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HomeMy WebLinkAboutRCG_East Mill Residential Dev_Stormwater Report_02-2026 - Civil Design Group - Consultant Review - 0 Prescott Street 2/12/2026 STORMWATER MANAGEMENT REPORT FOR EAST MILL RESIDENTIAL DEVELOPMENT 0 PRESCOTT STREET NORTH ANDOVER, MA 01845 PREPARED FOR: RCG, LLC 17 Ivaloo Street, Suite 100 Somerville, MA 02143 PREPARED BY: C IVIL D ESIGN G ROUP, LLC 4 HIGH STREET, SUITE 155 NORTH ANDOVER, MA 01845 DATE: OCTOBER 2025 REVISED: FEBRUARY 2026 p: 978.794.5400 f: 978.965.3971 www.cdgengineering.com East Mill Redevelopment, North Andover MA TABLE OF CONTENTS PAGE I.STORMWATER MANAGEMENT NARRATIVE 1.0 SITE LOCATION AND DESCRIPTION…………………………………………………… 1 2.0 METHODOLOGY……………………………………………………………………………. 1 3.0 SOILS & GROUNDWATER…….…………………………………………………………… 1 4.0 POINTS OF ANALYSIS……………………………………………………………………… 2 5.0 EXISTING DRAINAGE WATERSHEDS…………………………..………………………. 2 6.0 PROPOSED DRAINAGE WATERSHEDS…………………………………………………. 2 7.0 PEAK FLOW RATE ………………………………………………………………………… 3 8.0 WATER QUALITY………………………………………………………………………….. 3 9.0 GROUNDWATER RECHARGE …………………………………….………………………. 4 10.0 DRAINAGE CONVEYANCE SYSTEM………………………………..…………………... 5 11.0 COMPLIANCE WITH THE MA DEP STORMWATER HANDBOOK…………………… 5 12.0 SUMMARY…………………………………………………………………………………. 7 II.LIST OF FIGURES FIGURE 1: USGS PLAN FIGURE 2: SOIL MAP FIGURE 3: PRE-DEVELOPMENT WATERSHEDS FIGURE 4: POST-DEVELOPMENT WATERSHEDS TEST PITS WATER QUALITY CALCULATIONS III.HYDROLOGICAL CALCULATIONS PRE-DEVELOPMENT HYDROCAD CALCULATIONS POST-DEVELOPMENT HYDROCAD CALCULATIONS IV.APPENDIX-1 MASSACHUSETTS DEP STORMWATER REPORT CHECKLIST V.APPENDIX-2 OPERATION AND MAINTENANCE PLAN (O&M) (WITH LONG-TERM POLLUTION PREVENTION PLAN) 0 p: 978-794-5400 f: 978.965.3935 www.cdgengineering.com East Mill Redevelopment, North Andover MA 1.0 SITE LOCATION AND DESCRIPTION Civil Design Group, LLC (CDG) has been retained byRCG, LLC to prepare this Stormwater Management Report for the construction of a residential development and to upgrade associated existing parking areas located on the East Mill campus on High Street, North Andover, Massachusetts (refer to Figure-1). The project includes the construction of a 92,000± square foot (footprint) residential building comprised of 296 units and the reconstruction/enahancement of existing parking areas including curb, landscaping and stormwater improvements within a 6.13± acre limit of work area within the site. According to FEMA flood insurance rate maps community panel number 2500980228G, effective date 07/08/2025, the area of the site to be redeveloped lies within Zone X, which is defined as areas determined to be outside the 0.2% (500-year) annual chance floodplain. The site does not include bordering vegetated wetlands and based on available MassGIS information, the site does not lie within an area mapped for rare and endangered species or certified vernal pools as mapped by the State of Massachusetts’ Natural Heritage and Endangered Species Program (NHESP) or within an Area of Critical Environmental Concern (ACEC). The site also does not lie within a surface water protection district. This study presents a comparative analysis of the pre-development and post-development hydrologic characteristics of the site, and outlines the proposed measures to mitigate flow, provide groundwater recharge, and improve water quality from the site in accordance with local and state requirements. The proposed best management practices (BMPs) one water quality unit and one (1) subsurface infiltration system (SIS) to provide mitigation of the peak flow rates for the 2, 10, 25 and 100-year storm events and to provide infiltration of onsite impervious areas and treat stormwater to the maximum extent practicable prior to discharging off site. 2.0 METHODOLOGY Technical Paper 40 (TP-40) was utilized to source the precipitation values Technical Release 55 (TR-55) methodology was utilized to determine weighted curve numbers (CNs) for each pre and post-development subcatchment area. Weighted CNs are based on ground cover type and hydrologic soil groups (HSGs). The times of concentration (Tc's) for each of the existing and proposed watersheds have been calculated. The areas that do not show a Tc travel path resulted in travel times of less than 6 minutes. CN and Tc values were then utilized to generate hydrographs using HydroCad 10.0, an industry standard software package that develops a hydrologic model based on the SCS method and computes peak discharges from rainfall runoff for urban and rural watersheds. 3.0 SOILS& GROUNDWATER According to the Natural Resources Conservation Service Web Soil Survey (Figure 2), the underlying soils on the site are classified as Urban Land and fine sandy loam. Based on test pits that were performed in August 2025, the underlying soils are primarily a sandy loam (HSG-B), therefore, this stormwater report utilizes a HSG rating of B for both the existing and proposed conditions for the purposes of capturing surface runoff curve numbers (CN). Furthermore, the proposed infiltration best management practices (BMPs) utilize an infiltration rate of 2.41 in/hr, which is representative of the sandy loam soil. 1 p: 978-794-5400 f: 978.965.3935 www.cdgengineering.com East Mill Redevelopment, North Andover MA 4.0 POINTS OF ANALYSIS Points of Analysis (POAs) are discharge points or lines that convey runoff from the study area via overland flow or through drain pipes. The pre-development and post-development areas of disturbance drain to four (4) POA’s listed and described below and shown on Figures 3 and 4. TABLE-1: POINTS OF ANALYSIS POINT OF ANALYSISDESCRIPTION A comparison point representing the existing culvert conveying POA-1 runoff from the existing drainage swale towards High Street (POA-2). A comparison line along the westerly portion of the limit of work POA-2 adjacent to the High Street/Prescott Street intersection that receives runoff via overland flow. A comparison line along the easterly portion of the site that collects POA-3 runoff via overland flow and discharged to the abutting property. A comparison line along the southerly portion of the site that collects POA-4 runoff via overland flow and discharged to the abutting property. 5.0 EXISTING DRAINAGE WATERSHEDS The existing watersheds are delineated based on topography, physical characteristics, drainage networks and limit of disturbance within the site limits and collect and direct stormwater towards the POAs. There are potential upstream areas that flow onsite, however, these areas flow through the property are not subject to be captured into the drainage or stormwater management system, therefore, these areas have been excluded from the stormwater analysis. As such, the total study area for the site is 6.13± acres and is divided into four (4) pre- development watersheds as described below: Subcatchment EX-1: The 2.69-acre watershed is comprised of rooftops, pavement and grass areas. Runoff travels via overland flow in a southerly direction towards POA-1. Subcatchment EX-2: The 2.80-acre watershed is comprised of pavement, grass and wooded areas. Runoff travels via overland flow in a westerly direction towards POA-2. Subcatchment EX-3: The 0.38-acre watershed is comprised of grass and wooded areas. Runoff travels via overland flow in an easterly direction towards POA-3. Subcatchment EX-4: The 0.27-acre watershed is comprised of pavement, grass and wooded areas. Runoff travels via overland flow in a southerly direction towards POA-4. 6.0 PROPOSED DRAINAGE WATERSHEDS Similar to the existing watersheds, the proposed watersheds are delineated based on topography, physical characteristics, drainage networks and limit of disturbance within the site limits and collect and direct stormwater towards the POAs. This area is divided into seven (7) post-development watersheds described below: 2 p: 978-794-5400 f: 978.965.3935 www.cdgengineering.com East Mill Redevelopment, North Andover MA Subcatchment PR-1: The 0.69-acre watershed is comprised of pavement and grassed area. Runoff travels via overland flow in a southerly direction towards POA-1. Subcatchment PR-2: The 2.54-acre watershed is comprised of pavement, grassed and wooded areas. Runoff travels via overland flow in a westerly direction towards POA-2. Subcatchment PR-2A: The 0.24-acre watershed is comprised of rooftop area. Runoff is collected via roof drains and discharged into the SIS. The outlet associated with the SIS flows towards POA-2. Subcatchment PR-2B: The 0.20-acre watershed is comprised of pavement and grassed areas. Runoff is collected via the onsite drainage system and discharged into the SIS. The outlet associated with the SIS flows towards POA-2. Subcatchment PR-2C: The 1.88-acre watershed is comprised of rooftop area. Runoff is collected via roof drains and discharged towards POA-2. Subcatchment PR-3: The 0.35-acre watershed is comprised of grass and wooded areas. Runoff travels via overland flow in an easterly direction towards POA-3. Subcatchment PR-4: The 0.24-acre watershed is comprised of pavement, grass and wooded areas. Runoff travels via overland flow in a southerly direction towards POA-4. 7.0 PEAK FLOW RATE MITIGATION The stormwater management system is designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates for the 2-year, 10-year, 25-year and 100-year, 24-hour storm events. Peak flow rates for the pre-development and post-development conditions are illustrated below: TABLE 2-1: PEAK FLOW RATE COMPARISON POINT 2-YEAR STORM 10-YEAR STORM 25-YEAR STORM 100-YEAR STORM OF EVENTEVENTEVENTEVENT (3.15”/24-HR) (4.83”/24-HR) (6.16”/24-HR) (8.94”/24-HR) ANALYSIS PRE (CFS) POST (CFS) PRE (CFS)POST (CFS PRE (CFS)POST (CFS) PRE (CFS)POST (CFS) POA-1 6.25 0.91 10.07 1.85 13.05 2.63 19.23 4.29 POA-2 6.90 6.23 12.36 12.08 16.93 16.57 26.83 26.30 POA-3 0.03 0.03 0.29 0.26 0.57 0.53 1.29 1.19 POA-4 0.29 0.28 0.63 0.60 0.93 0.87 1.57 1.44 3 p: 978-794-5400 f: 978.965.3935 www.cdgengineering.com East Mill Redevelopment, North Andover MA TABLE 2-2: VOLUME COMPARISON POINT 2-YEAR STORM 10-YEAR STORM 25-YEAR STORM 100-YEAR STORM OF EVENT EVENT EVENT EVENT (3.15”/24-HR) (4.83”/24-HR) (6.16”/24-HR) (8.94”/24-HR) ANALYSIS PRE (AF) POST (AF)PRE (AF) POST (AF) PRE (AF) POST (AF) PRE (AF) POST (AF) POA-1 0.558 0.078 0.926 0.158 1.220 0.226 1.838 0.375 POA-2 0.711 0.682 1.317 1.270 1.836 1.781 2.979 2.923 POA-3 0.008 0.008 0.030 0.028 0.053 0.049 0.112 0.103 POA-4 0.025 0.025 0.054 0.051 0.079 0.074 0.135 0.125 8.0 WATER QUALITY The redevelopment program includes measures to treat runoff from impervious areas prior to discharging offsite. New stormwater controls have been incorporated into the design that result in a reduction in annual stormwater pollutant loads from the site. Through the use of structural and non-structural BMPs, the water quality volume from the watersheds contributing to the proposed drainage system will undergo treatment. Currently, the total project area contains approximately 3.06± acres of impervious (pavement) area or 49% of the site. The redevelopment program increases the impervious area to 3.10± acres of impervious or 50% of the site, therefore the majority of the of the project area is considered a redevelopment and the balance will be treated as new development. Subcatchments PR-2A includes clean rooftop area, therefore, this watershed will be discharged directly to the subsurface infiltration system. The garage portion of the building totals 0.60 acres of non-rooftop impervious area and will be treated to at least 80% TSS removal (see attached water quality calculation). This watershed area exceeds the 0.04 acres of new impervious area from the project. Subcatchment PR-1A includes a reduction of overall and impervious area as compared to its existing counterpart, therefore, it’sreasonable to assume that the post-development runoff traversing through the existing swale will be treated to at least the same level as the pre-development condition. The following BMPs were selected to treat the average annual TSS load from stormwater runoff under the post-development condition. Deep Sump Hooded Catch Basins Stormwater runoff from proposed pavement areas will be directed via curbing and site grading to catch basins with deep sumps and hooded outlets. The catch basins will trap and remove sediment and larger particles from the stormwater and will improve the performance of subsequent BMP’s. The sumps will be a minimum of 4’ in depth and a regular inspection and cleaning schedule has been proposed to ensure optimal effectiveness. When properly designed and maintained, catch basin sumps are effective in reducing the sediment and pollutant load in runoff. Hydrodynamic Separator Hydrodynamic Separators are designed to remove heavy particles, floating debris and hydrocarbons from stormwater. Stormwater enters the system where floatables and oils are separated prior to the clarified stormwater runoff discharging to an outlet pipe. Since the Hydroworks units are designed to treat the required flow without overflow, bypass, surcharge, or scouring, and since they include a built- in bypass mechanism to accommodate high flow storm events, they are considered "offline" units under the DEP policy as proposed. Subsurface Infiltration Systems (SIS) 4 p: 978-794-5400 f: 978.965.3935 www.cdgengineering.com East Mill Redevelopment, North Andover MA Subsurface infiltration systems are designed to detain and infiltrate runoff from the site. The system is comprised of RetainIT concrete structures and crushed stone. Proper pretreatment (44% TSS removal min.) is required to in order to achieve 80% TSS. Runoff from the design storm is stored until it exfiltrates through the soil of the basin floor. 9.0GROUNDWATER RECHARGE The DEP Stormwater Management Policy addresses the importance of recharging groundwater and reducing surface runoff. For a redevelopment project, the net increase in site impervious area must be infiltrated to approximate the annual recharge from pre-development conditions. On this site, there is a net increase in impervious area equal to 0.04± acres. The required recharge equals a depth of runoff corresponding to the soil type multiplied by the net increase in impervious area for each soil type in the post development condition. Using a target factor of 0.35 inches for HSG-B, the total required recharge volume is as follows: Rv = (F) x (newly created impervious area) where, Rv =Required recharge volume (cubic feet) F = Target depth factor corresponding to the HSG. 2 Rv = 0.35-inch x 0.04 acres x (43,560 ft/acre) x (1 ft/12 inch) = 51 cubic feet The available storage within the SIS infiltration basin below the lowest outlet total 588± cubic feet, thereby exceeding the required recharge volume. The soil borings indicate that groundwater is at least 10’ below the existing ground surface (EL 91.00±), as such the proposed design accommodates 2’ separation to groundwater for the SIS. Below are the drawdown calculations for the infiltration BMP’s summarizing that each drawdown time will be less than 72 hours as follows: Drawdown calculation = Depth K Where k = 2.41 in/hour Subsurface Infiltration System -1 Drawdown calculation = 36 in = 15 hours < 72 hours = OK 2.41 in/hr 10.0 DRAINAGE CONVEYANCE SYSTEM The proposed stormwater conveyance system was designed to collect and convey runoff from developed areas to the associated stormwater management system BMP’s described in this report. The drainage system consists of one (1) subsurface infiltration system, catch basins, yard drains, manholes and associated piping. 11.0 COMPLIANCE WITH THE MASSACHUSETTS DEP STORMWATER HANDBOOK This study presents a comparative analysis of the pre-development and post-development hydrologic characteristics of the site, and outlines the proposed measures to mitigate flow, provide groundwater recharge, and improve water quality from the site. The best management practices (BMPs) outlined in this report include 5 p: 978-794-5400 f: 978.965.3935 www.cdgengineering.com East Mill Redevelopment, North Andover MA measures to meet the municipal and the Massachusetts Department of Environmental Protection (DEP) requirements. Below is a summary of how the design complies with each applicable DEP standard. Standard 1: No new stormwater conveyances may discharge untreated directly to or cause erosion in wetlands or waters of the Commonwealth. The proposed stormwater conveyance system does not include any new untreated discharges. The overland connection points will remain consistent with the existing condition. Standard 2: Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. As indicated above and within the supporting HydroCad calculations, the stormwater management system is designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. Standard 3: Loss of annual recharge to groundwater shall be eliminated or minimized through the use of infiltration measures including environmentally sensitive site design, low impact development techniques, stormwater best management practices, and good operation and maintenance. At a minimum, the annual recharge from the post-development site shall approximate the annual recharge from pre-development conditions based on soil type. This standard is met when the stormwater management system is designed to infiltrate the required recharge volume as determine in accordance with the Massachusetts Stormwater Handbook. There is a net increase of impervious area and the corresponding required volume of runoff will be recharged to groundwater. Standard 4: Stormwater management systems shall be designed to remove 80% of the average annual post- construction load of Total Suspended Solids (TSS). To aid in removal of total suspended solids, deep sump hooded catch basins and water quality units are proposed. Net increase of onsite non-rooftop impervious areas will be treated beyond 80%. Standard 5: For land uses with higher potential pollutant loads, source control and pollution prevention shall be implemented in accordance with the Massachusetts Stormwater Handbook to eliminate or reduce the discharge of stormwater runoff from such land uses to the maximum extent practicable. Not applicable. Standard 6: Stormwater discharges within the Zone II or Interim Wellhead Protection Area of a public water supply, and stormwater discharges near or to any other critical area, require the use of the specific source control and pollution prevention measures and the specific structural stormwater best management practices determined by the Department to be suitable for managing discharges to such areas, as provided in the Massachusetts Stormwater Handbook. Not applicable. 6 p: 978-794-5400 f: 978.965.3935 www.cdgengineering.com East Mill Redevelopment, North Andover MA Standard 7: A redevelopment project is required to meet the following Stormwater Management Standards only to the maximum extent practicable: Standard 2, Standard 3, and the pretreatment and structural best management practice requirements of Standards 4, 5, and 6. Existing stormwater discharges shall comply with Standard 1 only to the maximum extent practicable. A redevelopment project shall also comply with all other requirements of the Stormwater Management Standards and improve existing conditions. The proposed site complies with the applicable standards to new development and redevelopment. The proposed best management practices improve upon the existing conditions and mitigate for the proposed development impacts. Standard 8: A plan to control construction-related impacts including erosion, sedimentation and other pollutant sources during construction and land disturbance activities (construction period erosion, sedimentations, and pollution prevention plan) shall be developed and implemented. The ‘Demolition and Erosion Control Plan’ outlines and depicts measures to control construction related impacts including erosion, sedimentation and other pollutant sources during construction and land disturbance activities. Standard 9: A long-term operation and maintenance plan shall be developed and implemented to ensure that stormwater management systems function as designed. An Operation and Maintenance Plan (O&M) has been developed for each site that outlines maintenance requirements to ensure longevity of BMP’s. See Appendix A. Standard 10: All illicit discharges to the stormwater management system are prohibited. The proposed stormwater management system does not include any illicit discharges and furthermore the O&M plan includes an illicit discharge statement. 12.0 SUMMARY The stormwater management system for the proposed redevelopment includes measures for collecting, conveying, treating and controlling stormwater runoff from the site. Post-development peak runoff rates have been attenuated for the 2, 10, 25 and 100-year storm events and the collection system has been adequately designed to convey the contributing runoff. The stormwater management system incorporates both structural and non-structural BMP’s to adequately treat and recharge runoff from the proposed redevelopment area and is designed in accordance with the DEP Stormwater Management Policy to the maximum extent practicable. Comprehensive computations and calculations with supporting figures and plans are attached. 7 p: 978-794-5400 f: 978.965.3935 www.cdgengineering.com FIGURE-1 USGS PLAN ESIGN D ROUP, LLC www.cdgengineering.com 4 HIGH STREET SUITE 155 NORTH ANDOVER, MA 01845 IVIL p: 978-794-5400 f: 978-965-3971 G SITE C FIG-3 WATERSHEDS PRE-DEVELOPMENT CN =56 EX-3 AREA = 0.38 AC. CN =94 EX-1 AREA = 2.69 AC. ESIGN D ROUP, LLC www.cdgengineering.com p: 978-794-5400 f: 978-965-3971 IVIL G C EX-2 CN = 67 AREA = 2.80 AC. WATERSHED NOTES: FIG-4 8 7 = WATERSHEDS N PR-4 C POST-DEVELOPMENT 2 - R P CN = 66 AREA = 2.47 AC. PR-3 CN = 56 AREA = 0.35 AC. CN = 98 ESIGN D ROUP, LLC www.cdgengineering.com PR-1 CN = 80 p: 978-794-5400 f: 978-965-3971 IVIL G C CN = 98 PR-2A AREA = 0.24 AC. CN = 76 PR-2B AREA = 0.20 AC. 6 6 = N PR-2 C WATERSHED NOTES: : Other Topsoil <5 Slope (%) Longitude boulders, etc.) Depth Standing Water in Hole - - Soil Latitude (Moist) LOOSE Consistence - - 0 deg. F Soil Structure GRANUALR 7 , - - 0 Sunny Weather Stones Cobbles & None Surface Stones (e.g., cobbles, stones, % by Volume - - 10 Coarse Fragments Gravel Depth Weeping from Pit - - - 09:30 Time Percent Soil Log If yes: - - - Color Grass Vegetation 25 - 29 Redoximorphic Features - - - - ) 08 Date Depth - - - No 10YR 5/6 A Moist (Munsell) Soil Matrix: Color Civil Design Group, LLC ( - - S Yes (USDA Soil Texture , P.E. 1 - T Hole # woodland, agricultural field, vacant lot, etc.) r Commercial/Residential(e.g., C HTM /Laye Topsoil Philip Henry Soil Horizon Prescott Street, North Andover, M 34 118 - Additional Notes: - 0-12 12 34 Depth (in) TEST PIT LOG Site: Logged By: Test Pit Number: Land UseGroundwater Observed: : Other Topsoil <5 Slope (%) Longitude Depth Standing Water in Hole - - istence Soil Latitude (Moist) LOOSE Cons LAR - - Soil Structure GRANU 70 deg. F - - 0 Sunny,Weather Stones Cobbles & None Surface Stones (e.g., cobbles, stones, boulders, etc.) % by Volume - - 10 Coarse Fragments Gravel Depth Weeping from Pit - - - 09:30 Time Percent Soil Log If yes: - - - Color ass Gr Vegetation 25 - 29 Redoximorphic Features - - - - 08 Date Depth - - - No 10YR 5/6 Moist (Munsell) Soil Matrix: Color - - S Yes (USDA P.E. (Civil Design Group, LLC) Soil Texture 2 - T Hole # woodland, agricultural field, vacant lot, etc.) M Commercial/Residential(e.g., C HT /Layer Topsoil Soil Horizon 20 Prescott Street, North Andover, MA Use 48 Additional Notes: -1 0-9 9- 48 Depth (in) TEST PIT LOG Site: Logged By: Philip Henry, Test Pit Number: Land Groundwater Observed: : Other Topsoil <5 Slope (%) Longitude Depth Standing Water in Hole - - Soil Latitude (Moist) LOOSELOOSE Consistence - - Soil Structure GRANUALRGRANULAR 70 deg. F - - 0 0 ce Stones (e.g., cobbles, stones, boulders, etc.) Sunny,Weather Stones Cobbles & None Surfa % by Volume - - 1010 Coarse Fragments Gravel Depth Weeping from Pit Log - - - - 09:30 Time Percent Soil If yes: - - - - Color Grass Vegetation 25 - 29 Redoximorphic Features - - - - - 08 Date Depth - - - No 10YR 5/610YR 5/2 Moist (Munsell) Soil Matrix: Color - - S SL Yes (USDA Soil Texture 4 - T Hole # woodland, agricultural field, vacant lot, etc.) Commercial/Residential(e.g., C2 C1 HTM /Layer Topsoil Soil Horizon Prescott Street, North Andover, MA 90 120 66 - Additional Notes: - 0-9 9- 66 90 Depth (in) TEST PIT LOG Site: Logged By: Philip Henry, P.E. (Civil Design Group, LLC)Test Pit Number: Land UseGroundwater Observed: NRCC 24-hr D 2-Year Rainfall=3.15" Post Development Printed 12/29/2025 Prepared by Civil Design Group, LLC HydroCAD® 10.20-5c s/n 07576 © 2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond SIS-1: ElevationSurfaceStorageElevationSurfaceStorage (feet)(sq-ft)(cubic-feet)(feet)(sq-ft)(cubic-feet) 95.00 784 097.657842,078 95.057843997.707842,117 95.107847897.757842,156 95.1578411897.807842,195 95.2078415797.857842,234 95.2578419697.907842,274 95.3078423597.957842,313 95.3578427498.00784 2,352 95.40784314 95.45784353 95.50784392 95.55784431 95.60784470 95.65784510 95.70784549 95.75784588 95.80784627 95.85784666 95.90784706 95.95784745 96.00784784 96.05784823 96.10784862 96.15784902 96.20784941 96.25784980 96.307841,019 96.357841,058 96.407841,098 96.457841,137 96.507841,176 96.557841,215 96.607841,254 96.657841,294 96.707841,333 96.757841,372 96.807841,411 96.857841,450 96.907841,490 96.957841,529 97.007841,568 97.057841,607 97.107841,646 97.157841,686 97.207841,725 97.257841,764 97.307841,803 97.357841,842 97.407841,882 97.457841,921 97.507841,960 97.557841,999 97.607842,038 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for 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, the Stormwater Report (which should provide more substantive and detailed information) but is offered use only the tab here as a tool to help the applicant organize their Stormwater Management documentation for their key to move your 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 1 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 2 by Standard 8 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. SW Checklist.doc• 04/01/08Stormwater Report Checklist • Page 1of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report B.Stormwater Checklist and Certification The following checklist is intended to serve as a guide for applicants as to the elements that ordinarily need to be addressed in a complete Stormwater Report. The checklist is also intended to provide conservation commissions and other reviewing authorities with a summary of the components necessary for a comprehensive Stormwater Report that addresses the ten Stormwater Standards. Note:Because stormwater requirements vary from project to project, it is possible that a complete Stormwater Report may not include information on some of the subjects specified in the Checklist. If it is determined that a specific item does not apply to the project under review,please note that the item is not applicable (N.A.) and provide the reasons for that determination. A complete checklist must include the Certification set forth below signed by the Registered Professional Engineer who prepared the Stormwater Report. Registered Professional Engineer’s Certification I have reviewed the Stormwater Report, including the soil evaluation, computations, Long-term Pollution Prevention Plan, the Construction Period Erosion and Sedimentation Control Plan (if included), the Long- term Post-Construction Operation and Maintenance Plan, the Illicit Discharge Compliance Statement (if included) and the plans showing the stormwater management system, and have determined that they have been prepared in accordance with the requirements of the Stormwater Management Standards as further elaborated by the Massachusetts Stormwater Handbook. I have also determined that the information presented in the Stormwater Checklist is accurate and that the information presented in the Stormwater Report accurately reflects conditions at the site as of the date of this permit application. Registered Professional Engineer Block and Signature Signature and Date Checklist Project Type:Is the application for new development, redevelopment, or a mix of new and redevelopment? New development Redevelopment Mix of New Development and Redevelopment SW Checklist.doc• 04/01/08Stormwater Report Checklist • Page 2of 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: 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. SW Checklist.doc• 04/01/08Stormwater Report Checklist • Page 3of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection -Wetlands Program Checklist for Stormwater Report Checklist(continued) Standard 2: Peak Rate Attenuation Standard 2 waiver requested because the project is located in land subject to coastalstorm 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. 1 StaticSimple DynamicDynamic 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. 21E 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. 21E 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. SW Checklist.doc• 04/01/08Stormwater Report Checklist • Page 4of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection -Wetlands Program Checklist for 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; Streetsweeping 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. SW Checklist.doc• 04/01/08Stormwater Report Checklist • Page 5of 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: The ½” 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 proprietyBMP 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. SW Checklist.doc• 04/01/08Stormwater Report Checklist • Page 6of 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 a multi-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 a multi-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 (StandardNo. 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. SW Checklist.doc• 04/01/08Stormwater Report Checklist • Page 7of 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 SedimentationControl 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 ConstructionGeneral 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 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: A copy ofthe 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. SW Checklist.doc• 04/01/08Stormwater Report Checklist • Page 8of 8 OPERATION AND MAINTENANCE PLAN FOR EAST MILL RESIDENTIAL DEVELOPMENT 0 PRESCOTT STREET NORTH ANDOVER, MA 01845 PREPARED FOR: RCG, LLC 17 Ivaloo Street, Suite 100 Somerville, MA 02143 PREPARED BY: C IVIL D ESIGN G ROUP, LLC 4 HIGH STREET, SUITE 155 NORTH ANDOVER, MA 01845 DATE: OCTOBER 2025 REVISED: JANUARY 2026 TABLE OF CONTENTS 1.0 INTRODUCTION………………………………………………………………………..............................2 2.0 LONG TERM POLLUTION PREVENTION PLAN (LTPPP)………………………..………………...2 3.0 STORMWATER MANAGEMENT SYSTEM……………………………………………........................3 4.0 SNOW MANAGEMENT AND DEICING CONTROL………...………………………………………...4 5.0 ILLICIT DISCHARGE STATEMENT……...…………………………………………….........................4 APPENDIX A – OPERATION AND MAINTENANCE REPORT FORM FIGURE 1 – BMP LOCATION PLAN 1 p: 978-794-5400 f : 978.965.3971 www.cdgengineering.com Petroleum Products: Petroleum products shallbe stored in sealed containersandclearly labeled. Petroleum storage tanks shall be located a minimum of 100 linear feet from wetland resource areas, drainage ways, inlets and surface waters unless stored within a building. Petroleum storage tanks shallbe equipped with a secondary means of containment designed to provide a containment volume that is equal to 110% of the volume of the largest tank unless otherwise required. Drip pans or other form of containment shall be provided for all dispensers. Any asphalt substances used onsite will be applied according to the manufacturer's recommendations. Fertilizers, Herbicides and Pesticides: Fertilizers, herbicides and pesticides shall be used in the minimum amounts recommended by the manufacturer and applied to limit contact with stormwater. These products shall be stored in containers indoors. Paints and Cleaning Solvents: Paints and containers shall be properly stored in their original containers. Disposal of these products and their containers shall be in accordance with the manufacturer’s recommendations. Spill Prevention and Response: In the event of a spill of a hazardous substance the following response action items shall be followed in order to prevent or minimize discharge to the stormwater management system. 1. Spills shall be immediately addressed. 2. Spills of hazardous substances shall be remediated using the manufacturers’ protocol for cleanup. 3. Vehicular and fuel spills shall be remediated in accordance to local and state regulations. 4. The following equipment and materials shall be present on site and shall be clearly identifiable: a. Absorbent materials, brooms, dust pans, mops, rags, gloves, goggles, trash containers, etc. 5. Spills that are toxic or hazardous in nature shall be reported to the MA DEP and professional emergency contractor. 6. The owner shall designate individuals who will receive spill prevention and response training. These individuals will each become responsible for a particular phase of prevention and response. The names of these personnel shall be posted in the material storage area and in the management office. 3.0 STORMWATER MANAGEMENT SYSTEM The components of the stormwater management system shall be inspected, monitored and maintained in accordance with the following to ensure that the on-site stormwater management/BMP facilities for the project function as intended. Routine inspection and proper maintenance of these individual components is essential to providing the long-term enhancement of both the quality and quantity of the runoff from the site. The proposed stormwater management Best Management Practices (BMP’s have been designed to collect and convey runoff from developed areas in accordance with the Massachusetts DEP’s Stormwater Management Policy. Using the rational method to determine peak runoff flows, the onsite drainage system is designed for the 25-year storm event. The drainage system consists of catch basins, yard drains, a subsurface infiltration system, a water quality unit and associated piping and drainage manholes. 3 p: 978-794-5400 f : 978.965.3971 www.cdgengineering.com Street Sweeping Sweeping shall be performed twice a year, once in the spring and once in the fall, within the parking lot and driveway areas to reduce the amount of sediment and trash enteringthe catch basins. Deep Sump Hooded Catch Basins, Trench Drains & Yard Drains Stormwater runoff from proposed pavement areas is directed via curbing and site grading to catch basins with deep sumps and hooded outlets, trench drains and yard drains. These catch basin structures are designed to trap and remove sediment and larger particles from the stormwater and improve the performance of subsequent BMP’s. The catch basin sumps are a minimum of 4’ in depth and a routine inspection and cleaning schedule shall be followed to ensure optimal effectiveness. Inspection Frequency: Quarterly Cleaning Threshold(s): 18” sediment in sump; discernable layer of oil on surface; floating trash Equipment: Clamshell or vactor Subsurface Infiltration System (SIS) Subsurface infiltration system is designed to infiltrate runoff from the site. The system is comprised of pipe and stone. The system is equipped with an inspection port to facilitate inspection for sediment accumulation. Inspection Frequency: Quarterly Cleaning Threshold(s): 4” sediment Equipment: Water jet and vactor Hydrodynamic Separator Hydrodynamic Separators are designed to remove heavy particles, floating debris and hydrocarbons from stormwater. Stormwater enters the system where floatables and oils are separated prior to the clarified stormwater runoff discharging to an outlet pipe. See the attached Stormceptor product description sheets for additional information, including maintenance recommendations. Inspection Frequency: Quarterly Cleaning Threshold(s): Per manufacturer’s recommendations Equipment: Vactor 4.0 SNOW MANAGEMENT AND DEICING CONTROL The Owner shall contract with a company to properly clear and remove snow. The contractor shall be responsible for maintaining all roads, driveways, parking lots, sidewalks and pedestrian access onsite as well as along the right-of-way frontage. Snow shall be piled in the designated areas snow storage areas to the extent practicable. Snow shall be removed from the siteif the capacity of the designated areas is reached, and disposed of in accordance with applicable regulations and requirements. Deicing chemicals shall be kept indoors in a safe location and shall be clearly labeled. Deicing solutions such as calcium chloride, rock salt and/or sand may be used unless otherwise restricted by the municipality. Deicing methods shall be used in conjunction with snow removal to maintain safe pedestrian and vehicular access. 4 p: 978-794-5400 f : 978.965.3971 www.cdgengineering.com 5.0 ESTIMATED OPERATION AND MAINTENANCE BUDGET The estimated average annual operating and maintenance budget for the proposed system is shown below: Catch Basins: $200 each Proprietary Separator: $1,000 each Subsurface Infiltration System: $1,500 each Routine maintenance = $2,000 o Removal of trash o Annual street sweeping o Pipe network/outfall inspections 6.0 ILLICIT DISCHARGE STATEMENT The proposed stormwater management system consists of deep sump hooded catch basins, manholes, a hydrodynamic separator, and associated piping which is intended to collect and convey stormwater discharges from the site. The stormwater management system is not intended to convey any illicit discharges and or pollutants and as such, control measures that are identified within this report shall be strictly adhered to in order to minimize the risk of contamination. Any unknown existing illicit discharges that are discovered as part of the redevelopment of the subject site shall be eliminated in accordance with local, state and federal regulations. 5 p: 978-794-5400 f : 978.965.3971 www.cdgengineering.com APPENDIX-A OPERATION AND MAINTENANCE REPORT FORM 4 High Street, Suite 155 S TORMWATER D IVISION North Andover, MA 01845 Tel 978.794.5400 www.cdgengineering.com OF C IVIL D ESIGN G ROUP, LLC QUARTERLY STORMWATER INSPECTION REPORT Site:Residential Development Date: Address:Prescott Street, North Andover, MA 01845 Time: Inspector:Weather: BMP UnitSedimentOilLast Trash Cover # (inches) (inches) Cleaned Attention Recommended EXISTING OUTFALLS IN SWALE DMH-9 (HS5) CB-1 YD-1 YD-2 YD-3 YD-4 YD-5 YD-6 YD-7 TD-1 DMH-2 SUBSURFACE INFILTRATION SYSTEM (SIS) UnitSedimentOilLast Trash Grate # (inches) (inches) Cleaned Attention Recommended SIS-1 OCS-1 1 p: 978-794-5400 f : 978.965.3971 www.cdgengineering.com 1 2 3 M W E. U I I G V N I P M W 7 O O N/F 2 D D 5 N A 1 O E . C M K B PLAN FIGURE-1 BMP LOCATION ESIGN D ROUP, LLC www.cdgengineering.com 4 HIGH STREET SUITE 155 NORTH ANDOVER, MA 01845 IVIL p: 978-794-5400 f: 978-965-3971 G C P E R D L A W . O N/F N O T F I BK. 1410 PG. 17 L C B R I C 1 K S T O R Y B U I L D I N G 2 2 ® Hydroworks HydroStorm Operations & Maintenance Manual Version 1.0 Please call Hydroworks at 888-290-7900 or email us at support@hydroworks.com if you have any questions regarding the Inspection Checklist. Please fax a copy of the completed checklist to Hydroworks at 888-783-7271 for our records. I ntroduction The HydroStorm is a state of the art hydrodynamic separator. Hydrodynamic separators remove solids, debris and lighter than water (oil, trash, floating debris) pollutants from stormwater. Hydrodynamic separators and other water quality measures are mandated by regulatory agencies (Town/City, State, Federal Government) to protect storm water quality from pollution generated by urban development (traffic, people) as part of new development permitting requirements. As storm water treatment structures fill up with pollutants they become less and less effective in removing new pollution. Therefore, it is important that storm water treatment structures be maintained on a regular basis to ensure that they are operating at optimum performance. The HydroStorm is no different in this regard and this manual has been assembled to provide the owner/operator with the necessary information to inspect and coordinate maintenance of their HydroStorm. ® Hydroworks HydroStorm Operation The Hydroworks HydroStorm (HS) separator is a unique hydrodynamic by-pass separator. It incorporates a protected submerged pretreatment zone to collect larger solids, a treatment tank to remove finer solids, and a dual set of weirs to create a high flow bypass. High flows are conveyed directly to the outlet and do not enter the treatment area, however, the submerged pretreatment area still allows removal of coarse solids during high flows. Under normal or low flows, water enters an inlet area with a horizontal grate. The area underneath the grate is submerged with openings to the main treatment area of the separator. Coarse solids fall through the grate and are either trapped in the pretreatment area or conveyed into the main treatment area depending on the flow rate. Fines are transported into the main treatment area. Openings and weirs in the pretreatment area allow entry of water and solids into the main treatment area and cause water to rotate in the main treatment area creating a vortex motion. Water in the main treatment area is forced to rise along the walls of the separator to discharge from the treatment area to the downstream pipe. The vortex motion forces solids and floatables to the middle of the inner chamber. Floatables are trapped since the inlet to the treatment area is submerged. The design maximizes the retention of settled solids since solids are forced to the center of the inner chamber by the vortex motion of water while water must flow up the walls of the separator to discharge into the downstream pipe. A set of high flow weirs near the outlet pipe create a high flow bypass over both the pretreatment area and main treatment chamber. The rate of flow into the treatment area is regulated by the number and size of openings into the treatment chamber and the height of by-pass weirs. High flows flow over the weirs directly to the outlet pipe preventing the scour and resuspension of any fines collected in the treatment chamber. A central access tube is located in the structure to provide access for cleaning.The arrangement of the inlet area and bypass weirs near the outlet pipe facilitate the use of multiple inlet pipes. Figure 1. Hydroworks HydroStorm Operation Plan View Figure 2 is a profile view of the HydroStorm separator showing the flow patterns for low and high flows. Figure 2. Hydroworks HydroStorm Operation Profile View The HS 4i is an inlet version of the HS 4 separator. There is a catch-basin grate on top of the HS 4i. A funnel sits sits underneath the grate on the frame and directs the water to the inlet side of the separator to ensure all lows flows are properly treated. The whole funnel is removed for inspection and cleaning. Figure 3. Hydroworks HS 4i Funnel Inspection Procedure Floatables A visual inspection can be conducted for floatables by removing the covers and looking down into the center access tube of the separator. Separators with an inlet grate (HS 4i or custom separator) will have a plastic funnel located under the grate that must be removed from the frame prior to inspection or maintenance. If you are missing a funnel please contact Hydroworks at the numbers provided at the end of this document. TSS/Sediment Inspection for TSS build-up can be conducted using a Sludge Judge®, Core Pro®, AccuSludge® or equivalent sampling device that allows the measurement of the depth of TSS/sediment in the unit. These devices typically have a ball valve at the bottom of the tube that allows water and TSS to flow into the tube when lowering the tube into the unit. Once the unit touches the bottom of the device, it is quickly pulled upward such that the water and TSS in the tube forces the ball valve closed allowing the user to see a full core of water/TSS in the unit. The unit should be inspected for TSS through each of the access covers. Several readings (2 or 3) should be made at each access cover to ensure that an accurate TSS depth measurement is recorded. Frequency Construction Period The HydroStorm separator should be inspected every four weeks and after every large storm (over (12.5 mm) of rain) during the construction period. Post-Construction Period The Hydroworks HydroStorm separator should be inspected during the first year of operation for normal stabilized sites (grassed or paved areas). If the unit is subject to oil spills or runoff from unstabilized (storage piles, exposed soils) areas the HydroStorm separator should be inspected more frequently (4 times per year). The initial annual inspection will indicate the required future frequency of inspection and maintenance if the unit was maintained after the construction period. Reporting Reports should be prepared as part of each inspection and include the following information: 1. Date of inspection 2. GPS coordinates of Hydroworks unit 3. Time since last rainfall 4. Date of last inspection 5. Installation deficiencies (missing parts, incorrect installation of parts) 6. Structural deficiencies (concrete cracks, broken parts) 7. Operational deficiencies (leaks, blockages) 8. Presence of oil sheen or depth of oil layer 9. Estimate of depth/volume of floatables (trash, leaves) captured 10. Sediment depth measured 11. Recommendations for any repairs and/or maintenance for the unit 12. Estimation of time before maintenance is required if not required at time of inspection A sample inspection checklist is provided at the end of this manual. Maintenance Procedure The Hydroworks HydroStorm unit is typically maintained using a vacuum truck. There are numerous companies that can maintain the HydroStorm separator. Maintenance with a vacuum truck involves removing all of the water and sediment together. The water is then separated from the sediment on the truck or at the disposal facility. A c treatment tank of the unit. This is the primary location to maintain by vacuum truck. The pretreatment area can also be vacuumed and/or flushed into the lower treatment tank of the separator for cleaning via the central access once the water level is lowered below the pretreatment floor. In instances where a vacuum truck is not available other maintenance methods (i.e. clamshell bucket) can be used, but they will be less effective. If a clamshell bucket is used the water must be decanted prior to cleaning since the sediment is under water and typically fine in nature. Disposal of the water will depend on local requirements. Disposal options for the decanted water may include: 1. Discharge into a nearby sanitary sewer manhole 2. Discharge into a nearby LID practice (grassed swale, bioretention) 3. Discharge through a filter bag into a downstream storm drain connection The local municipality should be consulted for the allowable disposal options for both water and sediments prior to any maintenance operation. Once the water is decanted the sediment can be removed with the clamshell bucket. Disposal of the contents of the separator depend on local requirements. Maintenance of a Hydroworks HydroStorm unit will typically take 1 to 2 hours based on a vacuum truck and longer for other cleaning methods (i.e. clamshell bucket). Figure 3. Maintenance Access Frequency Construction Period A HydroStorm separator can fill with construction sediment quickly during the construction period. The HydroStorm must be maintained during the construction period when the depth of TSS/sediment reaches 24 (600 mm). It must also be maintained during the construction period if there is an appreciable depth of oil in the unit (more than a sheen) or if floatables other than oil cover over 50% of the area of the separator The HydroStorm separator should be maintained at the end of the construction period, prior to operation for the post-construction period. Post-Construction Period The HydroStorm was independently tested by Alden Research Laboratory in 2017. A HydroStorm HS 4 was tested for scour with a 50% sediment depth of 0.5 ft. Therefore, maintenance for sediment accumulation is required if the depth of sediment is 1 ft or greater in separators with standard water (sump) depths (Table 1). There will be designs with increased sediment storage based on specifications or site-specific criteria. A measurement of the total water depth in the separator through the central access tube should be taken and compared to water depth given in Table 1. The standard water depth from Table 1 should be subtracted from the measured water depth and the resulting extra depth should be added to the 1 ft to determine the site-specific sediment maintenance depth for that separator. For example, if the measured water depth in the HS-7 is 7 feet, then the sediment maintenance depth for that HS-7 is 2 ft (= 1 + 7 6) and the separator does not need to be cleaned for sediment accumulation until the measure sediment depth is 2 ft. The HydroStorm separator must also be maintained if there is an appreciable depth of oil in the unit (more than a sheen) or if floatables other than oil cover over 50% of the water surface of the separator. Table 1 Standard Dimensions for Hydroworks HydroStorm Models Sediment Maintenance Depth for Table 1 Total Water Model Diameter (ft) Total Water Depth(ft) Depth (ft) Њ HS-3 3 Ќ Њ HS-4 4 Ѝ Њ HS-5 5 Ѝ Њ HS-6 6 Ѝ Њ HS-7 7 Џ Њ HS-8 8 А Њ HS-9 9 А͵Ў Њ HS-10 10 Б Њ HS-11 11 В Њ HS-12 12 В͵Ў HYDROSTORM INSPECTION SHEET Date Date of Last Inspection Site City State Owner GPS Coordinates Date of last rainfall Site Characteristics Yes No Soil erosion evident Exposed material storage on site Large exposure to leaf litter (lots of trees) High traffic (vehicle) area HydroStorm Yes No Obstructions in the inlet or outlet * Missing internal components ** Improperly installed inlet or outlet pipes *** Internal component damage (cracked, broken, loose pieces) ** Floating debris in the separator (oil, leaves, trash) Large debris visible in the separator * Concrete cracks/deficiencies *** Exposed rebar ** Water seepage (water level not at outlet pipe invert) *** Water level depth below outlet pipe invert Routine Measurements Floating debris depth (13mm) 13mm) * Floating debris coverage < 50% of surface area > 50% surface area * Sludge depth < 12 (300mm) > 12 (300mm) * * Maintenance required ** Repairs required *** Further investigation is required Other Comments: ® Hydroworks HydroStorm One Year Limited Warranty Hydroworks, LLC warrants, to the purchaser and subsequent owner(s) during the warranty period subject to the terms and conditions hereof, the Hydroworks HydroStorm to be free from defects in material and workmanship under normal use and service, when properly installed, used, inspected and maintained in accordance with Hydroworks written instructions, for the period of the warranty. The standard warranty period is 1 year. The warranty period begins once the separator has been manufactured and is available for delivery. Any components determined to be defective, either by failure or by inspection, in material and workmanship will be repaired, replaced or remanufactu replace an entire insert or concrete section, or the complete unit. This warranty does not cover shipping charges, damages, labor, any costs incurred to obtain access to the unit, any costs to repair/replace any surface treatment/cover after repair/replacement, or other charges that may occur due to product failure, repair or replacement. This warranty does not apply to any material that has been disassembled or modified without prior approval of Hydroworks, LLC, that has been subjected to misuse, misapplication, neglect, alteration, accident or act of God, or that has not been installed, inspected, operated or maintained in accordance with Hydroworks, LLC instructions and is in lieu of all other warranties expressed or implied. Hydroworks, LLC does not authorize any representative or other person to expand or otherwise modify this limited warranty. The owner shall provide Hydroworks, LLC with written notice of any alleged defect in material or workmanship including a detailed description of the alleged defect upon discovery of the defect. Hydroworks, LLC should be contacted at 136 Central Ave., Clark, NJ 07066 or any other address as supplied by Hydroworks, LLC. (888-290-7900). This limited warranty is exclusive. There are no other warranties, express or implied, or merchantability or fitness for a particular purpose and none shall be created whether under the uniform commercial code, custom or usage in the industry or the course of dealings between the parties. Hydroworks, LLC will replace any goods that are defective under this warranty as the sole and exclusive remedy for breach of this warranty. Subject to the foregoing, all conditions, warranties, terms, undertakings or liabilities (including liability as to negligence), expressed or implied, and howsoever arising, as to the condition, suitability, fitness, safety, or title to the Hydroworks HydroStorm are hereby negated and excluded and Hydroworks, LLC gives and makes no such representation, warranty or undertaking except as expressly set forth herein. Under no circumstances shall Hydroworks, LLC be liable to the Purchaser or to any third party for product liability claims; claims arising from the design, shipment, or installation of the HydroStorm, or the cost of other goods or services related to the purchase and installation of the HydroStorm. For this Limited Warranty to apply, the HydroStorm must be installed in accordance with all site conditions required by state and Hydroworks, LLC expressly disclaims liability for special, consequential or incidental damages (even if it has been advised of the possibility of the same) or breach of expressed or implied warranty. Hydroworks, LLC shall not be liable for penalties or liquidated damages, including loss of production and profits; labor and materials; overhead costs; or other loss or expense incurred by the purchaser or any third party. Specifically excluded from limited warranty coverage are damages to the HydroStorm arising from ordinary wear and tear; alteration, accident, misuse, abuse or neglect; improper maintenance, failure of the product due to improper installation of the concrete sections or improper sizing; or any other event not caused by Hydroworks, LLC. This lim purchaser for claims related to the HydroStorm, whether the claim is based upon contract, tort, or other legal basis.