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Home My WebLink About02/20/2023 - 2nd Stormwater Peer Review - - 149 MAIN STREET %�. Horsley Wiften Group 0 SUStainable, Ehvirownental Solutions 112 W'at r `tr t-61 Floor-Boston,MBA 02109 .......... 5 -2 1 ho,r 1 ten February 20, 2023 Ms. Jean Enright, Planning Director North Andover Planning Board 120 Main Street North Andover, Massachusetts 01845 Ref: 2nd Stormwater Peer Review 149 Main Street & 14 Second Street 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 second review of the Stormwater Management Plan for the proposed mixed-use development at 149 Main Street & 14 Second Street, North Andover, MA. The plans and stormwater report were prepared by Langan Engineering & Environmental Services, Inc. on behalf of Main and Second, LLC (Applicant). The project proposes the demolition of the two existing buildings and the construction of a 14,800 square foot (sf) three- story mixed-use building with 22 at-grade parking spaces covered by the building, along with associated utilities, stormwater management, and landscaping on a previously developed 0.66- acre site. The stormwater management for the proposed building includes trench drains, a manhole, a water quality unit, and a subsurface infiltration system (SIS). It does not appear that the site is within the jurisdiction of the North Andover Conservation Commission. The following additional documents and plans were received by HW in response to our December 7, 2022 initial peer review: • Letter to Planning Director, regarding response to comments, prepared by Langan Engineering & Environmental Services, Inc, dated February 14, 2023 (7 pages); • Stormwater Management Plan for 149 Main Street & 14 Second Street, North Andover, prepared by Langan Engineering & Environmental Services, Inc, dated November 2022, revised February 2023 (210 pages); and • Permit Site Plans, 149 Main Street and 14 Second Street Development, North Andover, Massachusetts, prepared by Langan Engineering & Environmental Services, Inc, dated November 21, 2022, revised February 14, 2023 (8 Sheets). Stormwater Management Design Peer Review In accordance with the North Andover Zoning Bylaw §195-8.14. E. (8) A Stormwater management plan is required for all site plan review applications. The stormwater management plan shall be prepared in accordance with the latest version of the Massachusetts Stormwater Handbook (MSH) and demonstrate full compliance with the Massachusetts Stormwater Standards and the North Andover Stormwater Management and Erosion Control Regulations. HW offers the following comments concerning the stormwater management design. We have used the MSH as the basis for organizing our comments. However, in instances where the r � [f n. t- I, " ii tte n G ro u p �IM Horsley W'Itten Group, [iris. Town of North Andover February 20, 2023 Page 2of6 additional criteria established in §250-22 of the North Andover Code requires further recommendations; we have referenced these as well. The following comments correlate to our December 7, 2022 initial peer review letter, follow up comments are provided in bold font. 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. It appears that the existing site sheet flows onto Main Street and Second Street and is captured by the existing municipal drainage system. Runoff appears to flow north down Main Street and east down Second Street with a low point at the two catch basins at the intersection of Main and Second Streets. Under proposed conditions the Applicant has intercepted the runoff from the site and piped it into the municipal drainage system. It does not appear that the stormwater is directed into a wetland resource area. However, HW recommends that the Applicant document where the municipal drainage system eventually outlets. The Applicant has confirmed with the North Andover engineering department that the municipal system ultimately discharges into the Merrimack River approximately 2,300 feet away. HW has no further comment. 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. The Applicant has drawn the existing and proposed watershed maps within the property boundaries of the Project Site. It appears that the parcels directly to the south of the site at 159 Main Street and 161 Main Street may flow onto the proposed development. HW recommends that the Applicant clarify where the runoff from 159 and 161 Main Street is directed under existing and proposed conditions. The Applicant has visited the site and adjusted the watershed areas on the Existing and Proposed Drainage Area Plans to include the offsite area. HW has no further comment. b. If the proposed stormwater features are capturing offsite runoff, HW recommends that the Applicant confirm the stormwater systems are sized adequately. The Applicant has updated the stormwater calculations to include the offsite areas. HW has no further comment. c. HW has reviewed the HydroCAD model provided in the Stormwater Report. We concur with the curve numbers and time of concentration (Tc) values included in the model. No further comment needed. d. The Applicant has utilized precipitation values in accordance with the Northeast Regional Climate Center (NRCC). HW recommends that the Applicant use precipitation values equal to or greater than the values provided by National Oceanic and Atmospheric Administration (NOAA) Atlas 14 for the 24-hour storm events, as outlined in §250-23 E. (19) of the North Andover Code. The Applicant has revised the precipitation depths as suggested. HW has no further comment. �� i��µ�� ...........0 �i :i��: � �� ' � � . � �li � . �S e I 0 121 �0C'iu]1(� Town of North Andover February 20, 2023 Page 3of6 e. 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 but not the peak volumes for the 2-year, 10-year, 25-year, and 100-year storm events. HW recommends that the Applicant add the peak volumes to Table 1 in the narrative. The Applicant has revised Table 1 to include the peak volumes. The Applicant has reduced the peak rate slightly for all storm events analyzed. The peak volume is comparable between the existing and proposed calculations. To be conservative the Applicant has not included exfiltration in the HydroCAD model. As the system will likely infiltrate the volume would be reduced under proposed conditions. f. HW recommends that the Applicant review the proposed contours at the top of curbs. Furthermore, HW recommends that the Applicant add spot grades along the patio areas to confirm runoff is being directed away from the building and towards the trench drains. The Applicant has added additional spot grades as requested. HW has no further comment. g. The Applicant has proposed a subsurface infiltration system to manage the roof runoff and a portion of the parking lot. The system includes 431 R-Tanks that are 13.8 inches in height with 3 inches of stone placed below the tanks and 6 inches of stone placed over the tanks. HW recommends that the Applicant include the total number of tanks to be installed on the plan set. The Applicant has added the total number of R-Tanks to Sheet CG101. HW has no further comment. h. The Applicant has noted that the subsurface system is a combined detention/infiltration system. The HydroCAD model does not include an exfiltration rate to indicate that infiltration has been included. HW recommends that the Applicant clarify the type of stormwater practice proposing. The Applicant has explained that the proposed subsurface system will allow infiltration to occur, with a separation to groundwater of at least 2 feet. To be conservative the Applicant has not included exfiltration in the HydroCAD model. HW has no further comment. i. The soil test pits provided indicate that a concrete slab was encountered in the area where the subsurface stormwater system is proposed. HW recommends that the Applicant indicate on the plan set that the concrete slab will be removed in its entirety as well as any fill encountered beneath the subsurface stormwater system. The Applicant has clarified the limits of the concrete slab and added notes requiring its removal as well as additional soil testing to occur once removed. The Planning Board may choose to include documentation of the concrete slab, the additional soil testing, and the possible replacement of the in-situ soil, if necessary, as a condition of approval. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. It appears from adjacent test pits that the subsurface infiltration system will have greater �� i��µ�� ...........0 �i :i��: � �� ' � � . � �li � . �S e I 0 121 �0 ]II(� : Town of North Andover February 20, 2023 Page 4 of 6 than 2 feet of separation to Estimated Seasonal High Groundwater (ESHGW) but less than 4 feet. HW recommends that the Applicant provide a mounding analysis per the MSH Volume 3, Chapter 1, Page 28. Furthermore, HW recommends that additional soil testing is conducted prior to installation of the system to confirm that adequate separation has been provided. The Applicant has provided the requested mounding analysis and confirmed that additional soil testing will be provided prior to construction. HW has no further comment. b. The Applicant has provided the required recharge volume and drawdown time calculations per the MSH Volume 3, Chapter 1, Pages 15 and 25. The recharge calculations indicate an exfiltration rate of 1.02 inches per hour (iph). HW concurs that this value is reasonable however as noted previously additional soil testing beneath the subsurface infiltration system should be conducted prior to installation. HW further notes that additional soil testing should be performed by a soil professional, and documentation provided to the Planning Board. The Applicant is amenable to conducting additional soil testing as noted above. HW recommends that the Planning Board include as a condition of approval receipt of the soil testing and confirmation from a professional engineer that the proposed design will function as anticipated. 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 noted in its narrative that the proposed stormwater system has been designed to treat one-half inch of water quality volume. Per §250-23 B. (1)(b) new developments are required to retain the volume of runoff equivalent to one inch multiplied by the total post-construction impervious surface. Per§250-23 C. (1)(b) redevelopment projects are required to retain the volume of runoff equivalent to 0.8 inches multiplied by the total post-construction impervious surface. Per§250-23 C. (2) when both new development and redevelopment are proposed for a project site, the redevelopment and new development work shall be conducted per the applicable regulations. HW recommends that the Applicant review the proposed design and confirm compliance with §250-23 Design and Performance Criteria. The Applicant has noted that the proposed project will have less than 1 acre of disturbance and additional criteria is not required. HW has no further comment. b. HW recommends that the Applicant provide documentation to support the TSS removal provided by the Trench Drain Filter. The Applicant has provided the requested documentation. The long-term functionality of the trench drains requires routine cleaning of the filters. The vendors documentation recommends servicing the trenches at least three times a year and changing the filter medium once per year. HW recommends that the Applicant revise the long-term O&M Plan to be consistency with the vendor's recommendations. III . �. � ��' ��^��: � � �� : � � IC . - vli �� II ii ii � Town of North Andover February 20, 2023 Page 5 of 6 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The site is not considered a LUHPPL. Therefore, Standard 5 is not applicable. No further comment needed. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone 11, 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. Therefore, Standard 6 is not applicable. No further comment needed. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project is a mix of new development and redevelopment. The area consisting of the existing parking lot behind the existing commercial building may be considered redevelopment. In this redevelopment area, a decrease in paved area is proposed and being converting to roof top which is considered an improvement. The proposed roof runoff is being managed by the subsurface infiltration system as new development. HW recommends that the Applicant respond to the other comments in this review letter to confirm it has adequately incorporated Standard 7. No further comment needed. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The proposed project requires land disturbance of under 1 acre. Therefore, a Stormwater Pollution Prevention Plan (SWPPP) per the EPA NPDES Construction General Permit will not be required. No further comment needed. b. HW recommends that the Applicant confirm that any stormwater runoff from the upgradient properties that may currently flow onto the site will not cause ponding on abutting properties during construction. The Applicant has included a note on Sheet CS002 requiring the contractor to maintain the existing drainage patterns. HW has no further comment. c. HW recommends that the Applicant explain how the site will be accessed during construction and locate the stabilized construction entrance on the erosion control plan. The Applicant has clarified how the site will be entered during construction. HW has no further comment. d. In accordance with §250-23 A. (7) of the North Andover Code the Applicant has identified five (5) trees to be removed within the limit of disturbance. The Applicant has illustrated six (6) trees to be planted along Main Street and Second Street. HW recommends that the Applicant confirm whether the critical root zones (CRZs) of any large trees will be impacted by the proposed development; construction activity over CRZs will potentially damage the root systems of trees and cause long-term degradation i �. . E ii ii se(''qa ir�u nd ov �� ...........Owl, � :1u'::1u" ':: "m, ": i" �� :�� III�� iii ��: �� Illu� �� III �� iii�� lii III ��:��lii iii��;��iii��.,,� ��..,m��°:��iii ��,�� Town of North Andover February 20, 2023 Page 6of6 of the tree's health. HW further recommends that any trees at the edge of the limit of work proposed to be protected are clearly marked in the field and a tree protection detail is added to the plan set. The Applicant has revised Sheet CE101 to indicate the removal of 9 trees. The Applicant has also noted that there will be 12 trees planted as part of the project. HW did not received the landscape plan. HW recommends that the Planning Board confirm that the proposed trees are adequate. 9. Standard 9 requires a Long-Term Operation and Maintenance (O & M) Plan to be provided. a. In accordance with the MSH Volume 1 Chapter 1 Page 23, the Applicant has provided a Long-Term Operation & Maintenance Plan as a standalone document as Appendix F of the Stormwater Management Plan. HW recommends that the Planning Board reference this document and require a signed O&M Plan as a condition of approval. The Applicant has provided a signed O&M Plan. HW recommends that the Applicant increase the frequency of cleaning the trench drains and filters as noted above. HW further recommends that the Planning Board reference this document as a condition of approval. b. HW recommends that the O&M Plan include a simple plan that is drawn to scale and shows the location of all stormwater practices within the parcel requiring inspections and long-term maintenance. The Applicant has included a simple sketch as suggested. HW has no further comment. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. The Applicant has provided an Illicit Discharge Compliance Statement in Appendix G of the Stormwater Management Plan. HW recommends that the Planning Board include a condition of approval requiring that the Illicit Discharge Compliance Statement be signed by the property owner prior to land disturbance. The Applicant has provided a signed Illicit Discharge Compliance Statement. HW has no further comment. Conclusions HW is satisfied that the Applicant has adequately addressed our comments. We recommend that the O&M Plan be revised as noted above. 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. Janet Carter Bernardo, P.E. 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