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HomeMy WebLinkAbout2026/03/03 - Response to 1st Stormwater Peer Review - 200 Bridle Path /,Iandover 1 East River Place consultants Methuen,Massachusetts 01844 inc. Tel.(978)687-3828 www.andoverconsultants.com March 3, 2026 Ms. Jean Enright, Planning Director North Andover Planning Department 120 Main Street North Andover, MA 01845 RE: 200 Bridle Path North Andover,Mass Response to Peer Review Memorandum#1 Dear Ms. Enright and Members of the Board: We are in receipt of a review letter for the above referenced project dated February 27, 2026 prepared by the Board's Peer Reviewer, Horsley Witten Group (HW). We have reproduced HW's comments below in italics with our response noted below in bold. Comment I —The Applicant has included erosion controls on the site plan including a 9-inch straw wattle on the north and east side of the project area and a stockpile location on the west side of the house. HW recommends that the Applicant provides a limit of work line on the site plan confirming the total area of disturbance. and includes erosion controls around the stockpile. Response—The site plan has been revised to include a clearly delineated limit of work line, as recommended. The total area of disturbance within the limit of work is approximately 15,880 square feet. In addition, erosion control measures have been added around the stockpile location to further minimize potential sediment impacts during construction. Comment 2—The Applicant has proposed a temporary construction access around the north side of the house. HW recommends that the Applicant provide a detail of the construction access. If feasible, HW recommends that the Applicant evaluate whether the construction access can be around the south side of the house furtherfrom the BVW. Note 4 on the Site Plan indicates that the existing driveway will be used as the construction entrance. The plan view and the note are not consistent. HW suggests that the Applicant considers construction matting or other measures to minimize the tracking of sediment onto the driveway and offsite per§250-25.E. (13) of the North Andover Code. Response— stabilized construction entrance detail has been added to the site plan as recommended, and the plan notes have been revised to clarify that the existing driveway will be used for construction access. The feasibility of relocating the temporary construction access to the south side of the house was evaluated; however, nearly the entire site lies within the 100-foot buffer zone, and the limited area between the existing dwelling,previously disturbed areas, and the bordering vegetated wetland constrains access options. Given that the majority of construction activities will occur on the northerly side of the site,the proposed access location represents the least environmentally impactful option. Comment 3— The Applicant has noted that the project includes proposed work consisting of two small additions to an existing single-family residence and is therefore exempt from the Massachusetts Stormwater Management Standards pursuant to 310 CMR 10.05(6)(1). The Applicant has not provided stormwater calculations for the proposed work. However, the Applicant has provided a stormwater trench adjacent to the proposed expanded driveway. HW recommends that the Applicant provides runoff calculations for the existing and proposed conditions to ensure that the stone trench is properly sized for the increased impervious area and that the proposed improvements do not create adverse conditions to downstream neighbors. Page 1 of 3 Civil Engineers•Land Surveyors•Land Planners P:\25\25-05\Docs\letters\2026-03-03_response to peer review comments.docx and over consultants inc. Response—As noted in the comment,the proposed improvements are exempt from the Massachusetts Stormwater Management Standards pursuant to 310 CMR 10.05(6)(1) and are not subject to State or local stormwater requirements.Nevertheless, a crushed stone infiltration trench has been incorporated into the site plan as a best management practice to offset a de minimis increase of approximately 340 square feet of impervious area. This increase consists of a minor driveway expansion (142 square feet) and a rear addition (198 square feet); the front addition is proposed over an existing paved driveway and therefore does not result in a net increase in impervious cover. The proposed crushed stone trench provides approximately 77.6 cubic feet of storage,which is sufficient to accommodate approximately 2.7 inches of runoff from the additional impervious area.As designed,the trench will mitigate any potential increase in runoff and will not create adverse drainage conditions for downstream properties. Comment 4—HW recommends that the Applicant clarify the total increased impervious area. HW could not confirm the impervious area to be removed and the total proposed impervious area to be constructed. HW recommends that the Applicant provides a stormwater calculation comparing the existing and proposed impervious areas and the runoff for each. HW further notes that a roof drain is indicated on the Site Plan discharging towards wetland flag SA. HW recommends that the Applicant clarify if this roof drain will remain after construction and if it is causing any erosion to the adjacent BVW. Response—The total increase in impervious area associated with the proposed project has been clarified on the revised site plan. The project results in a de minimis net increase of approximately 340 square feet of impervious area, consisting of a 142-square-foot driveway expansion and a 198-square-foot rear addition. The proposed front addition is located entirely over an existing paved driveway and therefore does not increase impervious cover.No existing impervious surfaces are proposed to be removed. Although the project is exempt from State and local stormwater management standards, a comparison of existing and proposed impervious areas and associated runoff has been provided to demonstrate that post-construction conditions will not result in adverse impacts. The proposed crushed stone infiltration trench provides approximately 77.6 cubic feet of storage,which is sufficient to accommodate approximately 2.7 inches of runoff generated by the net increase in impervious area. With respect to the roof drain shown on the site plan,the roof drain is proposed to remain following construction and discharges to a previously disturbed area. Based on site observations,the discharge has not resulted in erosion or adverse impacts to the adjacent bordering vegetated wetland.No changes to the roof drain discharge location are proposed,and existing conditions will be maintained. Comment S—The Applicant has noted the existing soil conditions as Hydrologic Soil Group (HSQ)B/D per the Natural Resources Conservation Service (NRCS). HW recommends that the Applicant provides the sizing calculations for the stormwater trench for this soil type. A soil test pit within the footprint of the trench would be appropriate to confirm the infiltration rate. The Board may consider requiring a test pit conducted prior to construction with documentation provided to the Board as a special condition. Response—As noted previously,the proposed project is exempt from the Massachusetts Stormwater Management Standards; however,the crushed stone infiltration trench has been included as a conservative best management practice to mitigate the de minimis increase in impervious area. The trench has been sized based on available NRCS soil mapping indicating Hydrologic Soil Group B/D, using storage volume rather than infiltration rate as the controlling design criterion.As designed,the trench provides approximately 77.6 cubic feet of storage,which is sufficient to accommodate approximately 2.7 inches of runoff from the net increase in impervious area, independent of infiltration performance. Page 2 of 3 P:\25\25-05\Docs\letters\2026-03-03_response to peer review comments.docx and over consultants inc. No soil test pit is proposed at this time, as the trench is not required for regulatory compliance and is intended primarily as runoff storage and attenuation. If infiltration rates are lower than anticipated due to localized soil conditions,the trench will continue to function as a subsurface storage feature and will not adversely affect adjacent resource areas.The Applicant understands that the Board may, at its discretion,require confirmation of subsurface conditions prior to construction and would comply with any such condition if imposed. Comment 6—The Applicant has provided Erosion and Sedimentation Control elements on the Site. It does not appear there are any notes for stabilization on the plans or in the supplementary information. HW recommends that the Applicant revise the plans as needed to clarify how the site will be stabilized. HW further recommends that the Applicant indicates how the landscaping will be restored at the end of construction. Response—The plans have been revised to include general erosion and sedimentation control notes addressing site stabilization as recommended. These notes specify that all disturbed areas will be stabilized upon completion of construction activities with loam and seed.Any temporary erosion control measures will remain in place until stabilization is achieved and will be removed upon approval by the Planning Board and Conservation Commission. Comment 7—HW notes the Applicant has proposed a stone trench along the driveway. The Applicant does not mention how this will be maintained or how this affects the proposed runoff. HW recommends that the Applicant provides information in the supplementary package explaining how the trench should be maintained after construction and at what frequency for the benefit of the homeowner. Response—The crushed stone trench is designed as a passive stormwater best management practice requiring minimal maintenance.Maintenance guidance for the homeowner has been added to the revised site plan as part of the detail and includes periodic inspection of the trench and contributing drainage areas,particularly following major storm events.Maintenance activities consist of removing accumulated sediment and debris (e.g.,leaves, litter)from the trench surface,ensuring runoff can enter the trench unimpeded, and repairing or replacing stone as needed. Inspections are recommended at least annually and after significant rainfall events, as part of routine residential landscaping maintenance.When properly maintained,the trench will continue to provide runoff storage and attenuation for the minor increase in impervious area without adversely affecting site drainage or adjacent resource areas. If you have any questions concerning these latest revisions, or require anything further, please feel free to contact me at your convenience. Sincerely, Andover Consultants Inc. 0 Dennis A. Griecci,P.E., LEED AP Enclosures Page 3 of 3 P:\25\25-05\Docs\letters\2026-03-03_response to peer review comments.docx