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HomeMy WebLinkAbout03/10/2025 - Revised Stormwater Report - - 430 OSGOOD STREET 3.0 PROJECT DESCRIPTION The Town of North Andover (Town) is proposing renovations at the existing athletic campus located at the North Andover High School (NAHS). The proposed improvements include (1) installing an infilled multipurpose synthetic turf field at the location of the existing baseball field, (2)the reconstruction of the existing bituminous concrete tennis courts, (3) relocation of various track and field events within the existing athletic fields, and (4) athletic lighting improvements. This report has been prepared in accordance with both the Massachusetts Stormwater Handbook and the Town of North Andover Wetland Protection Regulations. 3.1 Existing Conditions The athletic campus is located at NAHS. The existing site consists of an 8-lane running track and synthetic turf field north of the school building,and a multipurpose synthetic turf field and natural grass baseball field south of the school building.There is also a 6-court tennis battery in the south east corner of the site. The site is generally bounded by Route 133 to the west, the Cochichewick River to the south, wetlands to the east, and the Town Fire Department to the north. The parcel is zoned Residence 2 (132). Locus Map u �I ry lII r I ��1��✓� J I I jar y�' � � /�/. 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The tennis courts are located in 30A— Raynham silt loam (HSG C/D). A site soil evaluation consisting of a total of eighteen (18)test borings(performed by Nobis Group) and five (5)test pits (performed by Nobis Group) has been provided, refer to Attachment 5. Four (4) test borings were performed at the proposed athletic lighting locations at the track field for soil and foundation evaluation. Two (2) test borings were performed at the proposed athletic lighting locations at the stadium field for soil and foundation evaluation. Eight(8)test borings and five (5) test pits were performed at the proposed athletic lighting locations at the proposed multipurpose synthetic turf field for soil and foundation evaluation. Three (3) test borings were performed at the locations for potential future athletic lighting at the tennis courts for soil and foundation evaluation. The test pit logs indicate the soils at the baseball field vary between silt loam,sandy loam,and glacial till.Groundwater levels and the estimated seasonal high-water table (ESHWT) were not encountered in test pits TP-1 through TP-4. While the depth of ESHWT was observed in test pit TP-5, it should be noted that the ESHWT observations may be unreliable to perched groundwater conditions. Infiltration testing in the test pits produced an average saturated hydraulic conductivity of 0.61 in/hr,with a minimum value of 0.46 in/hr.Curve Number (CN)values for the infiltration computations were based on the hydraulic soil group (A-D)and the surface cover material (i.e. grass, pavement). The complete list of selected curve numbers is included in the drainage calculations (Refer to Attachment 7). 4.0 WETLANDS& ENVIRONMENTAL RESOURCE AREAS On November 4 and 29, 2024, LEC Environmental Consultants, Inc., (LEC) conducted a site evaluation to identify, characterize, and delineate jurisdictional Wetland Resource Areas, as determined through observations of existing plant communities, hydrologic and bankfull indicators in accordance with the Massachusetts Wetlands Protection Act (M.G.L. c. 131, s. 40) and Regulations (310 CMR 10.00), as well as the Town of North Andover Wetland Protection Regulations (Ch 190). 4.1 Wetland Resource Areas LEC determined that the Wetland Resource Areas associated with the site included Bordering Vegetated Wetland (BVW)and bank line to Cochichewick River and its associated Riverfront Area. LEC also identified the bank of an intermittent stream adjacent to the tennis court area. LEC demarcated the BVW boundaries with sequentially numbered, blaze orange surveyor's flagging tape, embossed with the words "LEC Resource Area Boundary" in bold, black print. LEC Page 2 of 164GA demarcated the bank lines with similar tape in blue. Refer to Attachment 1 for the Wetland Resource Area Analysis Report. 4.2 Performance Standards Due to proximity to wetlands, the project falls within both MassDEP state and local buffer and protection zones. The following is a summary of how the project meets the performance standards set forth in the state and local regulations: 310 CMR 10.54—Bank (3) Presumption. Where a proposed activity involves the removing,filling,dredging or altering of a Bank, the issuing authority shall presume that such area is significant to the interests specified in 310 CMR 10.54(1). The proposed work in and around the bank of the intermittent stream adjacent to the tennis courts is limited to that necessary to remove the failed culvert and pathway and perform wetland restoration in its place.This work will restore the connection of the intermittent stream as well as the two areas of bordering vegetated wetlands. 310 CMR 10.57—Land Subject to Flooding (4)(a) Bordering Land Subject to Flooding 1. Compensatory storage shall be provided for all flood storage volume that will be lost as the result of a proposed project within Bordering Land Subject to Flooding, when in the judgment of the issuing authority said loss will cause an increase or will contribute incrementally to an increase in the horizontal extent and level of flood waters during peak flows. 2. Work within Bordering Land Subject to Flooding,including that work required to provide the above-specified compensatory storage, shall not restrict flows so as to cause an increase in flood stage or velocity. The proposed project is located entirely outside of the 100-year flood zone, therefore no compensatory storage has been provided (See Attachment 4). 310 CMR 10.58—Riverfront Area 4(a) Protection of Other Resource Areas. The work shall meet the performance standards for all other resource areas within the riverfront area, as identified in 310 CMR 10.30(Coastal Bank), 10.32(Salt Marsh), 10.55(Bordering Vegetated Wetland), and 10.57(Land Subject to Flooding). When work in the riverfront area is also within the buffer zone to another resource area, the performance standards for the riverfront area shall contribute to the Page 3 of 16 4GA L,E protection of the interests of M.G.L. c. 131, §40 in lieu of any additional requirements that might otherwise be imposed on work in the buffer zone within the riverfront area. The work proposed within the 200'buffer of the Cochichewick River is limited to the installation of one(1)athletic light pole.The foundations for these poles are augured into place with limited temporary disturbance and minimal permanent disturbance, and their above ground component is limited to a 36"cylindrical foundation.All equipment setup and material lay down will take place outside of the Riverfront Area. Gale does not anticipate that the installation of this light will negatively impact the Cochichewick River. 4(b) Protection of Rare Species. No project may be permitted within the riverfront area which will have any adverse effect on specified habitat sites of rare wetland or upland, vertebrate or invertebrate species,as identified by the procedures established under 310 CMR 10.59 or 10.37,or which will have any adverse effect on vernal pool habitat certified prior to the filing of the Notice of Intent. According to the NHESP layer on the MassGIS MassMapper database, there are no NHESP mapped species within or adjacent to the project area. 4(c) Practicable and Substantially Equivalent Economic Alternatives. There must be no practicable and substantially equivalent economic alternative to the proposed project with less adverse effects on the interests identified in M.G.L. c. 131 §40. There are no practicable and substantially equivalent economic alternative to the proposed project to achieve the desired goals. 4(d) No Significant Adverse Impact. The work, including proposed mitigation measures, must have no significant adverse impact on the riverfront area to protect the interests identified in M.G.L. c. 131, §40. (5) Redevelopment within Previously Developed RiverfrontAreas;Restoration and Mitigation. Notwithstanding the provisions of 310 CMR 10.58(4)(c)and(d), the issuing authority may allow work to redevelop a previously developed riverfront area, provided the proposed work improves existing conditions. Redevelopment means replacement, rehabilitation or expansion of existing structures, improvement of existing roads, or reuse of degraded or previously developed areas. A previously developed riverfront area contains areas degraded prior to August 7, 1996 by impervious surfaces from existing structures or pavement, absence of topsoil,junkyards, or abandoned dumping grounds. 5(a) At a minimum, proposed work shall result in an improvement over existing conditions of the capacity of the riverfront area to protect the interests identified in M.G.L. c. 131 §40. Page 4 of 164GA When a lot is previously developed but no portion of the riverfront area is degraded, the requirements of 310 CMR 10.58(4)shall be met. Since the proposed work meets the general standards and will be performed entirely on a previously developed area, and the conditions are improved as detailed in the stormwater standards compliance section below(Section 6.0),it can be presumed that the project will have no significant adverse impact. 5(b) Stormwater management is provided according to standards established by the Department. Stormwater Management will be improved during this project's construction by increasing the stormwater detention volume and reducing the runoff volume that leaves the site. The stormwater management standards applicability is included in the notice of intent supporting documentation (refer to Section 6.0 below). 5(c) Within 200 foot riverfront areas, proposed work shall not be located closer to the river than existing conditions or 100 feet, whichever is less, or not closer than existing conditions within 25 foot riverfront areas, except in accordance with 310 CMR10.58(5)(f)or(g). 5(d) Proposed work, including expansion of existing structures, shall be located outside the riverfront area or toward the riverfront area boundary and away from the river, except in accordance with 310 CMR 10.58(5)(f)or(g). 5(e) The area of proposed work shall not exceed the amount of degraded area, provided that the proposed work may alter up to 10°o if the degraded area is less than 10% of the riverfront area, except in accordance with 310 CMR 10.58(5)(f)or(g). The work proposed within the 200'buffer of the Cochichewick River is limited to the installation of one(1)athletic light pole.The foundations for these poles are augured into place with limited temporary disturbance and minimal permanent disturbance, and their above ground component is limited to a 36"cylindrical foundation.The light pole will be installed in previously disturbed area. All equipment setup and material lay down will take place outside of the Riverfront Area.Gale does not anticipate that the installation of this light not negatively impact the Cochichewick River. Town of North Andover Wetland Protection Regulations • 25-foot No-Disturbance Zone (NDZ) The Town Wetland Protection Regulations define this zone as "...that portion of the Buffer Zoen which extends twenty-five(25')from the edge of those wetland resource areas identified in Section 1.3...Disturbance of any kind is prohibited within this Zone including but not limited Page 5 of 164GA to grading, landscaping, vegetation removal, dumping of landscaping debris, pruning,filling, excavating, stormwater discharge, roadway construction and/or driveway construction." • 50-foot No-Build Zone (NBZ) The Town Wetland Protection Regulations define this zone as "...that portion of the Buffer Zoen which extends fifty-five(50")from the edge of those wetland resource areas identified in Section 1.3...Construction of any kind is prohibited within this Zone including but not limited to foundations associated with single family homes, multi family dwellings, commercial and/or industrial buildings, porches, decks (i.e., footing, piling, sonotube), patios, house additions,building additions,pools and pool equipment and fences,septic systems, and sheds. Driveways, roadways, retaining walls and landscape boulder walls may be allowed in the 50- foot No-Build Zone when no other feasible location exists, or when it is necessary to maintain the hydrology of the resource.An alternatives analysis showing the net benefit of location the structure in the No-Build Zone is required. The proposed work at the baseball field takes place outside of the NDZ and NBZ. The proposed work at the tennis courts involves a replacement in kind of the court footprint, with minor adjustments to lower the overall amount of impervious area.Significant portions of the tennis court footprint are located in the NBZ and NDZ, but this is the continuation of an existing condition, with the courts having been in this location for 30+ years. As part of this project, the existing pedestrian access path coming from the north-west will be removed and relocated to the south-west, as the existing culvert connecting the intermittent stream has failed, causing the pathway to collapse. The area of the previous access path/culvert will undergo wetland restoration to connect the two areas of BVW. The proposed work at the track takes place outside of the NDZ, but small amounts of incidental grading are proposed within the NBZ. 5.0 STORMWATER MANAGEMENT CONCEPT To gain an understanding of the site hydrology in its current condition, Gale completed an on-site assessment and reviewed as built and design plans for the school campus. The following section describes the watershed analysis and current hydrologic condition of the site. Rainfall events were obtained from the Northeast Regional Climate Center (NRCC) and the National Oceanic and Atmospheric Administration (NOAA), using the higher of the two rainfall amounts between each source. The U.S.D.A. Soil Conservation Service (SCS)Technical Release 55 (TR-55), 1986, was used as the procedure for estimating runoff. HydroCAD, a SCS TR-20-based computer program was used for estimating peak discharges.TR-55 is a generally accepted model for use on small sites and begins with a rainfall amount uniformly imposed on the watershed over a specified time distribution. Mass rainfall is converted to mass runoff by using a runoff curve number(CN).The CN is based on soils, ground cover, impervious areas, interception, and surface storage. Runoff is then Page 6 of 164GA transformed into a hydrograph that depends on runoff travel time through segments of the watershed. HydroCAD modifies the CN value for watersheds that are comprised of 30% or less unconnected impervious area, which is impervious area that is not connected directly to the drainage system.This modified value is known as the UI Adjusted CN. Stormwater management computations for the full-build were performed using SCS-based HydroCAD, as well as for existing and proposed conditions curve numbers, times of concentrations and unit hydrograph computations. 5.1 Pre-Development Condition The project site and surrounding areas have been broken down into three (3) existing sub watersheds that reflect the contributing areas of runoff to the design points. Existing topography was used to determine the watersheds. Refer to Sheets "PRE" for the Existing Watershed Map (Attachment 6). 5.1.1 Pre-Development Watershed Areas Existing Watershed Area 1 (EWS-1): EWS-1 includes runoff from the existing natural grass and clay baseball field, the slopes to the north and east of the field,and the limited site access components around the field. The runoff from this watershed flows overland in the south-easterly direction into the Bordering Vegetated Wetlands at Design Point 1 (DP-1). Sub-Watershed EWS-1 Total Contributary Area (SF) 273,778 Curve Number(CN) 67 Time of Concentration (min) 19.2 Hydrologic Soil Group B, C, D Existing Watershed Area 2 (EWS-2): EWS-2 consists of the existing 6-court tennis battery, associated bituminous path, and surrounding vegetated area. Runoff from this area flows northwest into the Bordering Vegetated Wetlands at Design Point 2 (DP-2). Sub-Watershed EWS-2 Total Contributary Area (SF) 48,452 Curve Number(CN) 93 Time of Concentration (min) 6.0 Hydrologic Soil Group D Page 7 of 164GA Existing Watershed Area 3 (EWS-3): EWS-3 consists of an open grassed area with two existing shotput venues with concrete throwing pads and stone dust landing areas. Runoff from this area flows east directly into the Bordering Vegetated Wetlands at Design Point 3 (DP-3). Sub-Watershed EWS-3 Total Contributary Area (SF) 17,670 Curve Number(CN) 78 Time of Concentration (min) 7.9 Hydrologic Soil Group C, D 5.2 Post-Development Condition The NAHS Athletic Field Improvements Project generally includes the following scope as it relates to stormwater management: • Installation of a synthetic turf multipurpose field with base stone and subsurface drainage system including the following: - Permeable turf"carpet" - Uniformly graded permeable stone layer with average thickness of 8" - Flat panel drains under the turf field - Perforated pipe collection system around the perimeter of the turf field - Outlet control structure that connects to existing drainage system - Loam and seed treatment for all areas within the limit of work not receiving other types of surface treatment. • Reconstruction of six bituminous concrete tennis courts and associated bituminous concrete access walkways. • Installation of a shotput practice venue with concrete pads and stonedust. The synthetic turf field is comprised of permeable turf "carpet" installed on top of a uniformly graded stone base with an average thickness of 8" and a 36% void space for stormwater storage. Stormwater that enters the synthetic turf carpet will drain vertically into the base stone. In the event of a significant storm, the stormwater is temporarily stored within the void space of the stone base. The stormwater is also collected by flat panel drains, which are installed at the bottom of the stone base, thirty feet apart. This spacing allows ample opportunity for stormwater to infiltrate, while also providing a means of conveyance away from the turf field and toward the perimeter collector pipe. An exfiltration rate of 0.463 in/hr was used in calculations per Nobis's test pit report.The perimeter collector pipe provides additional storage of stormwater and prevents the possibility of stormwater from backing up into the playing field. The perimeter collector pipes lead into an outlet control structure, which includes a riser pipe that limits outflow until most of the storage capacity of the base stone has been filled. Page 8 of 164GA 5.2.1 Post-Development Watershed Areas The proposed development results in watershed characteristics that differ from the pre- development condition as a result of revised grading and drainage patterns as well as runoff characteristics of the proposed improvement areas.The post-development Design Point 1 (DP-1), Design Point 2 (DP-2), and Design Point 3 (DP-3) are the same as the pre- development Design Points. While runoff paths and drainage areas have changed, all watersheds still discharge stormwater into the same surrounding wetlands. Refer to Sheets "POST" for the Post-Development Watershed Map (Attachment 6). Proposed Watershed Area 1 (PWS-1): PWS-1 includes runoff from the areas surrounding the proposed multipurpose synthetic turf field, including bituminous walkways and grassed areas. The runoff from this watershed flows overland in a generally southwest direction into the Bordering Vegetated Wetlands at Design Point 1 (DP-1). Sub-Watershed PWS-1 Total Contributary Area (SF) 133,563 Curve Number(CN) 72 Time of Concentration (min) 8.1 Hydrologic Soil Group B, C, D Proposed Watershed Area 2 (PWS-2): PWS-2 consists of the proposed multipurpose synthetic turf field.Although synthetic turf is highly permeable, the synthetic turf field area is modeled conservatively using a CN of 98, which is the same as a pond. Runoff from the turf field area enters the base stone directly. The voids in the base stone provide storage while allowing infiltration into the subsurface soils. If the base stone exceeds its storage capacity, the excess volume is conveyed away from the area through an extensive of subsurface drains.The subsurface drains in turn flow into a perimeter drainage pipe system. The perimeter subsurface piping directs flow through a proposed outlet control structure (OCS) in the south side of the turf field. The OCS outfalls into an existing drainage system, which outfalls into the adjacent Bordering Vegetated Wetlands at Design Point 1 (DP-1). Sub-Watershed PWS-2 Total Contributary Area (SF) 140,836 Curve Number(CN) 98 Time of Concentration (min) 6.0 Hydrologic Soil Group B, C Page 9 of 164GA Proposed Watershed Area 3 (PWS-3): PWS-3 consists of the proposed tennis courts, the surrounding bituminous concrete walkways, and grassed areas. Runoff from this area flows north west directly into the Bordering Vegetated Wetlands at Design Point 2 (DP-2). PWS-3 is largely unchanged in the area of impervious surface from EWS-2,with slight changes to the court footprint and the relocation of the access pathway. Sub-Watershed PWS-3 Total Contributary Area (SF) 51,136 Curve Number(CN) 93 Time of Concentration (min) 6.0 Hydrologic Soil Group D Proposed Watershed Area 4(PWS-4): PWS-4 consists of a small area to the southeast of the existing running track that includes the proposed shotput practice venue and grassed areas. Stormwater runoff flows overland to the east towards the wetlands located at Design Point 3 (DP-3). Sub-Watershed PWS-4 Total Contributary Area (SF) 17,670 Curve Number(CN) 80 Time of Concentration (min) 7.9 Hydrologic Soil Group C, D 6.0 COMPLIANCE WITH STORMWATER STANDARDS (MASWMS) 6.1 Untreated Stormwater(Standard 1) The project is designed so that stormwater conveyances (outfalls/discharges) do not discharge untreated stormwater into or cause erosion to downstream properties, to the maximum extent practicable. The turf field, stone base, and subsurface drainage system attenuates peak flow and detains stormwater runoff for infiltration.The BMPs will reduce the runoff into the adjacent wetlands and prevent erosion. 6.2 Post-Development Peak Rates(Standard 2) A Hydrologic Study was performed to determine the rate of runoff for the 2, 10 and 100- year storm events under pre-development (existing) and proposed conditions. From these analyses, it was estimated that the proposed project would not increase the peak runoff rates above existing levels for all storm events modeled. The purpose of the Stormwater Management System is to minimize impacts to drainage patterns, Page 10 of 16L,E downstream property, and wetlands, by providing management of runoff prior to its release from the site or its discharge to wetlands. 6.2.1 Proposed Conditions As described under Section 6.2, the post-development curve numbers are greater than pre-development, which generally increases the runoff potential of the site. In the HydroCAD software, synthetic turf is modeled conservatively with a CN of 98, to model the direct contribution of stormwater into the base stone beneath the synthetic turf field. The base stone serves to collect, detain, and control the release of stormwater runoff, thereby attenuating the peak rate of runoff. The stone base promotes infiltration and groundwater recharge to the maximum extent feasible. 6.2.2 Peak Rate Summary Table 6.2.3 shows the peak rate of runoff for the existing and proposed site for the 2, 10 and 100-year design storms. Other than the 2- and 100-year storms for DP-3, the peak post-development runoff does not exceed the peak existing pre-development runoff in any of the three analysis points for any of the three storm conditions.The increase in the 2-and 100-year peak development runoff at DP-3 is negligible (<0.1 CFS) TABLE 6.2.3 Existing Proposed Analysis Design Runoff Runoff Point Storm (CFS) (CFS) 2-yr 2.1 1.8 DP-1 10-yr 6.8 5.6 100-yr 17.9 15.1 2-yr 3.1 3.1 DP-2 10-yr 4.8 4.8 100-y r 7.9 7.9 2-yr 0.5 0.6 DP-3 10-yr 1.1 1.1 100-yr 2.1 2.2 6.3 Recharge to Groundwater(Standard 3) The project controls the stormwater runoff from the site by attenuating and treating the runoff in the base stone. After permeating through the base stone, the runoff infiltrates into the soils beneath the field,with minimal stormwater draining through perforated flat panel under drains and perforated collector pipes. An outlet control structure is used to control runoff outflow to the existing drainage system by retaining stormwater and providing the opportunity for the runoff to infiltrate. Page 11 of 16L,E The total amount of impervious area in the project area = 1.530 acres = 66,647 sf. Some of these impervious surfaces are existing but were included in these calculations in an effort to be conservative. Of the 1.530 acres of impervious area, 0.417 acres are in HSG B, 0.152 acres are in HSG C, and 0.961 acres are in HSG D. Required Recharge Volume for the entire site was calculated in accordance with Standard 3: Rv = (F(B) * HSG B impervious area (acres)) + (F(C) * HSG C impervious area (acres)) + (F(D) * HSG D impervious area (acres)) Rv=((0.35/12) * 0.417 ac)+((0.25/12) * 0.152 ac)+((0.10/12) * 0.961 ac) =0.023 Ac-ft= 1,002 CF Rv= Required Recharge Volume F(B) =Target Depth Factor for HSG B=0.35 inches F(C) =Target Depth Factor for HSG C=0.25 inches F(D) =Target Depth Factor for HSG D=0.10 inches The 36%voids within the stone base below the riser pipe inlet will provide approximately 321465 CF of storage which exceeds the Required Recharge Volume of 1,002 CF. Required minimum surface area of the bottom of the infiltration structure was calculated in accordance with the Simple Dynamic Method, as outlined in the Massachusetts Stormwater Management Standards: A= 11002 CF/(0.33 ft+0.019 ft/h * 2h)=2,722 SF A = Minimum required surface area of the bottom of the infiltration structure Rv= Required Recharge Volume= 1,002 CF D = Depth of the Infiltration Facility capable of stormwater retention =4 inches=0.33 ft K =Saturated Hydraulic Conductivity=0.232 in/h =0.019 ft/h T =Allowable drawdown during the peak of the storm (2h) The synthetic turf field's base stone is used to meet this standard, as it is separated by a minimum of two feet(2')from the Estimated Seasonal High Groundwater(ESHGW)table and therefore will provide infiltration capabilities. The surface area of the synthetic turf fields is approximately 134,596 SF.This amount of infiltrative surface area allows for the vertical transport of stormwater into the underlying base stone,which contains 36%voids equivalent to storage area, and exceeds the minimum required surface area of the bottom of the infiltration structure of 2,722 SF. Page 12 of 16 L,E The drawdown time from the base stone for the required recharge volume is calculated as follows: TII'1'ledrawdown = Rv/ [(K)*(Bottom Area)] _ (1,002 ft3)/ [(0.019 ft/hr)*(134,596 ft2)] =0.39 hours or 24 minutes Rv=Storage Volume (ft3) K =Saturated Hydraulic Conductivity(ft/hr) Bottom Area = Bottom Area of Recharge Structure (ft2) The drawdown time for the infiltration areas was calculated to be 0.39 hours, or 24 minutes, less than the required drawdown time of 72 hours. 6.4 Water Quality(Standard 4) The proposed synthetic turf athletic field has low potential for accumulation of total suspended solids (TSS). The turf is not subject to fertilization, sedimentation, irrigation, or rigorous maintenance, thus lessening the ability to acquire TSS. Areas around the turf field are grassed as a deterrent to erosion and sedimentation. Runoff generated by the synthetic turf field will travel vertically, through approximately eight inches (8") of stone base, where it will infiltrate into the soils below. All of the runoff directed into the synthetic turf field is relatively "clean", because the impervious surfaces will not be subjected to vehicular loading, sanding, or salting. Therefore, they do not need to be treated for TSS removal. (Despite not needing to be treated, a TSS removal worksheet was completed for the synthetic turf system, see Attachment 7.) Vehicles operating over the turf field, the tennis courts, and other areas of improvements will be relatively small maintenance and service vehicles with limited potential for drops or spills of fluids. No oil-based products or exotic materials are necessary for the maintenance of the turf field, the tennis courts, or other improved areas. Per the North Andover Stormwater Regulations §250-23 C. (1), redevelopment sites shall be designed to meet a pollutant removal equivalent to 50%of the average annual load of total phosphorous (TP) related to the total post-construction impervious surface on the site. Phosphorous loading is anticipated to be low on the site, as the area will not be subject to regular vehicular loading, and the proposed synthetic turf playing surface will greatly reduce the amount of fertilization required on the project site. Per the HydroCAD report, the post construction condition has 1.53 ac or 66,650 SF of impervious area. The regulations note that one method of achieving this removal is retaining a volume of runoff equivalent to or greater than 0.8 inches multiplied by the total post construction impervious area. 0.8 inches * 1 f t * 66,650 f t2 _ 3 1 12 inches 1 4,443 f t Page 13 of 16L,E The base stone beneath the synthetic turf field has a total area of 134,596 SF, and the perimeter curb and outlet control structure retain stormwater up to a certain elevation, allowing stormwater the opportunity to infiltrate. square f ootage of basin* (elevation of riser—elevation of bottom of basin) = retention volume 134,596 f t2 * (103.95 f t— 103.85 f t) = 13,459 f t3 The synthetic turf base stone retains 13,459 CF of stormwater, more than the 4,443 CF required to treat for phosphorus via retaining 0.8 inch. 6.5 Land Uses with Higher Potential Pollutant Loads(Standard 5) The project is not a LUHPPL. 6.6 Critical Areas(Standard 6) The site does not lie within a critical area and is not listed in the DEP ACEC's List, Latest Edition. 6.7 Redevelopment(Standard 7) This project is a redevelopment project. However, the project, as designed, meets the stormwater standards for new construction. 6.8 Erosion and Sedimentation Controls (Standard 8) An Erosion and Sedimentation Control Plan is provided as part of the plan set submitted as part of the stormwater management report to the town. The project is covered under the Environmental Protection Agency (EPA) National Pollutant Discharge Elimination System (NPDES) Construction General Permit (CGP) and a will require a Stormwater Pollution Prevention Plan (SWPPP). The contractor will file a Notice of Intent (NOI) for work under the CGP and provide a SWPPP for construction related activities prior to the start of construction. 6.9 Operation and Maintenance Plan (Standard 9) An Operation and Maintenance Plan is provided as part of this NOI (Refer to Attachment 8). 6.10 Prohibition of Illicit Discharges(Standard 10) There are no illicit discharges to the proposed Stormwater Management System allowed as part of the construction activities or as part of the continuing operation and Page 14 of 164GA maintenance of the athletic facilities. A template for an illicit discharge compliance statement is included in the Operation and Management Plan. A completed statement will be submitted by the contractor prior to the discharge of stormwater to the post- construction Stormwater Management System (Refer to Attachment 8). 7.0 PRESERVATION OF WETLANDS An important component to any project near environmentally sensitive areas is the demonstration of impact mitigation or preservation. Mitigation measures may include the use of best management practices and low-impact development techniques. Mitigation measures associated with the proposed project include: a) Increased groundwater recharge opportunities presented by the base stone of the proposed synthetic turf field. b) Elimination of the fertilization, sedimentation, irrigation, or rigorous maintenance associated with natural grass fields. 7.1 Tennis Courts Alternative Analysis An alternatives analysis was conducted for the tennis court battery, as reconstruction in place would involve considerable work to be performed in the 100' Buffer Zone, 50' No- Build-Zone,and 25' No-Disturb-Zone of the bordering vegetated wetlands,although these areas have been previously disturbed by the original construction of the courts. The existing court battery is in poor condition, as the existing bituminous asphalt is approaching the end of its serviceable life (-20 years).The asphalt has already had crack repairs performed, which have since failed. As such, reconstruction of the pavement is warranted, and no other alternative is available to provide long-term improvements to the surface. Alternative locations for the tennis venue were explored to determine if the existing location could be returned to natural conditions. However, the high school campus is highly developed,with limited open space not already in use for athletic playing fields and the campus is also surrounded by wetlands on both the south and east sides. Therefore, any relocation of the tennis venue to another place on campus would either severely impact an existing athletic field or school parking. 8.0 SUMMARY The NAHS Athletic Campus Improvements Project is intended to improve the quality of the athletic and recreational surfaces for the residents of the Town of North Andover, students of NAHS, and the students at neighboring schools.The project is estimated to provide water quality improvements and peak flow reduction within the watershed. Page 15 of 16L,E The proposed synthetic turf field eliminates the need for routine maintenance and watering of the existing natural grass field, which can negatively impact the quality of the stormwater runoff, and cause aquifer drawdown through irrigation. The storage capacity of the pervious stone base of the turf field will provide peak runoff control and water quality improvements over existing conditions. The proposed tennis courts replace the existing deteriorated tennis courts without any net gain in impervious area. The new courts do not result in any increase in the peak flow of runoff in the adjacent resource areas and do not result in any deterioration of the water quality of the runoff into the adjacent resource areas. Other improvements to the rea at the proposed shotput practice area are relatively smaller in scope.These improvements do not result in any increase in peak runoff into the adjacent resource areas and do not result in any deterioration in water quality. The project, as proposed, is the "best fit" for this site which is closely constrained by major roadways, existing facilities, and resource areas. The project proves to be an overall betterment to the environment by exceeding all the Massachusetts Stormwater Management Standards. G:\719560\02 Design\permit reports\notice of intent\Stormwater Report Body-NAHS.docx Page 16 of 16L,E ENCLOSURE 3 Revised HydroCAD Reports EWS-2 EWS-1 EWS-3 Tennisdourt Area Baseball Fiel Area Sh put Area DP-1 DP-2 DP-3 Design Point 1 Design Point 2 Design P Point t 3 Subcat Reach Zon Link Routing Diagram for 719560_PRE Prepared by Gale Associates, Inc, Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC 719560_PRE Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 2 Project Notes Copied 9 events from MA-North Andover 24-hr S1 storm 719560_PRE Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 3 Rainfall Events Listing (selected events) Event# Event Storm Type Curve Mode Duration B/B Depth AMC Name (hours) (inches) 1 2-yr MA-North Andover 24-hr S1 2-yr Default 24.00 1 3.16 2 2 10-yr MA-North Andover 24-hr S1 10-yr Default 24.00 1 5.00 2 3 100-yr MA-North Andover 24-hr S1 100-yr Default 24.00 1 8.83 2 719560_PRE Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 4 Area Listing (all nodes) Area CN Description (acres) (subcatchment-numbers) 4.593 61 >75%Grass cover, Good, HSG B (EWS-1) 0.896 74 >75%Grass cover, Good, HSG C (EWS-1, EWS-3) 0.447 80 >75%Grass cover, Good, HSG D (EWS-1, EWS-2, EWS-3) 0.456 85 Stone Dust Parking and Infield Dust, HSG B (EWS-1) 0.071 87 Stonedust, HSG C (EWS-3) 0.369 98 Unconnected pavement, HSG B (EWS-1) 0.107 98 Unconnected pavement, HSG C (EWS-1, EWS-3) 0.927 98 Unconnected pavement, HSG D (EWS-1, EWS-2) 7.865 72 TOTAL AREA 719560_PRE Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pa_.ece55 Soil Listing (all nodes) Area Soil Subcatchment (acres) Group Numbers 0.000 HSG A 5.417 HSG B EWS-1 1.074 HSG C EWS-1, EWS-3 1.374 HSG D EWS-1, EWS-2, EWS-3 0.000 Other 7.865 TOTAL AREA 719560_PRE Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page Ground Covers(all nodes) HSG-A HSG-B HSG-C HSG-D Other Total Ground Subcatchment (acres) (acres) (acres) (acres) (acres) (acres) Cover Numbers 0.000 4.593 0.896 0.447 0.000 5.935 >75%Grass cover,Good EWS-1, EWS-2, EWS-3 0.000 0.456 0.000 0.000 0.000 0.456 Stone Dust Parking and Infield Dust EWS-1 0.000 0.000 0.071 0.000 0.000 0.071 Stonedust EWS-3 0.000 0.369 0.107 0.927 0.000 1.403 Unconnected pavement EWS-1, EWS-2, EWS-3 0.000 5.417 1.074 1.374 0.000 7.865 TOTAL AREA 719560_PRE MA-North Andover 24-hr S12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 7 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS,Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment EWS-1: Baseball Field Area Runoff Area=273,778 sf 8.63%Impervious Runoff Depth>0.52" Flow Length=600' Tc=19.2 min UI Adjusted CN=66 Runoff=2.13 cfs 0.271 of Subcatchment EWS-2: Tennis Court Area Runoff Area=51,136 sf 72.92%Impervious Runoff Depth>2.20" Flow Length=210' Tc=6.0 min CN=93 Runoff=3.14 cfs 0.215 of Subcatchment EWS-3: Shotput Area Runoff Area=17,670 sf 1.13% Impervious Runoff Depth>1.09" Flow Length=113' Tc=7.9 min CN=78 Runoff=0.51 cfs 0.037 of Pond DP-1: Design Point 1 Inflow=2.13 cfs 0.271 of Primary=2.13 cfs 0.271 of Pond DP-2: Design Point 2 Inflow=3.14 cfs 0.215 of Primary=3.14 cfs 0.215 of Pond DP-3: Design Point 3 Inflow=0.51 cfs 0.037 of Primary=0.51 cfs 0.037 of Total Runoff Area=7.865 ac Runoff Volume=0.522 of Average Runoff Depth=0.80" 82.16% Pervious=6.462 ac 17.84%Impervious=1.403 ac 719560_PRE MA-North Andover 24-hr S12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 8 Summary for Subcatchment EWS-1: Baseball Field Area Runoff = 2.13 cfs @ 12.26 hrs, Volume= 0.271 af, Depth> 0.52" Routed to Pond DP-1 : Design Point 1 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 2-yr Rainfall=3.16" Area(sf) CN Adj Description 165078 98 Unconnected pavement, HSG B 47452 98 Unconnected pavement, HSG C 37095 98 Unconnected pavement, HSG D 197847 85 Stone Dust Parking and Infield Dust, HSG B 28,941 74 >75%Grass cover, Good, HSG C 200,052 61 >75%Grass cover, Good, HSG B 17313 80 >75%Grass cover, Good, HSG D 273,778 67 66 Weighted Average, UI Adjusted 250,153 91.37% Pervious Area 23,625 8.63% Impervious Area 235625 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 9.2 50 0.0060 0.09 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 7.0 389 0.0033 0.92 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 2.7 131 0.0026 0.82 Shallow Concentrated Flow, C-D Unpaved Kv= 16.1 fps 0.3 30 0.1460 1.91 Shallow Concentrated Flow, D-E Woodland Kv=5.0 fps 19.2 600 Total 719560_PRE MA-North Andover 24-hr S12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 9 Subcatchment EWS-1: Baseball Field Area Hydrograph 2.13 cfs MA-North Andover 24-hr S1 2-yr Rainfall 3.16 Runoff Area=273 778 sf Runoff Vo ume 0.271 of Runoff Depth 0.52 Flow Length=600 Tc=19.2 min UI Adjusted CN=66 i 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 10 Summary for Subcatchment EWS-2: Tennis Court Area Runoff = 3.14 cfs @ 12.04 hrs, Volume= 0.215 af, Depth> 2.20" Routed to Pond DP-2 : Design Point 2 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 2-yr Rainfall=3.16" Area(so CN Description 371290 98 Unconnected pavement, HSG D 13)846 80 >75%Grass cover, Good, HSG D 515136 93 Weighted Average 13,846 27.08% Pervious Area 375290 72.92% Impervious Area 37,290 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 1.0 50 0.0080 0.82 Sheet Flow,A-B Smooth surfaces n=0.011 P2=3.16" 1.2 106 0.0053 1.48 Shallow Concentrated Flow, B-C Paved Kv=20.3 fps 0.2 54 0.0654 4.12 Shallow Concentrated Flow, C-D Unpaved Kv= 16.1 fps 3.6 Direct Entry, Balance to Min.Tc Value 6.0 210 Total Subcatchment EWS-2: Tennis Court Area Hydrograph LO Runoff 3.14 cfs MA-North Andover 24-hr S1 2-yr 3 � Rainfall 3.16 Runoff Area_51 136 sf Runoff Volume 0.215 of Runoff Depth>2.20" 2 � Flow Leng... th 210 o Tc 6.0 min C N=93 1 � 17/ 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 11 Summary for Subcatchment EWS-3: Shotput Area Runoff = 0.51 cfs @ 12.07 hrs, Volume= 0.037 af, Depth> 1.09" Routed to Pond DP-3 : Design Point 3 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 2-yr Rainfall=3.16" Area(so CN Description 3,076 87 Stonedust, HSG C 200 98 Unconnected pavement, HSG C 41298 80 >75%Grass cover, Good, HSG D 10)096 74 >75%Grass cover, Good, HSG C 17,670 78 Weighted Average 17,470 98.87% Pervious Area 200 1.13% Impervious Area 200 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.5 50 0.0100 0.11 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 0.4 63 0.0316 2.86 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 7.9 113 Total Subcatchment EWS-3: Shotput Area Hydrograph - - - - - - - - - - - - -0.55 0.51 cfs LO Runoff 0.5 MA-North Andover 24-hr S1 2-yr Rainfall=3.16 0.45 Runoff Area 17 670 sf 0.4 Runoff Volume=0.037 of 0.35 Runoff Depth>109 N Flow Len th=113 0.3 Tc=7.9 m i n o 0.25 � CN 78 0.2 0.15j 0.1 0.05 �� 0 / 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 12 Summary for Pond DP-1: Design Point 1 Inflow Area= 6.285 ac, 8.63% Impervious, Inflow Depth> 0.52" for 2-yr event Inflow = 2.13 cfs @ 12.26 hrs, Volume= 0.271 of Primary = 2.13 cfs @ 12.26 hrs, Volume= 0.271 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1R Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-1: Design Point 1 Hydrograph El Inflow i-q fr-f E Primary 2. 13 cfs Inflow Area=6.285 ac 2 j 1 r 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 13 Summary for Pond DP-2: Design Point 2 Inflow Area= 1.174 ac, 72.92% Impervious, Inflow Depth> 2.20" for 2-yr event Inflow = 3.14 cfs @ 12.04 hrs, Volume= 0.215 of Primary = 3.14 cfs @ 12.04 hrs, Volume= 0.215 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1 R Routing by Stor-Ind method,Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-2: Design Point 2 Hydrograph �Inflow 0 Primary 3.14 cfs I nfl ow Area=1 .174 ac 3 a 2 w u 3 0 LL 1 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 14 Summary for Pond DP-3: Design Point 3 Inflow Area= 0.406 ac, 1.13% Impervious, Inflow Depth> 1.09" for 2-yr event Inflow = 0.51 cfs @ 12.07 hrs, Volume= 0.037 of Primary = 0.51 cfs @ 12.07 hrs, Volume= 0.037 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1 R Routing by Stor-Ind method,Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-3: Design Point 3 Hydrograph �Inflow 0 Prima-C;1 rfcry 0.55 0.51 cfs Inflow Area=0.406 ac 0.5 0.45 0.4 0.35 a w 0.3 3 0 LL 0.25 0.2 0.15 0.1 0.05 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 15 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS,Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment EWS-1: Baseball Field Area Runoff Area=273,778 sf 8.63%Impervious Runoff Depth>1.49" Flow Length=600' Tc=19.2 min UI Adjusted CN=66 Runoff=6.78 cfs 0.779 of Subcatchment EWS-2: Tennis Court Area Runoff Area=51,136 sf 72.92%Impervious Runoff Depth>3.79" Flow Length=210' Tc=6.0 min CN=93 Runoff=4.81 cfs 0.371 of Subcatchment EWS-3: Shotput Area Runoff Area=17,670 sf 1.13% Impervious Runoff Depth>2.42" Flow Length=113' Tc=7.9 min CN=78 Runoff=1.05 cfs 0.082 of Pond DP-1: Design Point 1 Inflow=6.78 cfs 0.779 of Primary=6.78 cfs 0.779 of Pond DP-2: Design Point 2 Inflow=4.81 cfs 0.371 of Primary=4.81 cfs 0.371 of Pond DP-3: Design Point 3 Inflow=1.05 cfs 0.082 of Primary=1.05 cfs 0.082 of Total Runoff Area=7.865 ac Runoff Volume= 1.232 of Average Runoff Depth=1.88" 82.16% Pervious=6.462 ac 17.84%Impervious=1.403 ac 719560_PRE MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 16 Summary for Subcatchment EWS-1: Baseball Field Area Runoff = 6.78 cfs @ 12.23 hrs, Volume= 0.779 af, Depth> 1.49" Routed to Pond DP-1 : Design Point 1 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Area(sf) CN Adj Description 165078 98 Unconnected pavement, HSG B 47452 98 Unconnected pavement, HSG C 37095 98 Unconnected pavement, HSG D 197847 85 Stone Dust Parking and Infield Dust, HSG B 28,941 74 >75%Grass cover, Good, HSG C 200,052 61 >75%Grass cover, Good, HSG B 17313 80 >75%Grass cover, Good, HSG D 273,778 67 66 Weighted Average, UI Adjusted 250,153 91.37% Pervious Area 23,625 8.63% Impervious Area 235625 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 9.2 50 0.0060 0.09 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 7.0 389 0.0033 0.92 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 2.7 131 0.0026 0.82 Shallow Concentrated Flow, C-D Unpaved Kv= 16.1 fps 0.3 30 0.1460 1.91 Shallow Concentrated Flow, D-E Woodland Kv=5.0 fps 19.2 600 Total 719560_PRE MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 17 Subcatchment EWS-1: Baseball Field Area Hydrograph � Runoff 7 6.78 cfs MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Runoff Area=273,778 sf Runoff Volume 0.779 of WN Runoff De th 149 1102 Flow Leng th=600' U 4 Tc=19.2 min UI Adjusted CN 66 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 18 Summary for Subcatchment EWS-2: Tennis Court Area Runoff = 4.81 cfs @ 12.04 hrs, Volume= 0.371 af, Depth> 3.79" Routed to Pond DP-2 : Design Point 2 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Area(so CN Description 371290 98 Unconnected pavement, HSG D 13)846 80 >75%Grass cover, Good, HSG D 515136 93 Weighted Average 13,846 27.08% Pervious Area 375290 72.92% Impervious Area 37,290 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 1.0 50 0.0080 0.82 Sheet Flow,A-B Smooth surfaces n=0.011 P2=3.16" 1.2 106 0.0053 1.48 Shallow Concentrated Flow, B-C Paved Kv=20.3 fps 0.2 54 0.0654 4.12 Shallow Concentrated Flow, C-D Unpaved Kv= 16.1 fps 3.6 Direct Entry, Balance to Min.Tc Value 6.0 210 Total Subcatchment EWS-2: Tennis Court Area Hydrograph LEIRunoff 5 4.81 cfs MA-North Andover 24-hr S1 10-yr Rainfall_500 4 Runoff Area_51�136 sf � Runoff Volume 0.371 of Runoff Dep th 3.79 " 4 3 Flow Leng... th_210 o Tc-6.0 m i n C N 93 1 � r / /ui ui,,,,/',,,,,,-for,,, ,,,,,,,,✓ %/,,,, /// j 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 19 Summary for Subcatchment EWS-3: Shotput Area Runoff = 1.05 cfs @ 12.06 hrs, Volume= 0.082 af, Depth> 2.42" Routed to Pond DP-3 : Design Point 3 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Area(so CN Description 3,076 87 Stonedust, HSG C 200 98 Unconnected pavement, HSG C 41298 80 >75%Grass cover, Good, HSG D 10)096 74 >75%Grass cover, Good, HSG C 17,670 78 Weighted Average 17,470 98.87% Pervious Area 200 1.13% Impervious Area 200 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.5 50 0.0100 0.11 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 0.4 63 0.0316 2.86 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 7.9 113 Total Subcatchment EWS-3: Shotput Area Hydrograph LO Runoff 1.05 cfs MA-North Andover 24-hr S1 10-yr Rainfall 5.00 Runoff Area 17 670 sf Runoff Volume=0.082 of Runoff Depth>2.42 Flow Leng th 1 13 o Tc=7.9 m i n CN=78 c✓r, 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 20 Summary for Pond DP-1: Design Point 1 Inflow Area= 6.285 ac, 8.63% Impervious, Inflow Depth > 1.49" for 10-yr event Inflow = 6.78 cfs @ 12.23 hrs, Volume= 0.779 of Primary = 6.78 cfs @ 12.23 hrs, Volume= 0.779 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1R Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-1: Design Point 1 Hydrograph El Inflow -, - - - - - - - - - - E Primary 7 6.78 cfs Inflow Area=6.285 ac 5 3 0 3 '11, 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 21 Summary for Pond DP-2: Design Point 2 Inflow Area= 1.174 ac, 72.92% Impervious, Inflow Depth> 3.79" for 10-yr event Inflow = 4.81 cfs @ 12.04 hrs, Volume= 0.371 of Primary = 4.81 cfs @ 12.04 hrs, Volume= 0.371 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1 R Routing by Stor-Ind method,Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-2: Design Point 2 Hydrograph �Inflow 0 Primary 5 4.81 cfs Infl ow Area=1 .174 ac 4 w 3 u 3 0 LL 2 1 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 22 Summary for Pond DP-3: Design Point 3 Inflow Area= 0.406 ac, 1.13% Impervious, Inflow Depth> 2.42" for 10-yr event Inflow = 1.05 cfs @ 12.06 hrs, Volume= 0.082 of Primary = 1.05 cfs @ 12.06 hrs, Volume= 0.082 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1 R Routing by Stor-Ind method,Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-3: Design Point 3 Hydrograph M Inflow 0 Primary 1.05 cfs Inflow Area=0.406 ac 1 a w u 3 0 LL O 1111 1111 1111r 1111 1111 U U U U U 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 23 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS,Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment EWS-1: Baseball Field Area Runoff Area=273,778 sf 8.63%Impervious Runoff Depth>4.14" Flow Length=600' Tc=19.2 min UI Adjusted CN=66 Runoff=17.89 cfs 2.171 of Subcatchment EWS-2: Tennis Court Area Runoff Area=51,136 sf 72.92%Impervious Runoff Depth>7.08" Flow Length=210' Tc=6.0 min CN=93 Runoff=7.88 cfs 0.693 of Subcatchment EWS-3: Shotput Area Runoff Area=17,670 sf 1.13% Impervious Runoff Depth>5.56" Flow Length=113' Tc=7.9 min CN=78 Runoff=2.12 cfs 0.188 of Pond DP-1: Design Point 1 Inflow=17.89 cfs 2.171 of Primary=17.89 cfs 2.171 of Pond DP-2: Design Point 2 Inflow=7.88 cfs 0.693 of Primary=7.88 cfs 0.693 of Pond DP-3: Design Point 3 Inflow=2.12 cfs 0.188 of Primary=2.12 cfs 0.188 of Total Runoff Area=7.865 ac Runoff Volume=3.051 of Average Runoff Depth=4.66" 82.16% Pervious=6.462 ac 17.84%Impervious=1.403 ac 719560_PRE MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 24 Summary for Subcatchment EWS-1: Baseball Field Area Runoff = 17.89 cfs @ 12.22 hrs, Volume= 2.171 af, Depth> 4.14" Routed to Pond DP-1 : Design Point 1 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Area(sf) CN Adj Description 165078 98 Unconnected pavement, HSG B 47452 98 Unconnected pavement, HSG C 37095 98 Unconnected pavement, HSG D 197847 85 Stone Dust Parking and Infield Dust, HSG B 28,941 74 >75%Grass cover, Good, HSG C 200,052 61 >75%Grass cover, Good, HSG B 17313 80 >75%Grass cover, Good, HSG D 273,778 67 66 Weighted Average, UI Adjusted 250,153 91.37% Pervious Area 23,625 8.63% Impervious Area 235625 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 9.2 50 0.0060 0.09 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 7.0 389 0.0033 0.92 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 2.7 131 0.0026 0.82 Shallow Concentrated Flow, C-D Unpaved Kv= 16.1 fps 0.3 30 0.1460 1.91 Shallow Concentrated Flow, D-E Woodland Kv=5.0 fps 19.2 600 Total 719560_PRE MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 25 Subcatchment EWS-1: Baseball Field Area Hydrograph 20 - - - - - - - - - - - - - - - - - - El Runoff 19 17.89 cfs 18„ MA-North Andover 24-hr S1 100-yr 17 � Rainfall=883" 16 15 � Runoff Area-273 778 sf Runoff Volume=2.171 of 13 Runoff Depth>4.14IV 12 Flow Length 600 42 11 Tc=19.2 min 1° U I Adjusted C N=66 o 7 6 5 i 4 3 i 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 26 Summary for Subcatchment EWS-2: Tennis Court Area Runoff = 7.88 cfs @ 12.04 hrs, Volume= 0.693 af, Depth> 7.08" Routed to Pond DP-2 : Design Point 2 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Area(so CN Description 371290 98 Unconnected pavement, HSG D 13)846 80 >75%Grass cover, Good, HSG D 515136 93 Weighted Average 13,846 27.08% Pervious Area 375290 72.92% Impervious Area 37,290 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 1.0 50 0.0080 0.82 Sheet Flow,A-B Smooth surfaces n=0.011 P2=3.16" 1.2 106 0.0053 1.48 Shallow Concentrated Flow, B-C Paved Kv=20.3 fps 0.2 54 0.0654 4.12 Shallow Concentrated Flow, C-D Unpaved Kv= 16.1 fps 3.6 Direct Entry, Balance to Min.Tc Value 6.0 210 Total Subcatchment EWS-2: Tennis Court Area Hydrograph LO Runoff 7.88 cfs $ MA-North Andover 24-hr S1 100-yr Rinf11=a a 8 83 7 � Runoff Area_51 136 sf Runoff Volume 0.693 of Runoff Depth>7.08 5 Flow Leng th 21 0 � � Tc 6.O min CN 93 0 4 3 �j 2 0 1 1 1 1 1 1 1 0 0 1111 1 1 1 1 1 1 1 1 0 1 1111 1 1 1 1 1 1 1 1 1 0 1111 1 1 1 1 1 1 1 1 0 0 1111 1 11/0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 27 Summary for Subcatchment EWS-3: Shotput Area Runoff = 2.12 cfs @ 12.06 hrs, Volume= 0.188 af, Depth> 5.56" Routed to Pond DP-3 : Design Point 3 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Area(so CN Description 3,076 87 Stonedust, HSG C 200 98 Unconnected pavement, HSG C 41298 80 >75%Grass cover, Good, HSG D 10)096 74 >75%Grass cover, Good, HSG C 17,670 78 Weighted Average 17,470 98.87% Pervious Area 200 1.13% Impervious Area 200 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.5 50 0.0100 0.11 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 0.4 63 0.0316 2.86 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 7.9 113 Total Subcatchment EWS-3: Shotput Area Hydrograph LO Runoff 2.12 cfs MA-North Andover 24-hr S1 100-yr Rainfall-8.83 Runoff Area 17 670 sf Runoff Volume 0.188 of Runoff Dep th>5.56 Flow Leng th 113 N Tc 7.9 min CNo 78 1 r i 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 28 Summary for Pond DP-1: Design Point 1 Inflow Area= 6.285 ac, 8.63% Impervious, Inflow Depth > 4.14" for 100-yr event Inflow = 17.89 cfs @ 12.22 hrs, Volume= 2.171 of Primary = 17.89 cfs @ 12.22 hrs, Volume= 2.171 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1R Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-1: Design Point 1 Hydrograph 20 El Inflow -- Primary 19 17.89 cfs 18" Inflow Area=6.285 ac 17 16 �i 15 14 13 - - - - - 12 3 10 .22 9 8 7 6 4 i 2 ��i/!'i our', ,,;'.,,//; 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 29 Summary for Pond DP-2: Design Point 2 Inflow Area= 1.174 ac, 72.92% Impervious, Inflow Depth> 7.08" for 100-yr event Inflow = 7.88 cfs @ 12.04 hrs, Volume= 0.693 of Primary = 7.88 cfs @ 12.04 hrs, Volume= 0.693 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1 R Routing by Stor-Ind method,Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-2: Design Point 2 Hydrograph EM Inflow 0 Primary 7.88 ifs Infl ow Area=1 .174 ac 7 6 5 u 3 o q LL 3 2 1 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_PRE MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 30 Summary for Pond DP-3: Design Point 3 Inflow Area= 0.406 ac, 1.13% Impervious, Inflow Depth > 5.56" for 100-yr event Inflow = 2.12 cfs @ 12.06 hrs, Volume= 0.188 of Primary = 2.12 cfs @ 12.06 hrs, Volume= 0.188 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1R Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-3: Design Point 3 Hydrograph EM Inflow El Primary 2.12 cfs Inflow Area=0.406 ac 2 j 1 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) PWS-1 PWS-2 Remaing Base all Field Synt etic Turf Field Area PWS-3 R Te is Court Area Tu Base Stone DP-2 DP-1 PWS-4 Design Point 2 ZShotput Area Design Point 1 Z D P-3 Design Point 3 Subcat Reach Zon Link Routing Diagram for 719560_POST Prepared by Gale Associates, Inc, Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC 719560_POST Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 2 Project Notes Copied 9 events from MA-North Andover 24-hr S1 storm 719560_POST Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 3 Rainfall Events Listing (selected events) Event# Event Storm Type Curve Mode Duration B/B Depth AMC Name (hours) (inches) 1 2-yr MA-North Andover 24-hr S1 2-yr Default 24.00 1 3.16 2 2 10-yr MA-North Andover 24-hr S1 10-yr Default 24.00 1 5.00 2 3 100-yr MA-North Andover 24-hr S1 100-yr Default 24.00 1 8.83 2 719560_POST Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 4 Area Listing (all nodes) Area CN Description (acres) (subcatchment-numbers) 1.859 61 >75%Grass cover, Good, HSG B (PWS-1) 0.448 74 >75%Grass cover, Good, HSG C (PWS-1, PWS-4) 0.412 80 >75%Grass cover, Good, HSG D (PWS-1, PWS-3, PWS-4) 0.261 82 Stonedust parking and shotput, HSG B (PWS-1) 0.121 87 Stonedust, HSG C (PWS-4) 2.880 98 Synthetic turf,0%imp.,HSG B (PWS-2) 0.353 98 Synthetic turf,0%imp.,HSG C (PWS-2) 0.417 98 Unconnected pavement, HSG B (PWS-1) 0.152 98 Unconnected pavement, HSG C (PWS-1, PWS-4) 0.961 98 Unconnected pavement, HSG D (PWS-1, PWS-3,PWS-4) 7.865 86 TOTAL AREA 719560_POST Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pa_.ece55 Soil Listing (all nodes) Area Soil Subcatchment (acres) Group Numbers 0.000 HSG A 5.417 HSG B PWS-1, PWS-2 1.074 HSG C PWS-1, PWS-2, PWS-4 1.373 HSG D PWS-1, PWS-3, PWS-4 0.000 Other 7.865 TOTAL AREA 719560_POST Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pa_.ece66 Ground Covers(all nodes) HSG-A HSG-B HSG-C HSG-D Other Total Ground Subcatchment (acres) (acres) (acres) (acres) (acres) (acres) Cover Numbers 0.000 1.859 0.448 0.412 0.000 2.720 >75%Grass cover,Good PWS-1, PWS-3, PWS-4 0.000 0.000 0.121 0.000 0.000 0.121 Stonedust PWS-4 0.000 0.261 0.000 0.000 0.000 0.261 Stonedust parking and shotput PWS-1 0.000 2.880 0.353 0.000 0.000 3.233 Synthetic turf,0%imp. PWS-2 0.000 0.417 0.152 0.961 0.000 1.530 Unconnected pavement PWS-1, PWS-3, PWS-4 0.000 5.417 1.074 1.373 0.000 7.865 TOTAL AREA 719560_POST Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 7 Pipe Listing (all nodes) Line# Node In-Invert Out-Invert Length Slope n Width Diam/Height Inside-Fill Node Number (feet) (feet) (feet) (ft/ft) (inches) (inches) (inches) Name 1 TRF 98.00 96.00 65.0 0.0308 0.013 0.0 12.0 0.0 Turf Base Stone 719560_POST MA-North Andover 24-hr S 12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 8 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS,Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment PWS-1: Remaing Baseball Field Area Runoff Area=132,942 sf 20.69%Impervious Runoff Depth>0.60" Flow Length=113' Tc=8.1 min UI Adjusted CN=68 Runoff=1.79 cfs 0.153 of Subcatchment PWS-2: Synthetic Turf Field Runoff Area=140,836 sf 0.00%Impervious Runoff Depth>2.61" Tc=6.0 min CN=98 Runoff=9.73 cfs 0.703 of Subcatchment PWS-3: Tennis Court Area Runoff Area=51,136 sf 74.80%Impervious Runoff Depth>2.20" Flow Length=214' Tc=6.0 min CN=93 Runoff=3.14 cfs 0.215 of Subcatchment PWS-4: Shotput Area Runoff Area=17,670 sf 5.05% Impervious Runoff Depth>1.21" Flow Length=113' Tc=7.9 min CN=80 Runoff=0.57 cfs 0.041 of Pond DP-1: Design Point 1 Inflow=1.84 cfs 0.212 of Primary=1.84 cfs 0.212 of Pond DP-2: Design Point 2 Inflow=3.14 cfs 0.215 of Primary=3.14 cfs 0.215 of Pond DP-3: Design Point 3 Inflow=0.57 cfs 0.041 of Primary=0.57 cfs 0.041 of Pond TRF: Turf Base Stone Peak Elev=104.06' Storage=9,958 cf Inflow=9.73 cfs 0.703 of Discarded=0.72 cfs 0.641 of Primary=0.35 cfs 0.060 of Outflow=1.08 cfs 0.701 of Total Runoff Area=7.865 ac Runoff Volume= 1.112 of Average Runoff Depth=1.70" 80.54% Pervious=6.335 ac 19.46%Impervious=1.530 ac 719560_POST MA-North Andover 24-hr S 12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 9 Summary for Subcatchment PWS-1: Remaing Baseball Field Area Runoff = 1.79 cfs @ 12.08 hrs, Volume= 0.153 af, Depth> 0.60" Routed to Pond DP-1 : Design Point 1 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 2-yr Rainfall=3.16" Area(sf) CN Adj Description 18,175 98 Unconnected pavement, HSG B 67022 98 Unconnected pavement, HSG C 37315 98 Unconnected pavement, HSG D 127020 74 >75%Grass cover, Good, HSG C 11,363 82 Stonedust parking and shotput, HSG B 807987 61 >75%Grass cover, Good, HSG B 11060 80 >75%Grass cover, Good, HSG D 1327942 72 68 Weighted Average, UI Adjusted 105,430 79.31% Pervious Area 277512 20.69% Impervious Area 277512 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.5 50 0.0100 0.11 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 0.5 45 0.0100 1.61 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 0.1 18 0.2220 2.36 Shallow Concentrated Flow, C-D Woodland Kv=5.0 fps 8.1 113 Total 719560_POST MA-North Andover 24-hr S 12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 10 Subcatchment PWS-1: Remaing Baseball Field Area Hydrograph 1.79 cfs MA-North Andover 24-hr S1 2-yr Rainfall 3.16 Runoff Area 132 942 sf Runoff Volume=0.153 of Runoff Dep th>060 Flow Leng th=113 1 Tc=8.1 m i n UI Adjusted CN=68 O rr"/',,,u r ui", �M/15' , U '1 ­ u ­ uuu UU ' " 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 2-Yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 11 Summary for Subcatchment PWS-2: Synthetic Turf Field Runoff = 9.73 cfs @ 12.04 hrs, Volume= 0.703 af, Depth> 2.61" Routed to Pond TRF :Turf Base Stone Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 2-yr Rainfall=3.16" Area(so CN Description 125)459 98 Synthetic turf, 0% imp., HSG B 151377 98 Synthetic turf, 0% imp., HSG C 140,836 98 Weighted Average 140,836 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Subcatchment PWS-2: Synthetic Turf Field Hydrograph E Runoff 10 9.73 cfs MA-North Andover 24-hr S1 2-yr 9 - Rainfall 3.16 s Runoff Area 140,836 sf nffVlm .7 Runoff o u e 0 03f a 7 Runoff Depth>261 N T — in 6 c 60m CN 98 4 3 2 11 jjpp ............3 11F-;1F--;1 1111 1111r r i -25 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 2-Yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 12 Summary for Subcatchment PWS-3: Tennis Court Area Runoff = 3.14 cfs @ 12.04 hrs, Volume= 0.215 af, Depth> 2.20" Routed to Pond DP-2 : Design Point 2 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 2-yr Rainfall=3.16" Area(so CN Description 38)248 98 Unconnected pavement, HSG D 12,888 80 >75%Grass cover, Good, HSG D 515136 93 Weighted Average 12,888 25.20% Pervious Area 385248 74.80% Impervious Area 38,248 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 1.0 50 0.0083 0.84 Sheet Flow,A-B Smooth surfaces n=0.011 P2=3.16" 1.0 108 0.0083 1.85 Shallow Concentrated Flow, B-C Paved Kv=20.3 fps 0.2 56 0.0584 3.89 Shallow Concentrated Flow, C-D Unpaved Kv= 16.1 fps 3.8 Direct Entry, Balance to Min.Tc Value 6.0 214 Total Subcatchment PWS-3: Tennis Court Area Hydrograph LO Runoff 3.14 cfs MA-North Andover 24-hr S1 2-yr 3 � Rainfall 3.16 Runoff Area_51 136 sf Runoff Volume 0.215 of Runoff Depth>2.20" 2 � Flow Leng... th 214 o Tc 6.0 min C N=93 1 � 17/ 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 2-Yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 13 Summary for Subcatchment PWS-4: Shotput Area Runoff = 0.57 cfs @ 12.07 hrs, Volume= 0.041 af, Depth> 1.21" Routed to Pond DP-3 : Design Point 3 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 2-yr Rainfall=3.16" Area(so CN Description 5,265 87 Stonedust, HSG C 599 98 Unconnected pavement, HSG C 293 98 Unconnected pavement, HSG D 47005 80 >75%Grass cover, Good, HSG D 7,508 74 >75%Grass cover, Good, HSG C 17,670 80 Weighted Average 16)778 94.95% Pervious Area 892 5.05% Impervious Area 892 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.5 50 0.0100 0.11 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 0.4 63 0.0316 2.86 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 7.9 113 Total Subcatchment PWS-4: Shotput Area Hydrograph LEIRunoff 0.6 0.57 cfs 0.55 MA-North Andover 24-hr S1 2-yr �� Rainfall-316 0.5 � _Runoff Area—17 670 sf 0.45 Runoff Volume-0.041 of 0.4 Runoff Depth>1.21 N 0.35 g Flow Len th-113 t� �i Tc-7.9 min c 0.3 -N C 80 0.25 0.2 0.15 j 0.1 0.05 o ,% 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S 12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 14 Summary for Pond DP-1: Design Point 1 Inflow Area= 6.285 ac, 10.05% Impervious, Inflow Depth> 0.41" for 2-yr event Inflow = 1.84 cfs @ 12.09 hrs, Volume= 0.212 of Primary = 1.84 cfs @ 12.09 hrs, Volume= 0.212 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1R Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-1: Design Point 1 Hydrograph El 1 RAInflow 2 Primary 1.84 cfs Inflow Area=6.285 ac El oIM 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 15 Summary for Pond DP-2: Design Point 2 Inflow Area= 1.174 ac, 74.80% Impervious, Inflow Depth> 2.20" for 2-yr event Inflow = 3.14 cfs @ 12.04 hrs, Volume= 0.215 of Primary = 3.14 cfs @ 12.04 hrs, Volume= 0.215 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1 R Routing by Stor-Ind method,Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-2: Design Point 2 Hydrograph �Inflow 0 Primary 3.14 cfs I nfl ow Area=1 .174 ac 3 a 2 w u 3 0 LL 1 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 16 Summary for Pond DP-3: Design Point 3 Inflow Area= 0.406 ac, 5.05% Impervious, Inflow Depth> 1.21" for 2-yr event Inflow = 0.57 cfs @ 12.07 hrs, Volume= 0.041 of Primary = 0.57 cfs @ 12.07 hrs, Volume= 0.041 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1 R Routing by Stor-Ind method,Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-3: Design Point 3 Hydrograph n -C;7 r-fc �Inflow 0.6 0.57 cfs 0 Primary Inflow Area=0.406 ac 0.55 0.5 0.45 0.4 0.35 0 0.3 LL 0.25 0.2 0.15 v 0.1 0.05 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S 12-yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 17 Summary for Pond TRF: Turf Base Stone Inflow Area= 3.233 ac, 0.00% Impervious, Inflow Depth> 2.61" for 2-yr event Inflow = 9.73 cfs @ 12.04 hrs, Volume= 0.703 of Outflow = 1.08 cfs @ 12.68 hrs, Volume= 0.701 af, Atten=89%, Lag=38.2 min Discarded = 0.72 cfs @ 11.20 hrs, Volume= 0.641 of Primary = 0.35 cfs @ 12.68 hrs, Volume= 0.060 of Routed to Pond DP-1 : Design Point 1 Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Peak Elev= 104.06' @ 12.68 hrs Surf.Area= 134,596 sf Storage=9,958 cf Plug-Flow detention time=82.5 min calculated for 0.701 of(100%of inflow) Center-of-Mass det.time=80.8 min (819.8-739.0) Volume Invert Avail.Storage Storage Description #1 103.85' 32,465 cf Custom Stage Data(Irregular) Listed below(Recalc) 90,179 cf Overall x 36.0%Voids Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 103.85 1347596 1,519.0 0 0 134,596 104.52 1347596 1,519.0 90,179 907179 1351614 Device Routing Invert Outlet Devices #1 Primary 98.00' 12.0" Round Culvert L=65.0' CMP,square edge headwall, Ke=0.500 Inlet/Outlet Invert=98.00'/96.00' S=0.0308'/' Cc=0.900 n=0.013 Corrugated PE, smooth interior, Flow Area=0.79 sf #2 Device 1 103.95' 12.0"Horiz.Orifice/Grate C=0.600 Limited to weir flow at low heads #3 Discarded 103.85' 0.232 in/hr Exfiltration over Surface area Discarded OutFlow Max=0.72 cfs @ 11.20 hrs HW=103.86' (Free Discharge) L3=Exfiltration (Exfiltration Controls 0.72 cfs) Primary OutFlow Max=0.35 cfs @ 12.68 hrs HW=104.06' (Free Discharge) L1=Culvert (Passes 0.35 cfs of 8.90 cfs potential flow) L2=Orifice/Grate (Weir Controls 0.35 cfs @ 1.06 fps) 719560POST MA-North Andover 24-hr S1 2-Yr Rainfall=3.16" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD@ 10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 18 Pond TRF: Turf Base Stone Hydrograph EM 9.73 cfs Inflow Outflow Inflow Area=3.233 ac IM Disc El Primary arded 10 Peak Elev=104.06' 9 Storag a=9 958 cf 7 6 U o 4 3 1.08 cfs 2 ...........2 cfs 0.35 cfs 20/1 0 0 U I U u u u u U 0 0 1111 1111 11 1111 U U U U U U U u U u u 1111 1111 1111 1111 1111 9 M U U 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 19 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS,Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment PWS-1: Remaing Baseball Field Area Runoff Area=132,942 sf 20.69%Impervious Runoff Depth>1.64" Flow Length=113' Tc=8.1 min UI Adjusted CN=68 Runoff=5.20 cfs 0.417 of Subcatchment PWS-2: Synthetic Turf Field Runoff Area=140,836 sf 0.00%Impervious Runoff Depth>4.18" Tc=6.0 min CN=98 Runoff=14.02 cfs 1.125 of Subcatchment PWS-3: Tennis Court Area Runoff Area=51,136 sf 74.80%Impervious Runoff Depth>3.79" Flow Length=214' Tc=6.0 min CN=93 Runoff=4.81 cfs 0.371 of Subcatchment PWS-4: Shotput Area Runoff Area=17,670 sf 5.05% Impervious Runoff Depth>2.60" Flow Length=113' Tc=7.9 min CN=80 Runoff=1.12 cfs 0.088 of Pond DP-1: Design Point 1 Inflow=5.55 cfs 0.690 of Primary=5.55 cfs 0.690 of Pond DP-2: Design Point 2 Inflow=4.81 cfs 0.371 of Primary=4.81 cfs 0.371 of Pond DP-3: Design Point 3 Inflow=1.12 cfs 0.088 of Primary=1.12 cfs 0.088 of Pond TRF: Turf Base Stone Peak Elev=104.20' Storage=16,744 cf Inflow=14.02 cfs 1.125 of Discarded=0.72 cfs 0.778 of Primary=1.25 cfs 0.273 of Outflow=1.97 cfs 1.052 of Total Runoff Area=7.865 ac Runoff Volume=2.001 of Average Runoff Depth=3.05" 80.54% Pervious=6.335 ac 19.46%Impervious=1.530 ac 719560_POST MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 20 Summary for Subcatchment PWS-1: Remaing Baseball Field Area Runoff = 5.20 cfs @ 12.07 hrs, Volume= 0.417 af, Depth> 1.64" Routed to Pond DP-1 : Design Point 1 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Area(sf) CN Adj Description 18,175 98 Unconnected pavement, HSG B 67022 98 Unconnected pavement, HSG C 37315 98 Unconnected pavement, HSG D 127020 74 >75%Grass cover, Good, HSG C 11,363 82 Stonedust parking and shotput, HSG B 807987 61 >75%Grass cover, Good, HSG B 11060 80 >75%Grass cover, Good, HSG D 1327942 72 68 Weighted Average, UI Adjusted 105,430 79.31% Pervious Area 277512 20.69% Impervious Area 277512 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.5 50 0.0100 0.11 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 0.5 45 0.0100 1.61 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 0.1 18 0.2220 2.36 Shallow Concentrated Flow, C-D Woodland Kv=5.0 fps 8.1 113 Total 719560_POST MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 21 Subcatchment PWS-1: Remaing Baseball Field Area Hydrograph � Runoff 5.20 cfs 5 MA-North Andover 24-hr S1 10-yr Rainfall=5 00" Runoff Ar 1 2 42 s f ea 39 4 � Runoff Volume 0.417 of Runoff Dep th 164 y � -Flow Leng h_113 3 � Tc=8.1 m i n O UI Adjusted CN=68 i 2 i O 1111 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 22 Summary for Subcatchment PWS-2: Synthetic Turf Field Runoff = 14.02 cfs @ 12.04 hrs, Volume= 1.125 af, Depth> 4.18" Routed to Pond TRF :Turf Base Stone Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Area(sfl CN Description 125,459 98 Synthetic turf,0%imp., HSG B 151377 98 Synthetic turf,0%imp., HSG C 140,836 98 Weighted Average 140,836 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ftlsec) (cfs) 6.0 Direct Entry, Subcatchment PWS-2: Synthetic Turf Field Hydrograph 15 Runoff 14.02 cfs I I El 14 MA-North Andover 24-hr S1 10-yr 13 Rainfall=5.00" 12 Runoff Area=140,836 sf 11 Runoff Volume=1.125 of 10 Runoff Depth>4.18" N 9 Tc=6.0 min w 3 $ CN=98 o 7 LL 6 5 4 3 2 1 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 23 Summary for Subcatchment PWS-3: Tennis Court Area Runoff = 4.81 cfs @ 12.04 hrs, Volume= 0.371 af, Depth> 3.79" Routed to Pond DP-2 : Design Point 2 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Area(so CN Description 38)248 98 Unconnected pavement, HSG D 12,888 80 >75%Grass cover, Good, HSG D 515136 93 Weighted Average 12,888 25.20% Pervious Area 385248 74.80% Impervious Area 38,248 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 1.0 50 0.0083 0.84 Sheet Flow,A-B Smooth surfaces n=0.011 P2=3.16" 1.0 108 0.0083 1.85 Shallow Concentrated Flow, B-C Paved Kv=20.3 fps 0.2 56 0.0584 3.89 Shallow Concentrated Flow, C-D Unpaved Kv= 16.1 fps 3.8 Direct Entry, Balance to Min.Tc Value 6.0 214 Total Subcatchment PWS-3: Tennis Court Area Hydrograph LEIRunoff 5 4.81 cfs MA-North Andover 24-hr S1 10-yr Rainfall_500 4 Runoff Area_51�136 sf � Runoff Volume 0.371 of Runoff Dep th 3.79 " 4 3 Flow Leng... th_214 o Tc-6.0 m i n C N 93 1 � r / /ui ui,,,,/',,,,,,-for,,, ,,,,,,,,✓ %/,,,, /// j 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 24 Summary for Subcatchment PWS-4: Shotput Area Runoff = 1.12 cfs @ 12.06 hrs, Volume= 0.088 af, Depth> 2.60" Routed to Pond DP-3 : Design Point 3 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Area(so CN Description 5,265 87 Stonedust, HSG C 599 98 Unconnected pavement, HSG C 293 98 Unconnected pavement, HSG D 47005 80 >75%Grass cover, Good, HSG D 7,508 74 >75%Grass cover, Good, HSG C 17,670 80 Weighted Average 16)778 94.95% Pervious Area 892 5.05% Impervious Area 892 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.5 50 0.0100 0.11 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 0.4 63 0.0316 2.86 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 7.9 113 Total Subcatchment PWS-4: Shotput Area Hydrograph LO Runoff 1.12cfs MA-North Andover 24-hr S1 10-yr 1 Rainfall 5.00 Runoff Area 17 670 sf Runoff Volume=0.088 of Runoff Depth>260 Flow j Leng th=113 o �r Tc=7.9 m i n CN 80 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 25 Summary for Pond DP-1: Design Point 1 Inflow Area= 6.285 ac, 10.05% Impervious, Inflow Depth> 1.32" for 10-yr event Inflow = 5.55 cfs @ 12.08 hrs, Volume= 0.690 of Primary = 5.55 cfs @ 12.08 hrs, Volume= 0.690 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1R Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-1: Design Point 1 Hydrograph Inflow l Primary 6 5.55 cfs Inflow Area=6.285 ac 5 4 0 3 i 21 i 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 26 Summary for Pond DP-2: Design Point 2 Inflow Area= 1.174 ac, 74.80% Impervious, Inflow Depth> 3.79" for 10-yr event Inflow = 4.81 cfs @ 12.04 hrs, Volume= 0.371 of Primary = 4.81 cfs @ 12.04 hrs, Volume= 0.371 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1 R Routing by Stor-Ind method,Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-2: Design Point 2 Hydrograph �Inflow 0 Primary 5 4.81 cfs Infl ow Area=1 .174 ac 4 w 3 u 3 0 LL 2 1 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 27 Summary for Pond DP-3: Design Point 3 Inflow Area= 0.406 ac, 5.05% Impervious, Inflow Depth> 2.60" for 10-yr event Inflow = 1.12 cfs @ 12.06 hrs, Volume= 0.088 of Primary = 1.12 cfs @ 12.06 hrs, Volume= 0.088 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1 R Routing by Stor-Ind method,Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-3: Design Point 3 Hydrograph EM Inflow 0 Primary 1.12 cfs Inflow Area=0.406 ac 1 a w u 3 0 LL 0 u"U 9 9 1111 1111 f r 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 28 Summary for Pond TRF: Turf Base Stone Inflow Area= 3.233 ac, 0.00% Impervious, Inflow Depth > 4.18" for 10-yr event Inflow = 14.02 cfs @ 12.04 hrs, Volume= 1.125 of Outflow = 1.97 cfs @ 12.62 hrs, Volume= 1.052 af, Atten=86%, Lag=34.9 min Discarded = 0.72 cfs @ 10.10 hrs, Volume= 0.778 of Primary = 1.25 cfs @ 12.62 hrs, Volume= 0.273 of Routed to Pond DP-1 : Design Point 1 Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Peak Elev= 104.20' @ 12.62 hrs Surf.Area= 134,596 sf Storage= 16,744 cf Plug-Flow detention time= 101.3 min calculated for 1.051 of(93%of inflow) Center-of-Mass det.time=73.9 min (810.1 -736.2) Volume Invert Avail.Storage Storage Description #1 103.85' 32,465 cf Custom Stage Data(Irregular) Listed below(Recalc) 90,179 cf Overall x 36.0%Voids Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 103.85 1347596 1,519.0 0 0 134,596 104.52 1347596 1,519.0 90,179 907179 1351614 Device Routing Invert Outlet Devices #1 Primary 98.00' 12.0" Round Culvert L=65.0' CMP,square edge headwall, Ke=0.500 Inlet/Outlet Invert=98.00'/96.00' S=0.0308'/' Cc=0.900 n=0.013 Corrugated PE, smooth interior, Flow Area=0.79 sf #2 Device 1 103.95' 12.0"Horiz.Orifice/Grate C=0.600 Limited to weir flow at low heads #3 Discarded 103.85' 0.232 in/hr Exfiltration over Surface area Discarded OutFlow Max=0.72 cfs @ 10.10 hrs HW=103.86' (Free Discharge) L3=Exfiltration (Exfiltration Controls 0.72 cfs) Primary OutFlow Max=1.25 cfs @ 12.62 hrs HW=104.20' (Free Discharge) L1=Culvert (Passes 1.25 cfs of 8.98 cfs potential flow) L2=Orifice/Grate (Weir Controls 1.25 cfs @ 1.62 fps) 719560POST MA-North Andover 24-hrSI 10-yr Rainfall=5.00" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD@ 10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 29 Pond TRF: Turf Base Stone Hydrograph EM 14.02 cfs Inflow Outflow IM Inflow Area=3.233 ac Discarded El Primary 15 14 Peak Elev=104.20' 13 Sto ra a=16 744 cf 12 11 10 9 U 8 0 7 6 5 4 1.97 cfs 20.72 cfs 1.25 cfs i:;ji:j; i pajig;g r011 10 i j i� l O. 0 K O11 '11111VUvuuuUuu u u uv -W W 11 '11' ' ' uu u u u u U U 9 0 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 30 Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 points Runoff by SCS TR-20 method, UH=SCS,Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment PWS-1: Remaing Baseball Field Area Runoff Area=132,942 sf 20.69%Impervious Runoff Depth>4.40" Flow Length=113' Tc=8.1 min UI Adjusted CN=68 Runoff=12.80 cfs 1.119 of Subcatchment PWS-2: Synthetic Turf Field Runoff Area=140,836 sf 0.00%Impervious Runoff Depth>7.39" Tc=6.0 min CN=98 Runoff=22.18 cfs 1.990 of Subcatchment PWS-3: Tennis Court Area Runoff Area=51,136 sf 74.80%Impervious Runoff Depth>7.08" Flow Length=214' Tc=6.0 min CN=93 Runoff=7.88 cfs 0.693 of Subcatchment PWS-4: Shotput Area Runoff Area=17,670 sf 5.05% Impervious Runoff Depth>5.78" Flow Length=113' Tc=7.9 min CN=80 Runoff=2.19 cfs 0.196 of Pond DP-1: Design Point 1 Inflow=15.13 cfs 2.044 of Primary=15.13 cfs 2.044 of Pond DP-2: Design Point 2 Inflow=7.88 cfs 0.693 of Primary=7.88 cfs 0.693 of Pond DP-3: Design Point 3 Inflow=2.19 cfs 0.196 of Primary=2.19 cfs 0.196 of Pond TRF: Turf Base Stone Peak Elev=104.51' Storage=32,181 cf Inflow=22.18 cfs 1.990 of Discarded=0.72 cfs 0.881 of Primary=2.84 cfs 0.925 of Outflow=3.56 cfs 1.806 of Total Runoff Area=7.865 ac Runoff Volume=3.997 of Average Runoff Depth=6.10" 80.54% Pervious=6.335 ac 19.46%Impervious=1.530 ac 719560_POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 31 Summary for Subcatchment PWS-1: Remaing Baseball Field Area Runoff = 12.80 cfs @ 12.07 hrs, Volume= 1.119 af, Depth> 4.40" Routed to Pond DP-1 : Design Point 1 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Area(sf) CN Adj Description 18,175 98 Unconnected pavement, HSG B 67022 98 Unconnected pavement, HSG C 37315 98 Unconnected pavement, HSG D 127020 74 >75%Grass cover, Good, HSG C 11,363 82 Stonedust parking and shotput, HSG B 807987 61 >75%Grass cover, Good, HSG B 1,060 80 >75%Grass cover, Good, HSG D 1327942 72 68 Weighted Average, UI Adjusted 105,430 79.31% Pervious Area 277512 20.69% Impervious Area 277512 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.5 50 0.0100 0.11 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 0.5 45 0.0100 1.61 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 0.1 18 0.2220 2.36 Shallow Concentrated Flow, C-D Woodland Kv=5.0 fps 8.1 113 Total 719560_POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 32 Subcatchment PWS-1: Remaing Baseball Field Area Hydrograph 14 12.80 cfs Runoff 13 MA-North Andover 24-hr S1 100-yr 12 Rainfall=8.83" 11 Runoff Area=132,942 sf 10 Runoff Volume=1.119 of 9 Runoff Depth>4.40" Flow Length=113' Tc=8.1 min 7 UI Adjusted CN=68 LL 6 5 4 3 2 1 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 33 Summary for Subcatchment PWS-2: Synthetic Turf Field Runoff = 22.18 cfs @ 12.04 hrs, Volume= 1.990 af, Depth> 7.39" Routed to Pond TRF :Turf Base Stone Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Area(sfl CN Description 125,459 98 Synthetic turf,0%imp., HSG B 151377 98 Synthetic turf,0%imp., HSG C 140,836 98 Weighted Average 140,836 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ftlsec) (cfs) 6.0 Direct Entry, Subcatchment PWS-2: Synthetic Turf Field Hydrograph 24 Runoff 23 22.18 cfs El 22 MA-North Andover 24-hr S1 100-yr 20 Rainfall=8.83" 19 Runoff Area=140,836 sf �$ Runoff Volume=1.990 of 17 16 Runoff Depth>7,39" 15 TC=GA min 14 CN=98 13 3 12 LL 11 10 9 8 7 6 5 4 3 m 2 1 � 0 , 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 34 Summary for Subcatchment PWS-3: Tennis Court Area Runoff = 7.88 cfs @ 12.04 hrs, Volume= 0.693 af, Depth> 7.08" Routed to Pond DP-2 : Design Point 2 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Area(so CN Description 38,248 98 Unconnected pavement, HSG D 12)888 80 >75%Grass cover, Good, HSG D 515136 93 Weighted Average 12,888 25.20% Pervious Area 385248 74.80% Impervious Area 38,248 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 1.0 50 0.0083 0.84 Sheet Flow,A-B Smooth surfaces n=0.011 P2=3.16" 1.0 108 0.0083 1.85 Shallow Concentrated Flow, B-C Paved Kv=20.3 fps 0.2 56 0.0584 3.89 Shallow Concentrated Flow, C-D Unpaved Kv= 16.1 fps 3.8 Direct Entry, Balance to Min.Tc Value 6.0 214 Total Subcatchment PWS-3: Tennis Court Area Hydrograph LO Runoff 7.88 cfs $ MA-North Andover 24-hr S1 100-yr Rinf11=a a 8 83 7 � Runoff Area_51 136 sf Runoff Volume 0.693 of Runoff Depth>7.08 5 Flow Leng th 214 � � Tc 6.O min CN 93 0 4 3 �j 2 0 1 1 1 1 1 1 1 0 0 1111 1 1 1 1 1 1 1 1 0 1 1111 1 1 1 1 1 1 1 1 1 0 1111 1 1 1 1 1 1 1 1 0 0 1111 1 11/0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Pace 35 Summary for Subcatchment PWS-4: Shotput Area Runoff = 2.19 cfs @ 12.06 hrs, Volume= 0.196 af, Depth> 5.78" Routed to Pond DP-3 : Design Point 3 Runoff by SCS TR-20 method, UH=SCS,Weighted-CN,Time Span=5.00-20.00 hrs,dt=0.05 hrs MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Area(so CN Description 5,265 87 Stonedust, HSG C 599 98 Unconnected pavement, HSG C 293 98 Unconnected pavement, HSG D 47005 80 >75%Grass cover, Good, HSG D 7,508 74 >75%Grass cover, Good, HSG C 17,670 80 Weighted Average 16)778 94.95% Pervious Area 892 5.05% Impervious Area 892 100.00% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.5 50 0.0100 0.11 Sheet Flow,A-B Grass: Short n=0.150 P2=3.16" 0.4 63 0.0316 2.86 Shallow Concentrated Flow, B-C Unpaved Kv= 16.1 fps 7.9 113 Total Subcatchment PWS-4: Shotput Area Hydrograph LO Runoff 2.19 cfs MA-North Andover 24-hr S1 100-yr 2 Rainfall 8.83 Runoff Area 17 670 sf Runoff Volume 0.196 of Runoff Dep th>5.78 Flow Leng th 113 N Tc 7.9 min N- o C 80 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 36 Summary for Pond DP-1: Design Point 1 Inflow Area= 6.285 ac, 10.05% Impervious, Inflow Depth> 3.90" for 100-yr event Inflow = 15.13 cfs @ 12.07 hrs, Volume= 2.044 of Primary = 15.13 cfs @ 12.07 hrs, Volume= 2.044 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1R Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-1: Design Point 1 Hydrograph El Inflow F-1-,�1-'1 rf El Primary 16 15.13 cfs Inflow Area=6.285 ac 15 14 13 12 11 10 0 8 7 6 5 a 3 2 1 i��rr�r�r�r��'�,�.,,,..,..,..�.,,/,..,., 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD010.20-5c sln 00742 0 2023 HydroCAD Software Solutions LLC Page 37 Summary for Pond DP-2: Design Point 2 Inflow Area= 1.174 ac, 74.80% Impervious, Inflow Depth> 7.08" for 100-yr event Inflow = 7.88 cfs @ 12.04 hrs, Volume= 0.693 of Primary = 7.88 cfs @ 12.04 hrs, Volume= 0.693 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1 R Routing by Stor-Ind method,Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-2: Design Point 2 Hydrograph EM Inflow 0 Primary 7.88 ifs I nfl ow Area=1 .174 ac 7 6 5 u 3 o q LL 3 /2/3 1 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 38 Summary for Pond DP-3: Design Point 3 Inflow Area= 0.406 ac, 5.05% Impervious, Inflow Depth > 5.78" for 100-yr event Inflow = 2.19 cfs @ 12.06 hrs, Volume= 0.196 of Primary = 2.19 cfs @ 12.06 hrs, Volume= 0.196 af, Atten=0%, Lag=0.0 min Routed to nonexistent node 1R Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Pond DP-3: Design Point 3 Hydrograph Inflow El Primary 2.19 cfs Inflow Area=0.406 ac 2 0 1 i 0 U 9-F-71177111 11111 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 719560_POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD®10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 39 Summary for Pond TRF: Turf Base Stone Inflow Area= 3.233 ac, 0.00% Impervious, Inflow Depth > 7.39" for 100-yr event Inflow = 22.18 cfs @ 12.04 hrs, Volume= 1.990 of Outflow = 3.56 cfs @ 12.62 hrs, Volume= 1.806 af, Atten=84%, Lag=34.6 min Discarded = 0.72 cfs @ 6.90 hrs, Volume= 0.881 of Primary = 2.84 cfs @ 12.62 hrs, Volume= 0.925 of Routed to Pond DP-1 : Design Point 1 Routing by Stor-Ind method, Time Span=5.00-20.00 hrs,dt=0.05 hrs Peak Elev= 104.51' @ 12.62 hrs Surf.Area= 134,596 sf Storage=32,181 cf Plug-Flow detention time= 112.4 min calculated for 1.805 of(91%of inflow) Center-of-Mass det.time=75.1 min (809.9-734.8) Volume Invert Avail.Storage Storage Description #1 103.85' 32,465 cf Custom Stage Data(Irregular) Listed below(Recalc) 90,179 cf Overall x 36.0%Voids Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 103.85 1347596 1,519.0 0 0 134,596 104.52 1347596 1,519.0 90,179 907179 1351614 Device Routing Invert Outlet Devices #1 Primary 98.00' 12.0" Round Culvert L=65.0' CMP,square edge headwall, Ke=0.500 Inlet/Outlet Invert=98.00'/96.00' S=0.0308'/' Cc=0.900 n=0.013 Corrugated PE, smooth interior, Flow Area=0.79 sf #2 Device 1 103.95' 12.0"Horiz.Orifice/Grate C=0.600 Limited to weir flow at low heads #3 Discarded 103.85' 0.232 in/hr Exfiltration over Surface area Discarded OutFlow Max=0.72 cfs @ 6.90 hrs HW=103.86' (Free Discharge) L3=Exfiltration (Exfiltration Controls 0.72 cfs) Primary OutFlow Max=2.84 cfs @ 12.62 hrs HW=104.51' (Free Discharge) L1=Culvert (Passes 2.84 cfs of 9.18 cfs potential flow) L2=Orifice/Grate (Orifice Controls 2.84 cfs @ 3.62 fps) 719560POST MA-North Andover 24-hr S1 100-yr Rainfall=8.83" Prepared by Gale Associates, Inc Printed 2/24/2025 HydroCAD@ 10.20-5c s/n 00742 ©2023 HydroCAD Software Solutions LLC Page 40 Pond TRF: Turf Base Stone Hydrograph EM 22.18 cfs Inflow Outflow IM 24 Inflow Area=3.233 ac Discarded El Primary 22 Peak Elev=104.51' 20 Storag a=32 181 cf 18 16 402 14 U 0 U- 10 8 3.56 cfs 6 IIIN HIM,, ARM 2.84 cfs 0.72 cfs 3 1111 MII 2 -—----—------ le M� l 0/51, 0 1111 1111 1111 111, 9 U . 11, 11, 11 '11' ' M U U 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours)