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HomeMy WebLinkAbout07/24/2019 - Revised Drainage Report & Stormwater Management Plan (Part 1) - 481 Sutton Street North Andover Adult Center 1 Surry Drive North Andover, Massachusetts Applicant Town of North Andover Architect Catlin + Petrovick Architects PC , . � e Civil Engineer, Landscape Architect & Site Planner � ° LL DeVellis Zrein Inc. CIVI PO Box 307 tR Foxboro, MA 02035 a � www.develliszrein.com Rev. July 24, 2019 1 Adul�Center NOth • - 1 Drainage Report 1.0 Executive Summary 2.0 Existing Conditions Description of Contributing Area Existing Drainage Areas Soil Conditions Existing Drainage Area Summary Peak Discharge Runoff Rates 3.0 Proposed Conditions Description of Contributing Area Proposed Drainage Areas Proposed Drainage Area Summary Peak Discharge Runoff Rates Summary of Results 4.0 Methodology and Design Criteria Hydrologic Model Design Storms Time of Concentration Curve Numbers Design Criteria Rational Method 5.0 DEP Stormwater Management Standards 6.0 Operation and Maintenance Plan Appendix A - Hydrologic Calculations and Drain Pipe Calculations Hydrologic Model -Existing Conditions Existing Conditions Calculations Hydrologic Model -Proposed Conditions Proposed Conditions Calculations Appendix B —Supporting Calculations TSS Removal Calculations Infiltration Volume Calculations Pipe Calculations Appendix C—Test Pit Data Appendix D—Reduced Site Plans Deyellis Zrein, Inc. July 24,2019 2 'Adult North •• Drainage Report 1 . Executive Summary The Town of North Andover is proposing a new Adult Center to be located at the intersection of Surrey Drive and Sutton Street at 1 Surry Drive in North Andover, Massachusetts. This project consists of the redevelopment of the property and the construction of one building with associated site improvements, parking, landscaping, patios and walkways, stormwater mitigation and underground utilities. The site currently consists of two 2-family homes on Surrey Drive and Sutton Street. There are no rivers or wetlands associated with the Site or nearby and the Site is outside of any FEMA-FIRM 100 year flood zones or Natural Heritage areas of protected wildlife or vegetation. This report addresses the drainage characteristics of the proposed redevelopment project with respect to current and future stormwater runoff. It qualifies and quantifies the drainage mitigation with respect to stormwater runoff volumes, runoff rates, and stormwater quality as well as the addressing sediment and runoff controls during and after the construction process. This project is west of a multifamily site development planned project currently being designed and permitted concurrently but separately with this project. A portion of this project will be master planned with the abutting project with respect to site improvements such as access drives and utilities. DeVellis Zrein Inc. (DZI) has analyzed the pre-development and post-development conditions of the project site and developed a stormwater management plan to mitigate the impacts resulting from this proposed project. The report addresses the stormwater maintenance protocol required to help ensure that the drainage system is maintained properly and achieve longevity and effectiveness. The proposed construction will increase the impervious surface area on-site and the stormwater management system has been designed to mitigate any increase in stormwater runoff to ensure that the post-development peak runoff rate from the site will be less than to the existing peak runoff rates. Regulations require an applicant to match the rate in which stormwater leaves the Site. The future stormwater runoff from the development area will be reduced with drainage improvements such as a closed piping system with catch basin water quality control structures, an underground stormwater infiltration/detention basin and rain gardens. The future maintenance and upkeep of the site will be the responsibility of the Town of North Andover. The stormwater design addresses ease of parking lot maintenance concerns while meeting the all of the state and town stormwater requirements and standards. Massachusetts Performance Standards and Regulations for Stormwater Management "Best Management Practices" have all been exceeded. DeVellis Zrein, Inc. July 24,2019 3 1 •ult'Center -North •• Drainage Report The following narrative provides a description of both the existing and proposed site conditions, and the methodology for design and implementation of stormwater management systems for the project. 2. Existing Conditions The project site is approximately 1.8 acres, located at the intersection of Surrey Drive and Sutton Street at 1 Surry Drive and is comprised of lots to be combined during the permitting and development process. For the purpose of this report, the Site will be described as one site. There are no Massachusetts Department of Environmental Protection (DEP) regulatory resources on site or within jurisdictional buffer limits. The site is serviced by Municipal water and sewer and there are no wells or on-site septic systems. The site will be accessed from Sutton Street through a shared drive with the abutting development and it will have an exit to Surrey Drive. The site is currently fully developed and can be generally described as residentially landscaped with two family homes, driveways, sheds, grass and trees with residential utilities. The topography is gentle sloping with a 6 foot grade change across the Site. The majority of the Site slopes from east to west towards Surrey Drive with a small area sloping towards the north onto Sutton Street. The elevation ranges from approximately 164-feet (ft) at the northeast area of the Site to approximately 158 ft at the west area of the site. Description of Contributing Area The following is a brief description of the drainage area: The analysis has been prepared to identify each existing drainage area and the design has been performed to reduce pre- and post- runoff conditions to each area. The existing development area is approximately 1.8 acres and the area of effective drainage study is approximately 1.5 acres (Figure EX-1) and is categorized as with one distinct watersheds, EX-1 which is tributary to the Surrey Drive and Sutton Street closed drainage system. DZI has performed test pits throughout the site to determine subsurface conditions and current and historic high groundwater levels on the Site. For the purpose of this hydrologic analysis, the following assumptions were made: • Whenever possible, the property line and/or an arbitrary line, outside the limit of proposed work are delineated as the watershed boundary. • The total watershed area for the existing conditions is used as the comparison base for the watershed area in the proposed conditions. DeVellis Zrein, Inc. July 24,2019 4 WATERSHED LIMIT WATERSHED AREA f� `StJ 70N STREET DP DISCHARGE POINT n N l � IN P 3 VD l L _ 0' 25' 50' 100' Site Planning,Civil Engineering,Landscape Architecture Sketch No. Job#: Po Box 307 D I `Foxborough,MA �X Drawn by: IAZ Checked By: :508.473.41 14 phone illllldevelliszrein.com _ Date: 05.20.19 Rev.07.11.19 eVellis Zrein Inc. Project North Andover Scale: 1"=50' Title: Existing Watershed Map Adult Center Adult Center Drainage Report ��y�'| ����yl^J'f^��y�«� ��~�|| Conditions .~~ The soils are defined by the Soil Conservation Services (SCS) Soil Survey of Essex County, M8SS8ChUSettG. The site is comprised of one soil type, Type C with a small portion categorized 8o Urban Land. See copy of the S08 Soils Survey Of Essex County 81the end U/this memo. The following table lists the soil designation, soil name and the soil group, Table 1-S[S Soil Types Map Soil Name Soil Group Designation 305B Paxton fine sandy loam, C 3 tU8 percent slopes 602 Urban Land DOn8 Test pits have been performed in the areas of the stormwater infiltration system and rain garden areas. The soil o1uamdiouhon within these test pits are used for the ouulynix vviUdu. Existing Drainage Area Summary The following table Su0rD8riz8S the existing drainage area, including the p8[UO8Dt information used for the hVd[O|OgiC 8O8|ySiS: Existing Conditions Ora|nogeArea - Characteristics Drainage Area Curve Tc Area (acres) Number (min.) Peak Discharge Runoff Rates The existing peak flow rates, tributary to the drainage point, were calculated for the 0.5" and the 2, 10, and 100-ye8[ Gtnrnn events in 8uoo[d8ncm with guidelines given in DEP'e 8to[rnvv8te[ Management Policy. Results are presented in the f0||0vviDg SO8tiOD of this report. Flofe[ to Existing VV@[e[Sh9d Plan for 8delineation 0f the watershed 8[e8S and their respective points of concentration. July 24,2818 6 3 Hydrologic Soil Group—Essex County,Massachusetts,Northern Part 3 (North Andover Senior Center) F F n � 326123 326170 326220 326270 326320 326370 326420 325470 326520 3265M 42'42'45'N -�- b _� 42o 42'45"N r Q y_ h P V C V oil M n may mot b� valid at tads sc.I�. � 420 42'35'N 42o 42'35'N 325120 325170 326220 32EM 326320 326M 325420 325470 325E20 326M 3 3 Map Scale:1:2,280 iF printed on A landscape(11"x 8.5")sheet F Meters N " 0 30 60 120 180 Feet 0 100 200 406 600 Map projection:Web Mercator Gomercoordinates:WGS84 Edgetcs:UTM Zone 19N WGS84 USDA Natural Resources Web Soil Survey 5/18/2019 lim Conservation Service National Cooperative Soil Survey Page 1 of 4 Hydrologic Soil Group—Essex County,Massachusetts,Northern Part (North Andover Senior Center) MAP LEGEND MAP INFORMATION Area of Interest(AOI) ® C The soil surveys that comprise your AOI were mapped at Area of Interest(AOI) 1:15,800. ® CID Soils 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 0 AID water Features line placement.The maps do not show the small areas of Streams and Canals contrasting soils that could have been shown at a more detailed O B scale. ED Transportation B/D Rails Please rely on the bar scale on each map sheet for map 0 C Interstate Highways measurements. 0 CID US Routes Source of Map: Natural Resources Conservation Service Web Soil Survey URL: 0 D Major Roads Coordinate System: Web Mercator(EPSG:3857) Q 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 q distance and area.A projection that preserves area,such as the o, BE Aerial Photography Albers equal-area conic projection,should be used if more AID accurate calculations of distance or area are required. + B This product is generated from the USDA-NRCS certified data as BID of the version date(s)listed below. C Soil Survey Area: Essex County,Massachusetts,Northern Part Survey Area Data: Version 14,Sep 7,2018 CID Soil map units are labeled(as space allows)for map scales D 1:50,000 or larger. r Not rated or not available Date(s)aerial images were photographed: Aug 29,2014—Sep Soil Rating Points 19,2014 ® A The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background AID imagery displayed on these maps.As a result,some minor B shifting of map unit boundaries may be evident. BID USDA Natural Resources Web Soil Survey 5/18/2019 Conservation Service National Cooperative Soil Survey Page 2 of 4 Hydrologic Soil Group—Essex County,Massachusetts,Northern Part North Andover Senior Center Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 305B Paxton fine sandy loam, C 15.3 65.3% 3 to 8 percent slopes 305C Paxton fine sandy loam, C 1.0 4.4% 8 to 15 percent slopes 310B Woodbridge fine sandy C/D 1.8 7.7% loam,3 to 8 percent slopes 421 B Canton fine sandy loam, B 0.0 0.0% 0 to 8 percent slopes, very stony 602 Urban land 4.7 20.1% 651 Udorthents,smoothed A 0.6 2.5% Totals for Area of Interest 23.5 100.0% USDA Natural Resources Web Soil Survey 5/18/2019 Conservation Service National Cooperative Soil Survey Page 3 of 4 9 Hydrologic Soil Group—Essex County,Massachusetts,Northern Part North Andover Senior Center 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 5/18/2019 Conservation Service National Cooperative Soil Survey Page 4 of 4 10 lAdult Center North- • Drainage Report 3. Proposed Conditions The proposed project consists of the construction of a two-story Adult Center building with associated access drives, parking, a pervious patio and walkways, rain gardens, landscaping, utility services and drainage improvements. When impervious surfaces such as pavement and roof top are proposed, there will be an increase in stormwater runoff if mitigation is not provided. A stormwater management system is required to maintain the characteristics of the existing watersheds to the extent practicable. Meeting current conditions are the requirement. Runoff rates at the discharge point are required to be maintained to existing conditions by temporarily holding runoff and slowly releasing it off site to meet existing peak flow rates. The stormwater objectives of this project are summarized as follows: 1. Decrease the rate of runoff by providing stormwater retention 2. Provide a safe and environmentally sustainable solution to infiltrate stormwater on site such as rain gardens and separated systems. 3. Separate pavement runoff from roof runoff 4. Incorporate a stormwater system into aesthetically pleasing passive open space use 5. Provide a system that has longevity with minimal expense with a well understood maintenance protocol 6. Exceed proper engineering standards of North Andover's DPW the DEP The proposed development site will consist of two distinct watershed areas, PR-1 A and PR-1 B (Figure PR). Drainage area PR-1 A is approximately 0.8 acres and drain into rain gardens or a closed drainage system and enter into the onsite underground infiltration/detention system below the parking lot. Drainage area PR-1 B is approximately 0.8 acres and will be collected into the closed drainage system. These two areas will be combined to then connect to the Surrey Drive underground drainage system. The peak rates of runoff will not exceed the existing rates of runoff. Detailed description of each contributing area is provided below: Drainage Area PR-1 A Drainage Area PR-1 A encompasses the entire roof and perimeter landscape and parking areas surrounding the building with the following mitigation items. Roof Runoff: The building's roof is pitched to the sides and collected with piping. Stormwater runoff is considered clean and suitable for direct infiltration into the ground to provide groundwater recharge. The roof runoff will be collected and either piped directly to an on-site "rain garden" located behind the building aside the pervious. The raingarden will DeVellis Zrein, Inc. July 24,2019 11 ®� WATERSHED LIMIT WATERSHED AREA SUTTON STREET DP-1--■ DISCHARGE POINT .000. 7 t :::::::;:; .:::...:.; 9 ......... ... PR �:. DP-1 P -1A PR-1A ®• PR-1B w n N ®� O ■ �® OPR-1B M ............................... >- ■��■ -:1' r son ■-®-m-■MEMO a®®■® - - - 0' 25' 50' 100' Site Planning,Civil Engineering,Landscape Architecture Sketch No. Job#: Po Box 307 Poxborough,MA PR Drawn by: IAZ Checked By: D — 508.473.41 14 phone ____ _ develliszrein.com Date: 05.20.19 Rev.07.11.19 eVeIIIS Zf ein Inc. Project North Andover Scale: ill=50' Title: Proposed Watershed Map Adult Center Adult Center L North Andover, Drainage Report fill during rain events and drain dry through infiltration with an overflow provided into the closed drainage system. The front drop off area will sheet flow into a "rain garden" located at the front of the building. All areas within PR-1 A will eventually enter into the subsurface stormwater infiltration/detention area to reduce the rates of runoff by collection and infiltration. The volume of runoff contained within the rain gardens were not factored into the mitigation for peak attenuation as a safety factor in the design. Rain Gardens: Rain Gardens are proposed at the front and rear of the Adult Center.The rain gardens will support a variety of indigenous plants that can survive in wet and dry conditions.The top of the rain garden is flush with the surrounding grade and will provide easy access for garden enthusiasts. The rain garden is placed in areas that are not"out of sight/out of mind"as they can be easily incorporated into the outdoor programming within close proximity to the pervious patio and front entry. These rain garden have been designed to collect and in filtrate stormwater, however this drainage analysis has not,factored that into the calculations in order to provide a higher safety _factor when calculating the f•eduction in runoff volumes and rates. Water Quality Inlets: Where water is not collected by the raingardens, catchbasins equipped with water quality units capable of providing 80%total suspended solids (TSS) removal will capture, clean and route the stormwater to the onsite detention /detention basin or the town's closed drainage system. Detention /Infiltration Basin: An underground stormwater infiltration and detention basin is located in the western portion of the lot. It is equipped with pipes and manholes to provide access and inspection. The stormwater enters into the site and travels through a series of perforated pipes surrounded by washed crushed stone that allows stormwater to enter into the ground. This basin mitigates the runoff rate of stormwater leaving the site. Drainage Area PR-1 B Drainage Area PR-1 B encompasses parking and perimeter areas not incorporated into the above area. The area continues to sheetflow toward the western perimeter towards and into the Surrey Drive closed drainage system. To provide drainage protection to the southern abutters, a gentle swale and low collection areas are provided to direct water into the on-site mitigation system and away from the neighbors as well as provide added infiltration. A series of water quality units are provided to collect the stormwater and clean it to DEP standards. DeVellis Zrein, Inc. July 24,2019 13 Drainage Report Proposed Drainage Area Summary The following summarizes the proposed drainage areas, including the pertinent information used for the hydrologic analysis: Proposed Conditions Drainage Area Characteristics Summary: Drainage Area Area Curve T, (min.) (Acres) Number PR-1A 0.80 90 6.0 PR-1 B 0.80 80 6.0 Peak Discharge Runoff Rates The proposed peak flow rates, tributary to the drainage point, were calculated for the 2, 10 and 100-year storm events in accordance with guidelines given in DEP's Stormwater Management Policy. Results are presented in the following table. Refer to Proposed Watershed Plan for a delineation of the watershed areas and their respective points of concentration. Summary of Results As previously stated, the resultant post-development peak discharge rates for the discharge points are less than the pre-development peak discharge rates. The following table provides a summary of the pre and post development data. The following table demonstrates peak flows at the design points for each of the design storms has been met. Peak Rates of Runoff Leaving the Site: Location 0.5" rainfall 2-Yr Storm 10-Yr Storm 25-Yr Storm 100-Yr Storm Exist Prop Exist Prop Exist Prop Exist Prop Exist Prop (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) DP-1 0.00* 0.00* 1.54 1.31 3.53 3.44 5.17 14.98 8.93 7.82 *The HydroCAD program acknowledges there may be some runoff,however the small size of the site and the very low flow rounds the pre-and post-runoff to zero. DeVellis Zrein, Inc. July 24,2019 14 Adult Andover,North Drainage Report 4. Methodology and Design Criteria Hydrologic Model The drainage analysis was performed using the Soil Conservation Service (SCS) TR-20 method and the drainage software HydroCAD 7.10, as developed by Applied Microcomputer Systems. Data used in the design is as follows: Design Storms Rainfall data for the 0.5" rainfall, 2, 10, 25 and 100- year frequency rainfall events (for a 24-hour precipitation) was taken from the Rainfall Frequency Atlas of the Unites States (TP-40). The following table outlines the rainfall used for the TR-20 method. Rainfall Data Storm Event Rainfall 0.5'$ 0.5" 2-Year 3.20 inches 10-Year 4.80 inches 25-Year 6.0 inches 100-Year 8.60 inches Time of Concentration The `time of concentration' (T,,) for each watershed was determined by finding the time necessary for runoff to travel from the hydraulically most distant point in the watershed to the point of concentration. The travel path was drawn based on the topography and the time was calculated using the TR-55 Method and HydroCAD. A minimum T, of 6.0 minutes was used. Curve Numbers Based on the cover type and hydrologic soil group, a weighted curve number (CN) was determined for each of the watersheds utilizing the SCS TR-55 method. DeVellis Zrein, Inc. July 24,2019 15 Drainage Report 5. Department of Environmental Protection Stormwater Management Standards Standard 1:No new stormwater conveyances (e.g. outfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. The project does not propose any new untreated outfalls or discharge of untreated water into wetlands or waters of the Commonwealth. All proposed impervious surfaces will be collected and treated with a catch basin, water quality units, rain gardens and treated and detained on-site with a detention / recharge system. Standard 2:Stormwater management systems shall be designed so that the post-development peak discharge rates do not exceed pre-development peak discharge rates. This Standard may be waived for discharges to land subject to coastal storm flowage as defined in 310 CMR 10.04. The project will reduce the post-development stormwater peak discharge rate to pre-development conditions via infiltration pipes and a detention / recharge system. Standard 3:Loss of annual recharge to groundwater shall be eliminated or minimized through the use of 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 determined in accordance with the Massachusetts Stormwater Handbook. The intent of this standard is to ensure that the infiltration volume of precipitation into the ground under post-development conditions is at least as much as the infiltration volume under pre-development conditions. Standard 3 requires the restoration of recharge, using infiltration measures and careful site design. The project will provide groundwater recharge. The infiltration provided within the detention / recharge system recharges stormwater back into the ground per the required amounts. The NRCS classifies soils into one hydrologic groups, C, indicative of the minimum infiltration obtained for a soil after prolonged wetting. Group A soils have the lowest runoff potential and the highest infiltration rates, while Group D soils have the highest runoff potential and the lowest infiltration rates. The required recharge volume, the DeVellis Zrein, Inc. May 24,2019 Revised July 24,2019 16 AduKenter North Andover, MAI Drainage Report stormwater volume that must be infiltrated, was determined using existing site conditions and the infiltration rates set forth below. Hydrologic Group Volume to Recharge (Total Impervious Area) Hydrologic Volume to Recharge Total Group Impervious Area A 0.60 inches of runoff B 0.35 inches of runoff C 0.25 inches of runoff D 0.10 inches of runoff The soils are defined by the Soil Conservation Services (SCS) Soil Survey of Middlesex County, Massachusetts. The site is comprised of one soil type. Based on the published mapping and confirmed with the on-site soil testing, it was determined that the developable areas fall entirely within category C. Standard 4: Stormwater management systems shall be designed to remove 80% of the average annual post-construction load of Total Suspended Solids (TSS). This standard is met by this project: a) Suitable practices for source control and pollution prevention are identified in a long-term pollution prevention plan, and thereafter are implemented and maintained; b) Structural stormwater best management practices are sized to capture the required water quality volume as determined in accordance with the Massachusetts Stormwater Handbook; and c) Pretreatment is provided in accordance with the Massachusetts Stormwater Handbook. The stormwater runoff from the proposed parking spaces will exceed the 80%TSS removal as the project is equipped with catchbasins/water quality units, and a detention/ recharge basin. A long term Operation and Maintenance Plan associated with this project has been designed and is included within this report. DeVellis Zrein, Inc. May 24,2019 Revised July 24,2019 17 • • • 1 111 - Drainage Report Standard 5: Regards land uses with higher potential pollutant loads: This is Not Applicable. Standard 6:Stormwater discharges within the Zone 11 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. This is Not Applicable. Standard 7: Regards redevelopment projects: This project is not classified as a redevelopment project 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, sedimentation, and pollution prevention plan) shall be developed and implemented. The Grading and Drainage Plan contains provisions for the construction related items such as silt controls and Operation and Maintenance provisions for construction and post construction activities. This project schedule is to be coordinate with the abutting residential development and as such, items like shared earthwork, construction entrances, final limits of work etc. need more coordination efforts. The Site Drawings issued for Construction will contain more information and will be provided to the town throughout the process. A NPDES/SWPPP will be required and when a contractor is awarded the project, this plan will be submitted with all of the appropriate information on it. Standard 9: A Long -Term Operation and Maintenance (O&M) Plan shall be developed and implemented to ensure that stormwater management systems function as designed. The Long-Term Operation and Maintenance Plan has been prepared within this report and referenced on the plans that include the routine and non-routine maintenance tasks to be undertaken after construction is complete and a schedule for implementing those tasks. Standard 10: All illicit discharges to the stormwater management system are prohibited. DeVellis Zrein, Inc. May 24,2019 Revised July 24,2019 18 • Drainage Report Standard 10 prohibits illicit discharges to stormwater management systems. By acceptance of this document, the Town of North Andover acknowledges that the stormwater management system is the system for conveying, treating, and infiltrating stormwater on-site, including stormwater best management practices and any pipes intended to transport stormwater to the groundwater, a surface water, or municipal separate storm sewer system. Illicit discharges to the stormwater management system are discharges that are not entirely comprised of stormwater. This document shall serve as the Illicit Discharge Compliance Statement verifying that no illicit discharges exist on the site and within the pollution prevention plan measures to prevent illicit discharges to the stormwater management system, including wastewater discharges and discharges of stormwater contaminated by contact with process wastes, raw materials, toxic pollutants, hazardous substances, oil, or grease. DeVellis Zrein, Inc. May 24,2019 Revised July 24,2019 19 FAT 11, ® Drainage Report 6.Operation and Maintenance Plan Introduction DeVellis Zrein Inc. has prepared this report as a guide to establish maintenance protocol for the on-site drainage improvements serving the Proposed Adult Center. The goal of the Storm Water Operation and Maintenance Plan is not only to protect off-site wetlands and water resources abutting the site, but also to protect those resources in the region that may be affected by the activities at the site. The proposed site drainage improvements include: • Water Quality Inlets • Rain Gardens • Pervious Patio Pavers • Drain pipe network; • Detention and Infiltration System The proposed water quality treatment measures will result in improved removal of the total suspended solids (TSS) load in runoff from the site for the proposed parking improvements as well as throughout the existing parking areas. An effective drainage maintenance program will ensure that the removal of TSS from the stormwater runoff continues for the life of the facility. The Operation and Maintenance Plan will be implemented by the Owner of the property. Source Control The first tier of non-structural controls includes a comprehensive source control program of regular sweeping and maintenance of the stormwater management components. Pavement Sweeping Program While certain types of street sweepers are not effective for the removal of fine particulates and pollutants associated with them, most are quite effective for the removal of large quantities of sand, grit, and assorted inorganic and organic debris. Larger material carried in storm water poses an environmental threat not only by degrading aesthetics, but may also contribute pollutants as it degrades over time. In addition, larger materials may clog conveyance systems, reduce the efficiency and longevity of treatment systems and ultimately result in more maintenance downstream. The removal of contaminants directly from paved surfaces before contact with storm water is a valuable method for reducing pollutant loading in stormwater. It is proposed that the parking and drive areas will be cleaned with a street sweeper on a quarterly basis with at least four sweepings per year or more often as required if conditions require it. DeVellis Zrein, Inc. May 24,2019 Revised July 24,2019 20 ,Adult Center North Andover, Drainage Report Water Quality Unit The new water quality units at the site will be equipped with specific catchment systems that will need to be cleaned per manufacturer's specifications. The specific water quality unit is in the process of being discussed with the town and this section will be revised when the final structures have been chosen. Rain Garden The rain garden should be cared for like any flower garden with several exceptions. The plant selection has been made by a landscape architect and represents a selection that is indigenous to New England, can survive in wet and dry conditions with little use of fertilizers or excessive watering. The bottom strip of stone shall be maintained free of organics and dirt to allow infiltration. The inlet pipes or curb openings shall be kept clear of obstruction. Side slopes shall be kept planted and side erosion shall be avoided. Note that the drainage system's ability to mitigate peak runoff is not effected by the installation of the rain gardens and they are being proposed only as an amenity to the site. Pervious Patio Pavers While certain types of leaf blowers are not effective for the removal of fine particulates and pollutants associated with them, most are quite effective for the removal of sand, grit, and assorted inorganic and organic debris. Larger material carried in storm water poses an environmental threat not only by degrading aesthetics, but may also contribute pollutants as it degrades over time. In addition, larger materials may clog conveyance systems, reduce the efficiency and longevity of treatment systems and ultimately result in more maintenance downstream. The removal of contaminants directly from paver surfaces before contact with storm water is a valuable method for reducing pollutant loading in stormwater. It is proposed that the pervious patio paver patio be cleaned with a leaf blower on a semi-annual basis (spring and fall), with at least two blowings per year. Note that the drainage system's ability to mitigate peak runoff is not effected by the installation of the pervious pavers and they are being proposed only as an amenity to the site. Detention and Infiltration System The actual removal of sediments and associated pollutants and trash occurs only when inlets are cleaned out; therefore, regular maintenance is required. The stormwater that enters into the infiltration system will be devoid of sediment due to the TSS removal within the components leading up to the system. In order for sediment to reach the system, it would have to pass through the raingardens, catch basins and water quality inlets before reaching the infiltration system. All of the treatment components referenced provide a higher level of sediment removal than required and it is very unlikely that sediment will accumulate in the system. If sediment is observed DeVellis Zrein, Inc. May 24,2019 Revised July 24,2019 21 ® - M • • Drainage Report in the system it can be easily removed with a vacuum truck similar to a septic system pumper. The underground detention and infiltration basin has been designed with oversized manholes and pipes for easy access and viewing. There are 4-foot diameter manholes at corners of the system (4 total) and 18-inch header pipes along the sides connecting to 18-inch diameter perforated infiltration pipes, accessed from each manholes that are provided for easy viewing and maintenance. During Construction • Prior to construction, install tree protection and erosion and sediment control measures as shown on the plan and details. • The site contractor shall inspect all sediment and erosion control structures after each rainfall event and at the end of the working day. • All measures shall be maintained in good working order. If repair is necessary, it shall be initiated within 24 hours of inspection. • Silt shall be removed from the silt soxx if 3-inches or greater and as needed. • Sediment shall be contained within the construction site and away from drainage structures. • Damaged or deteriorated erosion control measures will be repaired immediately after identification • The silt soxx shall be kept in close contact with the ground and reset as necessary. • The contractor's site superintendent will be responsible for inspection, maintenance and repair activities. • All disturbed areas will be treated with 4" of topsoil and seed. • Remove siltation controls upon completion of permanent vegetation over disturbed areas. • A preconstruction meeting shall take place prior to construction and the contractor shall present a plan for vehicle entrance/exiting and vehicle washout areas. At the time of this report, there is no contractor involved in the project. It is the opinion of DeVellis Zrein, Inc. that it is in the best interest of the Town of North Andover not to dictate the means and methods of the specific site setup for the contractor, but rather require the contractor to provide this information prior to construction. Stormwater Management System Owner This site is owned by the Town of North Andover as well as a private party associated with the residential development concurrently being permitted. The logistics of construction and future maintenance is currently being coordinated and this will be updated. DeVellis Zrein, Inc. May 24,2019 Revised July 24,2019 22 ,Adult Center North Andover, Drainage Report Estimated Operations Budget It is not anticipated that the stormwater maintenance required would be considered extraordinary. A yearly estimated operations budget for consideration to carry out the Operations and Maintenance Plan requirements is as follows: • $0: Inspect the perimeter landscaping annually, in the spring, for erosion of side slopes, embankments, and accumulated sediment. Necessary sediment removal, earth repair and/or reseeding shall be performed immediately upon identification. • $1000: Clean all water quality structures annually to remove accumulated sand, sediment, and floatable products. Dispose and transport accumulated sediment off-site in accordance with applicable local, state and federal guidelines and regulations. This should be incorporated into the DPW routine maintenance protocol. • $400: Remove accumulated leaves and debris from catch basins and outlet openings. • $500: Routinely pick up and remove litter from the parking areas, islands and perimeter landscape area, in addition to pavement sweeping. • $500: Replant/replenish the rain gardens with specific plantings. Trim and prune as needed. DeVellis Zrein, Inc. May 24,2019 Revised July 24,2019 23 MKCIIW �,mlremnuyl Drainage Report Appendix A — Hydrologic Calculations and Drain Pipe Calculations • Hydrologic Model - Existing Conditions Stormwater Runoff Area Calculations Existing Conditions Calculations 0.5" Storm 2-Year Storm 10-Year Storm 25-Year Storm 100-Year Storm • Hydrologic Model - Proposed Conditions Stormwater Runoff Area Calculations Proposed Conditions Calculations 0.5" Storm 2-Year Storm 10-Year Storm 25-Year Storm 100-Year Storm DeVellis Zrein, Inc. May 24,2019 Revised July 24,2019 24 MuItcenter Mrth Andover, Drainage Report Hydrologic Model - Existing Conditions DeVellis Zrein, Inc. May 24,2019 Revised July 24,2019 25 EX � l Site Subcat Reach on ink Routing Diagram for Existing Conditions LL Prepared by DeVellis Zrein Inc., Printed 7/20/2019 HydroCAD®10.00-24 s/n 08761 ©2018 HydroCAD Software Solutions LLC 26 North Andover Senior Center Existing Conditions Prepared by DeVellis Zrein Inc. Printed 7/20/2019 HydroCAD® 10.00-24 s/n 08761 ©2018 HydroCAD Software Solutions LLC Pa ece22 Area Listing (all nodes) Area CN Description (acres) (subcatchment-numbers) 1.025 61 >75% Grass cover, Good, HSG B (EX-1) 0.489 98 Buildings, Paved Areas HSG B (EX-1) 1.514 73 TOTAL AREA 27 North Andover Senior Center Existing Conditions Type ///24-hr850 InchRainfall=0.50" Prepared Summary for Subcafchment EX-1: Site Runoff O.OUnfs @ 0.80hns, Vo|umm= 0.008of, Dooth= 0.00" Runoff by8C8TR-20 method, UH=SOS' Weighted-CN, Time 8p8n= 0.00-38.00 h[s, di= 0.05 hra Tvoo U| 24-hr 0.50 Inch Rainf8U=0.50" Area (sf) ON Description ° 21.317 98 Buildings, Paved Areas H8G B 44 65,970 73 Weighted Average 44,653 67.69% Pervious Area 21,317 32.31% |mpon/ioUS Area Tc Length Slope Velocity Capacity Description 47 35 0.0150 0.12 Sheet Flow, P1 Grass: Short n= O.150 P2= 3.20" 2.0 llU 0.0180 0.94 Shallow Concentrated Flow, P2 Short Grass Pasture Kv= 7.0fpe 0.6 111 0.8270 3.34 Shallow Concentrated Flow, P3 Paved Kv= 20.3 fps 7.3 256 Total SUbcatchmenƒ EX-1: Site Mydrogroph OM Inch R, dillifall-A.50'! � � � � � Time (hours) North Andover Senior Center Existing Conditions 7yD80/24-hr 2-yearR8infa8=320" P[8DO[8d by [}eVelliS Z[QiU Inc. Printed 7/20/2019 � Summary for SubcatchM0e0fEX-1: Site Runoff = 1.54ofs@ 12.12 h[s, Vo|Ume= 0.124af, D8pth= 0.98" Runoff byS{}8TR-2O method, UH=GC8, VV8ight8d-CN, Time 8pan= O.UO-8O.0Oh[s' dt= 0.O5hra Typo ||| 24-hr 2-yearRninfa||=3.20" Area (sf) CN Description ° 21,317 98 Buildings, Paved Areas HS{S B 85,970 73 Weighted Average 44'653 G7.89% Pervious Area � 21,317 32.31% Impervious Area � To Length Slope Velocity Capacity Description ' 4.7 35 0.0150 8.12 Sheet F|oxx, P1 � Gr8aa: 8hort n= 0.150 P2= 3.20" � 2.0 110 0.0180 8.94 Shallow Concentrated Flow, p2 Short Grass Pasture Kv= 7.0fpa � 0.6 111 0.0278 3.34 Shallow Concentrated Flow, P3 � Paved Kv= 20.3 fps � 7.3 258 Total � � Subcatchment EX~1: Site Mydrogmopb Runoff Are9--' 65,9, 7&Sf Runoff a � � � � LL � � � � Time (hours) North Andover Senior Center Existing Conditions Type III 24-hK /0-yea/Ra/ht38=4.80" Prepared by [)8\/8lUS 7[eiD Inc. Printed 7/20/2019 Summary for SubcatchmentEX-1: Site Runoff = 3.53 cfa @ 12.11 hrs, Volume~ 0.288 af, Depth~ 2.12" Runoff bv8CSTR-20 method, UH=GC8, VVeighted'CN, Time 8pan= 0.8U'3U.0Ohro, dt= 0.U5hra Type III 24-hr 18'ye8rH8inf8U=4.80" Area (sf) CN Description ° 21,317 98 Buildings, Paved Areas H8GB 44 85,970 73 Weighted Average 44.653 67.69% Pmn/iuua Area 21.317 32.31% Impervious Area To Length Slope Velocity Capacity Description 4.7 35 0.8150 012 Sheet Flow, P1 Grasa: 8hort n= 0150 P2= 3.20" 2.0 118 0.0180 0.94 Shallow Concentrated Flow, P2 Short Grass Pasture Kv= 7.0fps 0.6 111 0.0270 3.34 Shallow Concentrated Flow, P3 Paved 73 256 Total SDbcatch0Nent EX-1: Siƒe Mydrmgmph 4. Runoff Area-65,9MM 3.5 cis � - � � � North Andover Senior Center Existing Conditions Type ///24-hr 25-Year Rainfall=6.00" Prepared by DeVellis Zrein Inc. Printed 7/20/2019 HydroCADOIO.00-24 s/nO8761 @2018 HydroCAD Software Solutions LLC Page 6 Summary for Subcatchment EX-1: Site Runoff = 5.17 cfs @ 12.11 hrs, Volume= 0.390 af, Depth= 3.09" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-30.00 hrs, dt= 0.05 hrs Type III 24-hr 25-Year Rainfall=6.00" Area (sf) CN Description 21,317 98 Buildings, Paved Areas HSG B 44,653 61 >75% Grass cover, Good, HSG B 65,970 73 Weighted Average 44,653 67.69% Pervious Area 21,317 32.31% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cf s) 4.7 35 0.0150 0.12 Sheet Flow, P1 Grass: Short n= 0.150 P2= 3.20" 2.0 110 0.0180 0.94 Shallow Concentrated Flow, P2 Short Grass Pasture Kv= 7.0 fps 0.6 111 0.0270 3.34 Shallow Concentrated Flow, P3 Paved Kv= 20.3 fps 7.3 256 Total Subcatchment EX-1: Site Hydrograph 5—1 7—c-f S- 5-- i ' 'e I I! 214Ihr" Typ �25-Y6a� R, �infall 1-6.00" 4. ..... � RunoffA rea-65,PMsf Runoff V616me=0.896 of 3- 1, ' "Runoff Depith- 3.09 2 LL Flow Lengt�, ='25' 6v 2 1 J I 1. �-1.- J�. -I Td--'73'Mih lbN=13 0 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) 31 North Andover Senior Center Existing Conditions 7yDe /824-hK / /R8infall=8.60" P[eD8R3d by DeVellis Zrein Inc. Printed 7/20/2019 Summary for SDbcatchmentEX-1: Site Runoff = 8.93 ofs @ 12.11 hrs. Vo|unno= 0.675 af. Doolh= 5.35" Runoff by8C8TR-28 method, UH=S(|S, VVeighted-(}N, Time 8pan= 0.UO-3O.OUhra. dt= O.05hra Type III 24-hr 100-yea[ Rainfa||=8.60" Area (sf) CN Description 85.878 73 Weighted Average 44.653 S7.68% Pervious Area 21'317 32.31% Impervious Area To Length Slope Velocity Capacity Description 4.7 35 0.0150 0.12 Sheet Hmnv p1 Greoo: 8hod n= 8.150 P2= 3.20" 2.0 110 0.0180 0.94 Shallow Concentrated Flow, P2 Short Grass Pasture Kv= 7.0fpe 0.6 111 0.0270 3.34 Shallow Concentrated F|ovx` p3 Paved Kv= 20.3 fps 7.3 256 Total SubcatchMNent EX-1: Site Hydrograph m � � 0 LL 'iA • North • Drainage Report Hydrologic Model - Proposed Conditions DeVellis Zrein Inc. May 24,2019 Revised July 24,2019 33 �PR1 A Detained n-Detained 1 P Detention B in DP-1 Subcat Reach on �Link Routing Diagram for Proposed Conditions-PIPE Prepared by DeVellis Zrein Inc., Printed 7/20/2019 HydroCADO 10.00-24 s/n 08761 @ 2018 HydroGAD Software Solutions LLC 34