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HomeMy WebLinkAbout2022-01-04 Stormwater Peer Review I I Horsley Witten Group Sustainable Environmental Solutions ` 112 Water Street 61'Floor•Boston,MA 02103 ` a 657-263-8193 hnrsleywitten,com v"- December 29, 2021 Ms. ,lean Enright, Planning Director Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Ref: Third Stormwater Peer Review 33 Appledore Lane 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 Plans for the proposed single family home expansion at 33 Appledore Lane, North Andover, MA. The plans were prepared for Sean and Lauren Delaney by Sullivan Engineering Group, LLC. The project proposes the addition of a second story to the existing 1-story garage, as well as an expanded driveway on the existing 0.90-acre lot. The proposed Stormwater management includes a system of two subsurface drywells, which are designed to capture drainage from the proposed additional impervious areas. The site is located within the Watershed Protection District, and a wetland area has been identified approximately 130 feet from the lot (at 11 Appledore Lane). Because the site is within 325 of a wetland resource within the Watershed Protection District, it is within the Non- Discharge Buffer Zone and requires a Special Permit. The following additional documents and plans were received by HW in response to our review letter dated December 16, 2021: • Response Letter, 33 Appledore Lane, North Andover, Massachusetts, prepared by Sullivan Engineering Group, LLC, dated December 28, 2021 (48 pages); • Long-Term Stormwater Operation & Maintenance Plan, 33 Appledore Lane, North Andover, Massachusetts, prepared by Sullivan Engineering Group, LLC, signed December 28, 2021 (1 page); and • Plot Plan of Land, 33 Appledore Lane, North Andover, Massachusetts, prepared for Sean Delaney by Sullivan Engineering Group, LLC, dated September 26, 2021 and revised December 28, 2021 (1 page) 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 HorsleyWitten.com @HorsleyWittenGroup Horsley Witten Group, Inc. Town of North Andover December 29, 2021 Page 2of7 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 dated December 16, 2021. Follow up comments are provided in bold italicized font. 1. Standard 7 states that 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 site plan provided by the Applicant features limited proposed grading and does not provide grading contours within the proposed driveway expansion. Based on the existing grading and the spot grades, it appears that the proposed trench drain is at a high point, and therefore runoff will not be directed to the proposed drywell for treatment. HW recommends that the Applicant revisit the grading to ensure that all runoff created by new impervious surfaces is directed to the proposed Stormwater management system. Furthermore, the spot grades provided indicate that the driveway may have a slope of 10% or greater. HW recommends that the Applicant revisit the spot grades and verify that the proposed driveway slope is reasonable. HW 12116121: The Applicant has provided additional proposed contours to the north of the driveway and included an arrow specifying a 1.4% slope from north to south along the driveway. The trench drain has been relocated to the south end of the driveway, which appears to capture the proposed runoff from the full area of the driveway. HW has no further comment. b. Based on the HydroCAD analysis provided by the Applicant, it appears that runoff from the 2-year storm is able to be stored within the proposed drywell without overflowing. Based on this analysis, it appears that the proposed drainage design will not result in erosion in nearby wetlands. HW 12116/21: No further comment is necessary. The Applicant complies with Standard 1. 2. Standard 2 requires that stormwater management systems shall be designed so that post- development pear discharge rates do not exceed pre-development peak discharge rates. a. In accordance with the North Andover Stormwater Regulations, Chapter 250, Section 27 the following amendments are recommended: i. A comparison of pre- and post-development hydrologic analyses on a subwatershed basis, rather than solely based on the additional impervious area. KAPr*cts1202 k21020 To%vn of North Andave:12102OE 33 Appledore\Repoit U 11229 3rd Peer Review_33 Appledore Lane.doex Town of North Andover December 29, 2021 Page 3 of 7 HW 12/16121: The Applicant has provided a pre-development hydrologic analysis and has expanded the area of analysis beyond the additional impervious area to a broader subwatershed area. In both the pre- and post-development watershed analyses, the Applicant has modeled two subwatersheds as having a time of concentration (Tc) of less than 6 minutes. Per standard TR-55 methodology, HW recommends that the Applicant revise the analyses to utilize a minimum Tc of 6 minutes. Furthermore, the Applicant has modelled grass areas in both pre- and post-development as being in "fair" condition, i.e. having only 50-75% of grass cover. HW recommends that the Applicant model all grass cover as being in "good" condition, or otherwise provide justification for the design selection of"fair." HW 12129121: The Applicant has revised the HydroCAD model as suggested HW has no further comment. ii. Addition of a summary table including peak discharge rates and total volume of discharge for all modelled storm events to easily evaluate the pre- and post-development values. HW 12116/21: The Applicant has provided a summary table in the Response Letter. HW recommends that the Applicant revise the table as necessary pending any updates to the HydroCAD analysis. HW 12129121: The Applicant has updated the summary table as suggested. HW has no further comment. iii. Adjust the rainfall data for all modelled storm events to match the values provided in Section B.2.a, including the '/2-inch and 25-year storms. HW 12116121: The Applicant has included an analysis of the 25-year storm but has not included an analysis of the %-inch storm. Furthermore, the precipitation depths analyzed for both the 25-year and 100-year storms are less than those required under Section B.2.a. HW recommends that the Applicant revise the analysis to provide all required storm events and depths. HW 12129121: The Applicant has included the %-inch storm and adjusted the precipitation rates as suggested HW has no further comment. b. Based on the HydroCAD analysis, it appears that stormwater captured during a 100- year storm event overtops the ceiling of the proposed drywell. It does not surcharge from the proposed trench drain, which serves as an overflow outlet given sufficient rainfall. Per Stormwater Regulations Chapter 250, Section 27.B.6, HW recommends that the Applicant ensure that any changes to the design or HydroCAD analysis (including rainfall depths or adjustments to the trench drain elevation) continue to prevent overflow during a 100-year storm event. HW 12/16/21: The updated HydroCAD analysis indicates that during the 100-year storm, runoff captured by the drainage system reaches an elevation below the «;11'roic:el.\2021121020'1'o%v�i nrNor(h Andnver\210201,:13 App1cdore\Repor1s121 1229_3rd Veer Review_33 Aphledore Lane.docx Town of North Andover December 29, 2021 Page 4 of 7 ceiling of the proposed drywell, as well as below the trench drain outlet invert. HW's original comment stands pending any additional updates to the HydroCAD analysis or to the design. HW 12/29/21: The updated HydroCAD analysis indicates that during the 100-year storm, runoff captured by the drainage system reaches an elevation below the ceiling of the proposed drywell, as well as below the trench drain outlet invert. HW has no further comment. c. The proposed drywell is modelled in HydroCAD with 36 inches of stone surrounding each wall. This appears to be consistent with the plan view of the drywell, however the detail for the drywell calls for 30 inches of stone. HW recommends that the Applicant revise the 1000 Gallon Dry Well Jumbo (H-20) detail for consistency. HW 12/16/21: The Applicant has revised the plans, the 1,000 Gallon Dry Well Jumbo (H-20) detail, and the HydroCAD analysis to feature 60 inches of crushed stone on all sides of the drywell. The plans and the HydroCAD analysis appear to be consistent with each other. HW has no further comment. d. The Applicant has not shown or noted a required cover between the drywells and the driveway surface. HW recommends that the Applicant confirm the minimum cover required. HW 12/16/21: The Applicant has indicated that 2 feet of cover will be provided over the drywells, meeting the minimum requirements for H-20 loading. HW recommends that the Applicant include the rim elevation of the access manholes on the plans for clarity. HW 12129121: The Applicant has included the drywell rim elevation as suggested. HW has no further comment. e. The 4-inch HDPE drainpipe shown connecting the proposed trench drain and the dry well appears to have a 45' bend, as well as a downward slope. HW recommends that the Applicant call out the slope and length of the pipe as well as the required elbow pipe to confirm constructability. HW 12116/21: The Applicant has specified the length and slope of the proposed HDPE pipe. The proposed drainage system appears to feature two 30' bends between the proposed manhole and the trench drain. HW recommends that the Applicant call out any elbow pipes required to construct the design as shown. HW 12129121: The Applicant has called out the bends as suggested. 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. The Applicant has not provided calculations of required recharge or drawdown time. HW recommends that the Applicant provide documentation to show compliance with Standard 3. K:IProiect,\2021121020'I'owji of North Andover121020E 33 Appledore\Repoil-121 1229_3rd Peer Revizrv_33 Appledorz Laiw.doex Town of North Andover December 29, 2021 Page 5 of 7 HW 12116121: The Applicant has provided calculations which indicate that the proposed drainage design is able to provide the required groundwater recharge volume. Additional calculations indicate that the proposed drainage system will fully drain within 72 hours. The Applicant appears to comply with Standard 3; HW has no further comment. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 1.0-inch of volume from the impervious area for water quality. a. The Applicant has not provided TSS removal calculations or calculations of water quality volume. HW recommends that the Applicant provide document to show compliance with Standard 4, HW 12/16/21: The Applicant has proposed a deep sump manhole to provide pretreatment to stormwater runoff that is generated by the driveway. TSS calculations provided by the Applicant indicate that the combination of the deep sump manhole and the proposed drywell will provide 85% TSS removal to all captured stormwater. Additional calculations indicate that the proposed drainage design will provide the required water quality volume for pollutant treatment. The Applicant appears to comply with Standard 4; HW has no further comment. 5. Standard 5 is related to projects with a Land Use of Nigher Potential Pollutant Loads (L UHPPL). a. The proposed development is not considered a LUHPPL and therefore, Standard 5 is not applicable to this project. HW 12116121: No further comment is necessary. 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 II or an IWPA area and therefore, Standard 6 is not applicable. HW 12/16/21: No further comment is necessary. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project is a combination of new development and redevelopment, and therefore the Applicant is required to meet the Stormwater Management Standards only to the maximum extent practicable for the redevelopment portion of the project. Once the Applicant has addressed the other comments in this letter, it appears that the requirements of Standard 7 will be met. HW 12/16/21: No further comment is necessary. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. In Accordance with the North Andover Stormwater Regulations, Chapter 250, Article VIII, the following amendments are recommended: i. Delineate the limits of work per Section 29.C.2.a. Ullrojee1.1202 k21020 Town of Nor1L Andovu\21020C 33 Alsl)ledo€'e\Rcpoilts 21 1229_3rd 1'm,Review 33 Applectore Lane.doex Town of North Andover December 29, 2021 Page 6of7 HW 12/16121: The Applicant has revised the plans to delineate the limit of work (LOW). The proposed erosion control mulch soxx appears to extend beyond the LOW. HW recommends that the Applicant revise the LOW to encompass all proposed site work. HW 12129121: The Applicant has revised the limit of work line as suggested. HW has no further comment. ii. Include notes of temporary and final site stabilization per Section 29.C.2.f. HW 12116/21: The Applicant has added the location of proposed erosion control blankets as well as mulch soxx. HW has no further comment. iii. Provide a construction sequence per Section 29.C.3.b. HW 12/16/21: The Applicant has not provided a construction sequence. HW's original comment stands. HW 12129121: The Applicant has included a General Construction Sequence in its Drainage Report. HW has no further comment. iv. Provide a maintenance schedule and istructions for erosion control upkeep per Sections 29.C.3.e and 30.A.11. HW 12/16121: In the Response Letter, the Applicant has included a description of erosion control upkeep activities. HW recommends that the Applicant revise the Erosion Control Detail to include this information. HW 12129121: The Applicant has updated the erosion co0ntrol detail as suggested. HW has no further comment. V. Designate a location for stockpiled soil per Section 30.A.18. HW 12/16/21: The Applicant has designated a soil stockpile location on the revised plans. HW has no further comment. vi. The northern corner of the site appears to be graded at 3H:1V. Include a detail for erosion control blankets per Section 30.A.28. HW 12/16/21: The Applicant has included a callout for erosion control blankets in the northern corner and has provided an Erosion Control Blanket detail. HW has no further comment. The Applicant complies with Standard 8. 9. Standard 9 requires a long-term operation and maintenance (O&M) plan shall be developed and implemented to ensure that stormwater management systems function as designed. a. The Applicant has not provided an O&M Plan. HW recommends that the Applicant provide an O&M Plan that meets the requirements of the MSH and North Andover Stormwater Regulations Chapter 250 Article 9. The O&M Plan should be a stand-alone document and be signed by the property owner(s). HW 12/16/21: The Applicant has provided an O&M Plan, which includes instructions on O&M for the proposed drainage system and the signature of the owner. HW recommends that the Applicant revise the frequency of maintenance K. ,ujectsl2Q.,1121Q2Q"[c urn of North Anctovecl2I020h.. AppledorzlRcports121 I229_3rd I'm-Review_33 Applednre Lane.dnex f Town of North Andover December 29, 2021 I Page 7 of 7 for the deep sump manhole to four times per year to be consistent with the deep sump catch basin requirements listed in MSH Vol. 2, Chap. 2. Furthermore, HW recommends that the Applicant provide a plan or map indicating the location of facilities 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 that an Illicit Discharge Compliance Statement be provided. a. The Applicant has not provided an Illicit Discharge Compliance Statement in the Drainage Report signed by the property owner. HW recommends that the Planning Board include a condition of approval requiring an Illicit Discharge Compliance Statement be signed by Sean or Lauren Delaney prior to land disturbance. HW 12/16121: The Applicant has not provided an Illicit Discharge Compliance Statement. HW's original comment stands. 11. Additional Comments: a. In addition to providing grading information within the extents of the proposed driveway, HW recommends that the Applicant include the proposed 95-contour north of the driveway. HW 12/16/21: The Applicant has revised the plans to include the proposed 95- contour. HW has no further comment. b. HW recommends that the Applicant include a detail for the proposed cape cod berm. HW 12116121: The Applicant has provided a Cape Cod Berm Detail on the plans. 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 jbernardo a@horsleywitten.com if you have any questions. Sincerely, HORSLEY WITTEN GROUP, INC. o'(-'41) Janet Carter Bernardo, P.E. Jonas Procton, E.I.T. Associate Principal Design Engineer KC\]'t-ojcels12021121020'1'own of North Andover121024G 33 Alil>ledorel[telxis1s121 I229.3rd Peer Review 33 Appledore Lane.doex 1 J 1 Horsley Group Witten G 5 p �� Sustainable Environmental Solutions 112 Water Street•61,Floor•Soston,MA 02109 � 857-263-8193 • horsleywitten.com 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 33 Appledore Lane 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 Plans for the proposed single family home expansion at 33 Appledore Lane, North Andover, MA, The plans were prepared for Sean and Lauren Delaney by Sullivan Engineering Group, LLC. The project proposes the addition of a second story to the existing 1-story garage, as well as an expanded driveway on the existing 0.90-acre lot. The proposed stormwater management includes a system of two subsurface drywells, which are designed to capture drainage from the proposed additional impervious areas. The site is located within the Watershed Protection District, and a wetland area has been identified approximately 130 feet from the lot (at 11 Appledore Lane). Because the site is within 325 of a wetland resource within the Watershed Protection District, it is within the Non- Discharge Buffer Zone and requires a Special Permit. The following additional documents and plans were received by HW: • Special Permit—Watershed Permit Application, 33 Appledore Lane, North Andover, Massachusetts, prepared for Sean and Lauren Delaney by Sullivan Engineering Group, LLC, dated October 19, 2021 (17 pages); • Response Letter, 33 Appledore Lane, North Andover, Massachusetts, prepared by Sullivan Engineering Group, LLC, dated December 8, 2021 (40 pages); • Long-Term Stormwater Operation & Maintenance Plan, 33 Appledore Lane, North Andover, Massachusetts, prepared by Sullivan Engineering Group, LLC, dated December 8, 2021 (1 page); and • Plot Plan of Land, 33 Appledore Lane, North Andover, Massachusetts, prepared for Sean Delaney by Sullivan Engineering Group, LLC, dated September 26, 2021 and revised December 7, 2021 (1 page) Horsleffl`€tten,corn In(F li Horsley%flenGroup Hc)rsley Witten Gmup, Inc, Town of North Andover December 16, 2021 Page 2 of 7 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 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. Follow up comments are provided in bold font. 1. Standard 1 states that no new stormwater conveyances (e.g. autfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. a. The site plan provided by the Applicant features limited proposed grading and does not provide grading contours within the proposed driveway expansion. Based on the existing grading and the spot grades, it appears that the proposed trench drain is at a high point, and therefore runoff will not be directed to the proposed drywell for treatment. HW recommends that the Applicant revisit the grading to ensure that all runoff created by new impervious surfaces is directed to the proposed stormwater management system. Furthermore, the spot grades provided indicate that the driveway may have a slope of 10% or greater. HW recommends that the Applicant revisit the spot grades and verify that the proposed driveway slope is reasonable. HW 12/16121: The Applicant has provided additional proposed contours to the north of the driveway and included an arrow specifying a 1.4% slope from north to south along the driveway. The trench drain has been relocated to the south end of the driveway, which appears to capture the proposed runoff from the full area of the driveway. HW has no further comment. b. Based on the HydroCAD analysis provided by the Applicant, it appears that runoff from the 2-year storm is able to be stored within the proposed drywell without overflowing. Based on this analysis, it appears that the proposed drainage design will not result in erosion in nearby wetlands. HW 12/16121: No further comment is necessary. 2. Standard 2 requires that stormwater management systems shall be designed so that post- development peak discharge rates do not exceed pre-development peak discharge rates. a. In accordance with the North Andover Stormwater Regulations, Chapter 250, Section 27 the following amendments are recommended; i. A comparison of pre- and post-development hydrologic analyses on a subwatershed basis, rather than solely based on the additional impervious area. K:1Projects12021\210201'o%%,n of Nofth Andover\2 1020Ei 33 Appledorellteliorls1211216 2ncf Peer Review 33 Appledore Lalie.doox Town of North Andover December 16, 2021 Page 3 of 7 HW 12116/21: The Applicant has provided a pre-development hydrologic analysis and has expanded the area of analysis beyond the additional impervious area to a broader subwatershed area. In both the pre-and post-development watershed analyses, the Applicant has modeled two subwatersheds as having a time of concentration (Tc) of less than 6 minutes. Per standard TR-55 methodology, HW recommends that the Applicant revise the analyses to utilize a minimum Te of 6 minutes. Furthermore, the Applicant has modelled grass areas in both pre- and post-development as being in "fair" condition, i.e. having only 50-75% of grass cover. HW recommends that the Applicant model all grass cover as being in "good" condition, or otherwise provide justification for the design selection of "fair." H. Addition of a summary table including peak discharge rates and total volume of discharge for all modelled storm events to easily evaluate the pre- and post-development values. HW 12/16121: The Applicant has provided a summary table in the Response Letter. HW recommends that the Applicant revise the table as necessary pending any updates to the HydroCAD analysis. iii. Adjust the rainfall data for all modelled storm events to match the values provided in Section B.2.a, including the '/2-inch and 25-year storms. HW 12116121, The Applicant has included an analysis of the 25-year storm but has not included an analysis of the %-inch storm. Furthermore, the precipitation depths analyzed for both the 25-year and 100-year storms are less than those required under Section 13.2.a. HW recommends that the Applicant revise the analysis to provide all required storm events and depths. b. Based on the HydroCAD analysis, it appears that stormwater captured during a 100- year storm event overtops the ceiling of the proposed drywell. It does not surcharge from the proposed trench drain, which serves as an overflow outlet given sufficient rainfall. Per Stormwater Regulations Chapter 250, Section 27.13.6, HW recommends that the Applicant ensure that any changes to the design or HydroCAD analysis (including rainfall depths or adjustments to the trench drain elevation) continue to prevent overflow during a 100-year storm event. HW 12116121: The updated HydroCAD analysis indicates that during the 100-year storm, runoff captured by the drainage system reaches an elevation below the ceiling of the proposed drywell, as well as below the trench drain outlet invert. HW's original comment stands pending any additional updates to the HydroCAD analysis or to the design. c. The proposed drywell is modelled in HydroCAD with 36 inches of stone surrounding each wall. This appears to be consistent with the plan view of the drywell, however the detail for the drywell calls for 30 inches of stone. HW recommends that the Applicant revise the 1000 Gallon Dry Well Jumbo (H-20) detail for consistency. 1011rojec1s12021121020 Towia of Noilli Attdover121020E 33 Appledore\Reports1211210 2nd Peer Review 33 Appledore Lane.don Town of North Andover December 16, 2021 Page 4 of 7 HW 12116121: The Applicant has revised the plans, the 1,000 Gallon Dry Well Jumbo (H-20) detail, and the HydroCAD analysis to feature 60 inches of crushed stone on all sides of the drywell. The plans and the HydroCAD analysis appear to be consistent with each other. HW has no further comment. d. The Applicant has not shown or noted a required cover between the drywells and the driveway surface. HW recommends that the Applicant confirm the minimum cover required. HW 12116/21: The Applicant has indicated that 2 feet of cover will be provided over the drywells, meeting the minimum requirements for H-20 loading. HW recommends that the Applicant include the rim elevation of the access manholes on the plans for clarity. e. The 4-inch HDPE drainpipe shown connecting the proposed trench drain and the dry well appears to have a 450 bend, as well as a downward slope. HW recommends that the Applicant call out the slope and length of the pipe as well as the required elbow pipe to confirm constructability. HW 12116/21: The Applicant has specified the length and slope of the proposed HDPE pipe. The proposed drainage system appears to feature two 30° bends between the proposed manhole and the trench drain. HW recommends that the Applicant call out any elbow pipes required to construct the design as shown. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. The Applicant has not provided calculations of required recharge or drawdown time. HW recommends that the Applicant provide documentation to show compliance with Standard 3. HW 12/16/21: The Applicant has provided calculations which indicate that the proposed drainage design is able to provide the required groundwater recharge volume. Additional calculations indicate that the proposed drainage system will fully drain within 72 hours. The Applicant appears to comply with Standard 3; HW has no further comment. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 1.0-inch of volume from the impervious area for water quality. a. The Applicant has not provided TSS removal calculations or calculations of water quality volume. HW recommends that the Applicant provide document to show compliance with Standard 4. HW 12/16/21: The Applicant has proposed a deep sump manhole to provide pretreatment to stormwater runoff that is generated by the driveway. TSS calculations provided by the Applicant indicate that the combination of the deep sump manhole and the proposed drywell will provide 85% TSS removal to all .captured stormwater. Additional calculations indicate that the proposed drainage design will provide the required water quality volume for pollutant treatment. The Applicant appears to comply with Standard 4; HW has no further comment. K:V'rojects12021%210201'own of Willi Andover\21020E 33 Appledos-eUteports121121 b 2nd I'm Review 33 Appledore Lalze.doex Town of North Andover December 16, 2021 Page 5 of 7 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The proposed development is not considered a LUHPPL and therefore, Standard 5 is not applicable to this project. HW 12116/21: No further comment is necessary. 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 and therefore, Standard 6 is not applicable. HW 12/16121: No further comment is necessary. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project is a combination of new development and redevelopment, and therefore the Applicant is required to meet the Stormwater Management Standards only to the maximum extent practicable for the redevelopment portion of the project. Once the Applicant has addressed the other comments in this letter, it appears that the requirements of Standard 7 will be met. HW 12116/21: No further comment is necessary. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources, a. In Accordance with the North Andover Stormwater Regulations, Chapter 250, Article VIII, the following amendments are recommended: i. Delineate the limits of work per Section 29.C.2.a. HW 12116/21: The Applicant has revised the plans to delineate the limit of worst (LOW). The proposed erosion control mulch soxx appears to extend beyond the LOW. HW recommends that the Applicant revise the LOW to encompass all proposed site work. ii. Include notes of temporary and final site stabilization per Section 29.C.2.f, HW 12/16/21: The Applicant has added the location of proposed erosion control blankets as well as mulch soxx. HW has no further comment. iii. Provide a construction sequence per Section 29.C.3.b. HW 12/16121: The Applicant has not provided a construction sequence. HW's original comment stands. iv. Provide a maintenance schedule and instructions for erosion control upkeep per Sections 29.C.3.e and 30.A.11. HW 12/16121: In the Response Letter, the Applicant has included a description of erosion control upkeep activities. HW recommends that the Applicant revise the Erosion Control Detail to include this information. V. Designate a location for stockpiled soil per Section 30.A.18. K:1Prgiec1s12t12 112 1 020"Gown of Norih Andover1210208 33 ApPledi�rel[2el)ortsl21 121 G_2nd Peer Review 33 Appledore Latmdocx Town of North Andover December 16, 2021 Page 6 of 7 HW 12116/21: The Applicant has designated a soil stockpile location on the revised plans. HW has no further comment. vi. The northern corner of the site appears to be graded at 3H:1 V. Include a detail for erosion control blankets per Section 30.A.28. HW 12116121: The Applicant has included a callout for erosion control blankets in the northern corner and has provided an Erosion Control Blanket detail. HW has no further comment. 9. Standard 9 requires a long-term operation and maintenance (O&M)plan shall be developed and implemented to ensure that storm water management systems function as designed. a. The Applicant has not provided an O&M Plan. HW recommends that the Applicant provide an O&M Plan that meets the requirements of the MSH and North Andover Stormwater Regulations Chapter 250 Article 9. The O&M Plan should be a stand-alone document and be signed by the property owner(s). HW 12/16/21: The Applicant has provided an O&M Plan, which includes instructions on O&M for the proposed drainage system and the signature of the owner. HW recommends that the Applicant revise the frequency of maintenance for the deep sump manhole to four times per year to be consistent with the deep sump catch basin requirements listed in MSH Vol. 2, Chap. 2. Furthermore, HW recommends that the Applicant provide a plan or map indicating the location of facilities to be maintained per North Andover Stormwater Regulations Chapter 250 Section 32.A,4. 10. Standard 10 requires that an Illicit Discharge Compliance Statement be provided. a. The Applicant has not provided an Illicit Discharge Compliance Statement in the Drainage Report signed by the property owner. HW recommends that the Planning Board include a condition of approval requiring an Illicit Discharge Compliance Statement be signed by Sean or Lauren Delaney 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. In addition to providing grading information within the extents of the proposed driveway, HW recommends that the Applicant include the proposed 95-contour north of the driveway. HW 12/16121: The Applicant has revised the plans to include the proposed 95- contour. HW has no further comment. b. HW recommends that the Applicant include a detail for the proposed cape cod berm. HW 12/16/21: The Applicant has provided a Cape Cod Berm Detail on the plans. HW has no further comment. KAVrojects12021121020 Town of Noilh Andover121020C 33 AppledurellZeports121121 G 2nd Peer Review 33 Appledore Lazle.doex 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 the remaining outstanding 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. Jonas Procton, E.I.T. Senior Project Manager Design Engineer K:111rojedsl2021%21020 Town of Noah Andover121020E 33 APlnledor4lftei)oris1211210 2nd Peer Review 33 Appledore Lane,docx Horsley Wiffen Group Sustainable Environmental Solutions 112 Water Street•811 Floor•Boston,MA 02169 857-263.8193-horsteywitten.cwm y, 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 33 Appledore Lane 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 Plans for the proposed single family home expansion at 33 Appledore Lane, North Andover, MA. The plans were prepared for Sean and Lauren Delaney by Sullivan Engineering Group, LLC. The project proposes the addition of a second story to the existing 1-story garage, as well as an expanded driveway on the existing 0.90-acre lot. The proposed Stormwater management includes a system of two subsurface drywells, which are designed to capture drainage from the proposed additional impervious areas. The site is located within the Watershed Protection District, and a wetland area has been identified approximately 130 feet from the lot (at 11 Appledore Lane). Because the site is within 325 of a wetland resource within the Watershed Protection District, it is within the Non- Discharge Buffer Zone and requires a Special Permit. The following documents and plans were received by HW: • Special Permit--Watershed Permit Application, 33 Appledore Lane, North Andover, Massachusetts, prepared for Sean and Lauren Delaney by Sullivan Engineering Group, LLC, dated October 19, 2021 (17 pages); and Plot Plan of Land, 33 Appledore Lane, North Andover, Massachusetts, prepared for Sean Delaney by Sullivan Engineering Group, LLC, dated September 26, 2021 (1 page) 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 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 Hors leyWtten.corn Er HorsleyWittenGroup Horsley Witten Group, Inc, Town of North Andover November 1, 2021 Page 2 of 4 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. 1. Standard 1 states that 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 site plan provided by the Applicant features limited proposed grading and does not provide grading contours within the proposed driveway expansion. Based on the existing grading and the spot grades, it appears that the proposed trench drain is at a high point, and therefore runoff will not be directed to the proposed drywell for treatment. HW recommends that the Applicant revisit the grading to ensure that all runoff created by new impervious surfaces is directed to the proposed stormwater management system. Furthermore, the spot grades provided indicate that the driveway may have a slope of 10% or greater. HW recommends that the Applicant revisit the spot grades and verify that the proposed driveway slope is reasonable. b. Based on the HydroCAD analysis provided by the Applicant, it appears that runoff from the 2-year storm is able to be stored within the proposed drywell without overflowing. Based on this analysis, it appears that the proposed drainage design will not result in erosion in nearby wetlands. 2. Standard 2 requires that stormwater management systems shall be designed so that post- development peak discharge rates do not exceed pre-development peak discharge rates. a. In accordance with the North Andover Stormwater Regulations, Chapter 250, Section 27 the following amendments are recommended: i. A comparison of pre- and post-development hydrologic analyses on a subwatershed basis, rather than solely based on the additional impervious area. ii. Addition of a summary table including peak discharge rates and total volume of discharge for all modelled storm events to easily evaluate the pre- and post-development values. iii. Adjust the rainfall data for all modelled storm events to match the values provided in Section B.2.a, including the '/2-inch and 25-year storms. b. Based on the HydroCAD analysis, it appears that stormwater captured during a 100- year storm event overtops the ceiling of the proposed drywell. It does not surcharge from the proposed trench drain, which serves as an overflow outlet given sufficient rainfall. Per Stormwater Regulations Chapter 250, Section 27.B.6, HW recommends that the Applicant ensure that any changes to the design or HydroCAD analysis (including rainfall depths or adjustments to the trench drain elevation) continue to prevent overflow during a 100-year storm event. c. The proposed drywell is modelled in HydroCAD with 36 inches of stone surrounding each wall. This appears to be consistent with the plan view of the drywell, however the detail for the drywell calls for 30 inches of stone. HW recommends that the Applicant revise the 1000 Galion Dry Well Jumbo (H-20) detail for consistency. IL Projecis12021121020 Town of North Andover121020T;33 Appledorellteparts121 1 101_1 st Peer Review 33 A ppledore Lane.docx Town of North Andover November 1, 2021 Page 3 of 4 d. The Applicant has not shown or noted a required cover between the drywells and the driveway surface. HW recommends that the Applicant confirm the minimum cover required. e. The 4-inch HDPE= drainpipe shown connecting the proposed trench drain and the dry well appears to have a 450 bend, as well as a downward slope. HW recommends that the Applicant call out the slope and length of the pipe as well as the required elbow pipe to confirm constructability. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. The Applicant has not provided calculations of required recharge or drawdown time. HW recommends that the Applicant provide documentation to show compliance with Standard 3. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 1.0-inch of volume from the impervious area for water quality. a. The Applicant has not provided TSS removal calculations or calculations of water quality volume. HW recommends that the Applicant provide document to show compliance with Standard 4. 5. Standard 5 is related to projects with a Land Use of Higher Potential Pollutant Loads (LUHPPL). a. The proposed development is not considered a LUHPPL and therefore, Standard 5 is not applicable to this project. 5. Standard 6 is related to projects with stormwater discharging into a critical area, a Zone !1 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 and therefore, Standard 6 is not applicable. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed project is a combination of new development and redevelopment, and therefore the Applicant is required to meet the Stormwater Management Standards only to the maximum extent practicable for the redevelopment portion of the project. Once the Applicant has addressed the other comments in this letter, it appears that the requirements of Standard 7 will be met. 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. In Accordance with the North Andover Stormwater Regulations, Chapter 250, Article VIII, the following amendments are recommended: I. Delineate the limits of work per Section 29.C.2.a. ii. Include notes of temporary and final site stabilization per Section 29.C.2.f. iii. Provide a construction sequence per Section 29.C.3.b. HAProjects12021121020 To»m of North AndoverN21020F 33 Ap1)1c(lore\Rcports1211101_I st Peer Review 33 Appledore Lane,doex Town of North Andover November 1, 2021 Page 4 of 4 iv. Provide a maintenance schedule and instructions for erosion control upkeep per Sections 29.C.3.e and 30.A.11. V. Designate a location for stockpiled soil per Section 30.A.18. vi. The northern corner of the site appears to be graded at 3H;1V. Include a detail for erosion control blankets per Section 30.A.28. 9. Standard 9 requires a long-term operation and maintenance (O&M) plan shall be developed and implemented to ensure that stormwater management systems function as designed. a. The Applicant has not provided an O&M Plan. HW recommends that the Applicant provide an O&M Plan that meets the requirements of the MSH and North Andover Stormwater Regulations Chapter 250 Article 9. The O&M Plan should be a stand-alone document and be signed by the property owner(s). 10. Standard 90 requires that an Illicit Discharge Compliance Statement be provided. a. The Applicant has not provided an Illicit Discharge Compliance Statement in the Drainage Report signed by the property owner. HW recommends that the Planning Board include a condition of approval requiring an Illicit Discharge Compliance Statement be signed by Sean or Lauren Delaney prior to land disturbance. 11. Additional Comments: a. In addition to providing grading information within the extents of the proposed driveway, HW recommends that the Applicant include the proposed 95-contour north of the driveway. b. HW recommends that the Applicant include a detail for the proposed cape cod berm. 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. �.. 9-- Janet Carter Bernardo, P.E. Jonas Procton, E.I.T. Senior Project Manager Design Engineer H.\Projects12 02 112 1 0 2 0 To%tm of NortU Andover121020L 33 Appledorc\Reports121 1101_1 st Peea•Revic,,v 33 App[edore L,tne.doc.c