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HomeMy WebLinkAbout2023-11-21 Initial Stormwater Peer Review WSP I HorsleyWitten G rouP Sustainable Environmental Solutions 112 Water Street-Ba Floor Boston,MA 02109 - 857-263.8193•horsleywilten.corn November 16, 2023 Ms. Jean Enright, Planning Director North Andover Planning Board 120 Main Street North Andover, Massachusetts 01845 Ref: Initial Stormwater Peer Review 173 Johnson 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 initial review of the Stormwater Management Report and Site Plan for the proposed development at 173 Johnson Street, North Andover, MA. The plans and stormwater report were prepared by Sullivan Engineering Group, LLC on behalf of Christopher J. Hughes (Applicant). The project proposes the construction of a 273 square foot (sf) addition to an existing single-family house. A drainage infiltration system is proposed to collect the entire roof area of the proposed addition roof. Roof runoff will be collected by gutters and roof drains and conveyed to a drainage infiltration field. The proposed work is located within the Watershed Protection District including the 325-foot Non-Discharge Zone. The following documents and plans were received by HW: • Special Permit— Watershed Permit Application, 173 Johnson Street, North Andover, MA, prepared by Sullivan Engineering Group, LLC, dated November 1, 2023 (70 pages). • Plot Plan of Land, 173 Johnson Street, North Andover, MA, prepared by Sullivan Engineering Group, LLC, dated October 19, 2023 (1 sheet). 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, Chapter 165 of the Town Bylaws. Chapter 165 further references Chapter 250. Stormwater Management and Erosion Control. HW offers the following comments concerning the stormwater management design. We have used the Massachusetts Stormwater Standards as the basis for organizing our comments, However, in instances where the additional criteria established in §250-27 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 evaluated one discharge point from the project site. Under existing HorsleyWilten.com ct,HorsleyWittenGroup Horsley Witten Group, Inc, Town of North Andover November 16, 2023 Page 2 of 4 conditions, the site property is modeled as one subcatchment area which flows overland to northern abutting properties. There are no existing stormwater practices. b. The Applicant proposes to construct a subsurface chamber system to infiltrate runoff from the proposed additional building roof. The system overflows through the downspout openings to the abutting northern properties via overland flow. The site is not discharging to wetlands or waters of the Commonwealth. 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. 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 under Documenting Compliance in the Stormwater Management Report. No further action required. b. In accordance with §250-22 B. (5) (a) a summary of proposed land area to be disturbed and existing and proposed impervious area should be provided as part of the narrative. HW recommends that the Applicant include the proposed land area to be disturbed and the existing and proposed impervious area in the narrative. c. The Applicant has modeled the vegetated area as Woods/grass comb., Good, HSG B in the HydroCAD model. According to the USDA online Web Soil Survey, 305C and 310C belong to Hydrologic Soil Group (HSG) C and CID, respectively. HW typically recommends that an Applicant use a more appropriate HSG in the HydroCAD model. However, in this instance it does not appear to make a difference as the Applicant has used the same values for pre- and post-development. No further action required. d. The Applicant has routed the roof subcatchment (2S) to the Cultec Infiltration Field (1 P) in the post-development HydroCAD model. The Cultec Infiltration Field can overflow via the downspout openings to Design Point 1. The Cultec Infiltration Field has been designed to fully retain the 100-year storm event. No further action required. e. The Applicant has used 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). No further action required. 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 volume and drawdown calculations. It appears that I` the subsurface chamber system provides sufficient recharge and will drawdown in less than 72 hours as required. No further action necessary. b. The separation from the bottom of the subsurface chamber system to the Estimated Seasonal High Groundwater (ESHGW) is more than 4 feet, and a mounding analysis is III not required. No further action necessary. KAProjects12021121020 Town of North Andove621020R 173 Johnson Street\Report1231116_SWPeerRoview_173 Johnson Slreet.docx r Town of North Andover November 16, 2023 Page 3 of 4 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 wafer quality. a. The Applicant has provided a TSS worksheet that lists the subsurface chamber system to provide 80% TSS removal. Per the §250-23 B (1) the Applicant is required to remove 90% of the average annual load of Total Suspended Solids (TSS) and 60% of the average annual load of Total Phosphorus. This can be achieved by"retaining the volume of runoff equivalent to, or greater than, one (1.0) inch multiplied by the total post- construction impervious surface area on the new development site". The Applicant has provided water quality volume calculations demonstrating that the subsurface chamber system retains the V storm. No further action required. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The project is not considered a LUHPPL. Standard 5 is not applicable. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone /1, or an Interim Wellhead Protection Area of a public water supply. a. The proposed work is located within the North Andover Watershed Protection District. In accordance with §195-4.19. B. (4)All construction in the Watershed Protection District shall comply with best management practices for erosion, siltation, and stormwater control in order to preserve the purity of the groundwater and the lake; to maintain the groundwater table; and to maintain the filtration and purification functions of the land. It appears that the proposed construction complies with best management practices for erosion, siltation, and stormwater control. The Applicant complies with Standard 6. 7. Standard 7 is related to projects considered Redevelopment. a. The project is proposing to increase impervious area and is not considered a redevelopment. Standard 7 is not applicable. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. It appears that the proposed erosion control barrier delineates a portion of the limit of work (LOW). HW recommends that the Applicant add a separate LOW line that includes the construction entrance and avoids any existing trees. b. HW recommends that the Applicant add a note stating, prior to any land disturbance activities commencing on the site, the developer shall physically mark limits of no land disturbance with tape, signs, or orange construction fence, so that workers can see the areas to be protected. The physical markers shall be inspected daily. c, It appears that there may be trees located near the proposed construction activities. HW notes that the Applicant has stated that no trees will be removed. HW recommends that the Applicant provide protection for any trees located near the proposed construction. 9. Standard 9 requires a Long-Term Operation and Maintenance (O & M) Plan to be provided. a. The Applicant has provided a description of the inspection and maintenance tasks required for the site in the Stormwater Report. HW recommends that the Applicant KAProjects12021121020 Town of North AndOvoA21020R 173 Johnson Street\Report1231116_SWPeerReview_i 73 Johnson Street.doex Town of North Andover November 16, 2023 Page 4 of 4 provide an O&M Plan as a standalone document to be signed by the owner, which includes the following: i. Stormwater management system owners; ii. Parties responsible for operation and maintenance; iii. An example maintenance log or checklist for each Stormwater practice that the homeowner can use to log maintenance; iv. A schedule for implementing routine and non-routine maintenance tasks to be undertaken after construction is complete; V. An estimated operations and maintenance budget; and vi. A simple sketch that is drawn to scale and shows the location of all stormwater practices requiring inspections and long-term maintenance. b. HW recommends that the Applicant mention the inspection ports for the subsurface chamber system in the O&M Plan. c. HW recommends including the manufacturers maintenance recommendations for the subsurface chamber systems for the owner's benefit in the O&M Plan. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. The Applicant has provided a signed Illicit Discharge Compliance Statement in the Stormwater Report. No further comment. Conclusions HW recommends that the Planning Board require that the Applicant address the few outstanding comments as part of the Board's review process, specifically associated with the erosion controls and the O&M Plan. 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 jernardo@horsIeywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. Janet Carter Bernardo, P.E. Veronica Seward-Aponte, E.I.T. Associate Principal Environmental Engineer KAProjects12021i21020 Town of North Andover121020R 173 Johnson Street\Report1231116_SWPeerReview 173 Johnson Street.docx