OutFlow Max=0.0 cfs @ 8.52 hrs HW=213.56' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=2.0 cfs @ 12.32 hrs HW=216.72' (FreeDischarge) L2=Culvert (Barrel Controls 2.0 cfs @ 3.52 fps) 11625.34 - PR Type 11124-hr 25-Year Rainfall=6.16„ Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 61 Pond P3: StormTrap ST2 Single 3-6 - Chamber Wizard Field A Chamber Model= StormTrapST2 SingleTrap 3-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 42.0"H => 26.77 sf x 15.401 = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 5222 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 3 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 40.75' Base Width 6.0" Stone Base +48.0" Chamber Height=4.50' Field Height 9 Chambers x 412.1 cf+ 3,424.5 cf Border= 7,133.E cf Chamber Storage 9 Chambers x 522.2 cf+ 4,522.9 cf Border= 9,222.5 cf Displacement 11,277.E cf Field - 9,222.5 cf Chambers= 2,055.1 cf Stone x 40.0%Voids = 822.0 cf Stone Storage Chamber Storage + Stone Storage= 7,955.7 cf = 0.183 of Overall Storage Efficiency = 70.5 Overall System Size = 61.50'x 40.75'x 4.50' 9 Chambers(plus border) 417.7 cy Field 76.1 cy Stone 11625.34 - PR 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 62 Pond P3: StormTrap ST2 Single 3-6 Hydrograph EM Inflow 5.1 CfS outflow Inflow Area=50 430 sf Discarded , 0 Primary Peak Elev=216.72' 5 Storag a=6,267 cf 1102 0 3,, 2.1 cfs 0 2.0 cfs 2- 0 r7jr7jr7j7j 171JF7117117��11711 1171IF71IF71IF71171171jr7llF711[711711711RIVVVFVVVFVVVTTTT-"U U U U U U U U 111111 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 63 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 48.10% Impervious, Inflow Depth = 4.06" for 25-Year event Inflow = 36.1 cfs @ 12.10 hrs, Volume= 127,716 cf Primary = 36.1 cfs @ 12.10 hrs, Volume= 127,716 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 EM Inflow 40 [36.E ifs Primary 38 36.1 cfs Inflow Area=377,520 sf 36 34 32 - 30 28 26 24 c. 22 20 16 14 12 ri 8 6 2 0 U U U U U U U U U U U U U U 1111 U 1111 1111 1111 1111 U 1111 1111 1111 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 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) II�,�, �Ilrylrypllll� II�,�, IIIIIIIIII ��)roposed 100 IIIIIIII SIII IIIIIIIRR III IIIIIIIIIIIIIIIII M III IIIIIIII IIIIIIIIIIIIIIIII 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 64 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=38,490 sf 45.49% Impervious Runoff Depth=6.16" Flow Length=235' Tc=6.0 min CN=85 Runoff=6.2 cfs 19,743 cf SubcatchmentPR-12: PR-12 Runoff Area=82,880 sf 63.75% Impervious Runoff Depth=6.63" Tc=6.0 min CN=89 Runoff=13.9 cfs 45,777 cf SubcatchmentPR-13: PR-13 Runoff Area=41,950 sf 8.39% Impervious Runoff Depth=5.10" Tc=6.0 min CN=76 Runoff=5.7 cfs 17,840 cf SubcatchmentPR-14: PR-14 Runoff Area=8,480 sf 81.96% Impervious Runoff Depth=7.22" Tc=6.0 min C N=94 Runoff=1.5 cfs 5,104 cf SubcatchmentPR-15: PR-15 Runoff Area=32,680 sf 13.77% Impervious Runoff Depth=5.22" Tc=6.0 min CN=77 Runoff=4.6 cfs 14,214 cf SubcatchmentPR-20: PR-20 Runoff Area=136,290 sf 46.99% Impervious Runoff Depth=6.16" Tc=6.0 min C N=85 Runoff=21.8 cfs 69,909 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 Elev=226.75' Storage=2,751 cf Inflow=6.2 cfs 19,743 cf Discarded=0.0 cfs 1,572 cf Primary=5.1 cfs 17,823 cf Outflow=5.2 cfs 19,395 cf Pond P2: StormTrapST2 Single 3-6 Peak EIev=220.87' Storage=7,862 cf Inflow=17.8 cfs 63,600 cf Discarded=0.0 cfs 2,795 cf Primary=17.8 cfs 57,665 cf Outflow=17.8 cfs 60,460 cf Pond P3: StormTrapST2 Single 3-6 Peak EIev=217.41' Storage=7,726 cf Inflow=7.2 cfs 22,944 cf Discarded=0.0 cfs 2,648 cf Primary=4.0 cfs 16,461 cf Outflow=4.0 cfs 197110 cf Link DP-1:AndoverStreet System Inflow=53.4 cfs 180,734 cf Primary=53.4 cfs 180,734 cf Total Runoff Area = 377,520 sf Runoff Volume = 195,071 cf Average Runoff Depth = 6.20" 51.90% Pervious = 195,920 sf 48.10% Impervious = 181,600 sf 11625.34 - PR 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 65 Summary for Subcatchment PR-11: PR-11 Runoff = 6.2 cfs @ 12.09 hrs, Volume= 19,743 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 201980 74 >75% Grass cover, Good, HSG C 9,960 98 Roof 7,550 98 Paved parking 381490 85 Weighted Average 20,980 54.51% Pervious Area 171510 45.49% 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" 0.6 70 0.0140 1.90 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 45 0.0400 3.22 Shallow Concentrated Flow, Unpaved Kv= 16.1 fps 0.2 35 0.0200 2.87 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.2 35 0.0200 2.87 Shallow Concentrated Flow, Paved Kv= 20.3 fps 4.8 235 Total, Increased to minimum Tc = 6.0 min 11625.34 - PR Type 11124-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 66 Subcatchment PR-11: PR-11 Hydrograph El Runoff 6.2 cfs Type III 24-hr 100-Year Rainfall=7.94" % Runoff Area=38,490 sf Runoff Volume=19,743 d Runoff Depth=6.16" 0 Flow Length=235' Tc=6.0 m i n 2 CN=85 j/�l %,07. ao %WOW 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 67 Summary for Subcatchment PR-12: PR-12 Runoff = 13.9 cfs @ 12.08 hrs, Volume= 45,777 cf, Depth= 6.63" Routed to Pond P2 : StormTrap ST2 Single 3-6 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 307040 74 >75% Grass cover, Good, HSG C 241340 98 Roof 281500 98 Paved parking 827880 89 Weighted Average 307040 36.25% Pervious Area 521840 63.75% 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 15 1 El Ru noff 11 cfs 14 / Type III 24-hr 13 12 100-Year Rainfall=7.94" Runoff Area=82,880 sf 10 % Runoff Volume=45,777 cf .� Runoff Depth=6.63" 0 7 Tc=6.0 m i n 6 ''j CN=89 j 4 3 2 ' � 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 68 Summary for Subcatchment PR-13: PR-13 Runoff = 5.7 cfs @ 12.09 hrs, Volume= 17,840 cf, Depth= 5.10" Routed to Pond P3 : StormTrap ST2 Single 3-6 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 381430 74 >75% Grass cover, Good, HSG C 0 98 Roof 3,520 98 Paved parking 411950 76 Weighted Average 38,430 91.61% Pervious Area 3520 8.39% 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 6 5.7 cfs Type III 24-hr 5 j 100=Year Rainfall=7.94" Runoff Area=41,950 sf 4 / Runoff Volume=17,840 cf Runoff Depth=5.10" 0 3 Tc=6.0 m i n CN=76 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 69 Summary for Subcatchment PR-14: PR-14 Runoff = 1.5 cfs @ 12.08 hrs, Volume= 5,104 cf, Depth= 7.22" Routed to Pond P3 : StormTrap ST2 Single 3-6 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 1,530 74 >75% Grass cover, Good, HSG C 6,770 98 Roof 180 98 Paved parking 8480 94 Weighted Average 1,530 18.04% Pervious Area 6,950 81.96% 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 1.5 cfs Type III 24=hr 100=Year Rainfall=7.94" % Runoff Area=8,480 sf ffVolume=5,104 Runo d Runoff Depth=7,22" 0 Tc=6,0 rein CN=94 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 70 Summary for Subcatchment PR-1 5: PR-15 Runoff = 4.6 cfs @ 12.09 hrs, Volume= 14,214 cf, Depth= 5.22" 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 281180 74 >75% Grass cover, Good, HSG C 0 98 Roof 4500 98 Paved parking 321680 77 Weighted Average 28,180 86.23% Pervious Area 4500 13.77% 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 5 LEI Runoff 4.6 cfs Type III 24-hr 4 / 100-Year Rainfall=7.94" RunoffArea=32,680 sf Runoff Volume=14,214 d 3%Uo , Runoff Depth=5.22" 0 Tc=6.0 m i n CN=77 r �� r 0M 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 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 71 Summary for Subcatchment PR-20: PR-20 Runoff = 21.8 cfs @ 12.09 hrs, Volume= 697909 cf, Depth= 6.16" 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 727250 74 >75% Grass cover, Good, HSG C 251540 98 Roof 381500 98 Paved parking 1367290 85 Weighted Average 727250 53.01% Pervious Area 641040 46.99% 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 24 El Runoff 23 21.8 cfs 22 21 Type III 24-hr % 19 M 1 00-Year Rainfall=7.94" 18 17 % Runoff Area=1 36 sf j 16 Runoff Volume=69,909 cf n 14 RunoffDepth=6.16" 13 - - - - - - �� - - - 12 3 Tc=6.0 min UL CN=85 8 �j 7 5 3 1 11"W'PI 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 72 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 73 Summary for Pond P1: StormTrap ST2 Single 2-0 Inflow Area = 38,490 sf, 45.49% Impervious, Inflow Depth = 6.16" for 100-Year event Inflow = 6.2 cfs @ 12.09 hrs, Volume= 19,743 cf Outflow = 5.2 cfs @ 12.14 hrs, Volume= 19,395 cf, Atten= 16%, Lag= 3.1 min Discarded = 0.0 cfs @ 12.14 hrs, Volume= 1,572 cf Primary = 5.1 cfs @ 12.14 hrs, Volume= 17,823 cf Routed to Pond P2 : StormTrap ST2 Single 3-6 Routing by Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.01 hrs Peak Elev= 226.75'@ 12.14 hrs Surf.Area= 1,644 sf Storage= 2,751 cf Plug-Flow detention time=48.4 min calculated for 19,389 cf(98% of inflow) Center-of-Mass det. time= 37.6 min ( 828.3 - 790.7 ) Volume Invert Avail.Storage Storage Description #1 A 223.60' 459 cf 23.79'W x 61.50'L x 3.00'H Field A 4,390 cf Overall - 3,242 cf Embedded = 1,148 cf x 40.0% Voids #2A 224.10' 2,242 cf StormTrap ST2 SingleTrap 2-Ox 3 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 8.48' x 46.19' Core + 6.66' Border = 21.79' x 59.50' System #3 224.40' 28 cf 4.00'D x 2.20'H Vertical Cone/CylindeFimpervious #4 226.60' 54 cf Custom Stage Data (Prismatic)Listed below(Recalc) 2,783 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) 226.60 110 0 0 226.90 250 54 54 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 @ 12.14 hrs HW=226.75' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=5.1 cfs @ 12.14 hrs HW=226.75' (Free Discharge) L2=Culvert (Inlet Controls 5.1 cfs @ 6.54 fps) 11625.34 - PR Type 11124-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 74 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 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 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 + 30.0" Chamber Height= 3.00' Field Height 3 Chambers x 231.7 cf+ 1547.2 cf Border= 2,242.3 cf Chamber Storage 3 Chambers x 326.4 cf+ 2,262.4 cf Border= 3,241.5 cf Displacement 4,389.E cf Field- 3,241.5 cf Chambers = 1,148.1 cf Stone x 40.0%Voids = 459.2 cf Stone Storage Chamber Storage + Stone Storage= 2,701.5 cf = 0.062 of Overall Storage Efficiency = 61.5 Overall System Size = 61.50'x 23.79'x 3.00' 3 Chambers(plus border) 162.E cy Field 42.5 cy Stone 11625.34 - PR 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 75 Pond P1: StormTrap ST2 Single 2-0 Hydrograph EM Inflow 6.2 cfs outflow Inflow Area=38,490 sf EM Discarded Primary Peak Elev=226.75' 6 5.2 cfs Storage=2,751 cf 5.1 cfs 3 , 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) 11625.34 - PR 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 76 Summary for Pond P2: StormTrap ST2 Single 3-6 Inflow Area = 121,370 sf, 57.96% Impervious, Inflow Depth = 6.29" for 100-Year event Inflow = 17.8 cfs @ 12.09 hrs, Volume= 63,600 cf Outflow = 17.8 cfs @ 12.10 hrs, Volume= 60,460 cf, Atten= 0%, Lag= 0.3 min Discarded = 0.0 cfs @ 9.67 hrs, Volume= 2,795 cf Primary = 17.8 cfs @ 12.10 hrs, Volume= 57,665 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= 220.87'@ 12.10 hrs Surf.Area= 2,494 sf Storage= 7,862 cf Plug-Flow detention time=62.1 min calculated for 60,440 cf(95% of inflow) Center-of-Mass det. time= 34.5 min ( 821.9 - 787.4 ) Volume Invert Avail.Storage Storage Description #1 A 216.50' 839 cf 32.27'W x 76.90'L x 4.50'H Field A 11,167 cf Overall - 9,069 cf Embedded = 2,098 cf x 40.0% Voids #2A 217.00' 7,000 cf StormTrap ST2 SingleTrap 3-6x 8 Inside #1 Inside= 101.7"W x 42.0"H => 26.77 sf x 15.40'L = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 522.2 cf 8 Chambers in 2 Rows 16.96' x 61.58' Core + 6.66' Border = 30.27' x 74.90' System #3 218.20' 54 cf 4.00'D x 4.30'H Vertical Cone/Cylinder #4 222.50' 2,138 cf Custom Stage Data (Prismatic)Listed below(Recalc) 10,031 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) 222.50 700 0 0 223.00 71850 2,138 27138 Device Routing Invert Outlet Devices #1 Discarded 216.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 218.20' 24.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 218.20'/218.10' S= 0.0200 '/' Cc= 0.900 n= 0.012, Flow Area= 3.14 sf #3 Device 2 220.00' 6.0' long x 3.00' rise Sharp-Crested Rectangular Weir 2 End Contraction(s) 3.0' Crest Height #4 Device 2 218.50' 10.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #5 Device 2 218.50' 10.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads 11625.34 - PR 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 77 Discarded Outf low Max=0.0 cfs @ 9.67 hrs HW=218.21' (Free Discharge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=17.7 cfs @ 12.10 hrs HW=220.86' (Free Discharge) L2=Culvert (Barrel Controls 17.7 cfs @ 5.64 fps) 3=Sharp-Crested Rectangular Weir(Passes < 15.8 cfs potential flow) 4=Orifice/Grate (Passes < 3.7 cfs potential flow) 5=Orifice/Grate (Passes < 3.7 cfs potential flow) 11625.34 - PR Type 11124-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 78 Pond P2: StormTrap ST2 Single 3-6 - Chamber Wizard Field A Chamber Model= StormTrapST2 SingleTrep 3-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 42.0"H => 26.77 sf x 15.401 = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 5222 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 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 +48.0" Chamber Height=4.50' Field Height 8 Chambers x 412.1 cf+ 3,703.3 cf Border= 7,000.4 cf Chamber Storage 8 Chambers x 522.2 cf+ 4,891.2 cf Border= 9,068.E cf Displacement 11,166.7 cf Field - 9,068.E cf Chambers= 2,098.1 cf Stone x 40.0%Voids = 839.2 cf Stone Storage Chamber Storage + Stone Storage= 7,839.E cf = 0.180 of Overall Storage Efficiency = 70.2 Overall System Size = 76.90'x 32.27'x 4.50' S Chambers(plus border) 413.E cy Field 77.7 cy Stone 11625.34 - PR 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 79 Pond P2: StormTrap ST2 Single 3-6 Hydrograph Inflow 17.8 cfs 11 outflow Discarded 17.8cfs Inflow Area=121,370 Sf o Prima ry 19 17.8 Cfs Peak Elev=220.87' 18 17 4 — Stora e 7 862 cf 16 14 13 12 10 o g EI UL 5 4 3 �: 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 9/15/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Page 80 Summary for Pond P3: StormTrap ST2 Single 3-6 Inflow Area = 50,430 sf, 20.76% Impervious, Inflow Depth = 5.46" for 100-Year event Inflow = 7.2 cfs @ 12.09 hrs, Volume= 22,944 cf Outflow = 4.0 cfs @ 12.21 hrs, Volume= 197110 cf, Atten= 45%, Lag= 7.4 min Discarded = 0.0 cfs @ 12.07 hrs, Volume= 2,648 cf Primary = 4.0 cfs @ 12.21 hrs, Volume= 16,461 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= 217.41'@ 12.21 hrs Surf.Area= 2,519 sf Storage= 7,726 cf Plug-Flow detention time= 147.4 min calculated for 19,103 cf(83% of inflow) Center-of-Mass det. time= 78.6 min ( 879.6 - 801.0 ) Volume Invert Avail.Storage Storage Description #1 A 213.50' 822 cf 40.75'W x 61.50'L x 4.50'H Field A 11,278 cf Overall - 9,222 cf Embedded = 2,055 cf x 40.0% Voids #2A 214.00' 7,134 cf StormTrap ST2 SingleTrap 3-6x 9 Inside #1 Inside= 101.7"W x 42.0"H => 26.77 sf x 15.40'L = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 522.2 cf 9 Chambers in 3 Rows 25.44' x 46.19' Core + 6.66' Border= 38.75' x 59.50' System #3 216.80' 25 cf 4.00'D x 2.00'H Vertical Cone/Cylinder #4 218.80' 38 cf Custom Stage Data (Prismatic)Listed below(Recalc) 8,018 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) 218.80 50 0 0 219.30 100 38 38 Device Routing Invert Outlet Devices #1 Discarded 213.50' 0.520 in/hr Exfiltration over Surface area #2 Primary 215.80' 12.0" Round Culvert L= 10.0' RCP, square edge headwall, Ke= 0.500 Inlet/ Outlet Invert= 215.80'/215.70' S= 0.0100 '/' Cc= 0.900 n= 0.012, Flow Area= 0.79 sf Discarded OutFlow Max=0.0 cfs @ 12.07 hrs HW=216.86' (FreeDischarge) L1=Exfi1tration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=4.0 cfs @ 12.21 hrs HW=217.41' (Free Discharge) L2=Culvert (Inlet Controls 4.0 cfs @ 5.07 fps) 11625.34 - PR Type 11124-hr 100-Year Rainfall=7.94" Prepared by VHB, Inc Printed 9115/2023 HydroCADO 10203c sln 01038 O 2023 HydroCAD Software Solutions LLC Page 81 Pond P3: StormTrap ST2 Single 3-6 - Chamber Wizard Field A Chamber Model= StormTrapST2 SingleTrap 3-6(StormTrapST2 SingleTrap@Type II+IV) Inside= 101.7"W x 42.0"H => 26.77 sf x 15.401 = 412.1 cf Outside= 101.7"W x 48.0"H => 33.92 sf x 15.401 = 5222 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 3 Rows x 101.7"Wide + 79.9" Side Border x 2 + 72.0" Side Stone x 2 = 40.75' Base Width 6.0" Stone Base +48.0" Chamber Height=4.50' Field Height 9 Chambers x 412.1 cf+ 3,424.5 cf Border= 7,133.E cf Chamber Storage 9 Chambers x 522.2 cf+ 4,522.9 cf Border= 9,222.5 cf Displacement 11,277.E cf Field - 9,222.5 cf Chambers= 2,055.1 cf Stone x 40.0%Voids = 822.0 cf Stone Storage Chamber Storage + Stone Storage= 7,955.7 cf = 0.183 of Overall Storage Efficiency = 70.5 Overall System Size = 61.50'x 40.75'x 4.50' 9 Chambers(plus border) 417.7 cy Field 76.1 cy Stone 11625.34 - PR 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 82 Pond P3: StormTrap ST2 Single 3-6 Hydrograph M Inflow 7.2 cfs Outflow El Discarded 8 Inflow Area=50,430 Sf 0 Primary Peak Elev=217.41' 7 Storag a=7,726 cf 5 4.0 cfs 4.0 cfs 4, 0 UL 2, 0 U U U U U U U U U U U-rllrlll7��711rllIF71lr7ll7llFI171IF7111 U U U U U U U U U U U U 11711711-111"111 1111 1111 1111'111'111 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 1111 1111 1111 1111'111 1111'111'111'111'111 1111'111 U A 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 /// 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 83 Summary for Link DP-1: Andover Street System Inflow Area = 377,520 sf, 48.10% Impervious, Inflow Depth = 5.74" for 100-Year event Inflow = 53.4 cfs @ 12.09 hrs, Volume= 180,734 cf Primary = 53.4 cfs @ 12.09 hrs, Volume= 180,734 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 EM Inflow 53.4 cfs El Primary 55„' 53.4 cfs Inflow Area=377,520 sf 50 45 40, 35.. o LL 25 20 - - - - j 10 - - - - - - - - - - - o I I I I 5 I I I 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) 0 110 0umo uummu l uuu uuum IIIIII IIIIIIIII I I I IIIIIIIIIIIIIIIIIIIIIeva I I B-12 Appendix B:Standard 2 Computations and Supporting Information \\vhb com\gbl\proj\Wat-LD\1162534 Greystar P3 Development\cad\Id\Eng\Stormwater\1162534-Ponding_dwg � ee .:ESTIMATED PONDING ELEVATION DURING PEAK OF j.. 100-YEAR STORM EVENT f 1 ELEVATION=217.41 j i� Turnpike Street/Route 114 f 1 ... �. f 1 219�T EX "'2191+EX 2196 % --227 I 2187 1 i,c ` 22 x 224 225 \-231 C1 1 AD! 218.7 N 1 t,s - 2273 1� 229 23 ;4 1 228 2k66+EX.. ' 1J4 AJ..... I 2164 218.2 ;...... ��,;�, 'PROPOSED 2161 EX I 63 2181 1 �u BUILDING 1 N _u ONDING 1 a `t._ ESTIMATED P PEAK Of I -�, ELEVATION DURING P .. ` x217.2 0 o e 100-YEAR STORM EVENT 111 FFE=224.0 FFE=228.0 z V-0 ENI 217.1 �:.� iv �, ELEVATION=-6 75 ' mi_240 124U 2 ;.-, 2306TC,. ..231,1 - c 1• C I T N 2301 BC 2307 C22 j 223.8 223.8 3.8 ,tC NN .. c 0_ p >21.GG�,UT 227. .: 1 € T p F- I 222.9 ,:. 2:s.�,.o:� a a€ .,N v 229.5 BC sk5� '. � 22.8 � o � 2301 BC EN EN SCII a o r N N.,.,.. i 4. ( EN EN, 229,8 TC - o 222.5 "'i i `� 'v� 229,3 BC" W" .� � I i 7.2.2_.5 :t y/ 2239 t # tf 223.9' x 222.7 22:3 8 'a 229.9 TC ve` 40 - �, ._\ 229.4 3C Dri 2278 ina :: ,. u 2236 Ad A r 22 :. 227.8 BC HYD \ 3.1 ivp l 226. JJ7q 227 v Z'3 6 - B 223 /` 0 225. )25.5 x 224.5 29.0Ex 2'1 FFE 220.0 2245 NN 225.s )26,8 Ex2243 ,l 2z5.7 27.7 Tc 1 ti 3:1 SLOPE(TYP) i, .`ts ,a... EN 227.2 BC x 225.9 EX t a \.::.... .. T s^:ti i'R23.7 225.9 .i. <, .. .,, z U3 50 2263 225.8 PROPOSED 22 2 j 2277 22792 EX , 225,7;. .. [�UILDING 2 .., 223.8riG1. � /� JJ59 226.3 A 216.4 BW \ 223 227,1 FFE=224.0 , 2258.225q 2270 EX 1 r 223.8 TNr 227.E :\ 2232 BINJJ4 22 -"22777 EX �. 2235x NVU 224 5 r > ESTIMATED aONDING V i 222 ELEVATION DURING PE4K OE 1" 1 00-YEAR STORM EVENT is , 2238 TW_. 2 .. .. vo _ „ / "...., ELEVATION=220.87 I.. .. � 3:1 SLOPE(TYP) / 2��" J ..., ' 000 I� F: x1180 EX m i Ptahert W / .. 's _ m `.., .: ,ate` A NpRTH \' co N,DoV co A F o R \' 100-Year Storm:Pending Elevations EXHIBIT B3 0 15 30 60 Feet Corner Development Project at Merrimack College 9/15/2023 North Andover,MA This page intentionally left blank. B-13 Appendix B: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 uuuuuuuuuu uuuumuuuuu �� uuu umuu Ipi a luuuu u 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 uuuou uuuuuo I hull IIIlid uuuuuuVl I uuu Ills I umomlllll II uuuuumuul u I uuuuuuum IIIIIIIIIIIIII I C-3 Appendix C:Standard 3 Computations and Supporting Documentation i 0 hb: Recharge Calculations Project Corner Development at Merrimack Project# 11625.34 College, North Andover, MA Calculated by SM Date 8/17/2023 Checked by X REQUIRED RECHARGE VOLUME Hydrologic Area Inches of Runoff Volume Soil Group (HSG) (ft) (in) (ft3) A 0 0.60 0 B 0 0.35 0 C 60,710 0.25 11265 D 0 0.10 0 TOTAL 1,265 CAPTURE AREA ADJUSTMENT Required Recharge Volume (ft) 11265 Total Site Net Impervious Area (ft2) 60,710 Total Site Impervious Area Draining to Recharge Facilities (ft2) 80,820 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 (ft2) (ft3) 1,463 649 Drawdown: (Vlnfiltration/ABottom)/Rawl's Rate Rawls Recharge Rate: 0.52 (in/hr) Drawdown Time: 10.24 (hours) 11625.34-Recharge&Drawdown Calculations.xlsx 1 of 2 i 0 hb: Recharge Calculations Project Corner Development at Merrimack Project# 11625.34 College, North Andover, MA Calculated by SM Date 8/17/2023 Checked by JK SYSTEM B: StormTrap SingleTrap (35H) Volumes provided below the lowest outlet at elevation: 218.5 Provided Volume: Bottom Area Volume (ft2) (ft) 21482 3,629 Drawdown: (Vlnfiltration/ABottom)/Rawl's Rate Rawls Recharge Rate: 0.52 (in/hr) Drawdown Time: 34 (hours) SYSTEM C: StormTrap SingleTrap (3.5'H) Volumes provided below the lowest outlet at elevation: 215.8 Provided Volume: Bottom Area Volume (ft) (ft) 21506 41314 Drawdown: (Vlnfiltration/ABottom)/Rawl's Rate Rawls Recharge Rate: 0.52 (in/hr) Drawdown Time: 40 (hours) RECHARGE VOLUME SUMMARY Required Recharge Volume: 1,265 (ft) Total Recharge Volume Provided: 81592 (ft) 11625.34-Recharge&Drawdown Calculations.xlsx 2 of 2 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/12/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond P1: StormTrap ST2 Single 2-0 Elevation Surface Storage (feet) (sq-ft) (cubic-feet) 223.60 13463 0 223.70 13463 59 223.80 1)463 117 223.90 1,463 176 224.00 1,463 234 224.10 13463 293 224.20 13463 411 224.30 13463 530 224.40 17463 649 224.50 13463 769 224.60 1,463 889 224.70 1,463 1,009 224.80 13463 1,129 224.90 13463 1,249 225.00 13463 1,369 225.10 13463 1,489 225.20 13463 1,609 225.30 1,463 1,729 225.40 1,463 11849 225.50 1,463 1,969 225.60 13463 2,089 225.70 13463 2,209 225.80 13463 2,329 225.90 13463 2,449 226.00 1,463 2,569 226.10 1,463 21690 226.20 1,463 2,697 226.30 13463 2,705 226.40 13463 2,713 226.50 13463 2,721 226.60 13573 2,729 226.70 13620 2,742 226.80 1,667 21760 226.90 11713 21783 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/12/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond P2: StormTrap ST2 Single 3-6 Elevation Surface Storage Elevation Surface Storage (feet) (sq-ft) (cubic-feet) (feet) (sq-ft) (cubic-feet) 216.50 23481 0 221.70 2,494 7,884 216.60 23481 99 221.80 2,494 7,885 216.70 23481 199 221.90 2,494 7,886 216.80 23481 298 222.00 2,494 7,887 216.90 23481 397 222.10 2,494 73889 217.00 23481 496 222.20 2,494 73890 217.10 2,481 705 222.30 2,494 7,891 217.20 2,481 913 222.40 2,494 7,892 217.30 2,481 11122 222.50 3,194 7,894 217.40 2,481 11331 222.60 4,624 8,035 217.50 2,481 1539 222.70 6,054 8,320 217.60 23481 1,748 222.80 7,484 8,747 217.70 23481 1,956 222.90 8,914 9,318 217.80 23481 21165 223.00 103344 10,031 217.90 23481 2,374 218.00 23481 2,582 218.10 2,481 2,791 218.20 2,494 2,999 218.30 2,494 3,209 218.40 2,494 31419 218.50 27494 3,629 218.60 23494 3,839 218.70 23494 4,049 218.80 23494 41258 218.90 23494 4,468 219.00 23494 4,678 219.10 23494 4,888 219.20 2,494 5,098 219.30 2,494 5,308 219.40 2,494 51517 219.50 2,494 51727 219.60 2,494 5,937 219.70 23494 6,147 219.80 23494 6,357 219.90 23494 61567 220.00 23494 6,776 220.10 23494 6,986 220.20 2,494 7,196 220.30 2,494 7,406 220.40 2,494 7,616 220.50 2,494 71826 220.60 2,494 7,835 220.70 2,494 7,845 220.80 23494 7,855 220.90 23494 71865 221.00 23494 7,875 221.10 23494 7,876 221.20 23494 7,877 221.30 2,494 7,879 221.40 2,494 7,880 221.50 2,494 71881 221.60 2,494 71882 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/12/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond P3: StormTrap ST2 Single 3-6 Elevation Surface Storage Elevation Surface Storage (feet) (sq-ft) (cubic-feet) (feet) (sq-ft) (cubic-feet) 213.50 23506 0 218.70 2519 7,980 213.60 23506 100 218.80 2569 7,981 213.70 23506 200 218.90 2579 7,986 213.80 23506 301 219.00 2,589 7,993 213.90 23506 401 219.10 2,599 83000 214.00 23506 501 219.20 2,609 83009 214.10 2,506 713 219.30 29619 89018 214.20 2506 925 214.30 2506 11137 214.40 2506 11349 214.50 2506 1560 214.60 23506 1,772 214.70 23506 1,984 214.80 23506 21196 214.90 23506 2,408 215.00 23506 2,620 215.10 2,506 2,831 215.20 2,506 3,043 215.30 2506 3,255 215.40 2506 31467 215.50 2506 3,679 215.60 23506 3,891 215.70 23506 4,102 215.80 27506 4,314 215.90 23506 4,526 216.00 23506 4,738 216.10 23506 4,950 216.20 2,506 5,162 216.30 2506 5,374 216.40 2506 51585 216.50 2506 51797 216.60 2506 6,009 216.70 23506 6,221 216.80 23519 6,433 216.90 23519 61646 217.00 23519 6,859 217.10 23519 7,072 217.20 2,519 7,285 217.30 2,519 7,498 217.40 2519 7,711 217.50 2519 71924 217.60 2519 7,934 217.70 2519 7,943 217.80 23519 7,952 217.90 23519 71961 218.00 23519 7,971 218.10 23519 7,972 218.20 23519 7,973 218.30 2,519 7,975 218.40 2519 7,976 218.50 2519 71977 218.60 2519 71978 uuuu°um uuumuuuS11111111, 11,111taged Sllllllta��Page A��o-eas yd 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 9/12/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond P1: StormTrap ST2 Single 2-0 Elevation Surface Storage (feet) (sq-ft) (cubic-feet) 223.60 13463 0 223.70 13463 59 223.80 1)463 117 223.90 1,463 176 224.00 1,463 234 224.10 13463 293 224.20 13463 411 224.30 13463 530 224.40 17463 649 224.50 13463 769 224.60 1,463 889 224.70 1,463 1,009 224.80 13463 1,129 224.90 13463 1,249 225.00 13463 1,369 225.10 13463 1,489 225.20 13463 1,609 225.30 1,463 1,729 225.40 1,463 11849 225.50 1,463 1,969 225.60 13463 2,089 225.70 13463 2,209 225.80 13463 2,329 225.90 13463 2,449 226.00 1,463 2,569 226.10 1,463 21690 226.20 1,463 2,697 226.30 13463 2,705 226.40 13463 2,713 226.50 13463 2,721 226.60 13573 2,729 226.70 13620 2,742 226.80 1,667 21760 226.90 11713 21783 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/12/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond P2: StormTrap ST2 Single 3-6 Elevation Surface Storage Elevation Surface Storage (feet) (sq-ft) (cubic-feet) (feet) (sq-ft) (cubic-feet) 216.50 23481 0 221.70 2,494 7,884 216.60 23481 99 221.80 2,494 7,885 216.70 23481 199 221.90 2,494 7,886 216.80 23481 298 222.00 2,494 7,887 216.90 23481 397 222.10 2,494 73889 217.00 23481 496 222.20 2,494 73890 217.10 2,481 705 222.30 2,494 7,891 217.20 2,481 913 222.40 2,494 7,892 217.30 2,481 11122 222.50 3,194 7,894 217.40 2,481 11331 222.60 4,624 8,035 217.50 2,481 1539 222.70 6,054 8,320 217.60 23481 1,748 222.80 7,484 8,747 217.70 23481 1,956 222.90 8,914 9,318 217.80 23481 21165 223.00 103344 10,031 217.90 23481 2,374 218.00 23481 2,582 218.10 2,481 2,791 218.20 2,494 2,999 218.30 2,494 3,209 218.40 2,494 31419 218.50 27494 3,629 218.60 23494 3,839 218.70 23494 4,049 218.80 23494 41258 218.90 23494 4,468 219.00 23494 4,678 219.10 23494 4,888 219.20 2,494 5,098 219.30 2,494 5,308 219.40 2,494 51517 219.50 2,494 51727 219.60 2,494 5,937 219.70 23494 6,147 219.80 23494 6,357 219.90 23494 61567 220.00 23494 6,776 220.10 23494 6,986 220.20 2,494 7,196 220.30 2,494 7,406 220.40 2,494 7,616 220.50 2,494 71826 220.60 2,494 7,835 220.70 2,494 7,845 220.80 23494 7,855 220.90 23494 71865 221.00 23494 7,875 221.10 23494 7,876 221.20 23494 7,877 221.30 2,494 7,879 221.40 2,494 7,880 221.50 2,494 71881 221.60 2,494 71882 11625.34 - PR Type /// 24-hr 25-Year Rainfall=6.16" Prepared by VHB, Inc Printed 9/12/2023 HydroCAD® 10.20-3c s/n 01038 ©2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond P3: StormTrap ST2 Single 3-6 Elevation Surface Storage Elevation Surface Storage (feet) (sq-ft) (cubic-feet) (feet) (sq-ft) (cubic-feet) 213.50 23506 0 218.70 2519 7,980 213.60 23506 100 218.80 2569 7,981 213.70 23506 200 218.90 2579 7,986 213.80 23506 301 219.00 2,589 7,993 213.90 23506 401 219.10 2,599 83000 214.00 23506 501 219.20 2,609 83009 214.10 2,506 713 219.30 29619 89018 214.20 2506 925 214.30 2506 11137 214.40 2506 11349 214.50 2506 1560 214.60 23506 1,772 214.70 23506 1,984 214.80 23506 21196 214.90 23506 2,408 215.00 23506 2,620 215.10 2,506 2,831 215.20 2,506 3,043 215.30 2506 3,255 215.40 2506 31467 215.50 2506 3,679 215.60 23506 3,891 215.70 23506 4,102 215.80 27506 4,314 215.90 23506 4,526 216.00 23506 4,738 216.10 23506 4,950 216.20 2,506 5,162 216.30 2506 5,374 216.40 2506 51585 216.50 2506 51797 216.60 2506 6,009 216.70 23506 6,221 216.80 23519 6,433 216.90 23519 61646 217.00 23519 6,859 217.10 23519 7,072 217.20 2,519 7,285 217.30 2,519 7,498 217.40 2519 7,711 217.50 2519 71924 217.60 2519 7,934 217.70 2519 7,943 217.80 23519 7,952 217.90 23519 71961 218.00 23519 7,971 218.10 23519 7,972 218.20 23519 7,973 218.30 2,519 7,975 218.40 2519 7,976 218.50 2519 71977 218.60 2519 71978 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 Wa�te��o- I Qua�� ilillitly Ie C II c u I I 1111111111 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 8/17/2023 Checked by J K Date Infiltration Systems Runoff from subcatchment area PR-1 1, PR-12, PR-13, and PR-14 Water Quality Storm Runoff Depth (in) 0.5 Total Impervious Area (ft2) 80,820 BASIN WQV: Required Volume: Runoff Depth to be Treated Required Volume (in) (ft) 0.5 31368 Provided Volume: Total Storage Capacity (ft3) System A- StormTrap SingleTrap (2.0'H) 649 System B - StormTrap SingleTrap (3.5'H) 31629 System C - StormTrap SingleTrap (3.5'H) 41314 81592 11625.34-Water Quality Volume Calculations.xlsx 1 of 1 mu �N liiuuu i uuu uuum 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: 17-Aug-2023 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, PR-12, PR-13, PR-14 A B C D E BMP TSS Removal Rate. Starting TS,S" Load** Amount Removed. Remaining Lead (D,- (C*D) 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 IIVI Illllu�lllll ��N uuumul uuumuuuu�uuu uuum N 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 8/17/2023 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 9 Yac Y(ac) (%) Structural BMPs 3.9 1.9 4.3 4.0 84% Impervious Area Disconnection - - - - Porous Pavement(w/underdrain) - - - - Untreated 0.7 0.1 0.2 0 0% TOTAL 1 4.7 2.0 4.5 4.0 79% Untreated Area Calculations oovhb Corner Development Project at Merrimack College # 11625.34 Project p � g Project Calculated by SM Date 8/17/2023 Checked by J K Date User Inputs Load Calculations z i Impervious TP Loading P Load of Impervious Area Impervious TSS Loading Rate TSS Load of Impervious Untreated Area ID Impervious Area(ft) Pervious Area(ft) Land Use Rate(Ib/ac/yr) (Ib/yr) (Ib/ac/yr) Area(Ib/yr) PR-15 4,500 27,750 Multi-Family and High Density Residential 1 2.3 0.2 439 45 11625.34-BMP WQ Credit Calculator.Asm Structural BMP Calculations m'-wvhb Project Corner Development at Merrimack College Project# 11625.34 North Andover,MA Calculated by SM Date 11625.34 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) 649 17,510 20,980 Multi-Family and High Density Residenti HSG C 0.4 Infiltration Trench 2.3 0.9 0.2 0.1 1.0 71% 0.7 System B Subsurface Infiltration System Loam(0.52 in/hr) 2,999 52,840 30,040 Multi-Family and High Density Residentil HSG C 0.7 Infiltration Trench 2.3 2.8 0.2 0.1 3.0 85% 2.5 System C Subsurface Infiltration System Loam(0.52 in/hr) 5,183 10,470 39,960 Multi-Family and High Density Residentil HSG C 1 5.9 1 Infiltration Trench 2.3 0.6 0.2 0.2 0.8 99% 117 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 uuuuumuuuu I uuu uumul uuumul loom IIW uuu uuum uuu uuum umuul uumuul uumm uuuummiCa�� IVV IIIIIIIIIIIIVI IIIIIIIIIIVI p IIIII 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. P uuu um°u pw uu e cll"t luuuumuu II 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