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HomeMy WebLinkAbout20160105 Consultant Review - Consultant Review - 254 GREAT POND ROAD 12/8/2015 Eggleston Environmental December 8, 2015 North Andover Planning Board 1600 Osgood Street North Andover,MA 01845 Attn: Jean Enright,Assistant Director of Community Development RE: Watershed Special Permit 254 Great Pond Road, Thomas and Nicole Friel-Petitioners Dear Ms. Enright and Board Members: Per your request, I have reviewed the November 11, 2015 Watershed Special Permit Application and November 10, 2015 Site Plan for the above-referenced project, both prepared by Sullivan Engineering Group, LLC. I also conducted a brief site visit on December 1,2015 to observe existing drainage patterns. My primary focus in this technical review is on the overall stormwater management approach and design concepts used in the project, as well as its compliance with the Town of North Andover's zoning requirements for Watershed Protection Districts and Site Plan Review. The proposed project is a 22' x23' addition and new decks on an existing single-family home. Existing drainage on the site is overland toward Lake Cochichewick. The entire project is within the Non-Disturbance Zone of the Watershed Protection District, except for a portion of the cantilevered deck that extends into the Conservation Zone. The proposed plan calls for a 500-gal diywell to infiltrate roof drainage from the proposed addition and the addition of several deed restrictions limiting the use of non- organic lawn chemicals and prohibiting coal-tar based pavement sealants. My comments on the application are outlined below: 1. Section 4.136 (3)(d) of the Zoning Bylaw prohibits the construction or placement of any new permanent structures within the Conservation Zone; it is unclear therefore whether the proposed cantilevered deck would be allowable. It is also unclear whether the project would entail any vegetation removal or cutting within the Conservation Zone to accommodate the new deck, as this is also prohibited. 2. The proposed work within the Non-Disturbance Zone is a use allowed by Special Permit under Section 4.136 (3)(c) of the Zoning Bylaw, and includes appropriate measures to prevent any significant degradation of the quality or quantity of water in or entering Lake Cochichewick. The proposed deed restrictions are consistent with what the Board has required of other residential projects in the District. 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 r 254 Great Pond Rd WSP 2 December 8, 2015 3. I note that the drainage calculations are based on outdated (1961) TP-40 rainfall volumes and not the larger volumes provided in the Atlas 14 update to TP-40 recently issued by NOAA. However, I believe that the drywell is sized appropriately for the proposed addition and that there is no need to revise the calculations at this time. 4. Roof downspouts should be screened to prevent blockage and preserve the infiltration system, and should include overflows to direct excess flow onto a pervious surface when the system capacity is exceeded. 5. It should be verified that the location of the proposed roof drywell is consistent with the design of the proposed addition, specifically that all of the roof drainage can be discharged on the southerly side of the addition. I appreciate the opportunity to assist the North Andover Planning Board with the review of this project, and hope that this information is suitable for your needs. Please feel free to contact me if you or the applicants have any questions regarding the issues addressed herein. Sincerely, EGGLESTON ENVIRONMENTAL 5S Lisa D. Eggleston, P.E.