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HomeMy WebLinkAbout2022-01-04 Stormwater Review WSP HorsleyWitten Group rou p , Sustainable Environmental Solutions � 112 Water street•fi"Floor•Soston,MA U21119 857-263-8193•harstaywitten.com December 29, 2021 Ms. Jean Enright, Planning Director Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Re: Third Stormwater Peer Review 212 Brentwood 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 third review of the Stormwater Management Report and Site Plan for the proposed improvements to 212 Brentwood Circle in North Andover, MA. The plans were prepared by Sullivan Engineering Group, LLC (Applicant) for John and Michelle Ternulb (Applicant). The project proposes the construction of an in-ground pool, patio, and shed in the back of the existing 1-acre site. The stormwater management for the proposed improvements includes 2-foot-deep river rock drainage trenches surrounding the proposed impervious site improvements. A total of 1,352 square feet(sf) of additional impervious area is proposed on site. The proposed development is located fully within the 325-foot Non-Discharge Buffer zone from the wetland area located at the adjacent#96 Brentwood Circle and requires a Special Watershed Permit. The following additional documents and plans were received by HW in response to our December 16, 2021, review letter: • Email from Jack Sullivan, dated December 27, 2021, regarding O&M Plan fpr 212 Brentwood Circle (1 page); • Response Letter, 212 Brentwood Circle, North Andover, Massachusetts, prepared by Sullivan Engineering Group, LLC, dated December 27, 2021 (90 pages); • Pool Maintenance and BMP Plan, 212 Brentwood Circle, North Andover, Massachusetts, prepared by Sullivan Engineering Group, LLC, dated December 27, 2021 (2 pages); and • 212 Brentwood Circle Plot Plan of Land, North Andover, Massachusetts, prepared by Sullivan Engineering Group, LLC, dated September 24, 2021 and revised December 27, 2021 (1 sheet). 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 HorslayWitlon.corn M PHorsleffiiltenGroup IM Horsley Witten Group, Inc. Town of North Andover December 29, 2021 Page 2 of 7 Stormwater Management and Erosion Control Regulations (Stormwater Regulations) adopted February 15, 2011, and the North Andover Stormwater Management and Erosion Control Bylaw (Bylaw). In accordance with North Andover Code §250-27 Stormwater Management Plan Design and Performance Criteria, this project is required to comply at a minimum with the performance standards of the MSH. Therefore, we have used the MSH 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. The comments below correlate to our second review letter dated December 16, 2021. Follow up comments are provided in hold italicized font. 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 is proposing river rock drainage trenches to manage runoff generated from the proposed improvements. It appears that no new stormwater conveyances will discharge untreated stormwater directly to wetlands or waters of the Commonwealth. HW 12/16121: No further comment is required. b. The proposed stormwater management consists of stone trenches capturing runoff from the proposed pool, patio, and shed. Based on the provided HydroCAD model, runoff generated from newly proposed impervious during the 2-year. 24-hour storm appears to be fully captured and infiltrated by these stone trenches; therefore, no discharge will cause erosion in wetlands or waters of the Commonwealth. The Applicant complies with Standard 1. HW 12/16/21: No further comment is required. 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. The Applicant has not included peak discharge rates for pre- or post-development conditions. HW recommends that the Applicant include at least one site discharge point of analysis in the provided stormwater calculations to compare pre- and post- construction runoff conditions and provide a table demonstrating a reduction in peak discharge rates for the 1/2-inch, 2-year, 10-year, 25-year, and 100-year storm events as outlined in North Andover Code §250-27(B.2). Additionally, HW recommends that the Applicant use precipitation values based on the NRCC Atlas of Precipitation Extremes for the Northeastern United States for the 24-hour storm events, as outlined in §250-27(B.2.a). HW 12/16/21: The Applicant has provided an updated HydroCAD analysis that includes both pre- and post-development conditions. The Applicant has also provided a table demonstrating that post-development runoff volumes and peak rates will not increase relative to pre-development conditions. The Applicant has not included an analysis of the 1/2-inch storm event, and the precipitation depths modelled for the 25-and I00-year storm events are lower than the depths required in (B.2.a). HW recommends that the Applicant revise the KAProjects12021121020 Town of North AndoveA21020Q 212 BrenlwoodlReport\211229_3rd_5W Design Review_212 Brentwood.docx Town of North Andover December 29, 2021 Page 3 of 7 HydroCAD analysis to include the required precipitation events and depths. Furthermore, in both pre- and post-development analyses, the Applicant has modelled grass areas as being in "fair" condition, with only 50-75% cover. HW recommends that the Applicant revise the HydroCAD analyses to model grass areas as being in "good" condition, or otherwise provide justification for the decision to model the grass as "fair." HW 12129121: The Applicant has revised the HydroCAD model as requested and updated the Table comparing pre- and post-development flow rates and volumes. HW has no further comment. b. Per North Andover Code §250-26.17, a Stormwater Management Plan should include a drainage area map showing pre- and post-construction watersheds, subwatersheds, and stormwater flow paths, including municipal drainage system flows. HW recommends that the Applicant include drainage area maps as required and revise the catchments in the provided HydroCAD model to reflect the drainage area maps, including the entirety of catchments draining both towards the proposed stormwater management systems and off-site, not just the additional impervious area. HW 12116121: The Applicant has provided drainage maps of both the pre- and post-construction watersheds, including stormwater flow paths and design points. The HydroCAD model has been updated to include existing grass and impervious surfaces, in addition to proposed impervious surfaces. HW has no further comment. c. Based on the site grading, at least a portion of runoff generated from the existing patio appears to be directed towards the proposed 4-foot-wide river rock drainage trench. HW recommends that the Applicant include all impervious area draining towards the proposed stormwater management practices in the HydroCAD analysis. HW 12/16/21: The Applicant does not appear to have included any area from the existing patio in the subwatersheds that drain to the river rock drainage trenches. HW recommends that the Applicant revise the drainage area maps to delineate subwatersheds 2S_1, 2S_2, and 2S_3, and update the HydroCAD to reflect the land uses in each subwatershed. Subwatersheds should include the entire area that will drain to each stormwater control measure or discharge point, not just the area of the proposed impervious surfaces. HW 12129121: The Applicant has revised the drainage area map and areas of the subcatchments as suggested. HW has no further comment. d. HW recommends that the Applicant include the design elevations for both stone trenches (top and bottom of stone) in the site plan and consider including construction details for the proposed stone trenches. HW 12116/21: The Applicant has revised the plans to include top and bottom of stone elevations for all proposed trenches. Based on the dimensions provided, it seems that the HydroCAD model overestimates the size of the proposed 4'X2' infiltration trench. HW estimates a total surface area of 264 square feet (sf), while the Applicant has modelled the system with a surface area of 280 sf. HW UProjects12021121020 Town of North Andover121020D 212 Brenlwood\Report1211229_3rd_SW Design Review_212 Brentwood.doox Town of North Andover December 29, 2021 Page 4 of 7 recommends that the Applicant revise the HydroCAD model to be consistent with the trench dimensions shown on the plans. HW 12129121: The Applicant has increased the size of both trenches and has adjusted to HydroCAD model to be consistent. HW has 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. No recharge or drawdown calculations have been provided for the proposed site improvements. HW recommends that the Applicant calculate the Required Recharge Volume (RRv)for the proposed impervious area as outlined in MSH Volume 3 Chapter 1, pages 15-16, and the drawdown time for each infiltration practice. HW 12/16/21: The Applicant has provided drawdown calculations in which an infiltration rate of 2.41 inches per hour is used to calculate the drawdown time from the peak elevation of stormwater in each trench following the 100-year storm. HW recommends that the Applicant revise the calculation to measure the time required to drain the trenches when full using an infiltration rate of 1.02 inches per hour, the rate which corresponds to the sandy loam identified at the site. Additionally, HW recommends that the Applicant calculate the RRv and demonstrate that the proposed infiltration practices will provide sufficient groundwater recharge. HW 12129121: The Applicant has revised the drawdown calculations as requested and the infiltration practices will provide sufficient recharge. HW has no further comment. b. No soil data has been provided for the project. HW recommends that the Applicant include site-wide soils information as outlined in the MSH and North Andover regulations. HW 12/16/21: The Applicant has provided soil data based on a test pit conducted between the proposed infiltration trenches. HW has no further comment. c. The provided HydroCAD model uses a field percolation rate of 12 minutes per inch (MPI) for the exfiltration rate of the proposed stone trenches, but no soil data has been included. HW recommends that the Applicant include soil testing data and indicate the soil test pit locations on the site plan. HW 12116/21: The Applicant has included the location of the percolation test along with the inclusion of the soil test pit information. HW recommends that the Applicant provide a log of the percolation test, including information on depth of water and time to infiltrate. Furthermore, as the Applicant utilizes the measured percolation rate in the HydroCAD analysis, HW recommends that the Applicant divide the observed percolation rate by 2 as a factor of safety and revise the HydroCAD analysis accordingly. HW 12129121. The Applicant has adjusted the exfiltration rate used in.the HydroCAD model as suggested. HW has no further comment. MF`rojecis12021121020 Town of North Andover12102011 212 BrentwoodlRepWr 211220_3rd_SW Design Review_212 Brentwood.docx R Town of North Andover December 29, 2021 Page 5 of 7 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 1/2-inch of volume from the impervious area for water quality. a. No TSS or water quality volume calculations have been provided for this project. However, the land uses of roofs, lawn, pool, and patio do not generate suspended solids that require removal. The Applicant complies with Standard 4. HW 12116/21: No further comment is required. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The proposed residential development is not considered a LUHPPL. Therefore, Standard 5 is not applicable to this project. HW 12/16/21: No further comment is required. 6. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone i1, or an Interim Wellhead Protection Area of a public water supply. a. The proposed development is not within a critical area, Zone ll or an IWPA area. Therefore, Standard 6 is not applicable. HW 12116/21: No further comment is required. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project involves solely the construction of new impervious area and is not considered redevelopment. Therefore, Standard 7 is not applicable. HW 12/16/21: No further comment is required. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The Applicant has proposed a staked silt fence around the limit of work. HW recommends that the erosion control detail be added to the plan. HW 12/16/21: The Applicant has provided an Erosion Control Barrier detail on the revised plans. HW recommends that the Applicant revise the detail to show wood posts on the side of the erosion control barrier opposite from the direction of oncoming flow. HW 12129121: The Applicant has revised the erosion control barrier detail as suggested. HW has no further comment. b. In accordance with the MSH and North Andover Code §250-29, HW recommends that the Applicant include dewatering facilities (if required based on the soils investigation), a soil stockpile, and temporary and permanent site stabilization practices. HW 12116/21, The Applicant has revised the plans to designate a proposed soil stockpile area. The Applicant has indicated that no dewatering will be required as KAProiects12021121020 Town of North Andover121020D 212 BrentwootllReport1211229 3rd-SW Design Review 212 Brentwood-dux Town of North Andover December 29, 2021 Page 6 of 7 part of construction. The Applicant has described temporary and permanent site stabilization practices in the erosion and sediment control narrative. HW has no further comment. c. HW recommends that the Applicant clearly delineate the project's limits of disturbance. HW 12116121: The Applicant has delineated the limit of disturbance on the revised plans. HW recommends that the Applicant expand the limit of disturbance line to encompass all areas of proposed activity, including the full extents of the proposed silt fencing. HW 12129121: The Applicant has adjusted the limit of disturbance line as suggested. HW has no further comment. d. HW recommends that the Applicant include an erosion and sediment control narrative in accordance with North Andover Code §250-29(3). HW 12116121: The Applicant has included an erosion and sediment control narrative as part of the Response Fetter. HW has no further comment. e. The Applicant has stated that no trees will be cut as part of the proposed site improvements. The proposed construction access and shed are proposed near the existing treeline which appears to contain a series of large mature trees. HW recommends that the Applicant confirm whether the critical root zones (CRZs) of these trees will be impacted by the proposed development; construction activity over CRZs will potentially damage the root systems of trees and cause long-term degradation of the tree's health. HW 12116/21: The Applicant has indicated that no trees are proposed for removal, although some limbs may be trimmed. HW recommends that the Applicant provide a tree protection detail and delineate tree protection fencing on the plans in areas where work is proposed beyond the treeline. HW 12129121: The Applicant has included a free protection detail and added a note regarding protecting the existing trees during construction. HW has no further comment. The Applicant complies with Standard B. 9. Standard 9 requires a Long-Term Operation and Maintenance (0 & M) Plan to be provided. a. No O&M Plan has been provided for the proposed project. HW recommends that the Applicant provide an O&M Plan meeting the requirements outlined in the MSH and North Andover Code §250 Article IX. This O&M Plan should be a stand-alone document and be signed by the property owner(s). HW 12116/21: The Applicant has provided an O&M Plan which includes instructions for chemical storage, pool maintenance, and infiltration trench maintenance. For consistency with the Infiltration Trench Maintenance section of the Plan, HW recommends that the Applicant revise the instructions of Section b on page 2 of the O&M plan to require twice annual inspection of the river rock trenches. KAProjects12021129020 Town of North Andover121020D 212 BreiztwoodlReportl211229_3rd_SW Design Review 212 Brentwood.dou I Town of North Andover December 29, 2021 Page 7 of 7 Furthermore, HW recommends that the Applicant provide a plan or map indicating the location of stormwater practices to be maintained per North Andover Stormwater Regulations Chapter 250 Section 32.A.4. HW 12129121: The Applicant has requested that the Site plan be utilized as the requested sketch attached to the O&M Plan. As the Site Plan is only one sheet with limited notes and details, HW has no issue with the request. The Applicant complies with Standard 9. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. No Illicit Discharge Compliance Statement has been provided. HW recommends that the Planning Board include a condition of approval requiring an Illicit Discharge Compliance Statement signed by the property owner prior to land disturbance. HW 12116121: The Applicant has not provided an Illicit Discharge Compliance Statement. HW's original comment stands. 11.Additional Comments: a. The North Andover Code §250-26(10) requires that the existing topography be provided 50 feet beyond the perimeter of the parcel and 2-foot interval contours for the entirety of the site. HW 12116121: The Applicant has provided existing 2-foot contours for the west side of the site and has extended all existing contours beyond the site at least 10 feet. HW has no further comment. b. The proposed site plan includes the existing onsite sanitary sewer connection but appears to be missing other utilities. HW recommends that the Applicant include the approximate locations of all existing infrastructure on the site plan, including the water service, electrical, and gas as applicable. HW 12/16/21: The Applicant has revised the plans to include water and gas services connecting to the site from Brentwood Circle. HW has no further comment. Conclusions HW is satisfied that the Applicant has adequately addressed our comments. Please contact Janet Bernardo at 508-833-6600 or at jernardo@horsleywitten.com if you have any questions. Sincerely, HORSLEY WITTEN GROUP, INC. Janet Carter Bernardo, P.E. Jonas Procton, E.I.T. Associate Principal Design Engineer KAPfojec1s\2021\21020 Town of Norih Andover121020D 212 13rentwoodlRoport1211229 3rd—SW Design Review_212 Brentwood.doex i s .-X Horsley Witten Group Sttatainable Envirr�r�t errlal Saltllior� 112 Water Street•6",Ftoor •Boston,MA 02109 " 857-263.8193•horsleywitten.com 61 December 16, 2021 Ms. Jean Enright, Planning Director Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Ref: Second Stormwater Peer Review 212 Brentwood 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 Stormwater Management Report and Site Plan for the proposed improvements to 212 Brentwood Circle in North Andover, MA. The plans were prepared by Sullivan Engineering Group, LLC (Applicant) for John and Michelle Ternullo (Applicant). The project proposes the construction of an in-ground pool, patio, and shed in the back of the existing 1-acre site. The stormwater management for the proposed improvements includes 2-foot-deep river rock drainage trenches surrounding the proposed impervious site improvements. A total of 1,352 square feet (sf) of additional impervious area is proposed on site. The proposed development is located fully within the 325-foot Non-Discharge Buffer Zone from the wetland area located at the adjacent#96 Brentwood Circle and requires a Special Watershed Permit. The following additional documents and plans were received by HW: • Special Permit - Watershed Permit Application for 212 Brentwood Circle, prepared by Sullivan Engineering Group, LLC, dated September 27, 2021 (23 pages); 0 Response Letter, 212 Brentwood Circle, North Andover, Massachusetts, prepared by Sullivan Engineering Group, LLC, dated December 7, 2021 (66 pages); • Pool Maintenance and BMP Plan, 212 Brentwood Circle, North Andover, Massachusetts, prepared by Sullivan Engineering Group, LLC, dated December 8, 2021 (2 pages); and • 212 Brentwood Circle Plot Plan of Land, North Andover, Massachusetts, prepared by Sullivan Engineering Group, LLC, dated September 24, 2021 and revised December 6, 2021 (1 sheet). 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 f orsleyWitten.corn 91 @HorsleyWittenGroup IM Horsley Mitten Group, Inc. Town of North Andover December 16, 2021 Page 2 of 7 February 15, 2011, and the North Andover Stormwater Management and Erosion Control Bylaw (Bylaw), In accordance with North Andover Code §250-27 Stormwater Management Plan Design and Performance Criteria, this project is required to comply at a minimum with the performance standards of the MSH. Therefore, we have used the MSH 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. The comments below correlate to our initial review dated November 1, 2021. Fallow up comments are provided in bold font. 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 is proposing river rock drainage trenches to manage runoff generated from the proposed improvements. It appears that no new stormwater conveyances will discharge untreated stormwater directly to wetlands or waters of the Commonwealth. HW 12116/21: No further comment is required. b. The proposed stormwater management consists of stone trenches capturing runoff from the proposed pool, patio, and shed. Based on the provided HydroCAD model, runoff generated from newly proposed impervious during the 2-year. 24-hour storm appears to be fully captured and infiltrated by these stone trenches; therefore, no discharge will cause erosion in wetlands or waters of the Commonwealth. The Applicant complies with Standard 1. HW 12116/21: No further comment is required. 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. The Applicant has not included peak discharge rates for pre- or post-development conditions. HW recommends that the Applicant include at least one site discharge point of analysis in the provided stormwater calculations to compare pre- and post- construction runoff conditions and provide a table demonstrating a reduction in peak discharge rates for the '/2-inch, 2-year, 10-year, 25-year, and 100-year storm events as outlined in North Andover Code §250-27(B.2). Additionally, HW recommends that the Applicant use precipitation values based on the NRCC Atlas of Precipitation Extremes for the Northeastern United States for the 24-hour storm events, as outlined in §250-27(B.2.a). HW 12/16/21: The Applicant has provided an updated HydroCAD analysis that includes both pre-and post-development conditions. The Applicant has also provided a table demonstrating that post-development runoff volumes and peak rates will not increase relative to pre-development conditions. The Applicant has not included an analysis of the %-inch storm event, and the precipitation depths modelled for the 25-and 100-year storm events are lower than the depths required in (13 2.a). HW recommends that the Applicant revise the HydroCAD analysis to include the required precipitation events and depths. KAProiects12021121020 Town of North Andover121020D 212 BrentwoodlRepoi11211216_SW Design Review_212 Brentwood.dou Town of North Andover December 16, 2021 Page 3 of 7 Furthermore, in both pre- and post-development analyses, the Applicant has modelled grass areas as being in "fair" condition, with only 50-75% cover. HW recommends that the Applicant revise the HydroCAD analyses to model grass areas as being in "good" condition, or otherwise provide justification for the decision to model the grass as "fair." b. Per North Andover Code §250-26.17, a stormwater Management Plan should include a drainage area map showing pre- and post-construction watersheds, subwatersheds, and stormwater flow paths, including municipal drainage system flows. HW recommends that the Applicant include drainage area maps as required and revise the catchments in the provided HydroCAD model to reflect the drainage area maps, including the entirety of catchments draining both towards the proposed stormwater management systems and off-site, not just the additional impervious area. HW 12116/21: The Applicant has provided drainage maps of both the pre- and post-construction watersheds, including stormwater flow paths and design points. The HydroCAD model has been updated to include existing grass and impervious surfaces, in addition to proposed impervious surfaces. HW has no further comment. c. Based on the site grading, at least a portion of runoff generated from the existing patio appears to be directed towards the proposed 4-foot-wide river rock drainage trench. HW recommends that the Applicant include all impervious area draining towards the proposed stormwater management practices in the HydroCAD analysis. HW 12/16/21: The Applicant does not appear to have included any area from the existing patio in the subwatersheds that drain to the river rock drainage trenches. HW recommends that the Applicant revise the drainage area maps to delineate subwatersheds 2S_1, 2S_2, and 2S_3, and update the HydroCAD to reflect the land uses in each subwatershed. Subwatersheds should include the entire area that will drain to each stormwater control measure or discharge point, not just the area of the proposed impervious surfaces. d. HW recommends that the Applicant include the design elevations for both stone trenches (top and bottom of stone) in the site plan and consider including construction details for the proposed stone trenches. HW 12/16/21: The Applicant has revised the plans to include top and bottom of stone elevations for all proposed trenches. Based on the dimensions provided, it seems that the HydroCAD model overestimates the size of the proposed 4'X2' infiltration trench. HW estimates a total surface area of 264 square feet (sf), while the Applicant has modelled the system with a surface area of 280 sf. HW recommends that the Applicant revise the HydroCAD model to be consistent with the trench dimensions shown on the plans. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. No recharge or drawdown calculations have been provided for the proposed site improvements. HW recommends that the Applicant calculate the Required Recharge Volume (RRv) for the proposed impervious area as outlined in MSH Volume 3 Chapter K:Trojects12021121020 Town of North Andover121020D 212 Brentwood\Repo;11211216_SW Design Review 212 Brentwood.docx Town of North Andover December 16, 2021 Page 4 of 7 1, pages 15-16, and the drawdown time for each infiltration practice. HW 12/16/21: The Applicant has provided drawdown calculations in which an infiltration rate of 2.41 inches per hour is used to calculate the drawdown time from the peak elevation of stormwater in each trench following the 100-year storm. HW recommends that the Applicant revise the calculation to measure the time required to drain the trenches when full using an infiltration rate of 1.02 inches per hour, the rate which corresponds to the sandy loam identified at the site. Additionally, HW recommends that the Applicant calculate the RRv and demonstrate that the proposed infiltration practices will provide sufficient groundwater recharge. b. No soil data has been provided for the project. HW recommends that the Applicant include site-wide soils information as outlined in the MSH and North Andover regulations. HW 12116/21: The Applicant has provided soil data based on a test pit conducted between the proposed infiltration trenches. HW has no further comment. c. The provided HydroCAD model uses a field percolation rate of 12 minutes per inch (MPI) for the exfiltration rate of the proposed stone trenches, but no soil data has been included. HW recommends that the Applicant include soil testing data and indicate the soil test pit locations on the site plan. HW 12/16/21: The Applicant has included the location of the percolation test along with the inclusion of the soil test pit information. HW recommends that the Applicant provide a log of the percolation test, including information on depth of water and time to infiltrate. Furthermore, as the Applicant utilizes the measured percolation rate in the HydroCAD analysis, HW recommends that the Applicant divide the observed percolation rate by 2 as a factor of safety and revise the HydroCAD analysis accordingly. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 1/2-inch of volume from the impervious area for water quality. a. No TSS or water quality volume calculations have been provided for this project. However, the land uses of roofs, lawn, pool, and patio do not generate suspended solids that require removal. The Applicant complies with Standard 4. HW 12/16/21: No further comment is required. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The proposed residential development is not considered a LUHPPL. Therefore, Standard 5 is not applicable to this project. HW 12116/21: No further comment is required. K:1Proiects12021121020 Town of North Andover121020©212 Brentwood\Report1211215_SW❑esign Review 212 Brentwood.docx Town of North Andover December 16, 2021 Page 5 of 7 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 proposed development is not within a critical area, Zone 11 or an IWPA area. Therefore, Standard 6 is not applicable. HW 12116i21: No further comment is required. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project involves solely the construction of new impervious area and is not considered redevelopment. Therefore, Standard 7 is not applicable. HW 12116121: No further comment is required. 8. Standard S requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The Applicant has proposed a staked silt fence around the limit of work. HW recommends that the erosion control detail be added to the plan. HW 12/16/21: The Applicant has provided an Erosion Control Barrier detail on the revised plans. HW recommends that the Applicant revise the detail to show wood posts on the side of the erosion control barrier opposite from the direction of oncoming flow. b. In accordance with the MSH and North Andover Code §250-29, HW recommends that the Applicant include dewatering facilities (if required based on the soils investigation), a soil stockpile, and temporary and permanent site stabilization practices. HW 12/16121: The Applicant has revised the plans to designate a proposed soil stockpile area. The Applicant has indicated that no dewatering will be required as part of construction. The Applicant has described temporary and permanent site stabilization practices in the erosion and sediment control narrative. HW has no further comment. c. HW recommends that the Applicant clearly delineate the project's limits of disturbance. HW 12116121: The Applicant has delineated the limit of disturbance on the revised plans. HW recommends that the Applicant expand the limit of disturbance line to encompass all areas of proposed activity, including the full extents of the proposed silt fencing. d. HW recommends that the Applicant include an erosion and sediment control narrative in accordance with North Andover Code §250-29(3). HW 12116/21: The Applicant has included an erosion and sediment control narrative as part of the Response Letter. HW has no further comment. e. The Applicant has stated that no trees will be cut as part of the proposed site improvements. The proposed construction access and shed are proposed near the existing treeline which appears to contain a series of large mature trees. HW recommends that the Applicant confirm whether the critical root zones (CRZs) of these trees will be impacted by the proposed development; construction activity over CRZs will potentially damage the root systems of trees and cause long-term degradation of the K\ProjedsM21121020 Town of North Andover121020D 212 BrenlwooMepor11211216_SW Design Roview_212 Brentwood.docx Town of North Andover December 16, 2021 Page 6of7 tree's health. HW 12/16/21: The Applicant has indicated that no trees are proposed for removal, although some limbs may be trimmed. HW recommends that the Applicant provide a tree protection detail and delineate tree protection fencing on the plans in areas where work is proposed beyond the treeline. 9. Standard 9 requires a Long-Term Operation and Maintenance (O & M) Plan to be provided. a. No O&M Plan has been provided for the proposed project. HW recommends that the Applicant provide an O&M Plan meeting the requirements outlined in the MSH and North Andover Code §250 Article IX. This O&M Plan should be a stand-alone document and be signed by the property owners). HW 12/16/21: The Applicant has provided an O&M Plan which includes instructions for chemical storage, pool maintenance, and infiltration trench maintenance. For consistency with the Infiltration Trench Maintenance section of the Plan, HW recommends that the Applicant revise the instructions of Section b on page 2 of the O&M plan to require twice annual inspection of the river rock trenches. Furthermore, HW recommends that the Applicant provide a plan or map indicating the location of stormwater practices to be maintained per North Andover Stormwater Regulations Chapter 250 Section 32.A.4. 10. Standard 10 requires an Illicit Discharge Compliance Statement be provided. a. No Illicit Discharge Compliance Statement has been provided. HW recommends that the Planning Board include a condition of approval requiring an Illicit Discharge Compliance Statement signed by the property owner prior to land disturbance. HW 12/16/21: The Applicant has not provided an Illicit Discharge Compliance Statement. HW's original comment stands. 11. Additional Comments: a. The North Andover Code §250-26(10) requires that the existing topography be provided 50 feet beyond the perimeter of the parcel and 2-foot interval contours for the entirety of the site. HW 12/16121: The Applicant has provided existing 2-foot contours for the west side of the site and has extended all existing contours beyond the site at least 10 feet. HW has no further comment. b. The proposed site plan includes the existing onsite sanitary sewer connection but appears to be missing other utilities. HW recommends that the Applicant include the approximate locations of all existing infrastructure on the site plan, including the water service, electrical, and gas as applicable. HW 12/16121: The Applicant has revised the plans to include water and gas services connecting to the site from Brentwood Circle. HW has no further comment. i0l?rojects12021 Q1020 Town of North Andover121020D 212 Brentwood\Report1211216_SW Design Review_212 Brentwood,docx Town of North Andover December 16, 2021 Page 7 of 7 Conclusions HW recommends that the Planning Board require that the Applicant provide a written response to address these comments as part of the Board's review process. 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 jbernardo@horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. Janet Carter Bernardo, P.E. Jonas Procton, E.I.T. Associate Principal Design Engineer KAProjects12021121020 Town of North Andover121020D 212 Brentwood%Report1211216_SW Design Review_212 Brentwood.docx I Horsley Witten Group Sustainable ,environmental Solutions 112 Water Street-V1 Floor•Boston,MA 02109 857-263.8193•horsleywilten,eom November 1, 2021 Ms. Jean Enright, Planning Director Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Ref: Initial Stormwater Peer Review 212 Brentwood 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 initial review of the Stormwater Management Report and Site Plan for the proposed improvements to 212 Brentwood Circle in North Andover, MA. The plans were prepared by Sullivan Engineering Group, LLC (Applicant) for John and Michelle Ternullo (Applicant). The project proposes the construction of an in-ground pool, patio, and shed in the back of the existing 1-acre site. The stormwater management for the proposed improvements includes 2-foot-deep river rock drainage trenches surrounding the proposed impervious site improvements. A total of 1,352 square feet (sf) of additional impervious area is proposed on site. The proposed development is located fully within the 325-foot Non-Discharge Buffer Zone from the wetland area located at the adjacent#96 Brentwood Circle and requires a Special Watershed Permit. The following documents and plans were received by HW: • Special Permit - Watershed Permit Application for 212 Brentwood Circle, prepared by Sullivan Engineering Group, dated September 27, 2021 (23 pages), and • 212 Brentwood Circle Plot Plan of Land, North Andover, MA, prepared by Sullivan Engineering Group (1 Sheet). 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) adapted February 15, 2011, and the North Andover Stormwater Management and Erosion Control Bylaw (Bylaw). In accordance with North Andover Code §250-27 Stormwater Management Plan Design and Performance Criteria, this project is required to comply at a minimum with the performance standards of the MSH. Therefore, we have used the MSH 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 I-9orsleyWitten.corn M cr HorsleyWittenGroup IM Horsley Witten Group, Inc. Town of North Andover November 1, 2021 Page 2 of 4 1. Standard 1: No new stormwater conveyances (e.g., outfalis) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. a. The Applicant is proposing river rock drainage trenches to manage runoff generated from the proposed improvements. It appears that no new stormwater conveyances will discharge untreated stormwater directly to wetlands or waters of the Commonwealth. b. The proposed stormwater management consists of stone trenches capturing runoff from the proposed pool, patio, and shed. Based on the provided HydroCAD model, runoff generated from newly proposed impervious during the 2-year. 24-hour storm appears to be fully captured and infiltrated by these stone trenches; therefore, no discharge will cause erosion in wetlands or waters of the Commonwealth. The Applicant complies with Standard 1. 2. Standard 2: Storm water management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. a. The Applicant has not included peak discharge rates for pre- or post-development conditions. HW recommends that the Applicant include at least one site discharge point of analysis in the provided stormwater calculations to compare pre- and post- construction runoff conditions and provide a table demonstrating a reduction in peak discharge rates for the '/2-inch, 2-year, 10-year, 25-year, and 100-year storm events as outlined in North Andover Code §250-27(B.2). Additionally, HW recommends that the Applicant use precipitation values based on the NRCC Atlas of Precipitation Extremes for the Northeastern United States for the 24-hour storm events, as outlined in §250-27(B.2,a). b. Per North Andover Code §250-26.17, a Stormwater Management Plan should include a drainage area map showing pre- and post-construction watersheds, subwatersheds, and stormwater flow paths, including municipal drainage system flows. HW recommends that the Applicant include drainage area maps as required and revise the catchments in the provided HydroCAD model to reflect the drainage area maps, including the entirety of catchments draining both towards the proposed stormwater management systems and off-site, not just the additional impervious area. c. Based on the site grading, at least a portion of runoff generated from the existing patio appears to be directed towards the proposed 4-foot-wide river rock drainage trench. HW recommends that the Applicant include all impervious area draining towards the proposed stormwater management practices in the HydroCAD analysis. d. HW recommends that the Applicant include the design elevations for both stone trenches (top and bottom of stone) in the site plan and consider including construction details for the proposed stone trenches. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. No recharge or drawdown calculations have been provided for the proposed site improvements. HW recommends that the Applicant calculate the Required Recharge Volume (RRv) for the proposed impervious area as outlined in MSH Volume 3 Chapter H:TrojectsW021\21020 Town of North Andover121020D 212 Brentwood\Report1211101_SW Design Review 212 Brentwood.doox 1 Town of North Andover November 1, 2021 Page 3 of 4 1, pages 15-16, and the drawdown time for each infiltration practice. b. No soil data has been provided for the project. HW recommends that the Applicant include site-wide soils information as outlined in the MSH and North Andover regulations. c. The provided HydroCA❑ model uses a field percolation rate of 12 minutes per inch (MPI) for the exfiltration rate of the proposed stone trenches, but no soil data has been included. HW recommends that the Applicant include soil testing data and indicate the soil test pit locations on the site plan. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 9/2-inch of volume from the impervious area for water quality. a. No TSS or water quality volume calculations have been provided for this project. However, the land uses of roofs, lawn, pool, and patio do not generate suspended solids that require removal. The Applicant.complies with Standard 4. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The proposed residential development is not considered a LUHPPL. Therefore, Standard 5 is not applicable to this project. 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 proposed development is not within a critical area, Zone II or an IWPA area. Therefore, Standard 6 is not applicable. 7. Standard 7 is related to projects considered Redevelopment, a, The proposed project involves solely the construction of new impervious area and is not considered redevelopment. Therefore, Standard 7 is not applicable. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The Applicant has proposed a staked silt fence around the limit of work. HW recommends that the erosion control detail be added to the plan. b. In accordance with the MSH and North Andover Code §250-29, HW recommends that the Applicant include dewatering facilities (if required based on the soils investigation), a soil stockpile, and temporary and permanent site stabilization practices. c. HW recommends that the Applicant clearly delineate the project's limits of disturbance. d. HW recommends that the Applicant include an erosion and sediment control narrative in accordance with North Andover Code §250-29(3). e. The Applicant has stated that no trees will be cut as part of the proposed site improvements. The proposed construction access and shed are proposed near the existing treeline which appears to contain a series of large mature trees. HW �I HAProjects12021i21020 Town of North Andover121020D 212 Brentwood\Report1211101_SW Design Review 212 Brentwood.docx Town of North Andover November 1, 2021 Page 4 of 4 recommends that the Applicant confirm whether the critical root zones (CRZs) of these trees will be impacted by the proposed development; construction activity over CRZs will potentially damage the root systems of trees and cause long-term degradation of the tree's health. 9. Standard 9 requires a Long-Term Operation and Maintenance (O & M) Plan to be provided. a. No O&M Plan has been provided for the proposed project. HW recommends that the Applicant provide an O&M Plan meeting the requirements outlined in the MSH and North Andover Code §250 Article IX. This O&M Plan should be a stand-alone document and be signed by the property owner(s). 10. Standard 90 requires an illicit Discharge Compliance Statement be provided. a. No Illicit Discharge Compliance Statement has been provided. HW recommends that the Planning Board include a condition of approval requiring an Illicit Discharge Compliance Statement signed by the property owner prior to land disturbance. 11. Additional Comments: a. The North Andover Code §250-26(10) requires that the existing topography be provided 50 feet beyond the perimeter of the parcel and 2-foot interval contours for the entirety of the site. b. The proposed site plan includes the existing onsite sanitary sewer connection but appears to be missing other utilities. HW recommends that the Applicant include the approximate locations of all existing infrastructure on the site plan, including the water service, electrical, and gas as applicable. Conclusions HW recommends that the Planning Board require that the Applicant provide a written response to address these comments as part of the Board's review process. 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. Janet Carter Bernardo, P.E. Peter Ogonek, E.I.T. Associate Principal Project Engineer H:1Projects12021121020 Town of North Andover121020D 212 Brentwood\Report1211101 SW Design Review- 212 Brentwood.docx