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HomeMy WebLinkAbout2020-03-10 Stormwater Review (HWG) Horsley Witten Group Sustainable Environmental Solutions 112 Water Street•611 Floor•Boston,MA 02109 657-263-8183•horsteywMen.00rn W February 17, 2020 Ms. Monica Gregoire, Staff Planner Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Ref: 3rd Stormwater Peer Review Andover Pest Control, 633 Turnpike Street North Andover, MA Dear Ms. Gregoire and Board Members: The Horsley Witten Group, Inc. (HW) is pleased to provide the North Andover Planning Board and Conservation Commission with this letter report summarizing our third peer review of the Stormwater Management Report and Site Plan for the proposed project at 633 Turnpike Street, North Andover, Massachusetts. The plans were prepared for Michael Ryley, Andover Pest Control (Applicant) by Marchionda &Associates, L.P. HW understands that the Applicant has applied for an Order of Conditions to expand the driveway and parking area on a 21,875 square foot(sf) lot. The Applicant proposes to install a rain garden, vegetated filter strip, and stone diaphragm to manage stormwater runoff. The proposed alterations represent an additional 3,845 sf of impervious cover. The property falls within the 100-foot buffer zone of a bordering vegetated wetland located along the rear of the parcel; no disturbances are proposed within the 25-foot wetland buffer. The following additional documents and plans were received by HW in response to our secondl February 12, 2020 pee review letter: • Site Plan--633 Turnpike Street in North Andover, Massachusetts, prepared by Marchionda & Associates, L.P., dated December 16, 2019, revised February 13, 2020; and • Site Plan Detail--633 Turnpike Street in North Andover, Massachusetts, prepared by Marchionda &Associates, L.P., dated December 16, 2019, revised February 13, 2020. Stormwater Management Design Peer Review HW offers the following overall comments concerning the stormwater management design as per the Massachusetts Stormwater Handbook(MSH) dated February 2008, the North Andover Stormwater Management and Erosion Control Regulations(Stormwater Regulations) adopted February 5, 2011, and the North Andover Stormwater Management and Erosion Control Bylaw(Bylaw). The comments below correlate with our February 41h and 121h, 2020 peer review letters, additional comments are provided in bold font. 1. Standard 1 states that no new stormwater conveyances may cause erosion in wetlands of the Commonwealth. a. The Applicant has proposed a rain garden surrounded by a berm to contain and recharge the stormwater runoff from the impervious area of the parcel. The Applicant HorsleyWiften.corn In t3)HorsIeyWittenGroup ®Horsley Witten Group, Inc. Town of North Andover February 17, 2020 Page 2 of 4 indicates that the berm is set at elevation 246.1 with a weir at elevation 245.6. The peak elevation of the rain garden during the 100-year storm event is 245.80. It appears that there will be no untreated stormwater conveyance which may cause erosion in the wetlands. February 4, 2020: It appears that the Applicant complies with Standard 1. February 12, 2020: No further comment. 2. Standard 2 requires that post-development runoff does not exceed pre-development runoff off- site. a. February 4, 2020: The Applicant has used a time of concentration (Tc) of 3 minutes for existing conditions and a Tc ranging from 3-4.8 minutes for proposed conditions, according to the HydroCAD output. HW recommends that the Applicant revise the HydroCAD analysis to utilize Tc values of at least 5 minutes, as is standard practice under the TR-20 method. February 12, 2020: The Applicant has adequately addressed this comment and has revised the Tc values in the existing and proposed HydroCAD model. No further comment. b. February 4, 2020: The Applicant has indicated that an 8-foot long weir is proposed in the rain garden at elevation 245.6, however it is not clear where this weir will be located on the Site Plan. The narrative indicates that the stormwater will overflow into the driveway prior to discharging into the wetlands. HW recommends that the Applicant provide a level spreader at a location that will ensure that stormwater will not overflow the proposed berm towards an abutting property. Furthermore, HW recommends that a detail is provided for the proper construction of the weir. February 12, 2020: The Applicant has clarified the location of the weir and provided the requested detail. In accordance with the HydroCAD model the stormwater within the rain garden will peak at approximately 4-inches during a 100-year storm event. No further comment. c. February 4, 2020: Based on the proposed grading on the Site Plan, it seems that a gap is present between the perimeter berm (elevation 246.1) and the proposed elevation 246 contour line in the vicinity of the proposed shed. Due to this low point, it seems that stormwater may bypass the proposed rain garden weir and spill onto the abutting property on the northwestern boundary of the site during heavy rain events. HW proposes that the Applicant either extend the berm to meet the proposed shed or spot grade the gap between the berm and the shed to be set at a higher elevation than the rain garden weir. February 12, 2020: The HydroCAD model indicates that the peak elevation during a 100- year storm event will be 245.68. The proposed overflow weir is set at 245.60. There are two locations that the proposed surface grade could be lower than 245.6 as indicated on the attached sketch. HW recommends that spot grades are added to the plan to verify that the stormwater will not flow onto an abutting property bypassing the proposed weir. Furthermore, HW recommends relocating one of the downspouts so that they both discharge into the rain garden and call out the material of the pipe. February 17, 2020: The Applicant has provided a revised site plan which includes spot grades as recommended. Furthermore, the Applicant has eliminated the K;1Projects12018l18065 N Andover On-Cal1118065N 633 Turnpike Street\ReportsUhird Repon\200217 3rd Peer Review 633 Tnnipike Street.docx Town of North Andover February 17, 2020 Page 3 of 4 downspout pipes to the rain garden as there was not adequate coverage. The down spouts will direct the stormwater runoff overland towards the rain garden. The grass filter strip and stone diaphragm will provide the required pretreatment. No further comment, the Applicant complies with Standard 2. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. February 4, 2020: The Applicant has provided groundwater recharge calculations, which indicate that the required volume of stormwater will recharge under the proposed stormwater management design, and that the proposed rain garden will drain in less than 72 hours. February 12, 2020: No further comment. b. February 4, 2020: The Applicant has conducted soil test pits and designed the bottom of the rain garden to maintain 2 feet of separation to the Estimated Seasonal High Ground Water(ESHGW). In accordance with Volume 3, Chapter 1, Page 38 of the MSH, a mounding analysis is only required when the vertical separation from the bottom of an exfiltration system to seasonal high groundwater is less than four(4) feet and the recharge system is proposed to attenuate the peak discharge from a 10-year or higher 24-hour storm. It appears that the proposed rain garden does not fully attenuate the 10- year storm event therefore a mounding analysis is not required. It appears that the Applicant complies with Standard 3. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids(TSS) and to treat 0.5-inches of volume from the impervious area for water quality. a. February 4, 2020: The HydroCAD analysis provided by the Applicant indicates that a volume greater than the water quality volume can be held by the proposed rain garden. February 12, 2020: No further comment. b. February 4, 2020: According to Volume 2, Chapter 2 of the MSH, the bottom layer of a rain garden should be coarse gravel, pea gravel, or sand; bioretention soil should be a mix of sand, topsoil, and compost. HW recommends that the Applicant revise the rain garden design to include a gravel or sand layer, and that the Applicant specify the contents of the bioretention soil mix to be used in order to receive treatment credit. February 12, 2020: The Applicant has revised the Typical Rain Garden Detail as requested. No further comment. 5. Standard 5 is related to projects with a Land Use of Nigher Potential Pollutant Loads (LUHPPL). a. February 4, 2020: The project is not considered an LUHPPL and therefore Standard 5 is not applicable. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone 11 or an Interim Wellhead Protection Area of a public water supply. a. February 4, 2020: The project site does not discharge into a critical area therefore Standard 6 is not applicable to this project. 7. Standard 7 is related to projects considered Redevelopment. KN'rojects120 1 811 8065 N Andover On-Ca1h18065N 633 Twiipike StreeAReports\Third Report1200217_3rd Peer Review_633 Turnpike Slreet.doct Town of North Andover February 17, 2020 Page 4 of 4 a. February 4, 2020: The project site is not considered a redevelopment due to a proposed increase in impervious cover, therefore Standard 7 is not applicable to this project. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation or other pollutant sources. a. February 4, 2020: HW has reviewed the Applicant's proposed erosion controls and has the following recommendations: i. February 4, 2020: Extend the erosion control barrier to include the eastern corner of the site. February 12, 2020: The Applicant has extended the erosion control barrier as recommended. ii. February 4, 2020: Per the North Andover Stormwater Regulations, Section 8.21, include a temporary construction tracking pad at the site entrance/exit. February 12, 2020: The Applicant has added the temporary tracking pad as recommended. No further comment. 9. Standard 9 requires a Long-Term Operation and Maintenance (0& M) Plan to be provided a. February 4, 2020: The Applicant has provided an O&M Plan that meets the requirements of MSH Volume 2, Chapter 2 for the proposed BMPs. It appears that the Applicant complies with Standard 9. 10. Standard 10 requires an Illicit Discharge Compliance Statement to be provided. a. February 4, 2020: The Applicant has indicated that an Illicit Discharge Compliance Statement will be prepared prior to discharging to post-construction BMP's. HW recommends that the Statement is signed prior to any land disturbance. Please contact Janet Bernardo at 857-263-8193 or at jbernardo@horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. Janet Carter Bernardo, P.E. Senior Project Manager K:\ProjectsUOt8118065 N Andover On-Ca1111 S065N 633'1'u€rtpike Street\Reports\Third Repor11200217_3rd[leer Review_633 Turrrp€ke Street.doex Horsley Wiffen Group Sustainable Environmental Solutions 112 Water Street-V Floor•Boston,MA 02109 857-263-8193 horsleywitten.00m February 4, 2020 Ms. Monica Gregoire, Staff Planner Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Ref: 633 Turnpike Street North Andover, MA Dear Ms. Gregoire and Board Members: The Horsley Witten Group, Inc. (HW) is pleased to provide the North Andover Planning Board and Conservation Commission with this letter report summarizing our initial peer review of the Stormwater Management. Report and Site Plan for the proposed project at 633 Turnpike Street, North Andover, Massachusetts. The plans were prepared for Andover Pest Control (Applicant) by Marchionda & Associates, L.P. HW understands that the Applicant has applied for an Order of Conditions to expand the driveway and parking area on a 21,875 square foot(sf) lot. The Applicant proposes to install a rain garden, vegetated filter strip, and stone diaphragm to manage stormwater runoff. The proposed alterations represent an additional 3,845 sf of impervious cover. The property falls within the 100-foot buffer zone of a bordering vegetated wetland located along the rear of the parcel; no disturbances are proposed within the 25-foot wetland buffer. The following documents and plans were received by HW: • Stormwater Management Report, 633 Turnpike Street, North Andover, Massachusetts, prepared by Marchionda &Associates, L.P., dated November 5, 2019; and • Site Plan —633 Turnpike Street in North Andover, Massachusetts, prepared by Marchionda &Associates, L.P., dated December 16, 2019. Stormwater Management design Peer Review HW offers the following overall comments concerning the stormwater management design as per the Massachusetts Stormwater Handbook (MSH) dated February 2008, the North Andover Stormwater Management and Erosion Control Regulations (Stormwater Regulations) adopted February 5, 2011, and the North Andover Stormwater Management and Erosion Control Bylaw (Bylaw). The comments below correlate with the MSH standards and where the more stringent Town requirements are applicable additional comments are noted. Town of North Andover February 4, 2020 Page 3 of 4 higher 24-hour storm. It appears that the proposed rain garden does not fully attenuate the 10-year storm event therefore a mounding analysis is not required. It appears that the Applicant complies with Standard 3. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 0.5-inches of volume from the impervious area for water quality. a. The HydroCAD analysis provided by the Applicant indicates that a volume greater than the water quality volume can be held by the proposed rain garden. b. According to Volume 2, Chapter 2 of the MSH, the bottom layer of a rain garden should be coarse gravel, pea gravel, or sand; bioretention soil should be a mix of sand, topsoil, and compost. HW recommends that the Applicant revise the rain garden design to include a gravel or sand layer, and that the Applicant specify the contents of the bioretention soil mix to be used in order to receive treatment credit. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The project is not considered an LUHPPL and therefore Standard 5 is not applicable. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone 11 or an Interim Wellhead Protection Area of a public water supply. a. The project site does not discharge into a critical area therefore Standard 6 is not applicable to this project. 7. Standard 7 is related to projects considered Redevelopment. a. The project site is not considered a redevelopment due to a proposed increase in impervious cover, therefore Standard 7 is not applicable to this project. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation or other pollutant sources. a. HW has reviewed the Applicant's proposed erosion controls and has the following recommendations: i. Extend the erosion control barrier to include the eastern corner of the site. ii. Per the North Andover Stormwater Regulations, Section 8.21, include a temporary construction tracking pad at the site entrance/exit. 9. Standard 9 requires a Long-Term Operation and Maintenance (O &M) Plan to be provided. a. The Applicant has provided an O&M Plan that meets the requirements of MSH Volume 2, Chapter 2 for the proposed BMPs. It appears that the Applicant complies with Standard 9. 10. Standard 90 requires an Illicit Discharge Compliance Statement to be provided. a. The Applicant has indicated that an Illicit Discharge Compliance Statement will be prepared prior to discharging to post-construction BMP's. HW recommends that the Statement is signed prior to any land disturbance. K:IP€ojects120 1 811 5065 N Attdo�,cr Oit-('otkl'3065N 633 Tut7€l)ike Str4etiReportsli'irst Relxn i�200204 Peer Review 633 1'wllpike strctt.doex