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Home My WebLink About01/16/2024 - Initial Stormwater Peer Review - - %�. Horsley Wiften Group 0 SUStainable, Ehvirownental Solutions 112 W'at r `tr t-61 Floor-Boston,MBA 02109 .......... January 16, 2024 Ms. Jean Enright, Planning Director North Andover Planning Board 120 Main Street North Andover, Massachusetts 01845 Ref: Initial Stormwater Peer Review Redevelopment of North Andover Mall North Andover, Massachusetts Dear Ms. Enright and Board Members: The Horsley Witten Group, Inc. (HW) is pleased to provide the North Andover Planning Board with this letter report summarizing our initial review of the Stormwater Report and Site Plan for the proposed redevelopment of the North Andover Mall at 350 Winthrop Ave, North Andover, MA. The plans and Stormwater Report were prepared by R.J. O'Connell & Associates, Inc. on behalf of DSM Realty, Inc. (Applicant). The redevelopment project proposes the renovation of a portion of the existing 244,415 square foot (sf) building, involving the exchange of store locations for two of the current tenants and the relocation of existing loading docks in association with the tenant location exchange. The proposed redevelopment will mostly match existing edge of pavement locations except in areas adjacent to an intermittent stream, where the edge of pavement will be moved further away from the stream. The removal of this portion of existing pavement as well as the addition of proposed landscape islands will result in an overall reduction of impervious cover from 581,918 sf in existing conditions to 528,121 sf in proposed conditions. This is a decrease of 54,650 sf of impervious surface. The proposed redevelopment's stormwater management system includes wet basins with sediment forebays, a water quality swale, and trench drains that direct runoff to hydrodynamic particle separators. The proposed parking lot area has also been regraded to provide additional flood storage capacity. A large portion of the parking lot is within the 100-year flood zone (Zone AE) and the floodway associated with the Shawsheen River bisects the northwest corner of the parcel. There are also wetland resource areas and buffer zones within the northern and southern portions of the property. The following documents and plans were received by HW: • Stormwater Report, North Andover Mall, 350 Winthrop Avenue, North Andover, MA, prepared for DSM Realty, Inc. (Applicant), prepared by R.J. O'Connell &Associates, Inc., dated December 8, 2023 (345 pages); • Special Permit Amendment-Site Plan Review, Application for The Redevelopment of North Andover Mall, prepared for DSM Realty, Inc. (Applicant), prepared by R.J. O'Connell &Associates, Inc., dated December 8, 2023 (56 pages); • Letter to the Planning Director, Special Permit Submission, prepared by R.J. O'Connell & Associates, Inc. on behalf of Delta M B LLC, dated December 13, 2023 (2 pages); and r � [f n. t- I, " ii tte n G ro u p �IM Horsley Wtten Group, [iris. Town of North Andover January 16, 2024 Page 2of7 • Site Plan for Redevelopment of North Andover Mall — North Andover, MA, prepared for DSM Realty, Inc. (Applicant), prepared by R.J. O'Connell & Associates, Inc., dated December 8, 2023 (23 sheets). 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 VI - 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 §250-22 of the North Andover Code requires 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 points of analysis (POA). i) POA-1 is where the site discharges to the Shawsheen River on the northwest side of the parcel. The large parking lot west of the building flows towards the intermittent stream and the Shawsheen River. Under proposed conditions the impervious surface towards POA-1 is being reduced by more than 50,000 sf and the Applicant has proposed several stormwater practices for water quality. The wet basins reduce the peak flow rate, and the outfall weirs will reduce the velocity at the discharge point. No further action requested. ii) POA-2 is the existing wetland resource area (series A) located along the north side of the property. The existing building and parking area on the east side of the building flows towards POA-2 via a closed drainage system that outlets at the edge of the wetland. Under proposed conditions the Applicant is reducing the impervious cover slightly, adding water quality units, and adding a 4-foot-wide French Drain along the edge of the pavement. The Applicant is maintaining the existing drainage system and outfalls. HW recommends that the Applicant confirm that the existing outfalls are not causing erosion in the wetland (Series A). HW notes that the Applicant has included calculations for riprap aprons which it may be proposing at the two existing outfalls. However, it is not clear where the aprons are to be located. HW also notes that if riprap aprons are proposed in the wetlands this should be included as fill when submitting a Notice of Intent to the Conservation Commission. iii) POA-3 is the existing wetland resource area (Series C) on the south side of the parcel. The proposed catchment area is identical to the existing catchment area. There are no impervious areas within the watershed to POA-3. No further action III i��.l��.��c II �� " ��..':.�. ��I�� l�ui i III i� iii 111��m �° iii �� ':��o�� III,� iii 111 ��Andover iii Town of North Andover January 16, 2024 Page 3of7 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 requested. b. The Applicant has designed two wet basins that overflow towards the Shawsheen River. The dimensions of the proposed spillways are not consistent between the HydroCAD model, and the Grading and Drainage Plan (Sheet C-3). HW recommends that the Applicant review the design and confirm the dimensions are consistent. c. HW recommends that the Applicant provide a detail of the proposed Drainage Channel and check dams in the plan set. d. In accordance with §250-22 B. (6) a summary of pre- and post-development peak rates and volumes of stormwater demonstrating no adverse impacts should be provided as part of the narrative. The Applicant has provided the peak flows and the peak volumes for the 2-year, 10-year, 25-year, and 100-year storm events to show that post- development rates and volumes do not exceed pre-development rates and volumes. Point of Analysis #1 Storm Existing Flow Proposed Flow Existing Proposed Frequency Rate (cfs) Rate (cfs) Volume (af) Volume (af) 2-Year 26.0 1.9 1.94 0.68 10-Year 51.3 32.1 3.83 2.43 25-Year 67.8 48.9 5.09 3.63 100-Year 93.4 71.2 7.09 5.56 Point of Analysis #2 Storm Existing Flow Proposed Flow Existing Proposed Frequency Rate (cfs) Rate (cfs) Volume (af) Volume (af) 2-Year 12.8 12.7 1.00 1.00 10-Year 33.4 33.3 2.44 2.43 25-Year 47.7 47.6 3.46 3.46 100-Year 70.8 70.7 5.14 5.13 i��.l��.��c II �� " ��..':.�. ��I��"Owl, �� III i�� iii 111��m �° iii �� ':��o�� III,�� iii 111 ��Andover iii Town of North Andover January 16, 2024 Page 4 of 7 Point of Analysis #3 Storm Existing Flow Proposed Flow Existing Proposed Frequency Rate (cfs) Rate (cfs) Volume (af) Volume (af) 2-Year 0.00 0.00 0.00 0.00 10-Year 0.00 0.00 0.00 0.00 25-Year 0.10 0.10 0.05 0.05 100-Year 0.60 0.60 0.18 0.18 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. The Applicant has reduced the total impervious surface by more than 1 acre. The annual recharge from post-development is greater than the pre-development conditions. No further action 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 that states an Oil Grit Separator has a TSS Removal Rate of 80%. Page 11, Chapter 1, Volume 1 of the Massachusetts Stormwater Handbook states that an Oil Grit Separator has a TSS Removal Rate of 25%. HW recommends that the Applicant justify the use of the 80% TSS Removal Rate and provide applicable documentation from a third-party reviewer supporting the listed TSS removal rate. b. HW recommends that the Applicant clarify the impervious area directed towards CDS Units 1 and 2. c. Per §250-23 C. (1)(b) redevelopments sites are required to retain the volume of runoff equivalent to 0.8 inch multiplied by the total post-construction impervious surface or meet a combination of retention and treatment that achieves the above standards listed under§250-23 C. (1). The Applicant should clarify the Phosphorous removal calculations. A curve for porous pavement was included but not one for the Water Quality Swale. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The MSH states that a LUHPPL includes parking lots with high intensity uses such as the parking lot of a mall. The Applicant has proposed stormwater practices that the MSH has determined suitable to treat runoff from such land uses. These stormwater practices include oil grit separators, sediment forebays, drainage channel, and wet basins. No further action requested. rc 11 �. .. �. . . �. �.. III JI. � 1 II Iu �:III 1�iiirt A �v iii il' 1 LWI� 1 III 1�iiirt and v iii Town of North Andover January 16, 2024 Page 5 of 7 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone II, 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. However, the Applicant has acknowledged that some endangered species including bald eagles may be within the Project Area which may trigger Standard 6. The Applicant has proposed stormwater practices that the MSH has determined suitable to treat runoff from such land uses. No further action requested. 7. Standard 7 is related to projects considered Redevelopment. a. This project is a redevelopment and is required to comply with the Stormwater Management Standards to the maximum extent practicable. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The Applicant has provided a draft Stormwater Pollution Prevention Plan (SWPPP) as required by EPA for land disturbance of greater than 1 acre. The plan includes source control and pollution prevention measures, stormwater practices to address erosion and sedimentation, stabilization measures, and procedures for operating and maintaining the BMPs. The plan also identifies the parties responsible for implementing the plan. The Planning Board may choose to require a final signed SWPPP a minimum of 14 days prior to land disturbance. b. The Applicant has included a 9-inch straw wattle as an erosion control barrier. Considering the proximity of the resource areas and the Shawsheen River, HW recommends that the Applicant include a more robust erosion control barrier for any work within 25 feet of a wetland. Details of all erosion controls practices should be included in the Plan Set. 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 in Appendix E of the Stormwater Report. The O&M Plan can be removed from the Stormwater Report and be a standalone document for use by the property owner. b. HW recommends that the Applicant include an estimated budget within the O&M Plan. c. HW recommends that the Applicant include a simple sketch within the O&M Plan that is drawn to scale and shows the location of stormwater BMPs in each treatment train along with the discharge point. d. HW recommends that the Planning Board reference this document and consider requesting receipt of a signed O&M Plan as a condition of approval. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. The Applicant has provided an Illicit Discharge Compliance Statement as part of the Operation & Maintenance Plan. The Planning Board may choose to require receipt of a signed statement prior to land disturbance. III JI 1u III 1�iiirt A �� iii il' 1 LWI2 III 1�iiirt and o iii Town of North Andover January 16, 2024 Page 6of7 11. 100-year Flood Plain a. The Applicant has provided compensatory flood storage calculations in the Stormwater Report. HW notes that it appears that the Applicant has included the storage volume in the wet basins and sediment forebays. In accordance with paragraph 10.57(4)(a)l. of the Wetlands Protection Act, "Such compensatory volume shall have an unrestricted hydraulic connection to the same waterway or water body."The vol u me below elevation 26 that is not hydraulically connected to the waterway should not be included as storage. HW recommends that the Applicant confirm it has provided adequate storage in accordance with 310 CMR 10.57. b. A large portion of the property appears on the Federal Emergency Management Agency (FEMA) Flood Insurance Map as being in Zone AE, which is associated with elevation 33 on the map dated September 17, 2012. FEMA has produced a preliminary map dated February 20, 2023, where a larger portion of the parcel is within the 100-year flood plain and it is assigned elevation 33.6. HW notes that when an elevation is assigned to a flood zone the land survey should delineate the extent of the flood plain by the actual contour elevation and not by the shape outlined on the FEMA map. HW recommends that the Applicant redraw the 100-year flood plain line under existing and proposed conditions using the more conservative elevation of 33.6. i glifl� �ol,�'' I ', �/ I¢� r i r, ri V 1 + rI M w r /r- I wm, Y, 1' o � u' ,,rj0 r f ,;/'i//, // f rr, ,nU' ,�',,1,u�r ^L ro��ilY, r,✓?(/�, a V� / ,ri I �Sri ('11r 16'/i,%I7Yll//r,: :i,,��,11u�ll v; rg ,r ,,:( qi. 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Irt� ^ u r.I �, ir��I"lll��"��II ��I��'�� " ��II��'��':�� u� I�" III�� iii 111 l��m �° iii ��1��'�� ';��it�� III��iiirt Andover Town of North Andover January 16, 2024 Page 7of7 Conclusions HW recommends that the Planning Board require that the Applicant provide a written response to address these comments as part of the Board's review process. The Applicant is advised that 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. n �- ^ Janet Carter Bernardo, P.E. Ava Schully Associate Principal Staff Engineer III JI 1u w�:III 1 w iiirt A ��w iii il' 10 III 1 w iiirt and w w iii