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Home My WebLink About03/14/2025 - 2nd HWG Stormwater Peer Review - - 430 OSGOOD STREET %�. Horsley Wiften Group 0 SLIStainable, Ehvirownental Solutions 112 W'at r `tr t-61 Floor-Boston,MBA 02109 .......... 5 -2 1 ho,r 1 ten March 14, 2025 Ms. Jean Enright, Planning Director North Andover Planning Board 120 Main Street North Andover, Massachusetts 01845 Ref: Second Stormwater Peer Review North Andover Public Schools North Andover High School Athletic Campus Improvements 430 Osgood Street, North Andover, Massachusetts Mass DEP File No. 242-1906 Dear Ms. Enright and Board Members: The Horsley Witten Group, Inc. (HW) is pleased to provide the North Andover Planning Board with this letter summarizing our second review of the Stormwater Management Report and Site Plans for the proposed athletic field improvements at the North Andover High School located at 430 Osgood Street, North Andover, MA. The Site Plans and Stormwater Management Report were prepared by Gale Associates, Inc. on behalf of North Andover Public Schools (Applicant). The Applicant is proposing to make several improvements to the existing athletic facilities at the North Andover High School campus, including the installation of a multipurpose synthetic turf field with a stone base and subsurface drainage system, reconstruction of existing tennis courts, and installation of a shot put and discus cage. Additional site improvements include new fencing, walkways, athletic lighting, drainage improvements, and wetland restoration. The watershed area evaluated consists of 7.86 acres. Under existing conditions there are 1.40 acres of impervious area that include the tennis courts, concrete pads, sidewalks and a portion of Wayne Street adjacent to the athletic field. Under proposed conditions the impervious area associated with tennis courts, concrete pads, sidewalks, and roadway increases to 1.53 acres. An additional 3.23 acres of synthetic fields are proposed which have been correctly modeled as impervious. A portion of the proposed work site is within the 100-foot buffer zone of the onsite bordering vegetated wetland (BVW) and the bank of the intermittent stream located adjacent to the tennis courts. The installation of one light pole is within the 200-foot riverfront area of the Cochichewick River. The proposed work involving the replacement of the tennis courts is within the 25-foot No Disturbance Zone (NDZ) and the 50-foot No-Build Zone (NBZ). The project will require an Order of Conditions from the North Andover Conservation Commission. The proposed stormwater management elements include a stone base system to capture and manage the stormwater from the artificial turf field and replacement of a failed culvert. The following additional documents and plans were received by HW in response to our initial review letter dated February 20, 2025: • Response to Comments letter, issued to Jean Enright, prepared by Gale Associates, Inc., dated March 10, 2025, with enclosures (237 pages). r � [f n. t- I, y"W ii tte n G ro u p �IM Horsley W'Itten Group, [iris. Town of North Andover March 14, 2025 Page 2of9 Stormwater Management Design Peer Review HW offers the following comments concerning the stormwater management design as per the Massachusetts Stormwater Handbook (MSH) dated February 2008, and the North Andover Chapter 165 Stormwater Management and Erosion Control Bylaw (Bylaw), and the Chapter 250 Stormwater Management and Erosion Control regulations (Stormwater Regulations) adopted June 21, 2022. In accordance with Stormwater Regulations, Article V -Applicability, §250-9 activities entailing land disturbance of over 43,560 square feet must obtain a Land Disturbance Permit. In accordance with the Stormwater Regulations, Article VII - Stormwater Management Plan, §250- 21. B. The Stormwater Management Plan shall be designed to meet the most recent version of the Massachusetts Stormwater Standards. Therefore, we have used the Massachusetts Stormwater Standards as the basis for organizing our comments. However, in instances where the additional criteria established in §250-23 of the North Andover Code require further recommendations, we have referenced these as well. 1. Standard 1: No new stormwater conveyances (e.g., outfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. a. The Applicant has analyzed the pre- and post-development stormwater runoff to three design points (DP). i) DP-1 is the Bordering Vegetated Wetland (BVW) series #2, located southwest of the existing baseball field portion of the site, next to the Chochichewick River. Under existing conditions, it appears that runoff from the existing baseball field sheet flows overland in a southwest direction towards the BVW at DP-1, while a portion of the field drains to Wayne Street, where it flows along the gutter line to an opening in the curb that is sloped towards the wetland. Under proposed conditions, runoff from the synthetic turf field enters the base stone beneath it, where it can infiltrate into the subsurface soils or be conveyed through the subsurface flat panel drains piped to a proposed outlet control structure (OCS) on the southside of the field. The OCS discharges via a 12-inch pipe into an existing DMH. Runoff from the areas surrounding the proposed synthetic turf field continues to flow overland in a southwest direction toward the BVW at DP-1. HW recommends that the Applicant: (1) Confirm where the existing catch basins drain to. March 14, 2025: The Applicant has stated that the existing catch basins are piped towards the 5-series BVW via 24-inch corrugated metal pipes. The approximate locations of the existing pipes have been added to Sheets C001 and C002. No further action is requested. (2) Confirms what the "apparent manhole" and "apparent OCS/sediment trap" are and where they discharge to (noted on page C001 Baseball Existing Conditions Plan). March 14, 2025: The Applicant has clarified that the apparent manhole and apparent OCS were observed by Gale and located on the existing conditions plan. The structures are piped towards the 5-series BVW via 24- inch corrugated metal pipes. The approximate locations of the existing pipes have been added to Sheets C001 and C002. No further action is Ilf I iii�� I'l f III��..iii llll I�iir�l� � .iii��l' � 181 Ilh.....11l Ilh.....11l ii:IIII µ a.' °lull„. Ih iu II�°.�'llllll .. ��.iii� ��'�� °� �I iiil� IIliiil�'�. iirl......I iii Illy.µ Ilh,�l .III�� °��. Town of North Andover March 14, 2025 Page 3of9 requested. (3) Clarifies the grading and purpose of the proposed 3/-inch stone swale along the north side of the baseball field. March 14, 2024: The Applicant has clarified that an existing infiltration trench is located at the toe of the slope and will remain. The infiltration trench will be amended, and a detail has been added to Sheet C503. No further action is requested. ii) DP-2 is the BVW series #4 and series #7, at the bank of the intermittent stream adjacent to (west of) the tennis court area, a 24-inch failed culvert connects the two wetlands. The intermittent stream flows southerly through a 24-inch culvert into Cochichewick River. The proposed project includes removal of the failed culvert and the restoration of the adjacent wetlands to reestablish the intermittent stream. Under existing conditions, runoff from the existing tennis courts and surrounding area flows northwest into the BVW at DP-2. Under proposed conditions, the surface areas remain largely the same, except for the relocation of the access walkway. March 14, 2025: No further action is requested. iii) DP-3 is the BVW series#8 associated with an intermittent stream that flows southerly along the eastern portion of the property boundary, starting from the area adjacent to (east of) the existing track and field facility, and flowing south past the tennis courts, eventually discharging to the Cochichewick River. Under existing conditions, runoff from the existing shotput venues and surrounding grassed areas flows in an easterly direction into the BVW at DP-3- Under proposed conditions, conditions remain largely the same. March 14, 2025: No further action is requested. 2. Standard 2: Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. a. HW has reviewed the Existing and Proposed Drainage Conditions figures and the HydroCAD model. The subcatchment areas, surface materials, curve numbers, times of concentrations, and flow patterns appear reasonable. No further action is requested. March 14, 2025: No further action is requested. b. Per §250-23 A. (1) of the North Andover Stormwater Regulations, Low-impact development (LID) site planning and design strategies must be implemented to the maximum extent feasible. The Applicant has incorporated LID techniques in the proposed project, including installation of a stone base and subsurface drainage system for the artificial turf field. HW recommends that the Applicant document other LID options it considered for the Project Area. March 14, 2025: The Applicant has documented the various LID strategies incorporated into the proposed stormwater management system. No further action is requested. �, Ilf ii " �� 1� � I Ilh.....11l Ilh.....11l ii IIII µ °1 ii ld .....��, 1 Town of North Andover March 14, 2025 Page 4 of 9 c. In accordance with §250-23 E. (19) the Applicant must utilize the 24-hour rainfall data taken from National Oceanic and Atmospheric Administration (NOAA) Atlas 14 for the rainfall precipitation depths. These values are 2-year, 3.16 inches; 10-year, 5.00 inches; and 100-year, 7.93 inches. The Applicant's rainfall events were obtained from the Northeast Regional Climate Center (NRCC), which differ slightly from the regulations (2- year, 3.13 inches; 10-year, 4.79 inches; 100-year, 8.83 inches. HW recommends that the Applicant utilize the higher of the two references. HW notes that the Applicant used the 1-year event instead of the 2-year event in the existing conditions model. March 14, 2025: The Applicant has adjusted the precipitation depths used in the HydroCAD model as suggested. No further action is requested. d. HW notes that there is a rectangle on the drawings on the athletic field near the access driveway that appears to be labeled Approx. Location of Subsurface Detention Basin. HW recommends that the Applicant clarify the rectangle and the callout. March 14, 2025: The Applicant has clarified that the rectangle is an existing detention basin that will remain. The top of the structure is between elevations 103.97 and 104.17. It appears that the 12-inch flat panel drains will be installed a few inches above the existing structure. No further action is requested. e. In accordance with §250-23 E. (11) the pre- and post-development peak rates and volumes of stormwater should be calculated. The Applicant has provided the peak flows for the 2-year, 10-year, and 100-year storm events, as shown in Table 6.2.3 within Section 6 of the application narrative. The hydrology report provides pre-development estimates for 1-year, 10-year and 100-year events, and post-development estimates for 2-year, 10-year and 100-year events. HW recommends that the Applicant provides the 2-year estimate for existing conditions. These calculations show that post-development rates do not exceed pre-development rates, with the exception of flows to DP-3 for the 2- year and 100-year storm events. However, these differences are negligible. HW has provided the peak flows and peak volumes in the tables below from the hydrology reports provided. The volume of runoff to DP-1 decreases and volumes to DP-2 remain stable. Runoff volumes to DP-3 increase slightly. March 14, 2025: The Applicant has adjusted the HydroCAD model. HW has updated the tables below. No further action is requested. Design Point - 1 Storm Existing Flow Proposed Flow Existing Proposed Frequency Rate (cfs) Rate (cfs) Volume (af) Volume (af) 2-Yr (3.16") 2.13 1.84 0.271 0.212 10-Yr (5.0") 6.78 5.55 0.779 0.690 100-Yr (8.83") 17.89 15.13 2.171 2.044 �� Ilf I iii�� (� � D 1�� f III��..iii llll I�iir�l� � .iii��l � 181 Ilh.....11l Ilh.....11l ii:IIII µ a.' � °lull„. Ih iu II�°.�'llllll .. ��.iii� ��'��I °� �I iiild Iliiil�'�. ii��......�iii l Ily.µ .III�� °��. Town of North Andover March 14, 2025 Page 5 of 9 Design Point - 2 Storm Existing Flow Proposed Flow Existing Proposed Frequency Rate (cfs) Rate (cfs) Volume (af) Volume (af) 2-Yr (3-16") 3.14 3.14 0.215 0.215 10-Yr (5.0") 4.81 4.81 0.371 0.371 100-Yr (8.83") 7.88 7.88 0.693 0.693 Design Point - 3 Storm Existing Flow Proposed Flow Existing Proposed Frequency Rate (cfs) Rate (cfs) Volume (af) Volume (af) 2-Yr (3.16") 0.51 0.57 0.037 0.041 10-Yr (5.0") 1.05 1.12 0.082 0.088 100-Yr (8.83") 2.12 2.19 0.188 0.196 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. The Applicant has conducted 5 test pits within the proposed artificial turf field area. The test pits indicate refusal between 4.5 to 5 feet from the surface, due to the density of the glacial till present throughout the site. Redoximorphic features were observed in TP-5 at 2 feet below the surface. The Test Pit Memo from Nobis notes that they encountered a perched water table and at test pit TP-3 it seeped into the bottom of the test pit resulting in over a foot of standing water. There are no test pits within the other athletic facility areas, but a total of eighteen (18) test borings at the proposed lighting locations are planned and in progress, including 4 at the track field, 2 at the stadium, 8 at the proposed synthetic turf field, and 4 at the tennis courts. HW recommends that the Applicant provide the results of the additional borings once completed. March 14, 2025: The Applicant has included as Enclosure 5, the updated Geotechnical Engineering Report, prepared by Nobis Group, dated February 28, 2025. No further action is requested. b. The Applicant has included recharge calculations in Section 6.3 of the Stormwater Report indicating that the total amount of impervious surface in the Project Area of 66,647 sf, requires 1,002 cubic feet of recharge volume. The Applicant has stated that it is providing approximately 44,865 CF of storage. The HydroCAD model indicates that the Turf Base Stone field has available storage of 32,465 CF. HW recommends that the Applicant clarify the value of 44,865 CF. March 14, 2025: The Applicant has adjusted the calculations in Section 6.3 and has confirmed that the available storage provided will be 32,465 CF. No further Ilf ii " (5 MI' III llll iirl .iii l' 181 Ilh.....11l Ilh.....11l ii IIII µ °1 ii ld .....��, 1 Town of North Andover March 14, 2025 Page 6of9 action is requested. c. The Applicant has provided a detail of the Turf Field sections on Sheet C503. HW recommends that the Applicant add elevations to the sections. The Applicant has included a note on Detail 1 stating that the trenches shall be over excavated by 12 inches in all directions. HW recommends that the Applicant clarify the estimated elevation of the perched water table and confirm it will over excavate below it. March 14, 2025: The Applicant has added a note to Sheet C503 requiring the contractor to over excavate to a depth at least 12 inches below the perched water table. No further action is requested. d. The Applicant has noted that the bottom of the turf field's base stone is 2 feet above the estimated seasonal high groundwater (ESHGW) table. HW was not able to confirm the ESHGW and request that the Applicant clarify how it was determined. March 14, 2025: The Applicant has documented how it was determined that the base stone will be a minimum of 2 feet above the ESHGW table. Considering the over excavation of the perched water table, HW concurs with the Applicant's response. No further action is requested. e. HW recommends that the Applicant clearly address questions raised by the Conservation Agent regarding how the stormwater infiltrating through the proposed artificial turf field will behave over the dense layer of glacial till that is present throughout the site. March 14, 2025: The Applicant has documented how it anticipates the stormwater will flow through the system. Including the over excavation and the proposed stone base, HW concurs with the Applicant's response. No further action is requested. f. HW notes that in the Nobis Engineering Geotechnical Report the saturated hydraulic conductivity rate for TP-4 is listed as 0.463 iph within the glacial till layer. Further noted by Nobis is that the MassDEP Stormwater Standard requires a minimum factor of safety of 2 be applied to field-derived values. In accordance with Volume 3, Chapter 1, page 13 of the MSH, HW recommends that the Applicant use an exfiltration rate of 1/2 times 0.463 iph (0.2315 iph) in the HydroCAD model and in the drawdown calculations. March 14, 2025: The Applicant has adjusted the exfiltration rate used in the HydroCAD model. No further action is requested. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 1-inch of volume from the impervious area for water quality. a. The Applicant has provided a TSS worksheet within the Pre and Post Development Hydrology Reports (see Attachment 7 of Application). The TSS worksheet illustrates that the proposed synthetic turf field will provide 80% TSS removal with the proposed infiltration basin. HW concurs with the percent removal as designed. March 14, 2025: No further action is requested. �� Ilf I iii�� D 1�� f III��..iii llll I�iir�l� � .iii��l � 181 Ilh.....11l Ilh.....11l ii:IIII µ a.' � °lull„. Ih iu II�°.�'llllll .. ��.iii� ��'��I °� �I iiild Iliiil�'�. ii��......� l Ily.µ .III�� °��. Town of North Andover March 14, 2025 Page 7of9 b. The Applicant has noted that the impervious area proposed within the Project Area consists of sidewalks, tennis courts and concrete pads that are not subject to vehicle loading. HW notes that an existing section of Wayne Street is within the catchment area. It is not clear how this portion of the road is being managed and if there is any opportunity to treat this runoff prior to discharging into the wetland. March 14, 2025: The Applicant has noted that the runoff from Wayne Street will continue to be managed in the same way it is under existing conditions. HW notes that it would be beneficial to the wetlands if there is any opportunity to provide additional treatment prior to flowing into the wetlands. c. HW recommends that the Applicant address the Phosphorous removal calculations in accordance with §250-23 C. (1) of the North Andover Stormwater Regulations. March 14, 2025: The Applicant has provided the required Phosphorous removal calculations. No further action is requested. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The Project Area is not considered a LUHPPL. Standard 5 is not applicable. March 14, 2025: No further action is requested. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone ll, or an Interim Wellhead Protection Area of a public water supply. a. The proposed development is not discharging near or into a critical area, Zone II or an IWPA area. Standard 6 is not applicable. March 14, 2025: No further action is requested. 7. Standard 7 is related to projects considered Redevelopment. a. This project can be considered a mix of new and redevelopment. The redeveloped portion of the project is required to comply with the Stormwater Management Standards to the maximum extent practicable for Standards 1-6. The increased impervious area is required to comply with the 10 Standards. The Applicant is intending to comply fully with the 10 standards. March 14, 2025: No further action is requested. b. The redevelopment project, as proposed, appears to comply with the Stormwater Management Standards and will improve existing conditions. March 14, 2025: No further action is requested. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The Applicant has acknowledged that a Stormwater Pollution Prevention Plan (SWPPP) is required by EPA and noted that the contractor will provide a SWPPP for construction related activities prior to the start of construction. The Planning Board may choose to require a final signed SWPPP a minimum of 14 days prior to land disturbance. March 14, 2025: Suggested condition of approval. Ilf ii " (5 D 1 III llll iirl .iii l' 181 Ilh.....11l Ilh.....11l ii IIII µ °1 ii ld .....��, 1 Town of North Andover March 14, 2025 Page 8of9 b. The Applicant has included details of a construction entrance, erosion matting, 12-inch silt sock, stockpile area, temporary construction fencing for dust control, loam and seed, and inlet protection as part of the proposed erosion control measures in the Permit Plan Set (Attachment 10). The Erosion Control Plan for each athletic facility shows the locations of silt sock sediment controls and potential staging/stockpile areas. The Operation & Maintenance (O&M) Plan includes further details and directions for erosion control in "Section I: Construction Activities." March 14, 2025: No further action is requested. 9. Standard 9 requires a Long-Term Operation and Maintenance (O & M) Plan to be provided. a. The Applicant has provided an Operation and Maintenance Plan as Attachment 8 of the Stormwater Management Report. The O&M Plan can be removed from the Stormwater Management Report and used as a standalone document by the property owner. The North Andover Public Schools may have a separate O&M Plan for the other existing facilities at the High School Athletic Campus, including another artificial turf field that was previously installed. If feasible, combining the O&M Plan for this project with the existing O&M Plan for the entire property would be beneficial. March 14, 2025: HW recommends that the proposed O&M Plan be combined with or be expanded to include the stormwater practices for the entire High School campus. b. HW recommends that the Applicant include a simple sketch with callout for the various stormwater practices that require long term inspections and maintenance. March 14, 2025: The Applicant has stated that a simple sketch has been provided. However, HW was not able to locate it in the documents received. HW recommends that the Applicant provided a simple sketch with callouts for the various stormwater practices requiring long term inspections and maintenance. c. HW recommends that the Applicant specify the party or parties responsible for the routine inspection and maintenance of the BMPs. March 14, 2025: The Applicant has noted that the North Andover Public Schools will be responsible for long-term maintenance. No further action is requested. d. HW recommends that the Applicant include an estimated operations and maintenance budget within the O&M Plan. March 14, 2025: The Applicant has included the estimated budget as suggested. No further action is requested. e. HW notes that the North Andover Conservation Agent has requested that the Applicant specify what maintenance activities, exactly, are included as "preventative maintenance" for the turf field as noted on page 2 of the O&M Plan. March 14, 2025: The Applicant has included maintenance of the Synthetic Turf Field in Part B of the O&M Plan. No further action is requested. Ilf ii " (5 (DW11 C111, III llll iirl .iii l81 Ilh.....11l Ilh.....11l ii IIII µ °1 ii ld .....��, 1 Town of North Andover March 14, 2025 Page 9of9 f. HW notes that the North Andover Conservation Agent has requested that the Applicant specify whether the maintenance of manholes and cleanouts for the synthetic turf field be done with a vacuum truck or another method (see pg. 2 of the O&M Plan). March 14, 2025: The Applicant has noted in the O&M Plan that a vacuum truck is the preferred cleaning method for the catch basins. No further action is requested. g. HW recommends that the Planning Board consider requesting receipt of a signed O&M Plan as a condition of approval. March 14, 2025: Suggested condition of approval. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. A template for an illicit discharge compliance statement is included in the Operation and Management Plan. The Applicant has noted that a completed statement will be submitted by the contractor prior to the discharge of stormwater to the postconstruction Stormwater Management System. HW recommends that the Planning Board request receipt of an Illicit Discharge Compliance Statement signed by the property owner prior to land disturbance. March 14, 2025: Suggested condition of approval. Conclusions HW recommends that the Planning Board requires that the Applicant provide a written response to address the few outstanding comments as part of the Board's review process. The Applicant is advised that the provision of these comments does not relieve him/her of the responsibility to comply with all Town of North Andover Codes and By-Laws, Commonwealth of Massachusetts laws, and federal regulations as applicable to this project. Please contact Janet Bernardo at 508-833-6600 or at jbernardo@horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. y III ^a .m fi 4 Janet Carter Bernardo, P.E. Principal Ilf II ii II " III " (5 (DW11 C111, III llll Il iirl .iii 111 III Ilh.....11l Ilh.....11l ii IIII � I a.' ^:�I µ I �' II i". °lulllll. Ih iu II�°.�'llllll IIIII.. I L iii ��I�'� � °� II iiil� �� IIL.�� iii��IIL �Il�lii III I� iii ��I �iiil�'L ii��......�iii Illy.µ fi�llh,�l LIII�� I� °III I.