The URL can be used to link to this page

Home My WebLink About230315 HW2ndPeer Review_34 Glenore - - 34 GLENORE CIRCLE Horsley Witten Group usf f iabfe Etiviror menta Solutions 112 Wafer Street•80"Floor•Boston,AAA 02109 „ 857-263-8193•horsleywit¢en.com March 15, 2023 Ms. Jean Enright, Planning Director North Andover Planning Board 120 Main Street North Andover, Massachusetts 01845 Ref: Special Watershed Permit Peer Review 34 Glenore Circle 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 Watershed Permit Application for the proposed pool construction at 34 Glenore Circle, North Andover, MA. The plans were prepared by Sullivan Engineering Group, LLC, on behalf of David & Marianne Sweetser (Applicant). The project proposes the construction of an inground pool with an enclosure, a pervious paver patio, a firepit, and a deck. The stormwater from the pool enclosure roof will be directed to a proposed subsurface infiltration system (SIS). The proposed work will not include tree removal. The proposed construction is approximately 190 feet from the onsite wetland resource area, located along the eastern border of the site. The proposed work is over 200 feet from Lake Cochichewick, within the Watershed Protection District and within the 325-foot Non-Discharge buffer to a wetland resource. In accordance with §195-4.19. B. of the North Andover Zoning Bylaws, any surface or subsurface discharge proposed within the Non-Discharge Buffer Zone requires a Special Watershed Permit. The following additional documents and plans were received by HW in response to our February 6, 2023 initial peer review: • Letter to North Andover Planning Board, regarding Response to Peer Review, prepared by Sullivan Engineering Group, LLC, dated March 14, 2023 (79 pages); • Stormwater Operation & Maintenance, 34 Glenore Circle, North Andover, MA, prepared by Sullivan Engineering Group, LLC (2 pages); and • Plot Plan of Land, 34 Glenore Circle, North Andover, MA, prepared by Sullivan Engineering Group, LLC, dated January 23, 2023, revised March 14, 2023 (1 sheet). Stormwater Management Design Peer Review 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. Horsley%tMen.com 9116 Horslley%ttenCrou Horsley Witten Group, Inc. Town of North Andover March 15, 2023 Page 2 of 4 The following comments correlate to our February 6, 2023 initial peer review. Follow up comments are provided in bold font. 1. It appears that the proposed grading is minimal, with the new patio being set on the relatively level existing lawn area. No further action required. 2. The bottom of the proposed SIS is located 3 feet above the Estimated Seasonal High Groundwater Table (ESHGWT). HW recommends that the Applicant conduct a mounding analysis to confirm that the groundwater will not mound up into the chamber system. The Applicant has provided a mounding analysis that indicates the groundwater will not mound into the system. HW has no further comment. 3. It appears that the Applicant is not proposing an overflow outlet for the SIS. HW recommends that the Applicant confirm where stormwater will be directed if the system is at capacity. The Applicant has provided an Overflow Downspout Detail. HW has no further comment. 4. The Applicant has provided adequate recharge volume within the SIS. No further action required. 5. The Applicant has provided a watershed map in the Stormwater Report Plan. HW understands that the existing and proposed catchment areas are identical for this project. No further action required. 6. The Applicant has analyzed two subcatchment areas draining to two design points under existing conditions. It appears that Design Point 1 is the bordering vegetated wetland (BVW) to the east, and Design Point 2 is the catch basin located in the grass at the end of the driveway. It appears that a small portion of Subcatchment 2 along the southern property boundary drains to Design Point 1. No further action required. 7. According to the HydroCAD model, the total runoff area is 62,142 sf. However, based on the existing conditions watershed figure provided in the Stormwater Report Plan, it appears that the total runoff area is closer to 75,000 sf. HW recommends that the Applicant verify the total runoff area for the watershed, specifically the area listed as subcatchment area 1. The Applicant has adjusted the subcatchment areas modeled in HydroCAD. HW concurs with the revised values. No further action required. Iragaap,1 ,w1 1020 1.oavn d h,k:a h@ ,n daveA2H+°:OM 3,4 Gen we 15 ^raaPeil rRevaBi 3,14 33enor,: Town of North Andover March 15, 2023 Page 3 of 4 8. HW recommends that the Applicant confirm the area of grass cover under existing and proposed conditions and adjust the HydroCAD model accordingly. The Applicant has adjusted the subcatchment areas modeled in HydroCAD, specifically the area of grass in subcatchment 1 S. HW concurs with the revised values. No further action required. 9. The Applicant has used the precipitation depths as defined in the Hydrology Handbook for Essex County. HW understands that the 2008 Massachusetts Stormwater Handbook (MSH) is being updated soon to require precipitation depths as specified by the NOAA Atlas 14 Precipitation Frequency Estimates. HW recommends that the Applicant consider revising its HydroCAD model for the 10- and 25-year storm to use the more conservative depths as listed in the Table below: Recurrence Interval Hydrology Handbook NOAA Atlas 14 (inches) (inches) 10 year 4.80 5.04 25 year 6.00 6.20 The Applicant has adjusted the precipitation depths in the HydroCAD model as suggested. HW has no further comment. 10. The Applicant is proposing the installation of a silt fence erosion control barrier at the limit of work. HW concurs with the chosen erosion control measures. No further action required. 11. The Applicant has proposed inserting a silt sack in the existing catch basin. HW recommends that the Applicant provide a silt sack detail. The Applicant has added the silt sack detail as requested. HW has no further comment. 12. The Applicant has included a proposed materials staging and soil stockpile area on the site plan which is outside of the 150-foot non-disturbance zone. No further action required. 13. HW recommends that a standalone Operation & Maintenance (O&M) Plan be provided to the homeowner for long term maintenance of the existing catch basin, permeable pavers, roof drains, and SIS. HW further recommends that a plan is attached to the O&M Plan that clearly illustrates where all stormwater practices are located on the property. The Applicant has provided a standalone O&M Plan for the homeowner's use. The Planning Board may choose to require that the property owner sign the O&M Plan. Iragaap,1 ,w1 1020 1.oavn d h,k:a h@ ,n daveA2H+°:OM 3,4 Gen we 15 ^raaPeil rRevaBi 3,14 33enor,: Town of North Andover March 15, 2023 Page 4 of 4 14. The Applicant has provided an Illicit Discharge Statement. HW recommends that the Town require the Illicit Discharge Statement to be signed by the property owner. The Applicant has provided a signed Illicit Discharge Statement. No further action required. 15. HW recommends that the Applicant explain to the Planning Board the methodology for pumping out the pool at the end of the season. Specifically, where will the pool water be pumped to and how will the Applicant confirm that pool chemicals will not be discharged towards the resource area. The pool maintenance should be included in the O&M Plan for the owners use. The Applicant has explained that the pool will not be pumped out seasonally. It is within an enclosure for year-round use. HW suggests that the Planning Board include a condition that if it is necessary to drain the pool in the future, the pool will be pumped out into the chamber system after it has properly dechlorinated. Conclusions HW is satisfied that the Applicant has adequately addressed our 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. Please contact Janet Bernardo at 508-833-6600 or at jernardo@horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. n 13 Janet Carter Bernardo, P.E. Associate Principal Iragaap,1 ,w1 1020 1.oavn d h,k:a h@ ,n daveA2H+°:OM 3,4 Gen we 15 ^raaPeil rRevaBi 3,14 33enor,: