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HomeMy WebLinkAbout2026/07/06 - 1st Stormwater Peer Review - 492 Sutton Street Horsley W*itten Grou Sustainable V i� ;,l ,� i ' V Vn li a Solutions 112 t r Street,® 'Floor Boston,MA 02109 July 6, 2026 Ms. Jean Enright, Planning Director Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Re: Initial Stormwater Peer Review 492 Sutton 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 report summarizing our initial review of the Watershed Special Permit Application for the proposed improvements at 492 Sutton Street in North Andover, MA. The plans were prepared by McClure Engineering Company on behalf of the Lawrence Municipal Airport (Applicant). The Applicant has noted that the Lawrence Municipal Airport property contains over 400 acres of land. The project proposes the construction of a new 7,069 square foot (sf) administration building and the reconfiguring of the parking lot, as well as utility, stormwater, and landscaping improvements. The stormwater improvements include the addition of a stormwater infiltration basin, two vegetated detention ponds, and one manufactured cartridge filtration unit. It appears that the proposed actions will increase the total impervious area on the site by approximately 7,360 sf. The total land disturbance is somewhere between 49,300 sf and 53,500 sf. Based on the Resource Area Map in the Stormwater Management Report, there are no wetland resource areas or buffer zones within 100 feet of the project area. The following documents and plans were reviewed by HW: • Stormwater Management Report, 492 Sutton Street, North Andover, MA, prepared by McClure Engineering Company, dated June 16, 2026 (202 pages); • Memorandum for Site Plan Review Special Permit, 492 Sutton Street, North Andover, MA, prepared by McClure Engineering Company, dated June 16, 2026 (8 pages); • Long Term Operation and Maintenance Plan, Lawrence Municipal Airport—Administration Building, 492 Sutton Street, North Andover, MA, prepared by McClure Engineering Company, dated June 16, 2026 (33 pages); • Special Permit—Site Plan Review Application, 492 Sutton Street, North Andover, MA, prepared by the City of Lawrence Municipal Airport Commission, dated June 17, 2026 (2 pages); and Town of North Andover July 6, 2026 Page 2of8 • Lawrence Airport Administration Building Permit Plans, 492 Sutton Street, North Andover, MA, prepared by McClure Engineering Company, dated June 15, 2026: o Cover Sheet C000 o Legend &Abbreviations C001 o Civil Notes C002 o Existing Conditions Plan EX-1 (CO03) o Construction Phasing Plan C004 o Demolition Plan C101 o Overall Site Plan C102 o Site Plan C103 o Site Layout Plan C104 o Grading & Drainage Plan C105 o Utility Plan C106 o Erosion & Sedimentation Control Plan C107 o Signage & Pavement Markings Plan C108 o Landscape Plan C109 o Civil Details C501 — C509 o Vehicle Turning Movement Plan C601 o Architectural First Floor Plan A100 o Architectural Building Elevations A201 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 Chapter 250 Stormwater Management and Erosion Control regulations (Stormwater Regulations) adopted June 21, 2022. In accordance with §195-8.14.E.(8) All applications for site plan review shall include the submittal of a stormwater management plan prepared in accordance with the latest version of the Massachusetts Stormwater Handbook and additional criteria established herein and demonstrating full compliance with the Massachusetts Stormwater Standards and the North Andover Stormwater Management and Erosion Control Regulations promulgated under Chapter 165 of the Town Bylaws (Stormwater Management and Erosion Control Bylaw). 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. Town of North Andover July 6, 2026 Page 3of8 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 evaluated the pre-development site at two Design Points (DP). i. DP-1 is an existing catch basin located on the northeast side of the existing Administration Building. Within the existing parking lot there are several catch basins that pipe the stormwater that falls within the project area to DP-1. ii. DP-2 is the remaining project area that is not piped to DP-1 but flows offsite to the north towards the airfield. Stormwater from half of the existing administration building flows towards DP-2. b. The Applicant has evaluated the post-development site at the same two design points. Additional catch basins and stormwater practices have been incorporated to manage the stormwater from the reconfigured parking lot and the proposed roof runoff prior to being piped to DP-1. The total area and the impervious cover that overflows offsite towards DP-2 has been reduced under proposed conditions. c. The Applicant is not proposing any new untreated conveyance systems that outfall into a wetland. It appears that the Applicant has complied with Standard 1. 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. Within Section 3 of the Stormwater Management Report, the Applicant states that the total proposed land disturbance area is approximately 49,300 sf. However, the Limit of Work on the Permit Plans appears to be closer to 53,500 sf. HW recommends that the Applicant confirm the total anticipated land disturbance for documentation purposes. b. The Applicant has submitted a Pre-Development Drainage Map. EX-2 shows a time of concentration (Tc)flow path that passes through an area with an existing silt fence. HW recommends that the Applicant revisit the Tc flow path for EX-2. HW has reviewed the other Tc values and has no other comment. c. HW has reviewed the Applicants HydroCAD model, including the routing diagram, surface areas, curve numbers (CN), and precipitation depths and found the values to be reasonable. No further action is required. Town of North Andover July 6, 2026 Page 4 of 8 d. In Section 2.4 of the Stormwater Management Report, the Applicant has provided summary tables illustrating that the Proposed Design Storm Peak Flows are less than the Existing Peak Flows. HW agrees that the peak flows are reduced under proposed conditions for the 2-, 10-, and 25-year events. During the 100-year event the peak flow to DP-1 increases slightly. However, the overall reduction flowing north has been reduced. The Applicant has included a Net Change column with the Table in Section 2.4. HW agrees that the Applicant has reduced the peak flows but does not agree that the total percentage net change is listed correctly. e. The Applicant has provided tables showing that the Proposed Design Storm Volumes are reduced compared to the Existing Design Storm Volumes. There is a minimal increase of volume during the 100-year storm event to DP-1. However, the total reduction from the project area is reduced over existing conditions. Like the peak flows, HW agrees that the Applicant has reduced the peak volumes, but we do not agree that the total percentage net change is listed correctly in Section 2.5 of the Stormwater Management Report. f. The Applicant has proposed Area Drain AD-3 in Vegetated Detention Area 02 (VDA-02). It does not appear that the outfall pipe is shown on the plan view indicating which structure the outfall pipe is directed to. HW recommends that the Applicant includes the pipe from AD-3 to the existing catch basin EX-4 on Drawing C105. g. HW notes that the borings provided in the Stormwater Management Report indicate several feet of fill was observed beneath the proposed stormwater basins. HW recommends that the Applicant includes a note on Drawing C509 stating that all fill material below the Stormwater Basin or below the Vegetated Detention Areas will be removed and replaced with clean fill meeting the design criteria. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. The Applicant has provided recharge calculations in Appendix G of the Stormwater Management Report. HW could not confirm the impervious area listed for the Stormwater Basin or Vegetated Detention Area 01. The values listed in Appendix G are not consistent with the HydroCAD model. HW recommends that the Applicant confirm the impervious area directed towards each of the stormwater basins. It is HW's opinion that the water surface is not considered impervious for the recharge or water quality calculations. However, using a CN of 98 for the water in the HydroCAD model is reasonable. Town of North Andover July 6, 2026 Page 5 of 8 b. The Applicant has provided recharge calculations. However, no stage storage calculations have been provided to verify the volume available within the basins below the overflows. HW recommends that the Applicant provides the stage storage HydroCAD print out. c. The Applicant has included the test boring logs for the borings conducted within the footprints of the stormwater basins. It appears that the Applicant has provided more than 2 feet but less than 4 feet of separation between the bottom of the Basins and the estimated seasonal high groundwater (ESHGW) elevations. Mounding analyses are required in compliance with Volume 3, Chapter 1, page 28 of the MSH. HW notes that the Applicant has included one mounding analysis in Appendix K of the Stormwater Management Report. However, there are three infiltration practices that should be evaluated. Furthermore, HW recommends that the Applicant includes documentation for the various inputs used in the Hantush spreadsheet. d. HW recommends that the Applicant add the location of test boring B-4 to Drawings EX-1 and C105. e. The Applicant has provided draw down calculations. However, the volume utilized in the calculation should be the volume stored below the outfall and not the required recharge volume. HW recommends that the Applicant revised the calculations in accordance with Volume 3, Chapter 1, page 26 of the MSH. HW notes that the Applicant has included a calculation utilizing the provided recharge volume. However, the volume listed for the Stormwater Basin is not consistent with the volume listed under the recharge calculations provided previously. f. HW appreciates that the Applicant has not included the recharge volume from the Stormwater Basin in the total provided recharge. However, it is HW's opinion that this volume can be included for total recharge. 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 third party documentation for the TSS removal for the Contech Jellyfish Filter. HW notes that the Applicant has used a Rain Guardian as pretreatment for the Vegetated Detention Areas. HW agrees that the Rain Guardian does provide pretreatment. However, we recommend that the Applicant provide the third-party documentation to be included in the project file. b. The Applicant has provided the TSS removal calculations for the various treatment trains prior to the stormwater reaching the existing catch basin at DP-1. HW agrees that including the Jellyfish structure provides a minimum of 80% TSS removal for the proposed development. Town of North Andover July 6, 2026 Page 6of8 c. The Applicant has provided water quality calculations to document whether the proposed development is retaining 0.5 inches of runoff over the impervious area. The Applicant has included the two Vegetated Detention Areas to calculate the water quality volume. The Stormwater Basin has additional volume. However, it is managing very little impervious area, so the Applicant has not included the Stormwater Basin in its total water quality volume. HW agrees that the volume retained in the Stormwater Basin should not be included in the water quality volume calculation. The Jellyfish is providing additional means to improve water quality for this redevelopment. No further action is requested. d. The Applicant has included Total Phosphorous Reduction Calculations. It is not clear how the SCM Load was calculated. HW recommends that the Applicant document how the SCM Load (P) values provided were determined. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The proposed administration building with a 45-space parking lot is not considered a LUHPPL assuming the site will not generate more than 1,000 vehicle trips per day. HW does not believe that Standard 5 is applicable. However, we recommend that the Applicant confirm that the anticipated vehicle trips per day are less than 1,000. 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, Therefore Standard 6 is not applicable. No further action is requested. 7. Standard 7 is related to projects considered Redevelopment. a. The Applicant is increasing the impervious area by approximately 7,400 sf. The proposed project is a mix of new and redevelopment. The Applicant is required to comply with the Stormwater Management Standards for the new development and is allowed to comply to the maximum extent practicable for the previously developed portions of the site. The Applicant is also required to improve existing conditions. On page 11 of the Stormwater Report the Applicant has outlined how it is improving existing conditions. HW agrees that the proposed stormwater improvements and Long-Term Operation & Maintenance Plan are an improvement. No further action is requested. Town of North Andover July 6, 2026 Page 7of8 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The proposed project will be disturbing greater than one acre of land, therefore the Applicant is required to obtain a Construction General Permit and prepare a Stormwater Pollution Prevention Plan (SWPPP) in accordance with the EPA NPDES Program. The SWPPP should include source control and pollution prevention measures, stormwater practices to address erosion and sedimentation, stabilization measures, and procedures for operating and maintaining the proposed stormwater practices during construction. The plan should also identify the parties responsible for implementing the plan. The Planning Board may choose to require a signed SWPPP a minimum of 14 days prior to land disturbance as a Condition of Approval. b. HW recommends that the Applicant include a stockpile location and confirm it is surrounded by erosion controls. c. HW recommends that the Applicant includes inlet protection on catch basins within 100 feet of the construction entrance. d. HW notes that on Drawings C102 and C107, the limits of work around the proposed stormwater basin should include the Contractor Staging Area shown on Drawing C004. e. HW recommends that the Applicant clearly illustrate on Drawing C102 the emergency access route that must remain accessible throughout construction. 9. Standard 9 requires a Long-Term Operation and Maintenance (O & M) Plan to be provided. a. The Applicant has provided a stand-alone Long-Term O&M Plan. The O&M Plan includes a description of each stormwater practice with an inspection log, the manufacture's guidelines for the proprietary structures, an estimated budget, and a simple sketch illustrating where each of the stormwater practices is located within the project area. The Planning Board may choose to require receipt of a Long-Term Operation and Maintenance Plan signed by the property owner as a Condition of Approval. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. The Applicant has provided an unsigned Illicit Discharge Statement. The Planning Board may choose to require receipt of an Illicit Discharge Statement signed by the property owner as a Condition of Approval. 11. Within the Permit Plans in the Overall Site Plan, the Applicant states "Relief is requested from Section »»> of the North Andover Bylaw." HW recommends clarifying which section of the North Andover Bylaw relief is requested from. Town of North Andover July 6, 2026 Page 8of8 Conclusions HW recommends that the Planning Board requires the Applicant to provide a written response to address these comments. 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. We appreciate the opportunity to assist the Town of North Andover with this project review. Please contact Janet Bernardo at 508-833-6600 or at ibernardo(cD-horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. I u µ vr ur ,i" eiwwf Janet Carter Bernardo, PE Ariel Shramko, EIT Principal Staff Engineer