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HomeMy WebLinkAbout2020-10-06 Stormwater Review SPR Horsley rou Witten G 5 Sustainable Environmental Solutions i 112 Water Street•61,Fioor•Beaton,MA 02109 657-283.6193•horsleywitterimm August 13, 2020 Ms. Jean Enright, Planning Director g g Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Ref: Initial Stormwater Peer Review Bake N Joy Foods, Inc. 335 Willow Street 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 development at 335 Willow Street, North Andover, MA. The plans were prepared for Muffin 3X, LLC (Applicant) by the Morin-Cameron Group, Inc. HW understands that the Applicant is proposing to construct two additions totaling 8,708 square feet (sf) onto an existing building and configuring the existing parking area. The Applicant is proposing to remove 370 sf of pavement from the existing parking area and repair a riprap-lined discharge to a bordering vegetated wetland (BVW) located on the south side of the property. The project proposes to develop a 3.58-acre parcel that currently contains one existing building and two parking areas. The site contains a BVW, and portions of the existing building and parking areas are within the 25-, 50-, and 100-foot wetland offsets. Construction activities are proposed within the 100-foot wetland offset, and regrading and riprap repair are proposed within the 25-foot offset. The site is not within an Area of Critical Concern or a Water Resource Protection District and is outside of the FEMA 100-year flood zone. The following documents and plans were received by HW: • Site Plan Review Cover Letter for Bake N Joy Foods, Inc. —335 Willow Street South, North Andover, Massachusetts, prepared by the Morin-Cameron Group, Inc., dated July 29, 2020; • Stormwater Management/Technical Report for 335 Willow Street, North Andover, Massachusetts, prepared by the Morin-Cameron Group, dated July 29, 2020; • Site Re-Development Plans, 335 Willow Street, North Andover, Massachusetts, prepared by the Morin-Cameron Group, Inc., dated July 29, 2020, which include: o Cover Sheet Sheet 1 of 11 o Existing Conditions Plan Sheet 2 of 11 o Site Layout Plan Sheet 3 of 11 o Grading & Drainage Plan Sheet 4 of 11 o Utility Plan Sheet 5 of 11 HorsleyWitten.com @HorsleyWittenGroup Horsley Witten Group, Inc. Town of North Andover August 13, 2020 Page 2of5 o Landscape Plan Shoot 6 of 11 o Photometric Plan Sheet 7 of I 1 o Photometric Plan Sheet 8 of 11 o Construction Details Sheet 9 of 11 o Construction Details Sheet 10 of 11 o Building Elevations Sheet 11 of 11 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). The comments below correlate with the MSH standards and where the more stringent Town requirements are applicable additional comments are noted. The development is reducing the existing parking area. However it is increasing the building footprint therefore increasing the total area of impervious surfaces and is therefore considered new development. 1. Standard I states that no new stormwater conveyances (e.g. outtalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. a. The Applicant has noted that proposed impervious surfaces are comprised of roof area, and therefore that new stormwater conveyances qualify as treated (including those discharged directly to wetland areas). Portions of proposed drainage area PSI and PS2B are comprised of roof areas that are directed onto pavement before discharging at Design Point (DP) 1 and DP2. Because the stormwater is proposed to drain over pavement without receiving treatment, it is HW's opinion that the rooftop runoff from PSI and PS2B is considered untreated. HW recommends that the Applicant revise the stormwater management design to disconnect the roof runoff from the pavement sheet flow. b. The Applicant has proposed to remove sediment from the existing riprap discharge point at DP1 and install new riprap in the same location. HW recommends that the Applicant provide riprap sizing calculations to verify that runoff will not cause erosion in the adjacent BVW area and revise the site plans to include a detail of the proposed riprap. The Applicant may choose to consider options that allow for easy maintenance of the outfali. 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. The Applicant has proposed three (3) existing drainage areas, accounting for the southwest, southeast, and northeast corners of the site. The Applicant does not appear to have included an analysis or description of runoff from the northwest corner of the site. HW recommends that Applicant analyze the northwest drainage area or justify its exclusion from the drainage analysis. KAProjects12018U 8065 N Andover On-CaM18065S 335 willow Street Soull)lRepotts1200813_t st Storunaater Peer Review_335 willow Street Soullt.docx I a i Town of North Andover August 13, 2020 Page 3 of 5 b. The Applicant has indicated that runoff from proposed drainage area PS213 is I conveyed by a roof leader under the proposed building entrance ramp to the south parking area, but has not clearly specified this feature on the Grading & Drainage Plan (Sheet 4). HW recommends that the Applicant revise the site plans to clearly label this drainpipe/structure and include the outlet elevation. If feasible HW recommends providing a means to infiltrate this roof runoff. It appears that icing within the parking lot could be a concern where the roof drain outlets. c. On the Outlet Control Structure Detail provided on the Construction Details (Sheet 10), the Applicant notes that the OCS outlet has an invert of 248.8, the plan view { provided on Sheet 10 indicates the OCS outlet has an invert of 248.3, and on Sheet 4 the OCS is noted as having an outlet invert of 245.8 +/-. HW recommends that the Applicant revise the site plans to indicate a consistent outlet invert elevation. d. The HydroCAD analysis performed by the Applicant utilizes a 2-year design storm rainfall depth of 3.15 inches. HW recommends that the Applicant revise the HydroCAD analysis to utilize a 2-year design storm rainfall depth of at least 3.20 inches (per North Andover Bylaw 7.2.B.b). 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. The Applicant has proposed a bottom invert for the Underground Chamber System within 4 feet of the estimated seasonal high groundwater elevation (ESHGW). The Applicant has designed the system to discharge during the 10-year storm event, therefore a mounding analysis is not required per MSH Vol. 3. No action needed. The Applicant appears to comply with Standard 3. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 0.5-inch of volume from the impervious area for water quality. a. The Applicant has not provided a calculation of water quality volume (WQV) or TSS removal calculations. HW recommends that the Applicant provide these analyses and verify that the required WQV is captured by the proposed stormwater management system. 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 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 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 development is considered a hew development with an increase of impervious area, therefore Standard 7 is not applicable. K:IProjcclsV018118065 A'Andover Ott-Cn11118065S 335 Willow Street Soutli\Reports1200813_Is(Slornnwnter Peer Review 335 Willow Street South,doex Town of North Andover August 13, 2020 Page 4 of 5 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The Applicant has noted in the Construction Phase Best Management Practices Plan (CPBMPP) that a stabilized construction entrance/exit should be installed if required. Per Bylaw 8.2.k, HW recommends that the Applicant revise the CPBMPP and the site plans to require the installation of a stabilized construction entrance/exit. b. The Applicant has noted in the CPBMPP that netting should be installed at mulched areas with steep slopes. Per Bylaw 8.2.bb, HW recommends that the Applicant revise the CPBMPP to specify that netting should be installed on slopes of steepness 3:1 or greater. c. The Applicant has not provided a SWPPP in the Site Plan Review materials. Per Bylaw 8.0, HW recommends that provision of a SWPPP be conditional to Land Disturbance Permit approval. 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 provided an O&M Plan that appears to meet the standards established by MSH Vol. 2, Ch. 2 for maintenance of the proposed Subsurface Chamber System. b. The O&M Plan provided by the Applicant does not include instructions on maintenance of the riprap discharge area. HW recommends that the Applicant revise the O&M Plan to ensure proper upkeep of this area. c. The Applicant has not provided an O&M Log sheet. HW recommends that an O&M Log be provided at the end of the O&M Plan as a template for maintenance documentation. d. The Applicant has noted on the Site Layout Plan (Sheet 3)that a portion of the southeastern corner of the site is proposed to be a landscaping easement. Per Bylaw 9.1.a.vi, HW recommends that the Applicant revise the O&M Plan to refer to the existence and location of the proposed landscaping easement. e. The Applicant has not included the signature of the property owner on the O&M Plan. Per Bylaw 9.1.a.ii, HW recommends that the Applicant provide a signed version of the O&M Plan. 10. Standard 10 requires that an Illicit Discharge Compliance Statement be provided. a. The Applicant provided an Illicit Discharge Compliance Statement in the Stormwater Management/Technical Report signed by the Morin-Cameron Group, Inc. HW recommends that the Illicit Discharge Compliance Statement be signed by the property owner prior to land disturbance. 11. Miscellaneous Comments; a. North Andover Stormwater Regulations Section 7.2 IF require that plants be native to Essex County or cultivators of these native plants. Two of the three groundcovers (P. alopecuroides and Hosta) proposed for the site are not native. HW recommends that the Applicant substitute plants native to Essex County. K:Trojects12018118065 N Andover On-CalI\18065S 335 Willow Street SoothlReports1200813_t st Stonnwater Peer Review 335 Willow Street South.doex Town of North Andover August 13, 2020 Page 5 of 5 l COi1C(USlOr18 HW recommends that the Planning Board require that the Applicant 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. Jonas Procton, E.I.T. Senior Project Manager Design Engineer KOrojects12018118065 N Andover On-CalI\l8065S 335 Willow Street Sowh\Reports\200813_lst Stormwawr Peer Revietv_335 Willow Street south.docx f E • I Horsley Witten Group �� . Sustainable Environmental Solutions 912 Water 5t 6et.-80'Floor+:13lrston,MA 02109 t357-263-0193 Morsleywfiten.00m September 17, 2020 i Ms. Jean Enright, Planning Director Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Ref: Second Stormwater Peer Review Bake N Joy Foods, Inc. 335 Willow Street 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 development at 335 Willow Street, North Andover, MA. The plans were prepared for Muffin 3X, LLC (Applicant) by the Morin-Cameron Group, Inc. HW understands that the Applicant is proposing to construct two additions totaling 8,708 square feet (sf) onto an existing building and configuring the existing parking area. The Applicant is proposing to remove 370 sf of pavement from the existing parking area and repair a riprap-lined discharge to a bordering vegetated wetland (BVW) located on the south side of the property. The project proposes to develop a 3.58-acre parcel that currently contains one existing building and two parking areas. The site contains a BVW, and portions of the existing building and parking areas are within the 25-, 50-, and 100-foot wetland offsets. Construction activities are proposed within the 100-foot wetland offset, and regrading and riprap repair are proposed within the 25-foot offset. The site is not within an Area of Critical Concern or a Water Resource Protection District and is outside of the EEMA 100-year flood zone. HW had a phone conversation with the design engineers at Morin-Cameron on September 4, 2020 to review our initial comments. The following documents and plans were received by HW in response to our initial peer review letter dated August 13, 2020: • Letter to Jean Enright regarding Stormwater Peer Review, Bake N Joy Foods, Inc., 335 Willow Street South, North Andover, Massachusetts, prepared by the Morin-Cameron Group, Inc., dated September 14, 2020, with attachments (36 pages). • Site Re-Development Plans, 335 Willow Street, North Andover, Massachusetts, prepared by the Morin-Cameron Group, Inc., dated July 29, 2020, revised September 14, 2020, which include: o Cover Sheet Sheet 1 of 11 o Existing Conditions Plan Sheet 2 of 11 o Site Layout Plan Sheet 3 of 11 o Grading & Drainage Plan Sheet 4 of 11 HorsleyWitten.corn @HorsleyWittenGroup ®Horsley Wifiten Group, Inc. Town of North Andover September 17, 2020 Page 2 of 6 o Utility Plan Sheet 5 of 11 o Landscape Plan Sheet 6 of 11 o Photometric Plan Sheet 7 of 11 o Photometric Plan Sheet 8 of 1 I o Construction Details Sheet 9 of 11 o Construction Details Sheet 10 of 11 o Building Elevations Sheet I of 11 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). The comments below correlate with the MSH standards and where the more stringent Town requirements are applicable additional comments are noted. The development is reducing the existing parking area. However, it is increasing the building footprint therefore increasing the total area of impervious surfaces and is therefore considered new development. The following comments correlate to our initial peer review, follow up comments are provided in bold font. 1. Standard 9 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 Applicant has noted that proposed impervious surfaces are comprised of roof area, and therefore that new stormwater conveyances qualify as treated (including those discharged directly to wetland areas). Portions of proposed drainage area PSI and PS2B are comprised of roof areas that are directed onto pavement before discharging at Design Point (DP)I and DP2. Because the stormwater is proposed to drain over pavement without receiving treatment, it is HW's opinion that the rooftop runoff from PSI and PS2B is considered untreated. HW recommends that the Applicant revise the stormwater management design to disconnect the roof runoff from the pavement sheet flow. The Applicant has stated that due to the existing conditions, including the flat parking area and close proximity to the wetland, installing a new stormwater practice will have a more significant impact to the wetlands than cleaning the sediment from the existing discharge point. The Applicant is proposing to remove a significant amount of accumulated sediment and replace the riprap at the outfall. The Applicant is not creating a new conveyance to the wetland and the discharge should not cause erosion to the wetland. The discharge point is very close to the edge of the wetlands and during our phone conversation we discussed possible measures to improve it. The solution remained to replace the existing stone and remove the accumulated sediment. HW suggests that the Applicant investigate if a product like the Rain UProjectsQ0 1 811 80 6 5 N Andover On-Ca11118065S 335 Willow Street SoutMepor0200917 2nd Stormwater PCCr Review 335 Willow Street South.docx i Town of North Andover September 17, 2020 Page 3 of 6 Guardian Turret may be an improvement or if drivable grass/ plantabie concrete placed at the edge of the parking lot with the riprap stone closer to the wetlands may work to allow for easier maintenance. The location is difficult, and the improvement proposed by the Applicant may be the best option. b. The Applicant has proposed to remove sediment from the existing riprap discharge point at DPI and install new riprap in the same location. HW recommends that the Applicant provide riprap sizing calculations to verify that runoff will not cause erosion in the adjacent BVW area and revise the site plans to include a detail of the proposed riprap. The Applicant may choose to consider options that allow for easy maintenance of the outfall. The Applicant has provided riprap sizing calculations and added a detail to Sheet 10 of 11. HW has no further comment, 2. Standard 2 requires that 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 proposed three (3) existing drainage areas, accounting for the southwest, southeast, and northeast corners of the site. The Applicant does not appear to have included an analysis or description of runoff from the northwest corner of the site. HW recommends that Applicant analyze the northwest drainage area or justify its exclusion from the drainage analysis. The Applicant clarified the work proposed within the northwest portion of the site. The proposed crushed stone will be an improvement over the existing condition. No further comment. b. The Applicant has indicated that runoff from proposed drainage area PS213 is conveyed by a roof leader under the proposed building entrance ramp to the south parking area, but has not clearly specified this feature on the Grading & Drainage Plan (Sheet 4). HW recommends that the Applicant revise the site plans to clearly label this drainpipe/structure and include the outlet elevation. If feasible HW recommends providing a means to infiltrate this roof runoff. It appears that icing within the parking lot could be a concern where the roof drain outlets. The Applicant has revised the discharge from the roof leader and piped it to a landscaped area. This is an improvement over the original design. No further comment. c. On the Outlet Control Structure Detail provided on the Construction Details (Sheet I0), the Applicant notes that the OCS outlet has an invert of 248.8, the plan view provided on Sheet 10 indicates the OCS outlet has an invert of 248.3, and on Sheet 4 the OCS is noted as having an outlet invert of 245.8 +/-. HW recommends that the Applicant revise the site plans to indicate a consistent outlet invert elevation. The Applicant has revised the outlet control invert to be consistent on all plan views. No further comment. d. The HydroCAD analysis performed by the Applicant utilizes a 2-year design storm rainfall depth of 3.15 inches. HW recommends that the Applicant revise the KOrojectsl2018118065 N Andoti cr On-Call\180G5S 335 Willow Street SouthkReports12009172nd Storm titer Peer Review-335 Willow Street South.docx Town of North Andover September 17, 2020 Page 4 of 6 HydroCAD analysis to utilize a 2-year design storm rainfall depth of at least 3.20 inches (per North Andover Bylaw 7.2.B.b). The Applicant has revised the rainfall depth as requested. No further comment. 3. Standard 3 requires that the annual recharge from post-development shall approximate annual recharge from pre-development conditions. a. The Applicant has proposed a bottom invert for the Underground Chamber System within 4 feet of the estimated seasonal high groundwater elevation (ESHGW). The Applicant has designed the system to discharge during the 10-year storm event, therefore a mounding analysis is not required per MSH Vol. 3. No action needed. The Applicant appears to comply with Standard 3. No further comment needed. 4. Standard 4 requires that the stormwater system be designed to remove 80% Total Suspended Solids (TSS) and to treat 0.5-inch of volume from the impervious area for water quality. a. The Applicant has not provided a calculation of water quality volume (WQV) or TSS removal calculations. HW recommends that the Applicant provide these analyses and verify that the required WQV is captured by the proposed stormwater management system. The Applicant has reasonable responded to this comment. HW would have preferred to see some additional measures to improve water quality prior to discharging to the wetland. However, as the site is very constricted the proposed design and routine maintenance of the parking lot will be an improvement over the existing condition. 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 therefore, Standard 5 is not applicable to this project. No further comment needed. 6. Standard 6 is related to projects with storm water discharging into a critical area, a Zone ll 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 and therefore Standard 6 is not applicable. No further comment needed. 7. Standard 7 is related to projects considered Redevelopment. a. The proposed development is considered a new development with an increase of impervious area, therefore Standard 7 is not applicable. No further comment needed. KAProjectsM18118065 N Andover©n-Ca€1\18065S 335 Willow Street SoutIAReports1200917 2nd Stornmater Peer Review_335 Willow Street SOUth.dOCX F Town of North Andover I September 17, 2020 Page 5 of 6 i 8. Standard 8 requires a plan to control construction related impacts including erosion, sedimentation, or other pollutant sources. a. The Applicant has noted in the Construction Phase Best Management Practices Plan (CPBMPP) that a stabilized construction entrance/exit should be installed if required. Per Bylaw 8.2.k, HW recommends that the Applicant revise the CPBMPP and the site plans to require the installation of a stabilized construction entrance/exit. i The Applicant has added the construction entrance to Drawing 4 of 11. No further comment. b. The Applicant has noted in the CPBMPP that netting should be installed at mulched j areas with steep slopes. Per Bylaw 8.2.bb, HW recommends that the Applicant revise the CPBMPP to specify that netting should be installed on slopes of steepness 3:1 or greater. The Applicant has revised the CPBMPP as requested. No further comment. c. The Applicant has not provided a SWPPP in the Site Plan Review materials. Per Bylaw 8.0, HW recommends that provision of a SWPPP be conditional to Land Disturbance Permit approval. The Applicant has acknowledged that a SWPPP will be provided prior to land disturbance. The Planning Board may wish to include this as a condition of approval. 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 provided an O&M Plan that appears to meet the standards established by MSH Vol. 2, Ch. 2 for maintenance of the proposed Subsurface Chamber System. No further comment needed. b. The O&M Plan provided by the Applicant does not include instructions on maintenance of the riprap discharge area. HW recommends that the Applicant revise the O&M Plan to ensure proper upkeep of this area. The O&M Plan has been revised as requested. No further comment. c. The Applicant has not provided an O&M Log sheet. HW recommends that an O&M Log be provided at the end of the O&M Plan as a template for maintenance documentation. The O&M Plan has been revised to include the log as requested. No further comment. d. The Applicant has noted on the Site Layout Plan (Sheet 3) that a portion of the southeastern corner of the site is proposed to be a landscaping easement. Per Bylaw 9.1.a.vi, HW recommends that the Applicant revise the O&M Plan to refer to the existence and location of the proposed landscaping easement. The Applicant has clarified that the easement is existing. No further comment. K:IProjects�2018118065 N Andover On-Cal]\18065S 335 Willow Street SOWAReporisl2 OM 2nd Storinwater Deer Review 335 Wi€low Street Sou!€r.doeh Town of North Andover September 17, 2020 Page 6 of 6 e. The Applicant has not included the signature of the property owner on the O&M Plan. Per Bylaw 9.1.a.ii, HW recommends that the Applicant provide a signed version of the O&M Plan. The O&M Plan has been signed by the property owner. No further comment. 10. Standard 10 requires that an Illicit Discharge Compliance Statement be provided. a. The Applicant provided an Illicit Discharge Compliance Statement in the Stormwater Management/Technical Report signed by the Morin-Cameron Group, Inc. HW recommends that the Illicit Discharge Compliance Statement be signed by the property owner prior to land disturbance. The Applicant has provided a signed illicit discharge statement. No further comment. 11. Miscellaneous Comments: a. North Andover Stormwater Regulations Section 7.2 F require that plants be native to Essex County or cultivators of these native plants. Two of the three groundcovers (P. alopecuroides and Hosta) proposed for the site are not native. HW recommends that the Applicant substitute plants native to Essex County. The Applicant has revised the plant list as requested. No further comment. Conclusions HW is satisfied that the Applicant has adequately responded to our comments. The Applicant is advised that provision of these comments does not relieve him/her of the responsibility to comply with all Town of North Andover Codes and By-Laws, Commonwealth of Massachusetts laws, and federal regulations as applicable to this project. Please contact Janet Bernardo at 508-833-6600 or atjbernardo@horsleywitten.com if you have any questions regarding these comments. Sincerely, HORSLEY WITTEN GROUP, INC. Janet Carter Bernardo, P.E. Senior Project Manager KAProjeols12018\18065 N Andover On-Cal1U 8065S 335 Willow Street SouthltteporlsM0917,2nd Storinwater Peer Review_335 Willow Street Sootli.doex 1 o. I The M6rin-Cameron rr `1 ......... s ..._z vv r .. I I September 14, 2020 Ms. Jean Enright, Planning Director Planning Department Town of North Andover 120 Main Street North Andover, Massachusetts 01845 Ref: Initial Stormwater Peer Review Bake N Joy Foods, Inc. 335 Willow Street North Andover, Massachusetts Dear Ms. Enright and Board Members: We are in receipt of a peer review letter for the above-referenced project, dated August 13, 2020, prepared by The Horsley Witten Group, Inc. ("HWG"). We also had a subsequent phone conversation with Janet Bernardo, PE from HWG on September 411 to discuss the peer review comments. This response letter, along with the enclosed revised site plans and documentation, has been prepared to address the comments raised in the HWG review letter. This response letter is organized in the same format as the HWG review letter to address each item independently and help simplify the review. Stormwater Standards 1. Standard I a. The proposed project is comprised of a mix of new development and redevelopment, and includes a net increase in impervious area from the new roof (although total pavement area is decreased as described in comment #4). Roof area is considered "clean" runoff, and therefore does not require treatment prior to discharge. Portions of the new roof runoff will discharge onto the existing pavement, as is the case under existing conditions. The "clean" roof runoff does not contribute to an increase to the total suspended solids (TSS) load of the parking area. Given the site constraints of the gentle topography and the close proximity of the Bordering Vegetated Wetland, it is not practicable to install additional treatment measures for pavement areas. In order to improve the treatment of parking lot runoff, the proposed project includes removing accumulated sediment from the existing rip-rap outfall and re-constructing It with new rip-rap to restore the intended function of this outfall. The rip-rap outfall was also added to the Long Term Operation and Maintenance Plan to ensure that it is regularly inspected and maintained. b. The stormwater calculations have been revised to include riprap sizing calculations using the Isbash curve. The plans have also been revised to include a detail of the proposed riprap on Sheet 10 of 11. CIVIL ENGINEERS • LAND SURVEYORS e ENVIRONMENTAL CONSULTANTS ® LAND USE PLANNERS 66 Elm Street, Danvers, MA 01923 978,777,8586 FAX 978.774,3488 Providing Professional Services Since 1978 www.morincameron.com North Andover Planning Board September 14, 2020 2 2. Standard 2 a. The northwest section of the site has minimal site work proposed. All proposed work will be taking place within areas of existing pavement or existing landscaping. A concrete pad is proposed that is located within areas of existing pavement, and therefore no increase in impervious area is being created. The area between the curb and building is proposed to be replaced with crushed stone. The existing conditions of this area is a compacted, sparsely vegetated and non-maintained landscape area. The crushed stone will decrease the runoff curve number, provide stormwater storage and promote infiltration. However, since the northwest section will either remain in existing conditions or be slightly improved it was not included in the stormwater analysis for the project. b. A callout has been added to the roof leader on the Grading and Drainage Plan (Sheet 4 of 11). The roof leader location has been revised to have an outfak located on the down gradient side of the parking area and access driveway within a vegetated area. This new location will prevent any icing issues associated within the parking area and also promote infiltration as runoff will flow overland before flowing to Willow Street where it currently discharges. c. The outlet control structure outlet invert has been revised to elevation 248.8 on Sheet 4 of 10 and Sheet 10 of 10. d. The HydroCAD analysis has been revised to model the 2-year design storm with a rainfall depth of 3.2 inches in pre and post development conditions. A revised hydraulic analysis has been included with this response and a summary table for the 2-year event is shown below. Existing Conditions Proposed Conditions Change in Peak Design Point peak CFS (Peak CFS) (C DP-1 2.3 2.3 0 DP-2 1.0 0.8 -0.2 DP-3 0.9 0.7 -0.2 3. Standard 3 a. No response warranted. 4. Standard 4 a. The proposed project results in a reduction of pavement area by approximately 3,685 square feet, which corresponds to an increase in the water quality of runoff from paved surfaces. Due to the drainage limitations caused by the gentle topography and the close proximity of the Bordering Vegetated Wetland, it is not practicable to install additional treatment measures for the parking lot. In order to improve the existing conditions to the maximum extent practicable, the rip-rap spillway is proposed to be cleaned and replaced with new rip-rap. The rip-rap spillway was also added to the Long Term Operation and Maintenance Plan to ensure it functions properly into the future. Since the only runoff being directed towards a new BMP(infiltration chambers) is clean roof runoff, TSS calculations are not required. An additional improvement is that one of the existing roof downspouts that currently discharges directly onto T, North Andover Planning Board September 14, 2020 3 pavement is proposed to be discharged onto a concrete pad and overland flow over a small section of new vegetation before being discharged onto the pavement. 5. Standard 5 a. No response warranted. 6. Standard 6 a. No response warranted. 7. Standard 7 a. No response warranted. The proposed project is comprised of a mix of new development and redevelopment, and certain standards are met to the maximum extent practicable as described herein. 8. Standard 8 a. A stabilized entrance/exit location is now shown on the Grading and Drainage Plan on Sheet 4 of 11. However, in order to reduce potential sediment dislodgement and sediment transportation, it is our recommendation that the existing pavement be left in place as long as possible during construction. The construction entrance/exit shall be installed immediately after any pavement disturbance,as noted on the caltout. The Construction Phase Best Management Practices Plan (CPBMPP) has been revised to include description. b. The CPBMPP has been revised to specify slopes 3H:1V or greater shall have netting Installed. c. A NPDES SWPPP will be developed prior to any land disturbance. 9. Standard 9 a. No response warranted. b. The long term O & M has been revised to include maintenance of the riprap outfall. A maintenance log has also been included in the revised O & M. c. An O & M log sheet has been added to the long term O & M plan. d. There is no proposed landscaping easement. However, an existing landscaping easement does exist on the south-east corner of the property. This is also depicted on the existing conditions plan. No work is proposed within the easement; therefore It is not necessary to include it in the O & M. e, The revised tong term O & M now includes the owner's signature. 10. Standard 10 a. The illicit discharge statement was included with the stormwater and technical report. 11. Miscellaneous Comments a. The landscaping plans have been revised to include only Essex County native plantings. Black-eyed Susan was added to the plant list as a perennial groundcover. t � 1 North Andover Planning Board September 14, 2020 4 We trust that the revised plans and calculations, along with this response letter, address the comments raised in Horsley Witten Group, Inc.`s peer review letter. E i We look forward to meeting with the Planning Board at your next regularly scheduled meeting to formally present the proposed project, If you should have any questions prior to the meeting please do not hesitate to contact me. i Sincerely, ,I THE MORIN-CAMERON GROUP, INC. John M. Morin, PE Principal Enclosures cc: Muffin 3X, LLC {Via email} r 16 EE I ES1 ES2 ES3 SOUT -WEST SOUT -EAST NORT -EAST PARKING AREA PARKING AREA PARKING AREA DP1 DP2 DP3 BORDERING WILLOW STREET WILLOW STREET VEGETATED (SOUTH) (NORTH) WETLAND Subcat Reaeh on jpk Routing Diagram for 3908 Pre Development Watershed Analysis Prepared by The Morin-Cameron Group, Inc., Printed 911 512 02 0 HydroCAD®10.10 3a s!n 00401 02020}iydroCAD Software Solutions LLC r 'f 3908 Pre Development Watershed Analysis Prepared by The Morin-Cameron Group, Inc. Printed 9/15/2020 H droCAD® 10.10-3a sln 00401 O 2020 H droCAD Software Solutions LLC Pac ie 2 Area Listing (all nodes) 0 Area CN Description (sq-ft) (subcatchment-numbers) 16,056 74 >75% Grass cover, Good, HSG C (ES1, ES2, ES3) 4,578 80 >75% Grass cover, Good, HSG D (ES1, ES2) 1,758 98 Concrete, HSG C (ES1, ES2, ES3) 525 98 Concrete, HSG D (ES1, ES2) 932 96 Gravel surface, HSG C (ES3) 6,651 98 Paved parking, HSG C (ES2, ES3) 24,085 98 Paved parking, HSG D (ES1, ES2) 10,326 98 Roofs, HSG C (ES1, ES2, ES3) 8,213 98 Roofs, HSG D (ES1) I f ' i 3908 Pre Development Watershed Analysis p Y Prepared by The Morin-Cameron Group, Inc. Printed 9/15/2020 HydroCAD® 10.10-3a s/n 00401 O 2020 HydroCAD Software Solutions LLC Page 3 Soil Listing (all nodes) Area Soil Subcatchment (sq-ft) Group Numbers 0 HSG A 0 HSG S 35,723 HSG C ES1, ES2, ES3 37,401 HSG D ES1, ES2 0 Other f P E 3908 Pre Development Watershed Analysis NRCC 24-hr D 2-Year Rainfall=3.20" Prepared by The Morin-Cameron Group, Inc. Printed 9/15/2020 HydroCAD® 10.10-3a sln 00401 O 2020 HydroCAD Software Solutions LLC Page 4 Time span=0A0-36.00 hrs, dt=0.01 hrs, 3601 points x 3 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Subcatchment ES1: SOUTH-WEST Runoff Area=36,047 sf 88,00% Impervious Runoff Depth=2.75" Tc=6.0 min CN=96 Runoff=2.3 cfs 8,258 cf Subcatchment ES2: SOUTH-EAST Runoff Area=17,304 sf 71.42% Impervious Runoff Depth=2.26" Tc=6.0 min CN=91 Runoff=1.0 cfs 3,256 cf Subcatchment ES3: NORTH-EAST Runoff Area=19,773 sf 37.82% Impervious Runoff Depth=1.68" Tc=6.0 min CN=84 Runoff=0.9 cfs 2,772 cf Reach DP1: BORDERING VEGETATED WETLAND Inflow=2,3 cfs 8,258 of Outflow=2.3 cfs 8,258 cf Reach DP2: WILLOW STREET(SOUTH) Inflow=1.0 cfs 3,256 cf Outflow=1.0 cfs 3,256 cf Reach DP3: WILLOW STREET(NORTH) Inflow=0.9 cfs 2,772 cf Outflow=0.9 cfs. 2,772 cf if [� k f r r €i i I 3908 Pre Development Watershed Analysis NRCC 24-hr D 2-Year Rainfall=3.20" Prepared by The Morin-Cameron Group, Inc. Printed 9/15/2020 H droCAD® 10.10-3a s/n 00401 O 2020 H droCAD Software Solutions LLC Page 5 Summary for Subcatchment ES1: SOUTH-WEST PARKING AREA Runoff - 2.3 cfs @ 12.13 hrs, Volume= 8,258 cf, Depth= 2.75 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs NRCC 24-hr D 2-Year Rainfall=3.20" Areas CN Description 8,213 98 Roofs, HSG D 3,844 98 Roofs, HSG C 19,150 98 Paved parking, HSG D 86 98 Concrete, HSG C 428 98 Concrete, HSG D 649 74 >75% Grass cover, Good, HSG C 3,677 80 >75% Grass cover, Good, HSG D 36,047 96 Weighted Average 4,326 12.00% Pervious Area 31,721 88.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ftlft) (ft/sec) (cfs) 6.0 Direct Entry, Direct Entry (Tc = 6 min Min.) Summary for Subcatchment ES2: SOUTH-EAST PARKING AREA Runoff = 1.0 cfs @ 12.13 hrs, Volume= 3,256 cf, Depth= 2.26" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs NRCC 24-hr D 2-Year Rainfall=3.20" Area (so CN Description 3,152 98 Roofs, HSG C 3,414 98 Paved parking, HSG C 4,935 98 Paved parking, HSG D 761 98 Concrete, HSG C 97 98 Concrete, HSG D 4,044 74 >75% Grass cover, Good, HSG C 901 80 >75% Grass cover, Good, HSG D 17,304 91 Weighted Average 4,945 28.58% Pervious Area 12,359 71.42% Impervious Area Tc Length Slope Velocity Capacity Description min feet ftlft ft/sec cfs 6.0 Direct Entry, Direct Entry (Tc= 6 min Min.) < e 3908 Pre Development Watershed Analysis NRCC 24-hr D 2-Year Rainfall=3.20" Prepared by The Morin-Cameron Group, Inc. Printed 9/15/2020 H droCAD® 10.10-3a sln 00401 O 2020 H droCAD Software Solutions LLC Page 6 Summary for Subcatchment ES3: NORTH-EAST PARKING AREA Runoff = 0.9 cfs @ 12.13 hrs, Volume= 2,772 cf, Depth= 1.68" Runoff by SCS TR-20 method, UH-SCS, Weighted-CN, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs NRCC 24-hr D 2-Year Rainfall=3.20" Area (sf) CN Description 3,330 98 Roofs, HSG C 3,237 98 Paved parking, HSG C 911 98 Concrete, HSG C 11,363 74 >75% Grass cover, Good, HSG C 932 96 Gravel surface HSG C 19,773 84 Weighted Average 12,295 62.18% Pervious Area 7,478 37.82% Impervious Area Tc Length Slope Velocity Capacity Description min feet ftlft ftlsec cfs 6.0 Direct Entry, Direct Entry (Tc = 6 min Min,) Summary for Reach DP1: BORDERING VEGETATED WETLAND Inflow Area = 36,047 sf, 88.00% Impervious, Inflow Depth = 2.75" for 2-Year event Inflow = 2.3 cfs @ 12.13 hrs, Volume= 8,258 cf Outflow - 2.3 cfs @ 12.13 hrs, Volume= 8,258 cf, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs / 3 Summary for Reach DP2: WILLOW STREET (SOUTH) Inflow Area 17,304 sf, 71.42% Impervious, Inflow Depth = 2.26" for 2-Year event Inflow - 1.0 cfs @ 12.13 hrs, Volume= 3,256 cf Outflow = 1.0 cfs @ 12.13 hrs, Volume= 3,256 cf, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0,00-36,00 hrs, dt= 0.01 hrs 13 Summary for Reach DP3: WILLOW STREET (NORTH) Inflow Area = 19,773 sf, 37.82% Impervious, Inflow Depth = 1.68" for 2-Year event Inflow - 0.9 cfs @ 12.13 hrs, Volume= 2,772 cf Outflow = 0.9 cfs @ 12.13 hrs, Volume= 2,772 cf, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs 1 3 t y I I I I PS1 PS2 PS2A PS3 SOUT -WEST SOUT -EAST SOUTH-EAST ROOF NORT -EAST PARKING AREA PARKIN G AREA PARKING AREA DP1 DP2 P1 �` DP3 BORDERING WILLO TREET UNDE OUND WILLOW STREET VEGETATED (SO TH) CHAMBERS (NORTH) WETLAND PS2B PS3A SOUTHEAST ROOF SOUTH-EAST ROOF $UbGat Reach Orl �j�j( Routing Diagram for 3908 Post Development Watershed Analysis Prepared by The Morin-Cameron Group, Inc., Printed 9/15/2020 HydroCADQD 10.10-3a sin 00401 O 2020 HydroCAC Software Solutions LLC I 3908 Post Development Watershed Analysis Prepared by The Morin-Cameron Group, Inc. Printed 9/15/2020 HydroCAD® 10.10-3a sln 00401 ©2020 HydroCAD Software Solutions LLC Page 2 Area Listing (all nodes) Area CN Description (sq-ft) (subcatchment-numbers) 12,311 74 >75% Grass cover, Good, HSG C (PS2, PS3) 4,320 80 >75% Grass cover, Good, HSG D (PSI, PS2) 871 98 Concrete, HSG C (PS2, PS3) 2,820 98 Concrete, HSG D (PSI, PS2) 450 89 Gravel, HSG C (PS3) 6,420 98 Paved parking, HSG C (PS2, PS3) 19,223 98 Paved parking, HSG D (PSI, PS2) 15,671 98 Roofs, MSG C (PSI, PS2A, PS213, PS3, PS3A) 11,038 98 Roofs, HSG D (PS1, PS2i3) 3908 Post Development Watershed Analysis Prepared by The Morin-Cameron Group, Inc. Printed 9/15/2020 HydroCADO 10.10-3a s/n 00401 0 2020 HydroCAD Software Solutions LLC Page 3 Soil Listing (all nodes) Area Soil Subcatchment (sq-ft) Group Numbers 0 HSG A 0 HSG B 35,723 HSG C PS1, PS2, PS2A, PS2B, PS3, PS3A 37,401 HSG D PS1, PS2, PS2B 0 Other I J1 i 3908 Post Development Watershed Analysis NRCC 24-hr D 2-Year Rainfall=3.20" Prepared by The Morin-Cameron Group, Inc, Printed 9/15/2020 H droCADO 10.10-3a s/n 00401 C 2020 H droCAD Software Solutions LLC Pa e 4 Time span=0.00-36.00 hrs, dt=0.01 hrs, 3601 points x 3 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Subcatchment PS1: SOUTH-WEST Runoff Area=36,284 sf 90.13% Impervious Runoff Depth=2.75" Tc=6.0 min CN=96 Runoff=2.3 cfs 8,312 cf Subcatchment PS2: SOUTH-EAST Runoff Area=9,331 sf 76.36% Impervious Runoff Depth=2.45" Tc=6.0 min CN=93 Runoff=0.6 cfs 1,902 cf Subcatchment PS2A: SOUTH-EAST ROOF Runoff Area=4,643 sf 100.00% Impervious Runoff Depth=2.97" Tc=6.0 min CN=98 Runoff=0.3 cfs 1,148 cf Subcatchment PS2B: SOUTH-EAST ROOF Runoff Area=3,092 sf 100.00% Impervious Runoff Depth=2.97" Tc=6.0 min CN=98 Runoff=0.2 cfs 765 cf Subcatchment PS3: NORTH-EAST Runoff Area=17,865 sf 36.79% Impervious Runoff Depth=1.61" Tc=6.0 min CN=83 Runoff=0.7 cfs 2,396 cf Subcatchment PS3A: SOUTH-EAST ROOF Runoff Area=1,909 sf 100.00% Impervious Runoff Depth=2.97" Tc=6.0 min CN=98 Runoff=0.1 cfs 472 cf Reach DP1: BORDERING VEGETATED WETLAND Inflow=2.3 cfs 8,312 of Outflow=2.3 cfs 8,312 cf Reach DP2: WILLOW STREET(SOUTH) Inflow=0.8 cfs 2,666 cf Outflow=0.8 cfs 2,666 cf Reach DP3: WILLOW STREET(NORTH) Inflow=0.7 cfs 2,730 cf Outflow=0.7 cfs 2,730 cf Pond P1: UNDERGROUND CHAMBERS Peak Flev=249.73' Storage=552 cf Inflow=0.4 cfs 1,620 cf Discarded=0.0 cfs 1,286 cf Primary=0,1 cfs 335 cf Outflow=0.1 cfs 1,620 of I I i r i 1� I 3908 Post Development Watershed Analysis NRCC 24-hr D 2-Year Ralnfal1=3.20" Prepared by The Morin-Cameron Group, Inc. Printed 9115/2020 HydroCAD® 10.10-3a sin 00401 0 2020 HydroCAD Software Solutions LLC Page 5 Summary for Subcatchment PS1: SOUTH-WEST PARKING AREA j Runoff - 2.3 cfs @ 12.13 hrs, Volume= 8,312 cf, Depth= 2.75" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs NRCC 24-hr D 2-Year Rainfall=3.20" Area (so CN Description 10,881 98 Roofs, HSG D 3,277 98 Roofs, HSG C 15,757 98 Paved parking, HSG D * 2,787 98 Concrete, HSG D 3,582 80 >75% Grass cover, Good, HSG D 36,284 96 Weighted Average 3,582 9.87% Pervious Area 32,702 90.13% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ftlft) (ft/sec) (cfs) 6.0 Direct Entry, Direct Entry (Tc=6 min Mtn.) Summary for Subcatchment PS2: SOUTH-EAST PARKING AREA Runoff = 0.6 cfs @ 12.13 hrs, Volume= 1,902 cf, Depth= 2.45" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs NRCC 24-hr D 2-Year Rainfall=3.20" Area (sf) CN Description 3,184 98 Paved parking, HSG C 3,466 98 Paved parking, HSG D * 442 98 Concrete, HSG C * 33 98 Concrete, HSG D 1,468 74 >75% Grass cover, Good, HSG C 738 80 >75% Grass cover, Good, HSG D 9,331 93 Weighted Average 2,206 23.64% Pervious Area 7,125 76.36% Impervious Area Tc Length Slope Velocity Capacity Description min feet ft/ft ft/sec cfs 6.0 Direct Entry, Direct Entry (Tc = 6 min Min.) Summary for Subcatchment PS2A: SOUTH-EAST ROOF Runoff 0.3 cfs @ 12.13 hrs, Volume= 1,148 cf, Depth= 2.97" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs NRCC 24-hr D 2-Year Rainfall=3.20" i , Y 3908 Post Development Watershed Analysis NRCC 24-hr D 2-Year Rainfall=3.20" Prepared by The Morin-Cameron Group, Inc. Printed 9/15/2020 Hy droCAD® 10.10-3a s/n 00401 O 2020 H droCAD Software Solutions LLC Page 6 Area (sf) CN Description 4,643 98 Roofs, HSG C 4,643 100.00% Impervious Area 1 Te Length Slope Velocity Capacity Description min feet ft/ft ft/sec cfs 6.0 Direct Entry, Direct Entry (Tc = 6 min Min.) Summary for Subcatchment PS213: SOUTH-EAST ROOF Runoff - 0.2 cfs @ 12.13 hrs, Volume= 765 cf, Depth= 2.97" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs NRCC 24-hr D 2-Year Rainfall=3.20" Area (so CN Description 2,935 98 Roofs, HSG C 157 98 Roofs, HSG D 3,092 98 Weighted Average 3,092 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ftlft) (ft/sec) (cfs) 6.0 Direct Entry, Direct Entry (Tc = 6 min Min.) Summary for Subcatchment PS3: NORTH-EAST PARKING AREA Runoff = 0.7 cfs @ 12.13 hrs, Volume= 2,396 cf, Depth= 1.61" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs NRCC 24-hr D 2-Year Rainfall=3.20" Area (sf) CN Description 2,907 98 Roofs, HSG C 3,236 98 Paved parking, HSG C 429 98 Concrete, HSG C 10,843 74 >75% Grass cover, Good, HSG C 450 89 Gravel, HSG C 17,865 83 Weighted Average 11,293 63.21% Pervious Area 6,572 36.79% Impervious Area Tc Length Slope Velocity Capacity Description min feet ft/ft ft/sec cfs 6.0 Direct Entry, Direct Entry (Tc= 6 min Min.) 3908 Post Development Watershed Analysis NRCC 24-hr D 2-Year Rainfall=3.20 Prepared by The Morin-Cameron Group, Inc. Printed 9/15/2020 H droCADO 10.10-3a s/n 00401 0 2020 H droCAD Software Solutions LLC Page 7 Summary for Subcatchment PS3A: SOUTH-EAST ROOF Runoff = 0.1 cfs @ 12.13 hrs, Volume= 472 cf, Depth= 2.97" i Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs NRCC 24-hr D 2-Year Rainfall=3.20" Area (so CN Description 1,909 98 Roofs, HSG C 1,909 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Direct Entry (Tc 6 min Min.) Summary for Reach DP1: BORDERING VEGETATED WETLAND Inflow Area = 36,284 sf, 90.13% Impervious, Inflow Depth = 2.75" for 2-Year event Inflow - 2.3 cfs @ 12.13 hrs, Volume= 8,312 cf Outflow = 2.3 cfs @ 12.13 hrs, Volume= 8,312 cf, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs / 3 Summary for Reach DP2: WILLOW STREET (SOUTH) Inflow Area - 12,423 sf, 82.24% Impervious, Inflow Depth = 2.58" for 2-Year event Inflow - 0.8 cfs @ 12.13 hrs, Volume= 2,666 cf Outflow = 0.8 cfs @ 12.13 hrs, Volume= 2,666 cf, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs /3 Summary for Reach DP3: WILLOW STREET (NORTH) Inflow Area = 24,417 sf, 53.76% Impervious, Inflow Depth = 1.34" for 2-Year event Inflow = 0.7 cfs @ 12.13 hrs, Volume= 2,730 cf Outflow - 0.7 cfs @ 12.13 hrs, Volume= 2,730 cf, Atten= 0%, Lag= 0.0 min Routing by Dyn-Star-Ind method, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs 13 Summary for Pond Pl: UNDERGROUND CHAMBERS Inflow Area T 6,552 sf,100.00% impervious, Inflow Depth = 2.97" for 2-Year event Inflow - 0.4 cfs @ 12.13 hrs, Volume= 1,620 cf Outflow - 0.1 cfs @ 12.39 hrs, Volume= 1,620 cf, Atten= 79%, Lag= 15.9 min Discarded = 0.0 cfs @ 9.71 hrs, Volume= 1,286 cf Primary 0.1 cfs @ 12.39 hrs, Volume= 335 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-36.00 hrs, dt= 0.01 hrs /3 i 3908 Post Development Watershed Analysis NRCC 24-hr D 2-Year Rainfall=3.20" Prepared by The Morin-Cameron Group, Inc. Printed 9/15/2020 HydroCADO 10.10-3a s1n 00401 ©2020 HydroCAD Software Solutions LLC Page 8 Peak Elev= 249.73' @ 12.39 hrs Surf.Area= 586 sf Storage= 552 cf Plug-Flow detention time= (not calculated: outflow precedes inflow) Center-of-Mass det. time= 237.9 min ( 998.4 - 760.4 } Volume Invert Avail.Stora e Storage Description #1A 248.30' 530 cf 11.17'W x 52.501 x 3.54'H Field A 2,076 cf Overall - 753 cf Embedded = 1,324 cf x 40.0% Voids #2A 248.80' 753 cf Cultec R-330XLHD x 14 Inside#1 Effective Size= 47.8"W x 30.0"H => 7.45 sf x 7.001 = 52.2 cf Overall Size= 52.0"W x 30.5"H x 8.501 with 1.50' Overlap Row Length Adjustment= +1.50' x 7.45 sf x 2 rows 1,282 cf Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Discarded 248.30' 1.020 inlhr Exfiltration over Surface area #2 Primary 248.80' 12.0" Round Culvert L= 4.0' CPP, projecting, no headwall, Ke= 0.900 Inlet 1 Outlet Invert= 248.80' / 248.80' S= 0.0000 T Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 0.79 sf #3 Device 2 249.50' 3.0" Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #4 Device 2 251.30' 3.0"Vert. Orifice/Grate C= 0.600 Limited to weir flow at low heads #5 Primary 251.80' 4.0' long x 0.5' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 Coef. (English) 2.80 2.92 3.08 3.30 3.32 Discarded OutFlow Max=0.0 cfs @ 9.71 hrs HW=248.34' (Free Discharge) t---1=Exfiltration (Exfiltration Controls 0.0 cfs) Primary OutFlow Max=0.1 cfs @ 12.39 hrs HW=249.73' TW=0.00' (Dynamic Tailwater) 2=Culvert (Passes 0.1 cfs of 1.6 cfs potential flow) 3=Orifice/Grate (Orifice Controls 0.1 cfs @ 1.65 fps) =0rifice1Grate (Controls 0.0 cfs) =Broad-Crested Rectangular Weir ( Controls 0.0 cfs) r 1 July 29, 2020 Revised: September 14, 2020 Stormwater Management Calculations STANDARD 3: Recharge To Groundwater: Static Method • Calculate Impervious Area (From HydroCAD Model) Existing Impervious Area (HSG C Soil) = 51,558 SF Proposed Impervious Area (HSG C Soil) = 56,043 SF • Determine Rainfall Depth to be Recharged (MassDEP Stormwater Management Handbook: Table 2.3.2) Hydrologic Soil Group Recharge Rainfall Depth C 0.25" • Calculate Recharge Volume 'Rv' _ [0.25" x (56,043 SF— 51,558 SF)] / 12 SF-In = 94 CF 'Rv*' = 94 CF • Calculate Provided Recharge Schedule of Proposed Rechar e System Volumes HCAD Bottom Lowest System Outlet Total Recharge System ID of System or Top of Galley Volume Prodded Pi 248.30 249.50 446 Total Volume: 446 Recharge volume provided measured to lowest system outlet. Required Recharge Volume Summary Total Volume Provided Below Outlets = 446 CF Total Volume Required = 94 CF YerLf Drawdown Maximum 72-Hours: Static Method Recharge Bottom Drawdown HCAD Volume Surface Rawls Rate Time Description System ID (C ) Area (SF) Inches/Hour Rv/ (K x A) (Hours) RS1 446 586 1.02 8.9 Subsurface Storage "Design Complies with Recharge Volume Standard'* E i i i Sheet 4 of 10 8a 16,000 is 000 6,000 . r. 40 A � � LOW 0 20 6DD ,+ 250 100 60 D 0 2 d 6 vi 8 10 12 14 10 18 20' AllowaVeob Vetoelty(gW Bm"61 on 10"A arm Procedure 1,Ntemdne the deRW velocity. 2.Use velocity and ft JaA•1(WAA Curve)to detemfte basic rock size, 8,owe rock She is the D5omw. Q'60yf..) CFS 11 11 Design Guide MD#6 Rlprap Design Methods MRCS l;nglneering,Maryland October,2003 Page 22 i I 4 1 Construction Phase Best Management Practices (BMP'sl Erosion and Sedimentation will be controlled at the site by utilizing Structural Practices, Stabilization Practices, and Dust Control. These practices correspond with plans entitled "Site Redevelopment Plans in North Andover, Massachusetts, 335 Willow Street" prepared by The Morin-Cameron Group, Inc. dated July 29, 2020 as revised and approved by the North Andover Planning Board, hereinafter referred to as the Site Plans. Responsible Party Contact Information: Stormwater Management System Owner: Muffin 3X, LLC 351 Willow Street North Andover, MA 01845 P: (978) 683-1414 North Andover Department of Public Works: 384 Osgood Street North Andover, MA 01845 P: (978) 685-0950 North Andover Planning Board: Town Halt 120 Main Street North Andover, MA 01845 P: (978) 688-9535 North Andover Zoning Board of Appeals: Town Hall 120 Main Street North Andover, MA 01845 P: (978) 688-9545 North Andover Conservation Commission: Town Hatt 120 Main Street North Andover, MA 01845 P: (978) 688-9530 Site Design En ineer Information: The Morin-Cameron Group, Inc. 66 Elm Street Danvers, MA 01923 Phone: (978) 777-8586 Best Management Practices Operation and Maintenance PLan MCG Project No. 3908, 335 Willow Street, North Andover, Massachusetts July 29, 2020—Page 1 of 9 Revise September 14, 2020 ! ! i Structural Practices: 1} Silt Fence &Silt Sock--A siltation fence and sock barrier shall be installed in accordance with the approved plans where high rates of stormwater runoff are anticipated. a) Installation Schedule: Prior to Start of land disturbance a) Maintenance and Inspection: The site supervisor shall inspect the barrier at least once per week or after a major storm (3,15 inches of rainfall within a twenty-four-hour period), event and shall repair any damaged or affected areas of the barrier at the time they are noted. Remove sediment deposits promptly after storm events to provide adequate storage volume for the next rain and to reduce pressure on the barrier. Sediment will be removed from in front of the barrier when it becomes about 4" deep at the barrier. Take care to avoid undermining the barrier during cleanout. 2) Inlet Protection -- Inlet Protection will be utilized around the catch basin grates in the street layout in the closest down gradient structure, The inlet protection will allow the storm drain inlets to be used before final stabilization. This structural practice will allow early use of the drainage system. Siltsack or equivalent will be utilized for the inlet protection. Siltsack is manufactured by ACF Environmental. The telephone number is 800-448-3636, Regular flow siltsack will be utilized, and if it does not allow enough storm water flow, hi-flow siltsack will be utilized. Silt Sack (or equivalent) Inlet Protection Inspection/Maintenance Requirements a) The silt sack trapping devices and the catch basins should be inspected after every rain storm and repairs made as necessary, b) Sediment should be removed from the silt sack after the sediment has reached a maximum depth of one-half the depth of the trap, c) Sediment should be disposed of in a suitable area and protected from erosion by either structural or vegetative means. Sediment material removed shall be disposed of in accordance with all applicable local, state, and federal regulations. d) The silt sack must be replaced if it is ripped or torn in any way. e) Temporary traps should be removed and the area repaired as soon as the contributing drainage area to the inlet has been completely stabilized. Best Management Practices Operation and Maintenance Plan MCG Project No. 3908, 335 Witlow Street, North Andover, Massachusetts July 29, 2020—Page 2 of 9 Revise September 14, 2020 i I 3) Sediment Track-Out: The site supervisor will inspect and ensure that sediment is not tracked into the roadway. If tracking onto the roadway is noted, it shall be removed immediately via by hand or a mechanical street sweeper. Once pavement is disturbed, a Stabilized Construction entrance/exit (Crushed stone anti-tracking pad) will be installed at the entrance to the site. This will prevent trucks from tracking material onto the road from the construction site. If, at any point during the project, the tracking pad becomes ineffective due to accumulation of soil, the crushed stone shall be replaced. Details for construction of the stabilized entrance can be found in the details sheet that is part of the permit plan set associated with the project, The site supervisor will inspect the tracking pads weekly to ensure that they are properly limiting the tracking of soil onto the road. If tracking onto the roadway is noted, it shall be removed immediately via by hand or a mechanical street sweeper.) Stabilization Practices: Stabilization measures shall be implemented as soon as practicable in portions of the site where construction activities have temporarily or permanently ceased, but in no case more than 14 days after the construction activity in that portion of the site has temporarily or permanently ceased, with the following exceptions. • Where the initiation of stabilization measures by the 14t' day after construction activity temporary or permanently cease is precluded by snow cover, stabilization measures shall be initiated as soon as practicable. • Where construction activity will resume on a portion of the site within 21 days from when activities ceased, (e.g. the total time period that construction activity is temporarily ceased is less than 21 days) then stabilization measures do not have to be initiated on that portion of the site by the 14t' day after construction activity temporarily ceased. 1) Temporary Seeding --Temporary seeding will allow a short-term vegetative cover on disturbed site areas that may be in danger of erosion. Temporary seeding will be done at stock piles and disturbed portions of the site where construction activity will temporarily cease for at least 21 days. The temporary seeding will stabilize cleared and unvegetated areas that will not be brought into final grade for several weeks or months. Temporary Seeding Planting Procedures a) Planting should preferably be done between April 1s1 and June 30"', and September 1St through September 315t. If planting is done in the months of July and August, irrigation may be required. If planting is done between October 15t and March 315t, mulching should be applied immediately after planting. b) Before seeding, install structural practice controls. Utilize Amoco supergro or equivalent. Best Management Practices Operation and Maintenance Plan MCG Project No. 3908, 335 Willow Street, North Andover, Massachusetts July 29, 2020-Page 3 of 9 Revise September 14, 2020 i i i I I I it c) Select the appropriate seed species for temporary cover from the following table. Species Seeding Rate Seeding Rate Recommended Seeding Seed Cover (lbs./1,000 sq.) (tbs./acre) Dates required Annual 1 40 April 15t to June 1st 1/4 inch R e rass August 15th to Sept, 15th Foxtail 0.7 30 May 1st to June 3011 1/2 to 3/4 inch Millet Oats 2 80 April 151 to July 1 It 1 to 1-1/2 Au ust 151h to Sept. 151h inch Winter 3 120 August 15th to Oct. 15th 1 to 1-1/2 R e inch Apply the seed uniformly by hydroseeding, broadcasting, or by hand. d) Use effective mulch, such as clean grain straw; tacked and/or tied with netting to protect seedbed and encourage plant growth. TemporaU Seeding Ins ection Maintenance a) Inspect within 6 weeks of planting to see if stands are adequate. Check for damage within 24 hours of the end to a heavy rainfall, defined as a 2-year storm event (Le., 3.15 inches of rainfall within a twenty-four-hour period). Stands should be uniform and dense. Reseed and mulch damaged and sparse areas immediately. Tack or tie down mulch as necessary. b) Seeds should be supplied with adequate moisture. Furnish water as needed, especially in abnormally hot or dry weather. Water application rates should be controlled to prevent runoff. 2) Geotextiles - Geotextiles such as jute netting will be used in combination with other practices such as mulching to stabilize slopes. The following geotextile materials or equivalent are to be utilized for structural and nonstructural controls as shown in the following table. Practice Manufacturer Product Remarks Sediment Fence Amoco Woven polypropylene 0.425 mm opening 1198 orequivalent Construction Amoco Woven polypropylene 0.300 mm opening Entrance 2002 orequivalent Outlet Amoco Nonwoven polypropylene 0.150 mm opening Protection 4551 ore uivalent Erosion Control Amoco Supergro or equivalent Erosion control (slope stability) revegetation mix, open polypropylene fiber on degradable polypropylene net scrim Amoco may be reached at (800) 445-7732 Best Management Practices Operation and Maintenance Plan MCG Project No. 3908, 335 Willow Street, North Andover, Massachusetts July 29, 2020- Page 4 of 9 Revise September 14, 2020 I Geotextile Installation a) Netting and matting require firm, continuous contact between the materials and the soil. If there is no contact, the material will not hold the soil and erosion will occur underneath the material. Geotextile Inspection/Maintenance a) In the field, regular inspections should be made to check for cracks, tears, or breaches in the fabric, The appropriate repairs should be made. 3) Mulching and Netting — Mulching will provide immediate protection to exposed soils during the period of short construction delays, or over winter months through the application of plant residues, or other suitable materials, to exposed soil areas, In areas, which have been seeded either for temporary or permanent cover, mulching should immediately follow seeding. On steep slopes (slopes 3H:1V or greater), mulch must be supplemented with netting. The preferred mulching material is straw. Mulch (Hay or Straw) Materials and Installation a) Straw has been found to be one of the most effective organic mulch materials. The specifications for straw are described below, but other material may be appropriate. The straw should be air-dried; free of undesirable seeds & coarse materials. The application rate per 1,000 sq. is 90-100 lbs. (2-3 bales) and the application rate per acre is 2 tons (100-120 bales). The application should cover about 90% of the surface. The use of straw mulch is appropriate where mulch is maintained for more than three months. Straw mulch is subject to wind blowing unless anchored, is the most commonly used mulching material, and has the best microenvironment for germinating seeds. Mulch Maintenance a) Inspect after rainstorms to check for movement of mulch or erosion. If washout, breakage, or erosion occurs, repair surface, reseed, remulch, and install new netting, b) Straw or grass mulches that blow or wash away should be repaired promptly. c) If plastic netting is used to anchor mulch, care should be taken during initial mowing to keep the mower height high. Otherwise, the netting can wrap up on the mower blade shafts. After a period of time, the netting degrades and becomes less of a problem, d) Continue inspections until vegetation is well established. 4) Land Grading—Grading on fill slopes, cut slopes, and stockpile areas will be done with full siltation controls in place. Best Management Practices Operation and Maintenance Plan MCG Project No. 3908, 335 Willow Street, North Andover, Massachusetts July 29, 2020-Page 5 of 9 Revise September 14, 2020 I I d Land Grading Design/Installation Requirements a) Areas to be graded should be cleared and grubbed of all timber, logs, brush, rubbish, and vegetated matter that will interfere with the grading operation. Topsoil should be stripped and stockpiled for use on critical disturbed areas for establishment of vegetation. Cut slopes to be topsoiled should be thoroughly scarified to a minimum depth of 3-inches prior to placement of topsoil, j b) Fill materials should be generally free of brush, rubbish, rocks, and stumps, Frozen materials or soft and easily compressible materials should not be used in fills intended to support buildings, parking lots, roads, conduits, or other structures. c) Earth fill intended to support structural measures should be compacted to a minimum of 90 percent of Standard Proctor Test density with proper moisture control, or as otherwise specified by the engineer responsible for the design. Compaction of other fills should be to the density required to control sloughing, erosion or excessive moisture content. Maximum thickness of fill layers prior to compaction should not exceed 9 inches. d) The uppermost one foot of fill slopes should be compacted to at least 85 percent of the maximum unit weight (based on the modified AASHTO compaction test). This is usually accomplished by running heavy equipment over the fill. e) Fill should consist of material from borrow areas and excess cut will be stockpiled on site. All disturbed areas should be free draining, left with a neat and finished appearance, and should be protected from erosion. Land Grading Stabilization Inspection/Maintenance * a) All slopes should be checked periodically to see that vegetation is in good condition. Any rills or damage from erosion and animal burrowing should be repaired immediately to avoid further damage, b) If seeps develop on the slopes, the area should be evaluated to determine if the seep will cause an unstable condition. Subsurface drains or a gravel mulch may be required to solve seep problems. c) Areas requiring revegetation should be repaired immediately. Control undesirable vegetation such as weeds and woody growth to avoid bank stability problems in the future. 5) Topsoiling *-Topsoiling will help establish vegetation on all disturbed areas throughout the site during the seeding process. The soil texture of the topsoil to be used will be a sandy loam to a silt loam texture with 15% to 20% organic content. Topsoiling Placement Best Management Practices Operation and Maintenance Plan MCG Project No. 3908, 335 Willow Street, North Andover, Massachusetts July 29, 2020—Page 6 of 9 Revise September 14, 2020 '� F } i a) Topsoil should not be placed while in a frozen or muddy condition, when the subgrade is excessively wet, or when conditions exist that may otherwise be detrimental to proper grading or proposed seeding. b) Do not place topsoil on slopes steeper than 25:1, as it will tend to erode. 0 c) If topsoil and subsoil are not properly bonded, water will not infiltrate the soil profile evenly and it will be difficult to establish vegetation. The best method is to actually work the topsoil into the layer below for a depth of at least 6 inches. 6) Permanent Seeding — Permanent Seeding should be done immediately after the final design grades are achieved. Native species of plants should be used to establish perennial vegetative cover on disturbed areas. The revegetation should be done early enough in the fat( so that a good cover is established before cold weather comes and growth stops until the spring. A good cover is defined as vegetation covering 75 percent or more of the ground surface. Permanent Seeding Seedbed Preparation a) In infertile or coarse-textured subsoil, it Is best to stockpile topsoil and re-spread it over the finished slope at a minimum 2 to 6-inch depth and roll it to provide a firm seedbed. The topsoil must have a sandy loam to silt loam texture with 15% to 20% organic content. If construction fill operations have left soil exposed with a loose, rough, or irregular surface, smooth with blade and roll. b) Loosen the soil to a depth of 3-5 inches with suitable agricultural or construction equipment. c) Areas not to receive topsoil shall be treated to firm the seedbed after incorporation of the time and fertilizer so that it is depressed no more than 1/2 - 1 inch when stepped on with a shoe. Areas to receive topsoil shall not be firmed until after topsoiting and time and fertilizer is applied and incorporated, at which time it shall be treated to firm the seedbed as described above, Permanent Seeding Grass Selection/Application a) Select an appropriate cool or warm season grass based on site conditions and seeding date. Apply the seed uniformly by hydro-seeding, broadcasting, or by hand, Uniform seed distribution is essential. On steep slopes, hydroseeding may be the most effective seeding method. Surface roughening is particularly important when preparing slopes for hydroseeding. b) Lime and fertilize. Organic fertilizer shall be utilized in areas within the 100-foot buffer zone to a wetland resource area. c) Mulch the seedings with straw applied at the rate of 1/2 tons per acre. Anchor the mulch with erosion control netting or fabric on sloping areas. Amoco supergro or equivalent should be utilized. Best Management Practices Operation and Maintenance Plan MCG Project No. 3908, 335 Willow Street, North Andover, Massachusetts July 29, 2020-Page 7 of 9 Revise September 14, 2020 i i E E I Permanent Seeding Ins ection Maintenance a) Frequently inspect seeded areas for failure and make necessary repairs and reseed immediately. Conduct or follow-up survey after one year and replace failed plants where necessary. b) If vegetative cover is inadequate to prevent rill erosion, overseed and fertilize in accordance with soil test results. c) If a stand has less than 40% cover, reevaluate choice of plant materials and quantities of time and fertilizer. Re-establish the stand following seedbed preparation and seeding recommendations, omitting time and fertilizer in the absence of soil test results. If the season prevents resowing, mulch or jute netting is an effective temporary cover. d) Seeded areas should be fertilized during the second growing season. lime and fertilize thereafter at periodic intervals, as needed. Organic fertilizer shall be utilized in areas within the 100-foot buffer zone to a wetland resource area. Dust Control: Dust control will be utilized throughout the entire construction process of the site, For example, keeping disturbed surfaces moist during windy periods wilt be an effective control measure, especially for construction access roads. The use of dust control will prevent the movement of soil to offstte areas. However, care must be taken to not create runoff from excessive use of water to control dust. The following are methods of Dust Control that may be used on-site: • Vegetative Cover—The most practical method for disturbed areas not subject to traffic. • Calcium Chloride—Calcium chloride may be applied by mechanical spreader as loose, dry granules or flakes at a rate that keeps the surface moist but not so high as to cause water pollution or plant damage. • Sprinkling —The site may be sprinkled until the surface is wet. Sprinkling wilt be effective for dust control on haul roads and other traffic routes. • Stone— Stone will be used to stabilize construction roads and will provide dust control. The general contractor shalt employ an on-site water vehicle for the control of dust as necessary. Non-Stormwater Discharges: The construction de-watering and all non-stormwater discharges will be directed into a sediment dirt bag (or equivalent inlet protection) or a sediment basin, Sediment material removed shall be disposed of in accordance with all applicable local, state, and federal regulations. Best Management Practices Operation and Maintenance plan MCG Project No. 3908, 335 Willow Street, North Andover, Massachusetts July 29, 2020—Page 8 of 9 Revise September 14, 2020 The developer and site general contractor will comply with the E.P.A.'s Final General Permit for Construction De-watering Discharges, (N.P.D.E.S., Section 402 and 40 C.F.R. 122.26(b) (14) (x). Inspection/Maintenance: Operator personnel must inspect the construction site at least once every 14 calendar days and within 24 hours of a storm event of 1/2-inch or greater. The applicant shall be responsible to secure the services of a design professional or similar professional (inspector) on an on-going basis throughout all phases of the project. Refer to the Inspection/Maintenance Requirements presented earlier in the "Structural and Stabilization Practices." The inspector should review the erosion and sediment controls with respect to the following: • Whether or not the measure was installed/performed correctly. + Whether or not there has been damage to the measure since it was installed or performed. + What should be done to correct any problems with the measure. The inspector should document the findings and should request the required maintenance or repair for the pollution prevention measures when the inspector finds that it is necessary for the measure to be effective, The inspector should notify the appropriate person to make the required changes. It is essential that the inspector document the inspection of the pollution prevention measures. These records will be used to request maintenance and repair and to prove that the inspection and maintenance were performed. The forms list each of the measures to be inspected on the site, the inspector's name, the date of the inspection, the condition of the measure/area inspected, maintenance or repair performed and any changes which should be made to the Operation and Maintenance Plan to control or eliminate unforeseen pollution of storm water. Best Management Practices Operation and Maintenance Plan MCG Project No. 3908, 335 Willow Street, North Andover, Massachusetts JuLy 29, 2020—Page 9 of 9 Revise September 14, 2020 Lona Term Stormwater Best Management Practices Operation and Maintenance Plan for 335 Willow Street North Andover Massachusetts July 29, 2020 Revised September 14, 2020 The following operation and maintenance plan has been provided to satisfy the requirements of Standard 9 of the Mass DEP Stormwater Management Handbook associated with development of the site and associated infrastructure. The success of the Stormwater Management Plan depends on the proper implementation, operation and maintenance of several management components, The following procedures shall be implemented to ensure success of the Stormwater Management Plan, 1, The contractor shall comply with the details of construction of the site as shown on the approved plans. 2. The stormwater management system shall be inspected and maintained as indicated below. ' 3. Effective erosion control measurers during and after construction shall be maintained until a stable turf is established on all altered areas. 4. A Stormwater Management Maintenance Log is included at the end of this Appendix. Basic Information Stormwater Management System Owner: Muffin 3X, Ll_C 351 Willow St. North Andover, MA 01845 P: (978) 683-1414 North Andover Engineering Department: 384 Osgood Street North Andover, MA 01845 P: (978) 685-0950 North Andover Planning Board: Town Hall 120 Main Street North Andover, MA 01845 P: (978) 688-9535 North Andover Conservation Commission: Town Hall 120 Main Street North Andover, MA 01845 P:(978) 688-9530 Owner Signature: NOr Long Term Stormwater Best Management Practices Operation & Maintenance Plan 335 Willow Street, North Andover, Massachusetts July 29, 2020 Revised September 14,2020 Page 1 of 4 i i Erosion and Sedimentation Controls during Construction: The site and drainage construction contractor shall be responsible for managing stormwater during construction. Routine monitoring of disturbed soils shall be performed to ensure adequate runoff and j pollution control during construction. A sediment and erosion control barrier will be placed as shown on the Grading & Drainage Plan prior to the commencement of any clearing, grubbing, and earth removal or construction activity. The integrity of the erosion control barrier will be maintained by periodic inspection and replacement as necessary. The erosion control barrier will remain in place until the first course of pavement has been placed and all side slopes have been foamed and seeded and vegetation has been established. Operations and maintenance plans for the Stormwater Management construction phase and long term operation of the system have been attached to this report. General Conditions 1. The site contractor shall be responsible for scheduling regular inspections and maintenance of the stormwater BMP's until the project has been completed. The BMP maintenance shall be conducted as detailed in the following long-term pollution prevention plan and on the approved design plans: "Site Redevelopment Plan of Land in North Andover, Massachusetts, 335 Willow Street" prepared for Muffin Realty Trust by The Morin-Cameron Group, Inc. dated July 29, 2020. 2. All Stormwater BMP's shall be operated and maintained in accordance with the design plans and the following Long-Term Pollution Prevention Plan. 3. The owner shall: a, Maintain an Operation and Maintenance Log for the last three years, The Log shall include all BMP inspections, repairs, replacement activities and disposal activities (disposal material and disposal location shall be included in the Log); b. Make the log available to the North Andover Planning Board and Engineering Department upon request; c. Allow members and agents of the North Andover Planning Board and Engineering Department to enter the premises and ensure that the Owner has complied with the Operation and Maintenance Plan requirements for each BMP. 4. A recommended inspection and maintenance schedule is outlined below based on statewide averages. This inspection and maintenance schedule shall be adhered to at a minimum for the first year of service of all BMP's referenced in this document. At the commencement of the first year of service, a more accurate inspection/maintenance schedule shall be determined based on the level of service for this site. Long Term Stormwater Best Management Practices Operation & Maintenance Plan 335 Willow Street, North Andover, Massachusetts July 29, 2020 Revised September 14, 2020 Page 2 of 4 I Lon -Term Pollution Prevention Plan LTPPP I Ve etated Areas: Immediately after construction, monitoring of the erosion control systems shall occur until establishment of natural vegetation. Afterwards, vegetated areas shall be maintained as such. Vegetation shall be replaced as necessary to ensure proper stabilization of the site. Cost: Included with annual landscaping budget. Consult with local landscape contractors. Paved Areas: Sweepers shall sweep paved areas periodically during dry weather to remove excess sediments and to reduce the amount of sediments that the drainage system shall have to remove from the runoff. The sweeping shall be conducted primarily between March 1511,and November 151h. Special attention should be made to sweeping paved surfaces in March and April before spring rains wash residual sand into the drainage system. Cost: Consult with local landscaping companies for associated costs if necessary. Salt used for de-icing on the roadway during winter months shall be limited as much as possible as this will reduce the need for removal and treatment, Sand containing the minimum amount of calcium chloride (or approved equivalent) needed for handling may be applied as part of the routine winter maintenance activities, Subsurface Chamber System: The subsurface chamber system shall be monitored annually to ensure that it is draining properly. The outlet control structure shall be checked for debris accumulation twice per year, in the spring and fall. In the case that water remains in the system for greater than three(3) days after a storm event, an inspection is warranted and necessary maintenance or repairs should be addressed as necessary. Confirm that the orifices and outlet pipe in the outlet control structure is not obstructed by debris. The inspections shall be conducted by qualified personnel. Cost: Consult with local landscaping companies for associated costs if necessary. Public Safety Concerns: Manhole covers or inspection port covers shall not be left open and unattended at any time during inspection, cleaning or otherwise. Broken covers or frames shall be replaced immediately. At no time shall any person enter the subsurface structure unless measures have been taken to ensure safe access in accordance with OSHA enclosed space regulations. Rip-Rap Outfall: The rip-rap outfalt shall be checked for debris accumulation twice per year. Additional inspections should be scheduled during the first few months to make sure that the outfalt is functioning as intended. Trash, leaves, branches, etc, shall be removed from outfalt. Silt, sand and sediment, if significant accumulation occurs, shall be removed as required by means of mechanical excavation. Material removed from the forebay shalt be disposed of in accordance with all applicable local, state, and federal regulations. The outfall shall be kept free of woody vegetation and removal of woody vegetation shall be conducted between October 151h and April 15sh. Any slope erosion within the outfall shall be stabilized and repaired immediately and additional rip-rap added as required. Cost: $50041000 per cleaning if excavator is necessary to remove sediment. The owner should consult local landscape contractors for a detailed cost estimate. Long Term Stormwater Best Management Practices Operation & Maintenance Plan 335 Willow Street, North Andover, Massachusetts July 29, 2020 { Revised September 14, 2020 Page 3 of 4 i i Debris& Litter: All debris and litter shall be removed from the roadway and parking lots as necessary to prevent migration into the drainage system. Pesticides. Herbicides,,and Fertilizers: Pesticides and herbicides shall be used sparingly. Fertilizers shall be restricted to the use of organic fertilizers only. All fertilizers, herbicides, pesticides, sand and salt for deicing and the like shall be stored in dry area that is protected from weather. Cost: Included in the routine landscaping maintenance schedule. The Owner shall consult local landscaping contractors for details. Public Safety Concerns: Chemicals shall be stored in a secure area to prevent children from obtaining access to them. Any major spills shall be reported to municipal officials. Prevention of illicit Discharges: Illicit discharges to the stormwater management system are not allowed. Illicit discharges are discharges that are not comprised entirely of stormwater, Pursuant to Mass DEP Stormwater Standards the following activities or facilities are not considered illicit discharges:firefighting,water line flushing, landscape irrigation, uncontaminated groundwater, potable water sources, foundation drains, air conditioning condensation,footing drains, individual resident car washing,flows from riparian habitats and wetlands, dechtorinated water from swimming pools, water used for street washing and water used to clean residential building without detergents. To prevent illicit discharges to the stormwater management system the following policies should be implemented: 1. Provisions For Storing Materials And Waste Products Inside Or Under Cover 2. Vehicle Maintenance And Washing Controls 3. Requirements for Routine Inspections of the Stormwater Management System (Le.: subsurface infiltration system and outlet control structure.) 4. Spill Prevention and Response Plans. Snow Storage: Property owner shall inform their snow removal contractor of the designated areas for snow storage shown on the Site Layout Plan in the Site Redevelopment Plans. i Long Term Stormwater Best Management Practices Operation & Maintenance Plan 335 Willow Street, North Andover, Massachusetts July 29, 2020 Revised September 14, 2020 Page 4 of 4 TABLE 1: MAINTENANCE SCHEDULE FOR DRAINAGE STRUCTURES Structure Inspection Maintenance Riprap Outfall Inspect twice a year and after every major storm event* (April/October) Sediment to be removed as necessary. Use light equipment to remove the sediment and replace the riprap. Inspections should include the following: Remove debris on top of or at outlet of riprap. • Signs of differential settlement • Signs of erosions Remove vegetation that grows within riprap_ • Sediment accumulation • Signs of dislodgement Infiltration Inspect after every major storm event for first 3 months after construction to Rehabilitate structure if it fails due to clogging as generally evidenced Chambers,Outlet ensure the structures are working properly.* by retention of water for more than 72 hours after a storm event Control Structure, Drain manhole Thereafter,twice a year Remove any obstructions from outfets/pipes (April/October) Inspections should include the following: • Signs of differential settlement • Erosion • Tree growth on the embankments that were not part of the design plan Sediment accumulation • Health of turf • Cracked/Disconnected Roof Leaders • Clogged orifices, pipe obstructions *Major storm event:3.2 inches of rainfall in a 24 hour period(2 year storm) - - I Stormwater System Maintenance Loa 335 Willow Street, North Andover, MA The Following structures shall be inspected and maintained by the owner. BMP INSPECTION WORK DATE WORK COMMENTS STRUCTURE DATE PERFORMED PERFORMED Storm water Management Infrastructure Underground Infiltration Chambers Outlet Control Structure Drain Manhole Riprap Outfall i Illicit Discharge Compliance Statement I, John M_._Morin, P.E., hereby notify the North Andover Planning Board & Conservation Commission that I have not witnessed, nor am aware of any existing illicit discharges at the site known as 335 Willow Street in North Andover, Massachusetts. I also hereby certify that the development of said property as illustrated on the final plans entitled "Site Redevelopment Plan of Land in North Andover, Massachusetts, 335 Willow Street," prepared by The Morin-Cameron Group, Inc. dated July 29, 2020 and as revised and approved by the North Andover Planning Board & Conservation Commission and maintenance thereof In accordance with the "Construction Phase Best Management Practices plan" and "Long-Term Pollution Prevention Plan" prepared by The Morin- Cameron Group, Inc dated July 29, 2020 and as revised and approved by the North Andover Planning Board & Conservation Commission will not create any new illicit discharges. There is no warranty implied regarding future illicit discharges that may occur as a result of improper construction or maintenance of the stormwater management system or unforeseen accidents. Name: John M. Morin P.E. Company: The Morin-Cameron Group, Inc. Title: Owner's Representative Signature: Date, 1 z Owner Signature: 1114 Date: