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HomeMy WebLinkAbout20160419 Consultant Review/stormwater report - Consultant Review - 2302 TURNPIKE STREET 12/10/2015 Eggleston Environmental December 10, 2015 North Andover Planning Board 1600 Osgood Street North Andover,MA 01845 Attn: Jean Enright, Assistant Director of Community Development RE: Stormwater Review Earth Works Inc., 2302 Turnpike Street Dear Ms. Enright and Board Members: Per your request, I have reviewed the November 2015 Special Permit Application packet for the above-referenced project. Included in the materials I received and reviewed were the following: ■ Special Permit — Site Plan Review Application, Earth Works Inc., Petitioner, prepared by Mann&Mann, P.C. and dated November 13, 2015. ■ Stormwater Management Report & Mitigative Drainage Analysis for Proposed Commercial Development, #2302 Turnpike St (Route 114), Earth Works Inc. - Applicant, prepared by Williams & Sparages Engineers and dated November 14, 2015. ■ Site Development Plans (12 Sheets), #2302 Turnpike St., prepared by Williams & Sparages Engineers and dated November 4,2015. ■ Architectural Drawings, (7 Sheets), #2302 Turnpike St., Earth Works Ina — Applicant,prepared by Modus and dated November 13, 2015. I also conducted a brief site visit on December 1,2015 to observe existing conditions. My primary focus in this technical review is on the overall stormwater management approach and design concepts used in the project, as well as its compliance with the Town of North Andover's Site Plan Review regulations, the Massachusetts Department of Environmental Protection (DEP) Stormwater Management Standards and Regulations, and the North Andover Wetlands Bylaw. It is my understanding that a Notice of Intent (NOI) application for the project has been or will be filed concurrently with the Conservation Commission. My review is aimed at assisting both boards in their respective reviews of the project. 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 Earth Works Inc., Stormwater Review 2 December 10, 2015 The project site is an approximately 3.5-acre parcel located at the corner of Turnpike Street and Sharpners Pond Road and is presently occupied by a single-family home, barn and gravel access driveway. The property is mostly wooded with areas of grass and brush. There is a bordering vegetated wetland (BVW) located at the northerly corner of the property and an approximately 40-foot drop in grade across the site from Turnpike Street to the wetland. Drainage is overland toward the wetland. The proposed project calls for razing the existing structures and replacing them with a commercial complex comprised of two separate buildings, with paved driveways and parking and associated infrastructure. As proposed, drainage from the paved areas of the site would be conveyed through a closed drainage system and sediment forebay to a stormwater infiltration basin within the wetland buffer zone. Roof drainage from the larger building would be discharged to the infiltration basin directly, and roof drainage from the smaller building would drain overland. My comments on the proposed plan are outlined below: 1. DEP Stormwater Standard 1 requires that Low Impact Development (LID) measures for stormwater management be considered in the design of the project. The proposed project does not appear to incorporate any such measures, and no documentation of the LID measures considered and eliminated was included in the materials I reviewed. 2. I was unable to verify portions of the drainage analysis as there was no drainage area map included in the materials I reviewed. The DEP and local regulations require a delineation of the pre-and post-development subareas used in the analysis, including soil type and flow paths. 3. The mitigative drainage analysis and sizing of the proposed infiltration system are based on a design infiltration rate (1.02 in/hr) characteristic of Hydrologic Soil Group (HSG) B sandy loam and may significantly overestimate the rate of exfrltration from the system; there are no HSG B soils on the site. The NRCS soil map shows the site to be predominantly HSG C Paxton fine sandy loam, with an area in the southeast corner of the site mapped as Charlton-Rock Outcrop-Hollis complex. While the Stormwater Report treats this entire complex as HSG A, only the Charlton component is an HSG A soil; the other two components, rock outcrop and Hollis, are characterized as HSG D and are not suitable for infiltration. The proposed infiltration system appears to be located in an area of transition between the Paxton soils and the Charlton-Rock Outcrop-Hollis complex. None of the soil testing conducted on the site to date was within the actual footprint of the proposed system as is required by the MA Stormwater Handbook, nor were the tests sufficiently detailed (e.g. with grain-size analysis or infiltration testing) to distinguish between soil groups or to justify the design infiltration rate used. Additional soil testing is therefore needed within the proposed infiltration area to verify soil suitability and to establish the appropriate Earth Works Inc., Stormwater Review 3 December 10, 2015 design infiltration rate. Unless the entire area is determined to be Charlton soil, I would expect the rate to be significantly lower that the 1.02 in/hr used. 4. In accordance with the MA Stormwater Handbook, exfiltration from the basin should be calculated over the bottom area only. 5. The analysis should not assume any storage in the sediment forebay unless it can be demonstrated that the forebay will be fully dewatered (without exfiltration) between storms. 6. Based on the calculations, the peak elevation in the 100-yr storm would be 0.67 ft below the top of the berm. The infiltration basin should be designed with a foot of freeboard to protect the berm, and the berm/retaining wall should include an impervious core to prevent breakout. 7. As shown on the plan, a portion of the proposed infiltration basin is located within the 50-ft buffer to the BVW. The MA Stormwater Handbook requires infiltration structures to have a minimum 50-ft setback from wetlands, thus the basin needs to be re-graded to keep the top of the berm outside of the 50-ft buffer. 8. In order to maximize dispersal of the recharge and better mimic existing conditions, consideration should be given to infiltrating some or all of the runoff further upslope from the wetland, e.g, under the pavement and/or to the south of the building. Segregating the infiltration of roof runoff could also allow better treatment of the pavement runoff. 9. It appears that the grassed area to the north of the freestanding storage building and the area between the two driveways could be graded to better promote infiltration, including the roof runoff from the storage building. 10. The proposed infiltration basin is used to attenuate peals flows during the 10-yr and larger storm events and the separation to seasonal high groundwater is less than four feet, therefore a mounding analysis is required under Stormwater Standard#3. This was checked off in the Stormwater Checklist as being provided, but was not included in the materials I reviewed. 11. The plan shows a single roof drain on the northern side of the main building, and all of the roof runoff is modeled as draining to the infiltration basin via that drain. Based on the rooflines shown on the architectural drawings, however, it is not clear how the roof runoff from the pitched roofs at the front corner of the building would reach the drain. It is also not clear that the roof drain is sized to convey the 100-yr flow as is assumed in the model. 12. Given that much of the building roof is flat, consideration should be given to incorporating a green or blue roof design to help attenuate the rate of flow discharged from the roof. Earth Works Inc., Stormwater Review 4 December 10, 2015 13. Design details are needed for the double catchbasins, sediment forebay and infiltration basin berms, the overflow spillway, and the riprap aprons. The aprons should also be sized to prevent scour. 14. The proposed outlet hood should be specified on the catchbasin detail; I recommend the LeBaron Snout or Eliminator brands. 15. The Erosion & Sediment Control Plan should include measures to protect proposed infiltrations during construction, and to restore the infiltration capacity of any BMPs that are used as sediment traps during construction. The plan also calls for a silt fence sediment barrier; given the slopes involved I recommend the use of straw wattles or coir logs in addition to the silt fence. 16. As is indicated in the Stormwater Checklist, the proposed project entails the disturbance of more than one acre and will therefore require a Construction Stormwater Pollution Prevention Plan (SWPPP) and an NOI filed under the EPA Construction General Permit. This should be clearly indicated on the plans. The Conservation Commission and/or Planning Board may also want to require confirmation of NOI filing and the opportunity to review the SWPPP prior to implementation. 17. The Long Term Pollution Prevention Plan (LTPPP) included in the submittal is generic and generally not applicable to the project site. There are no proprietary separators proposed for this project, and I question whether any vehicle washing of tenant equipment should be conducted on the site unless a suitable area is designated and appropriate control measures identified. The LTPPP also references the Town of Middleton Conservation Commission. The plan should be revised to specifically address the intended use of the site for storage of landscaping equipment and materials and should identify appropriate measures to prevent exposure of any potential pollutants associated with that use. In particular, it should address loading and unloading operations, sediment tracking, equipment wash-down, dumpster management and materials storage. 18. Designated snow storage locations should be shown on the plan. To the extent possible, snow storage should be located upgradient of the stormwater BMPs. Snow should not be plowed directly into the infiltration basin or onto the slope to the east of the proposed storage building. 19. 1 have the following comments on the O&M Plan included in the submittal: ■ Per DEP requirements, the Plan should identify the name of the system owner and the party responsible for maintenance of the stormwater system. ■ The catchbasins should be cleaned a minimum of once per year and more often when sediment accumulation is within two feet of the outlet. (The same as one half of the sump depth,but more easily measured). Earth Works Inc., Stormwater Review 5 December 10, 2015 ® The infiltration basin should be inspected during and after several storms (e.g. 0.5-inch or greater) during the first year of operation. ■ The Plan should include periodic inspection of the driveway culvert and level spreader to ensure that they are functioning properly. ® I suggest combining the LTPPP with the O&M Plan, or at least moving the maintenance log forms from the LTPPP into the O&M Plan. ® The O&M Plan should include an estimated annual budget for maintenance and a simple figure showing the locations of the BMPs to be maintained. The figure should also show the designated snow storage locations referenced in the Plan. I appreciate the opportunity to assist the North Andover Planning Board and Conservation Commission with the review of this project, and hope that this information is suitable for your needs. Please feel free to contact me if you or the applicants have any questions regarding the issues addressed herein. Sincerely, EGGLESTON ENVIRONMENTAL r Lisa D. Eggleston, P.E. C: Jennifer Hughes, Conservation Administrator Project No. NAND-0033 February 10,2015 North Andover Planning BoardW-44WILLIAMS 1600 Osgood Street SPARAGES ENGINEERS . PLANNERS . SURVEYORS North Andover,MA 01845 cc Attn:Jean Enright,Assistant Director of Community Development Subject: Response to Stormwater Review by Eggleston Environmenta Earth Works Inc.,2302 Turnpike Street DEP File No. 242-1671 Dear Ms. Enright and Planning Board members: The purpose of this letter is to respond to the comments from Eggleston Environmental (EE) dated December 10,2015 regarding the proposed development located at 2302 Turnpike Street. The comments provided by Eggleston Environmental are shown in italics below with our responses shown in bold text that follows. 1. DEP Stornwater Standard 1 requires that Lozv Impact Development(LID)measures for stormmater management be considered in the design of the project. The proposed project does not appear to incorporate any such measures,and no documentation of the LID measures considered and eliminated zvas included in the materials I reviezved. In cooperation with Town officials,we have designed a proposed rain garden between the edge of pavement and right of way line on Sharpners Pond Road. Sharpners Pond Road was laid out by the U.S. government as an access road to a Nike Missile site in the late 1960s with a layout width of 150-feet. The site was eventually abandoned,but the right of way remains, now in control of the Town of North Andover. The idea for the rain garden was suggested by Jennifer Hughes,the Conservation Commission Administrator and has been reviewed by other Town officials. The applicant proposes to maintain the rain garden as part of their overall stormwater operation and maintenance plan. The location of the rain garden will allow for treatment of stormwater runoff from Sharpners Pond Road,where there is little treatment taking place today. Construction details from the rain garden are shown on Sheet C-12 of the plan set. 2. I was unable to verifij portions of the drainage analysis as there zvas no drainage area map inchrded in the materials I reviezved. The DEP and local regulations require a delineation of the pre-and post-development subareas used in the analysis, including soil type and flozv paths. Existing and Proposed Condition Watershed Maps were prepared and included in the original submission documents. We have attached additional copies of the watershed maps with this response letter for Lisa's use. There is an"Existing Conditions Watershed Map" and a"Proposed Conditions Watershed Map" outlining the sub-watersheds and containing regional soils information,as well as the location of the on-site soils testing we conducted. 189 North Main Street, Suite 101 ® Middleton, MA 01949 ® Tel: (978) 539-8088 ® www.wsengineers.com 6a Response to Stormwater Review Earth Works Inc., 2302 Turnpike Street North Andover, MA February 10, 2015 3. The mitigative drainage analysis and sizing of the proposed infiltration system are based on a design infiltration rate (1.02 in/hr)characteristic of Hydrologic Soil Group (HSG) B sandy loam and ntay significantly overestimate the rate of exfiltration front the system; there are no HSG B soils on the site. The. NRCS soil map shows the site to be predominantly HSG C Paxton fine sandy loam, with an area in the southeast corner of the site mapped as Charlton-Rock Outcrop-Hollis complex. While the Stormwater Report treats this entire complex as HSG A,only the Charlton component is an HSG A soil, the other two components, rock outcrop and Hollis,are characterized as HSG D and are not suitable for infiltration. The proposed infiltration system appears to be located in an area of transition between the Paxton soils and the Charlton-Rock Outcrop-Hollis complex. None of the soil testing conducted on the site to date was within the actual footprint of the proposed system as is required by the MA Stornwater Handbook, nor were the tests sufficiently detailed (e.g. with grain-size analysis or infiltration testing) to distinguish between soil groups or to justify the design infiltration rate used. Additional soil testing is therefore needed within the proposed infiltration area to verifij soil suitability and to establish the appropriate design infiltration rate. Unless the entire area is determined to be Charlton soil,I would expect the rate to be significantly lower than the 1.02 in/hr used. Although the NRCS soil map shows the site to be predominantly HSG C,in-situ soil testing by a Massachusetts Approved Soil Evaluator in the areas where proposed infiltration is occurring identifies more permeable soils consistent with HSG B approximately 2 feet below existing grade.The areas where proposed infiltration is occurring will have the upper less restrictive layers (i.e.,the A and B horizons) removed and replaced with a more permeable soil (at least 1.02 in/hr)to ensure the infiltration rate used in the drainage analysis is consistent with the existing immediate soil condition. The design infiltration rate is based upon the Rawls Rate of 1.02 in/hr for sandy loam as determined by on site soil testing and given that the "static"method is used to size the infiltration practice all that is required by the MA Stormwater Handbook is a soil textural analysis. Additional soil testing has been performed within the footprint of the infiltration portion of the stormwater management area.The additional soil testing is consistent with prior testing revealing more sandy loams,see soil logs in the revised Stormwater-Report. 4. In accordance with the MA Stormwater Handbook,exfiltration from the basin should be calculated over the bottom area only. Exfiltration from the infiltration practices is calculated over the bottom area only for determining drawdown time. 5. The analysis should not assume any storage in the sediment forebay unless it can be demonstrated that the forebay will be fidly dewatered (without exfiltration)between storms. Response to Stormwater Review Earth Works Inc., 2302 Turnpike Street North Andover, MA February 10, 2015 The volume of the forebay is small compared to that of the infiltration basin itself and has little impact on the overall hydraulic performance. However,the lower stages of the forebay are separated from the infiltration basin in the hydraulic model. 6. Based on the calculations, the peak elevation in the 100-yr storm would be 0.67 ft below the top of the berm. The infiltration basin should be designed with afoot of freeboard to protect the berm, and the berm/retaining wall should include an inipervious core to prevent breakout. The infiltration basin has been redesigned and now provides one foot of freeboard between the 100 year water level and the top of the berm. Furthermore,an impervious core of low permeability glacial till is proposed within the berm to help prevent breakout. 7. As shown on the plan,a portion of the proposed infiltration basin is located within the 50-ft buffer to the BVW. The MA Stormwater Handbook requires infiltration structures to have a fnininnon 50-ft setback from wetlands, thus the basin needs to be re-graded to keep the top of the berm outside of the 50-ft buffer. The infiltration basin has been regraded such that the top inside of the berm is outside the 50 foot buffer from the BVW. 8. In order to maximize dispersal of the recharge and better mimic existing conditions, consideration should be given to infiltrating some or all of the runoff fiirther upslope from the wetland,e.g. under the pavement and/or to the south of the building. Segregating the infiltration of roof runoff could also allow better treatinent of the pavement runoff. An additional infiltration practice has been added under the pavement at the rear of the building to handle most of the roof runoff from the main building. 9. It appears that the grassed area to the north of the freestanding storage building and the area between the tzvo drivezvays could be graded to better proanote infiltration, including the roof runoff from the storage building. No changes are proposed to the grassed area to the north of the freestanding storage building. The area between the two driveways has been regarded to accommodate a rain garden to promote additional infiltration and TSS removal. 10. The proposed infiltration basin is used to attenuate peak flozvs during the 10-yr and larger storm events and the separation to seasonal high groundwater is less than four feet, therefore a mounding analysis is required under Stormwater Standard#3. This was checked off in the Stormwater Checklist as being provided, but was not included in the materials I reviewed. The proposed infiltration basin has been regraded such that the infiltrating portion is 4-feet above the estimated seasonal high groundwater. It should be noted that in the hydraulic model,infiltration is limited to the horizontal and vertical extent associated with the recharge Response to Stormwater Review Earth Works Inc., 2302 Turnpike Street North Andover, MA February 10, 2015 and water quality volume only.Therefore,no infiltration credit is taken for the area outside the infiltrating portion or the upper hydraulic operating stages. 11. The plan shows a single roof drain on the northern side of the main building,and all of the roof runoff is modeled as draining to the infiltration basin via that drain. Based on the rooflines shown on the architectural drawings, however, it is not clear how the roof runoff from the pitched roofs at the front corner of the building would reach the drain. It is also not clear that the roof drain is sized to convey the 100-yr flow as is assumed in the model. The hydraulic model has been revised to exclude that portion of the pitched roof at the front not tributary or piped to the added subsurface infiltration structure at the rear of the building. The roof drain collecting network located at the northerly side of the building is sized to handle the 100 year flow from the remaining portion of the roof area of the main building. 12. Given that much of the building roof is flat, consideration should be given to incorporating a green or blue roof design to help attenuate the rate of flow discharged from the roof. We provided the applicant with information on green and blue roofs and a decision was made not to design this type of component into the project. The applicant cited concerns about the additional expense for installing a green or blue roof and the long-term maintenance and higher risk for leaks on a flat roof. As an alternative,the applicant has agreed to attenuate nearly all the flow discharging from the roof of the main building by the addition of a subsurface infiltration structure. 13. Design details are needed for the double catchbasins, sediment forebay and infiltration basin berms, the overflow spillway,and the riprap aprons. The aprons should also be sized to prevent scour. Design details are now provided for the double catchbasins,sediment forebay and infiltration basin berms,the overflow spillway,and the riprap aprons. 14. The proposed outlet hood should be specified on the catchbasin detail;I recommend the LeBaron Snout or Eliminator brands. "The Eliminator"brand outlet hood or catch basin trap is specified for all catch basins. 15. The Erosion &Sediment Control Plan should include measures to protect proposed infiltrations during construction,and to restore the infiltration capacity of any BMPs that are used as sediment traps during construction. The plan also calls for a silt fence sediment barrier;given the slopes involved I recommend the use of straw wattles or coir logs in addition to the silt fence. The Erosion&Sediment Control Plan has been revised to include additional measures to protect and restore the infiltration capacity during construction. Response to Stormwater Review Earth Works Inc., 2302 Turnpike Street North Andover, MA February 10, 2015 A 12 inch"Filtrexx Silt Soxx"has been added to the silt fence detail to provide additional erosion and sediment control. 16. As is indicated in the Stormwater Checklist, the proposed project entails the disturbance of more than one acre and will therefore require a Construction Storrs eater Pollution Prevention Plan (SWPPP)and an NOI filed under the EPA Construction General Permit. This should be clearly indicated on the plans. The Conservation Commission and/or Planning Board niay also want to require confirmation of NOI filing and the opportunity to review the SWPPP prior to implementation. A note has been added to the plans indicating the project requires coverage under the NPDES construction general permit and the preparation of a stormwater pollution prevention plan (SWPPP). The applicant will provide the Conservation Commission with confirmation of the "active" EPA NOI status and a copy of the SWPPP,when they are secured just prior to construction. 17. The Long Term Pollution Prevention Plan (LTPPP)inchided in the subinittal is generic and generally not applicable to the project site. There are no proprietary separators proposed for this project,and I question whether any vehicle washing of tenant equipment should be conducted on the site unless a suitable area is designated and appropriate control ineasures identified. The LTPPP also references the Town of Middleton Conservation Conunission. The plan should be revised to specifically address the intended use of tlX site for storage of landscaping equipment and materials and should identifij appropriate ineasures to prevent exposure of any potential pollutants associated with that use. In particular, it should address loading and unloading operations, sediment tracking,equipment wash-down, dunipster management and materials storage. The LTPPP has been revised to address the comments made by the reviewer. 18. Designated snow storage locations should be shown on the plan. To the extent possible, snow storage should be located upgradient of the stormwater BMPs. Snow should not be plowed directly into the infiltration basin or onto the slope to the east of the proposed storage building. Snow storage locations have been designated on the plan and are upgradient of the stormwater BMP. 19. I have the following coniments on the O&M Plan included in the subinittal; ■ Per DEP requirenients, the Plan should identifij the naive of the system owner and the party responsible for inaintenance of the stormwater systein. The name of the system owner and party responsible for system maintenance has been added to the O&M plan. ■ The catchbasins should be cleaned a minimum of once per year and more often when sediment accumulation is within tzao feet of the outlet. (The sane as one half of the sump depth, but snore easily measured). Response to Stormwater Review Earth Works Inc., 2302 Turnpike Street North Andover, MA February 10, 2015 The frequency of cleaning the catch basins has been revised to once per year or when the depth of deposits is greater than or equal to one half the depth from the bottom of the sump or one half the depth of the invert of the outlet pipe. ■ The infiltration basin should be inspected during and after several storms (e.g. 0.5-inch or greater) during the first year of operation. The frequency of inspection and maintenance of the infiltration basin during the first year of operation has been added to the O&M plan. ■ The Plan should include periodic inspection of the driveway culvert and level spreader to ensure that they are ficnctioning properly. The frequency of inspection and maintenance of the outlet of the rain garden (formerly a culvert) and level spreader has been added to the O&M plan. ■ I suggest combining the LTPPP with the O&M Plan,or at least moving the maintenance log forms from the LTPPP into the O&M Plan. The maintenance log forms from the LTPPP have been added to the O&M plan. ■ The O&M Plan should include an estimated annual budget for maintenance and a simple figure showing the locations of the BMPs to be maintained. The figure should also show the designated snow storage locations referenced in the Plan. An estimated annual budget for maintenance and a corresponding sketch plan has been added to the O&M plan. We trust that you will find the responses above adequately address the comments made by the technical review agent for the proposed development at 2302 Turnpike Street. If you have any questions,please do not hesitate to contact me directly. Very truly yours, � ik jr�� �� µ Christ-P-Sparages,PE Principal MEM: CPS Enclosures cc: Jennifer Hughes,North Andover Conservation Commission DEP NERO Lisa Eggleston,P.E. Attorney Jill Mann Danny Gill,Earth Works,Inc. Eggleston Environmental March 2, 2016 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Jean Enright, Assistant Director of Community Development RE: Stormwater Review Earth Works Inc., 2302 Turnpike Street Dear Ms. Enright and Board Members: In follow-up to my December 10, 2015 comments on the above-referenced project, I have received and reviewed the February 10, 2016 response letter, revised Site Plan (13 of 19 sheets) and revised Stormwater Report & Mitigative Drainage Analysis from Williams & Sparages. The revised plan reflects the addition of a rain garden to capture and treat some of the drainage onto the property from Sharpners Pond Road and a subsurface infiltration system for roof drainage from the main building, as well as some minor regrading of the proposed infiltration basin. The submittal also includes additional soils data from test pits conducted at the proposed infiltration locations and other requested information. A number of my previous comments have been satisfactorily addressed by this revised submittal. I do, however, have the following comments: 1. In response to my previous comment#3, Williams & Sparages argues that the soil testing conducted in the proposed infiltration areas indicate that the deeper soil layers where proposed infiltration would be occurring are more consistent with HSG B soils than with the HSG C soils indicated by the NRCS soil map, and that this justifies the use of the HSG B design infiltration rate to size the facilities and analyze peals runoff rates. The soils they refer to in the C horizon were logged as sandy loam and loamy sand. I would point out that the NRCS soil map indicates the site and the entire upland area surrounding it to be predominantly either Paxton or Woodbridge fine sandy loams, both classified as HSG C, and does not show any HSG B soils in the area. Further, the official NRCS series descriptions of both of these soil types indicate that there may be loam, fine sandy loam, sandy loam, or coarse sandy loam present within the C soil horizon. However, the saturated hydraulic conductivity is described as being low or moderately low in the substratum, and the design infiltration rates assigned to these soils are in the range of 0.17 to 0.27 in/hr, nearly an order of magnitude lower than the 1.02 in/hr used in the project design. 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 Earth Works Inc., Stormwater Review 2 March 2, 2016 I concur with Williams & Sparages that the MA Stormwater Handbook requires only a soil textural analysis when the static method is used to size the infiltration practice for recharge and water quality; since this volume is provided as dead storage (below the outlet) in the basin it will be infiltrated eventually regardless of the infiltration rate. My concern is with the design infiltration rate that is used in their HydroCAD model, as that is a dynamic analysis that assumes exfiltration at the prescribed rate throughout the runoff event. If the actual rate of exfiltration is slower than the assumed rate, e.g. more akin to that of a HSG C soil, it is not clear that the proposed infiltration facilities would fully mitigate the rate of runoff and provide the required freeboard in a 100-yr storm event. Therefore, in the absence of onsite permeability testing to validate the design assumptions, I believe that the more conservative approach would be to run the analysis with the design infiltration rate associated with the mapped soils. 2. The design detail for the proposed rain garden/bioretention cell calls for a ponding depth of 6 inches, however Sheet 6 of the plan calls for a rim elevation on the outlet structure that at 142.5 is more than a foot above the top of the soil. The specified rim elevation is also above the level of the berm. 3. The HydroCAD analysis assumes a rim elevation on the rain garden outlet structure of 142 but does not take into account the fact that the top of the proposed berm is also at elevation 142, hence water would just as likely flow over the berm as into the outlet culvert. 4. The response letter indicates that a figure showing snow storage locations and the BMPs to be maintained was added to the O&M Plan, however I was unable to locate such a figure in the revised submittal. Once again, I appreciate the opportunity to assist the North Andover Planning Board and Conservation Commission with the review of this project, and hope that this information is suitable for your needs. Please feel free to contact me if you or the applicants have any questions regarding the issues addressed herein. Sincerely, EGGLESTON ENVIRONMENTAL Lisa D. Eggleston, P.E. C: Jennifer Hughes, Conservation Administrator Project No. NAND-0033 March 3,2016 North Andover Planning BoardW-4WILLIAMS 1600 Osgood Street SPARAGES North Andover,MA 01845 ENGINEERS . PIANNERS , SURVEYORS Attn:Jean Enright,Assistant Director of Community Development Subject: Response to Stormwater Review by Eggleston Environmenta Earth Works Inc.,2302 Turnpike Street DEP File No. 242-1671 Dear Ms. Enright and Plaruung Board members: The purpose of this letter is to respond to the comments from Eggleston Environmental(EE)dated March 2,2016 regarding the proposed development located at 2302 Turnpike Street.The comments provided by Eggleston Environmental are shown in italics below with our responses shown in bold text that follows. 1. In response to my previous comment#3, Williams&Sparages argues that the soil testing conducted in the proposed infiltration areas indicate that the deeper soil layers where proposed infiltration would be occurring are more consistent with HSG B soils than with the HSG C soils indicated by the NRCS soil map, and that this justifies the use of the HSG B design infiltration rate to size the facilities and analyze peak runoff rates. The soils they refer to in the C horizon were logged as sandy loam and loamy sand. I would point out that the NRCS soil map indicates the site and the entire upland area surrounding it to be predominantly either Paxton or Woodbridge fine sandy loams, both classified as HSG C, and does not show any HSG B soils in the area. Further, the official NRCS series descriptions of both of these soil types indicate that there may be loam,fine sandy loam, sandy loam, or coarse sandy loam present within the C soil horizon. However, the saturated hydraulic conductivity is described as being low or moderately low in the substratum, and the design infiltration rates assigned to these soils are in the range of 0.17 to 0.27 in/hr, nearly an order of magnitude lower than tl:e 1.0211111ir used in the project design. I concur with Williams&Sparages that the MA Stormwater Handbook requires only a soil textural analysis when the static method is used to size the infiltration practicefor recharge and water quality;since this volume is provided as dead storage(below the outlet)in the basin it will be infiltrated eventually regardless of the infiltration rate.My concern is with the design infiltration rate that is used in their HydroCAD model, as that is a dynamic analysis that assumes exfiltration at the prescribed rate throughout the runoff event. If the actual rate of exfiltration is slower than the assumed rate, e.g. more akin to that of a HSG C soil, it is not clear that the proposed infiltration facilities would fully mitigate the rate of runoff and provide the required freeboard in a 100 yr storm event. Therefore, in the absence of onsite permeability testing to validate the design assumptions,I believe that the more conservative approach would be to run the analysis with the design infiltration rate associated with the mapped soils. 189 North Main Street, Suite 101 ® Middleton, MA 01949 o Tel: (978) 539-8088 9 www.wsengineers.com Response to Stormwater Review Earth Works Inc., 2302 Turnpike Street North Andover, MA March 3, 2016 Williams &Sparages has re-run the hydraulics assuming an exfiItration rate of 0.27 inches per hour for all stormwater management areas.The initial hydraulic design provided enough mitigation such that the revised hydraulic design is also capable of providing mitigation in all storms. See attached revised Total Peak Rate of Runoff Comparison Table and stormwater management area performance tables. The calculation settings for exfiltration out of the infiltration pond were and remain conservative given that the invert elevation that determines when exfiltration may begin was set to the bottom of the pond elevation excluding this area from exfiltration.This explains the initial relatively small exfiltration rate and the corresponding small impact on basin performance.The reduction of the exfiltration rate to 0.27 inches per hour reduces the calculated exfiltration rate from 0.02 cfs to 0.00 cfs and a negligible increase in water elevation in the higher frequency lower intensity storms. The impact of reducing the exfiltration rate mostly occurs during the higher frequency lower intensity storms and for the subsurface infiltration chambers given its relative smaller footprint and exfiltration at all elevations.The reduction of the exfiltration rate for the subsurface chambers results in a slight increase in water elevation and a corresponding increase in discharge thereby increasing the total flow.However,the increase in total flow is still less than the flow in the existing condition and therefore provides mitigation as mentioned above. 2. The design detail far the proposed rain garden/bioretention cell calls for a ponding depth of 6 inches, however Sheet 6 of the plan calls for a rim elevation on the outlet structure that at 142.5 is more than afoot above the top of the soil. T'he specified rim elevation is also above the level of the berm. The outlet structure was designed with a throat opening at elevation 142.00 and was the primary outlet device,the rim elevation is a result of the frame and grate placed on top of the structure. 3. The HydroCAD analysis assumes a rim elevation:on the rain garden outlet structure of 142 but does not take into account the fact that the top of the proposed berm is also at elevation 142, hence water would just as likelyflow over the berm as into the outlet culvert. The predicted 100 year water level in the rain garden was 141.63,below the berm elevation of 142.00.The hydraulic model is conservative and only accounts for storage and exfiltration beginning at elevation 139.25 and not the lower elevation of 138.75 which if included would drop the predicted 100 year water elevation further below the berm elevation of 142.00. Reducing the exfiltration rate results in an increase in the 100 year water level to elevation 141.77,therefore the rim of the outlet control structure is lowered to elevation 141.75 to better control the incoming flow regime and to ensure the water level remains below the berm elevation of 142.00. Response to Stormwater Review Earth Works Inc., 2302 Turnpike Street North Andover, MA March 3, 2016 Lowering the outlet control structure to elevation 141.75 results in a reduction in ponding depth. The beginning storage elevation remains the same at elevation 139.25 and the exfiltration rate is reduced to 0.27 inches per hour. 4. The response letter indicates that a figure showing snow storage locations and the BMPs to he maintained was added to the O&M Plan, however I was unable to locate such afigure in the revised submittal. The sketch plan designating the snow storage areas and stormwater management areas to be maintained was appended to the O&M plan but is attached herein for reference. We trust that you will find the responses above adequately address the comments made by the technical review agent for the proposed development at 2302 Turnpike Street. If you have any questions,please do not hesitate to contact me directly. Very truly yours, Matthew Moore,P.E. Project Engineer MEM:CPS Enclosures cc: Jennifer Hughes,North Andover Conservation Commission DEP NERO Lisa Eggleston,P.E. Attorney Jill Mann Danny Gill,Earth Works,Inc. Mitigative Drainage Analysis Proposed Commercial Development #2302 Turnpike Street North Andover, Massachusetts November 4,2015 Revised December 29,2015 Revised March 8,2016 Purpose: The purpose of this analysis is to compare the existing watershed condition to the proposed watershed condition or the post-development condition for the project located at#2302 Turnpike Street,North Andover,MA by analyzing the surface runoff rates to the Iimit of the watershed analysis shown on the accompanying watershed maps. The results of this analysis are presented in the summary table that follows. Introduction: The project is bounded to the east by Sharpners Pond Road, to the south by Turnpike Street(Route 114),to the west by residential properties located off Turnpike Street and to the north by property owned by the town of North Andover(CYR Yard Waste Facility)located off of Sharpners Pond Road. The property is currently occupied by a one story residential structure and barn.Access to the property is from a gravel drive off of Sharpners Pond Road, The property is mostly wooded with areas of grass and a mixture of brush and weeds. The site varies in elevation from approximately 160 feet at the high point in the roadway of Turnpike Street to an elevation of 119 feet at the existing bordering vegetated wetlands located at the northerly portion of the site. The proposal is to redevelop the site by razing the existing structure and construct a new two story (in the front)building,paved driveways,paved parking,landscaping,walkways,and a new drainage system for treatment of stormwater runoff. It should be noted that this is strictly a buffer zone project and there are no proposed disturbances to any wetlands. However,since the Applicant is proposing work within the 100' buffer zone from the edge of bordering vegetated wetlands a Notice of Intent(NOI)filing will be required with the North Andover Conservation Commission. Existing Condition Soils Analysis: In order to model the excess runoff for both the existing and proposed watershed condition,the parent soils on site were mapped using the Web Soil Survey (WSS)made available on the United States Department of Agriculture (USDA)National Resources Conservation Service(NRCS)website. Mitigative Drainage Analysis ##2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 Rev. March 8, 2016 The WSS provides vital soil data and information such as Hydrologic Soil Group (HSG)which is then input into a mathematical model to generate runoff curve numbers. The user inputs the soil cover type as well as the hydrologic soil group to generate a weighted curve number(CN)and also uses the topography of the land to generate a time of concentration(Tc)from which the stormwater runoff rate as well as volume may be calculated for a certain watershed for comparison. The soils present on site are comprised of Paxton,Freetown Muck,Charlton-Rock Outcrop-Hollis Complex and Urban Land.Paxton soils have a HSG rating of C and Urban Land which does not have a rating with the NRCS is assumed to have a HSG rating of C for the purposes of analysis.The Charlton-Rock Outcrop-Hollis Complex has a HSG rating of A/D and Freetown Muck has a HSG rating of D.The Charlton-Rock Outcrop-Hollis Complex is 60%Charlton,16% Rock Outcrop,15% Hollis,5%Woodbridge and 4% Ridgebury.The Hydrologic Soil Group rating for this area is assumed to be 60% HSG A and 40% HSG D.The soil boundary of the Freetown Muck is adjusted to coincide with the edge of the flagged bordering vegetated wetlands. Stormwater Modeling Methodology: The mathematical model used in this analysis was provided using the HydroCAD 10.00 Version developed by HydroCAD Software Solutions LLC. HydroCAD is a program used to model the hydrology and hydraulics of stormwater runoff and is based largely on programs and techniques developed by the NRCS,specifically TR-20 and TR-55 as well as other hydraulic calculation methods. HydroCAD allows the user,for a given rainfall event,to generate runoff hydrographs for single or multiple watersheds and is used to determine if a given drainage system is adequate under the desired conditions as well as to predict flooding or other impacts at specified locations such as erosion. Five design storm events were analyzed and the results presented in the Total Peak Rate of Runoff Comparison Table table that follows for the one(1), two(2),ten(10),twenty five(25)and the one- hundred(100)year storm events for comparison. Existing Condition Watershed: The selected edge of comparison is the edge of the flagged bordering vegetated wetlands for comparison with the proposed condition.The area tributary to this selected edge of comparison is 185,489 W. All the stormwater runoff from within the limit of watershed analysis flows to this selected edge of comparison. Using the methods described in the stormwater modeling methodology above,runoff curve numbers and times of concentration were generated for each watershed for the existing condition to be used for comparison with the proposed condition described below. A schematic of the 2 Mitigative Drainage Analysis #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 Rev, March 8, 2016 mathematical model as well as the results of the calculations for the 1 year,2 year, 10 year,25 year and 100 year,Type 111,24-hour storm events are included in this report. Proposed Condition Watershed: Similar to the existing condition watershed,the selected edge of comparison is the edge of the flagged bordering vegetated wetlands for comparison with the existing condition.The area tributary to this selected edge of comparison is 185,489 ft2. All the stormwater runoff from within the limit of watershed analysis flows to this selected edge of comparison. The proposed development requires the construction of a surface infiltration pond which will provide peak rate of runoff mitigation,water quality as well as groundwater recharge opportunity in the volume provided below the pond outlets. Runoff will be collected using deep-sump catch basins with hoods from the paved surfaces or collected through downspouts from roof areas and piped directly into the proposed infiltration basin,see plan for locations. Using the methods described in the stormwater modeling methodology above,runoff curve numbers and times of concentration were generated for each watershed for the proposed condition to be used for comparison with the existing condition.A schematic of the mathematical model as well as the results of the calculations for the 1 year,2 year,10 year,25 year and 100 year,Type 111,24- hour storm events are included in this report. Compliance with DEP Stormwater Management Standards: Standard 1: No nezv stormwater conveyances(e.g. outfalls)may discharge untreated stormwater directly to or cause erosion in zvetlands or wafers of the Contmonzoealth, All new stormwater runoff requiring treatment will be treated prior to being discharged towards the edge of the flagged bordering vegetated wetlands. Standard 2• Stornizvater nranagetnent systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. This Standard niap be waived for discharges to land subject to coastal storin flowage as defined in 310 CMIt 10.04. See the summary table that follows which demonstrates that the post-development peak discharge rates are less than the existing peak discharge rates. 3 Mitigative Drainage Analysis #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 Rev, March 8, 2016 Standard 3: Loss of annual recharge to ground7vater shall be eliminated or miniinized through the use of infiltration measures including environ nten tally sensitive site design,lozv impact development techniques, storinzvater best management practices,and good operation and maintenance. At a inininuan, the annual recharge from the post-development site shall approximate the annual recharge from the pre-development conditions based on soil type. This Standard is met when the storm7vater management system is designed to infiltrate the required recharge volume as determined in accordance with the Massachusetts Storm70ater Handbook. The project site has a Hydrologic Soil Group rating primarily of C and a small portion with a rating of A. Groundwater recharge is provided through the use of an infiltration basin which does not lie within an area of rapid 'infiltration as determined from a soil textural analaysis performed by Williams&Sparages,LLC.See attached calculations which demonstrate the project meets this standard. Standard 4: Storinwater management systents shall be designed to remove 80% of the average annual post-construction load of Total Suspended Solids(TSS). This Standard is met when: a. Suitable practices for source control and pollution prevention are identified in a long-term pollution prevention plan,and thereafter are implemented and maintained; b. Structural storinwater best management practices are sized to capture the required Water quality volume determined in accordance with the Massachusetts Storniwater Handbook,and c. Pretreatment is provided in accordance with the Massachusetts Storm7vater Handbook The proposed project will utilize deep-sump hooded catch basins and a sediment forebay to collect and pre-treat the stormwater runoff before discharging to an infiltration pond. It should be noted that runoff from certain types of roof areas are considered"clean" by DEP and therefore,do not require treatment. We have assumed that the roof types that are to be installed for this project will satisfy DEP's criteria. Portions of the project site are within an area of rapid infiltration rate as determined from a soil textural analaysis performed by Williams&Sparages,LLC,therefore the water quality volume is based on a runoff of one inch. Standard 5: For land uses with higher potential pollutant loads, source control and pollution prevention shall be implemented in accordance with the Massachusetts Storm7vater Handbook to eliminate or reduce the discharge of storm7vater runoff from such land uses to the ntaximum extent practicable. If through source control and/or pollution prevention all land uses zvith higher potential pollutant loads cannot be completely protected fioirt exposure to rain,snow melt,and storm7vater runoff, the proponent shall use specific structural stormwater BMPs deteriined by the Department to be suitable for such uses as provided in the Massachusetts Storm7vater Handbook. Storm7vater discharges from land uses with higher potential pollutant loads shall also 4 Mitigative Drainage Analysis #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 Rev. March 8, 2016 comply with the requirements of the Massachusetts Clean Waters Act,M.G.L. c. 21,§§26-53 and the regulations promulgated there under at 314 CMR 3.00,314 CMR 4,00 and 314 CMR 5.00. This project is not being considered as a LUHPPL. Standard 6: Storntwater discharges within the Zone II or Interim Wellhead Protection Area of a public water supply,and stormwater discharges near or to any other critical area, require the use of the specific souree control and pollution prevention ttteasures and the specific structural stornimater best ntanagentent practices determined by the Department to be suitable for managing discharges to such areas,as provided in the Massachusetts Stortttwater Handbook. A discharge is near a critical area if there is a strong likelihood of a significant impact occurring to said area, taking into account site-specific factors. Stortnwater discharges to Outstanding Resource Waters and Special Resource Waters shall be removed and set back front the receiving water or wetland and receive the highest and best practical method of treatment. A "storm water discharge"as defined in 314 CMR 3.04(2) (a) (1 or(b) to an Outstanding Resource Water or Special Resource Water shall comply with 314 CMR 3.00 and 314 CMR 4.00. Storntwater discharges to a Zone I or Zone A are prohibited unless essential to the operation of public water supply. The stormwater discharge from this property is not within an Interim Wellhead Protection Area of a public water supply nor within a Zone 11. Standard 7: A redevelopment project is required to ineet the following Stortttwater Management Standards only to the maximunt extent practicable:Standard 2, Standard 3,and the pretreatment and structural best managentent practice requirements of Standards 4,5,and 6. Existing stormwater discharges shall corltply with Standard 1 only to the tnaximunt extent practicable. A redevelopment project shall also comply with all other requirements of the Storntwater Management Standards and improve existing conditions. This project is not being considered as a redevelopment. Standard 8: A plan to control construction-related impacts including erosion,sedimentation and other pollutant sources during construction and land disturbance activities(construction period erosion, sedimentation,and pollution prevention plan)shall be developed and implemented. A Stormwater Pollution Prevention Plan(SWPPP)will be provided. Standard 9: A long-term operation and maintenance plan shall be developed and intpletnented to ensure that stormwater ntanagetnent systems function as designed. 5 Mitigative Drainage Analysis #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 Rev. March 8, 2016 A bong Term Operation and Maintenance Plan(O&M)will be provided. Standard 10: All illicit discharges to the stornavater management system are prohibited. There are no proposed illicit discharges into the Stormwater Management Systems to be constructed as shown on the site plan. Conclusion: As can be seen by examining the following summary&performance tables,the proposed stormwater management system is effective for mitigating the peak flow rates of runoff from the limit of the watershed analysis for the 1,2,10,25&100 year storm events. 6 Mitigative Drainage Analysis #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 Rev. March 8, 2016 Total Peak Rate of Runoff Comparison Table Existing Condition Proposed Condition 24 hour Type III Description Storm Event Peak Rate of Volume of Peak Rate of Volume of (year) Runoff Runoff Runoff Runoff Q (cfs) (ac-ft) Q (cfs) Q(cfs) 1 (2.5 inch) 1.9 0.17 1.6 0.30 Flow to edge 2(3.2 inch) 3.9 0.31 3.7 0.47 of BVW 10(4.8 inch) 9.5 0.70 9.0 0.91 25 (6.0 inch) 14.1 1.03 12.9 1.25 100(8.6 inch) 24.9 1.81 20.7 2.03 7 Mitigative Drainage Analysis #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 Rev. March 8, 2016 Proposed Stormwater Management Area #1 HydroCAD Pond 1P Top of Berm=132.3 Bottom of basin=128.0 8'L Stone Spillway=131.8 18" HDPE Culvert out=124.20 (Discharges into level spreader) Peak Rate of Runoff Out 24 hour Type III Peak Rate of (Q)cfs Peak Water Storm Event Runoff In Level(ft) (year) Q (cfs) *Exfiltration Stone 18" Total illwa (Discarded) S tone Culvert Outflow 1 3.3 0.00 0.0 0.9 0.9 129.93 2 4.6 0.00 0.0 1.9 1.9 130.20 10 7.5 0.00 0.0 4.4 4.4 130.61 25 9.7 0.00 0.0 6.0 6.0 130.84 100 14.3 0.00 0.0 8.8 8.8 131.28 *Calculated infiltration rate and peak water levels are based upon a rate of 0.27 inches per hour for Sandy Loams as found on Table 2-1 of the Hydrology Handbook of Conservation Commissioners, March 2002 using Rawls,Brakensiek and Saxton,1982. Mitigative Drainage Analysis #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 Rev. March 8, 2016 Proposed Stormwater Management Area #2 HydroCAD Pond 11P Bottom Stone=130.50 Bottom Chamber=131.00 Top Chamber=133.50 Top Stone=134.00 12"INV.=132.25 in 10"INV.=132.42 out(Discharges into level spreader) 24 hour Type III Peak Rate of Peak Rate of Runoff Out Storm Event Runoff In (Q)cfs Peak Water (year) Q(cfs) Level(ft) *Exfiltration 10" Total Discarded Culvert Outflow 1 0.8 0.01 0.3 0.3 132.68 2 1.0 0.01 0.7 0.7 132.88 10 1.6 0.01 1.4 1.4 133.11 25 2.0 0.01 1.7 1.7 133.26 100 2.8 0.01 2.4 2.4 133.68 *Calculated infiltration rate and peak water levels are based upon a rate of 0.27 inches per hour for Sandy Loams as found on Table 2-1 of the Hydrology Handbook of Conservation Commissioners, March 2002 using Rawls,Brakensiek and Saxton,1982. 9 Trlb to DGCBt DGCB7 t A DMH1 D H2 TO 0 I Trib to ettands Trib.to CB2 CB2 dB Storage Roof cs. DMH4 DMH orey 3 Fba Infiltration Basin ;;:gip':: Trib,to DGCB3 DGCB3 C,'- A Rain Garden Trib.to Wetlands Bldg Roof Slormlech �I�G�t. Rb:3Ch Qt� tnk. F Routing Diagram for Proposed_R3_EXFILTRATION red by(enter your company name here}, Printed 3/14/2016 AD®10.00.15 s/n 06611 0 2015 HydroCAD Software Solutions LLC Proposed_R3`EXFILTRATI ON Prepared by{enter your company name here} Printed 3/14/2016 HydroCAD®10.00-15 s/n 06611 ©2015 HydroCAD Software Solutions LLC page 2 Area Listing (all nodes) Area CN Description (sq-ft) (subcatchment-numbers) 4,636 39 >75%Grass cover, Good, HSG A (2S, 7S, 8S) 38,075 74 >75%Grass cover, Good, HSG C (1S, 2S,4S, 6S, 7S, 8S) 779 80 >75% Grass cover, Good, HSG D (7S, 8S) 1,089 98 Paved parking, HSG A (4S, 6S) 43,001 98 Paved parking, HSG C (1S,4S, 6S) 726 98 Paved parking, HSG D (4S, 6S) 17,683 98 Paved roads w/curbs&sewers, HSG C (1S, 2S, 6S, 7S) 20,331 98 Roofs, HSG C (1S, 3S, 5S) 2,449 98 Water Surface, HSG A (8S) 2,448 98 Water Surface, HSG C (8S) 1,632 98 Water Surface, HSG D (8S) 3,959 30 Woods, Good, HSG A (2S) 46,042 70 Woods, Good, HSG C (28, 7S) 2,639 77 Woods, Good, HSG D (2S) 185,489 83 TOTAL AREA Proposed_R3�EXFI LTRATI ON Prepared by{enter your company name here} Printed 3/14/2016 HydroCAD®10.00-15 s/n 06611 O 2015 HydroCAD Software Solutions LLC Page 3 Soil Listing (all nodes) Area Soil Subcatchment (sq-ft) Group Numbers 12,133 HSG A 2S, 4S, 6S, 7S, 8S 0 HSG B 167,580 HSG C 1 S, 2S, 3S, 4S, 5S, 6S, 7S, 8S 5,776 HSG D 2S, 4S, 6S, 7S, 8S 0 Other 186,489 TOTAL AREA Proposed_R3_EXIr I LTRATION Prepared by{enter your company name here) Printed 3/14/2016 HydroCAD®10.00-15 s/n 06611 ©2015 HydroCAD Software Solutions LLC Page 4 Ground Covers (all nodes) HSG-A HSG-B HSG-C HSG-D Other Total Ground (sq-ft) (sq-ft) (sq-ft) (sq-ft) (sq-ft) (sq-ft) Cover 4,636 0 38,075 779 0 43,490 >75%Grass cover, Good 1,089 0 43,001 726 0 44,816 Paved parking 0 0 17,683 0 0 17,683 Paved roads w/curbs& sewers 0 0 20,331 0 0 20,331 Roofs 2,449 0 2,448 1,632 0 6,529 Water Surface 3,959 0 46,042 2,639 0 52,640 Woods, Good 12,133 0 167,580 5,776 0 185,489 TOTAL AREA Proposed_R3_EXFILTRATION Prepared by{enter your company name here) Printed 3/14/2016 HydroCAD®10.00-15 s/n 06611 02015 HydroCAD Software Solutions LLC Page 5 Pipe Listing (all nodes) Line# Node In-Invert Out-Invert Length Slope n Diam/Width Height Inside-Fill Number (feet) (feet) (feet) (ft/ft) (inches) (inches) (inches) 1 1 P 124.20 124.00 7.0 0.0286 0.013 18.0 0.0 0.0 2 3P 143.52 142,24 64.0 0,0200 0.013 12.0 0.0 0.0 3 4P 142.24 140.00 164.0 0,0137 0.013 12.0 0.0 0.0 4 5P 138.71 134.03 67.0 0.0699 0.013 12.0 0.0 0.0 5 6P 130.36 130.00 36.0 0.0100 0.013 24.0 0.0 0.0 6 7P 131.29 130.61 29.0 0.0234 0.013 18.0 0.0 0.0 7 8P 134,33 134.27 6.0 0,0100 0.013 12.0 0.0 0.0 8 9P 132.59 131.54 105.0 0.0100 0.013 15.0 0.0 0.0 9 lip 132.42 124.00 81.0 0.1040 0.013 10.0 0.0 0.0 10 12P 137.00 133.00 51.0 0.0784 0.013 12.0 0.0 0.0 Proposed_R3�EXFILTRATION Type ///24-hr 100 yr Rainfall=8.60" Prepared by{enter your company name here} Printed 3/14/2016 H droCAD®10.00-15 s/n 06611 02015 W droCAD Software Solutions LLC Page 6 Time span=0.00-30.00 hrs, dt=0.05 hrs, 601 points x 2 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 1S., Trib to DGCB1 Runoff Area=20,367 sf 62.10% Impervious Runoff Depth=7.28" Flow Length=496' Tc=6.0 min CN=89 Runoff=3.65 cfs 12,349 of Subcatchment 2S: Trib to Wetlands Runoff Area=69,656 sf 15.15% Impervious Runoff Depth=5.22" Tc=6.0 min CN=72 Runoff=9.58 cfs 30,328 of Subcatchment 3S: Storage Roof Runoff Area=4,410 sf 100.00% Impervious Runoff Depth=8.36" Tc=6.0 min CN=98 Runoff=0.83 cfs 3,072 of Subcatchment 4S: Trib.to DGCB3 Runoff Area=31,476 sf 79.97% Impervious Runoff Depth=7.76" Tc=6.0 min CN=93 Runoff=5.83 cfs 20,350 of Subcatchment 5S: Bldg Roof Runoff Area=14,845 sf 100.00% Impervious Runoff Depth=8.36" Tc=6.0 min CN=98 Runoff=2.81 cfs 10,342 of Subcatchment 6S: Trib.to C132 Runoff Area=16,132 sf 83.46% Impervious Runoff Depth=7.88" Tc=6.0 min CN=94 Runoff=3.01 cfs 10,592 of Subcatchment 7S: Trib.to Wetlands Runoff Area=18,357 sf 9,48% Impervious Runoff Depth=5.35" Tc=6.0 min CN=73 Runoff=2.58 cfs 8,177 of Subcatchment 8S: Trib. to I Runoff Area=10,246 sf 63.72% Impervious Runoff Depth=6.91" Tc=6.0 min CN=86 Runoff=1.78 cfs 5,904 cf Pond 1P: Infiltration Basin Peak Elev=131.28' Storage=11,110 cf Inflow=14.33 cfs 48,758 of Discarded=0.00 cfs 395 of Primary=8.83 cfs 46,375 of Outflow=8.84 cfs 46,770 of Pond 2P: Forebay Peak Elev=131.29' Storage=440 of Inflow=12.49 cfs 43,291 of Outflow=12.55 cfs 42,855 of Pond 3P: DGCB1 Peak Eiev=144.95' Inflow=3.65 cfs 12,349 of 12.0" Round Culvert n=0.013 L=64.0' S=0.0200 T Outflow=3.65 cfs 12,349 of Pond 4P: DMH1 Peak Elev=143.67' Inflow=3.65 cfs 12,349 of 12.0" Round Culvert n=0.013 L=164.0' S=0.0137'/' Outflow=3.65 cfs 12,349 of Pond 5P: DMH2 Peak Eiev=140.14' Inflow=3.65 cfs 12,349 of 12.0" Round Culvert n=0.013 L=67.0' S=0.0699'/' Outflow=3.65 cfs 12,349 of Pond 6P: DMH3 Peak Elev=132.22' Inflow=12.49 cfs 43,291 of 24.0" Round Culvert n=0.013 L=36.0' S=0.0100 T Outflow=12.49 cfs 43,291 of Pond 713: DMH4 Peak Elev=133.28' inflow=8.84 cfs 30,942 of 18.0" Round Culvert n=0.013 L=29.0' S=0.0234'/' Outflow=8.84 cfs 30,942 of Pond 8P: C1132 Peak Elev=135.62' Inflow=3.01 cfs 10,592 of 12.0" Round Culvert n=0.013 L=6.0' S=0.0100'/' Outflow=3.01 cfs 10,592 of Proposed_R3_EXFILTRATION Type 11124-hr 100 yr Rainfall=8.60" Prepared by{enter your company name here} Printed 3/14/2016 HydroCAM 10.00-15 s/n 06611 ©2015 HydroCAD Software Solutions LLC Page 7 Pond 9P: DGCB3 Peak Elev=134.64' Inflow=5.83 cfs 20,350 of 15.0" Round Culvert n=0.013 L=105.0' S=0.0100'/' Outflow=5.83 cfs 20,350 cf Pond 11P: Stormtech Peak Elev=133.68' Storage=1,919 of Inflow=2.81 cfs 10,342 of Discarded=0.01 cfs 634 of Primary=2.41 cfs 8,559 of Outflow=2.42 cfs 9,193 of Pond 12P: Rain Garden Peak Elev=141.77' Storage=4,853 of Inflow=2.58 cfs 8,177 of Discarded=0.03 cfs 2,597 of Primary=0.16 cfs 1,541 of Outflow=0.20 cfs 4,138 of Link 1L: Inflow=20.69 cfs 89,875 of Primary=20.69 cfs 89,875 of Total Runoff Area=185,489 sf Runoff Volume=101,113 cf Average Runoff Depth=6.64" 51.83%Pervious=96,130 sf 48.17%Impervious=89,359 sf Proposed_R3_EXFI LTRATION Prepared by(enter your company name here) Printed 3/14/2016 HydroCAD010.00-15 s/n 06611 02016 HydroCAD Software Solutions LLC Page 1 Pipe Listing (selected nodes) Line# Node In-Invert Out-Invert Length Slope n Diam/Width Height Inside-Pill Number (feet) (feet) (feet) (ft/ft) (inches) (inches) (inches) 1 1 P 124.20 124.00 7.0 0.0286 0.013 18.0 0.0 0.0 2 11 P 132.42 124.00 81.0 0.1040 0.013 10.0 0.0 0.0 3 12P 137.00 133.00 51.0 0.0784 0.013 12.0 0.0 0.0 Proposed-R3_EXHL " TRATION Type 11124-hr 100 yr Rainfall=8.60 Prepared by{enter your company name here} Printed 3/14/2016 HydroCAD®10.00-15 s/n 06611 ©2015 HydroCAD Software Solutions LLC Page 2 Summary for Pond IP: Infiltration Basin Inflow Area= 78,221 sf, 73.91% Impervious, Inflow Depth = 7,48" for 100 yr event Inflow = 14.33 cfs @ 12.09 hrs, Volume= 48,758 of Outflow - 8.84 cfs @ 12.20 hrs, Volume= 46,770 of, Atten= 38%, Lag= 6.6 min Discarded = 0.00 cfs @ 8.10 hrs, Volume= 395 of Primary - 8.83 cfs @ 12.20 hrs, Volume= 46,375 of Routing by Dyn-Star-Ind method, Time Span= 0.00-30.00 hrs, dt=0.05 hrs/2 Peak Elev= 131.28'@ 12.20 hrs Surf.Area= 5,502 sf Storage= 11,110 cf Flood Elev= 132,30' Surf.Area=6,514 sf Storage= 17,227 of Plug-Flow detention time= 74.2 min calculated for 46,693 of(96% of inflow) Center-of-Mass det. time= 51.1 min (824.6-773.6 ) Volume Invert Avail.Storage Storage Description #1 128,00' 17,227 of Custom Stage Data(Prismatic) Listed below(Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 128.00 1,476 0 0 129.00 2,016 1,746 1,746 130.00 4,234 3,125 4,871 131.00 5,225 4,730 9,601 132.00 6,211 5,718 15,319 132.30 6,514 1,909 17,227 Device Routing Invert Outlet Devices #1 Device 3 129,10' 6.0"Vert. Orifice/Grate C=0.600 #2 Device 3 129,75' 18.0"Vert. Orifice/Grate C= 0.600 #3 Primary 124.20' 18.0" Round Culvert L= 7.0' CPP, square edge headwall, Ke= 0.500 Inlet/Outlet Invert= 124.20'/ 124.00' S= 0.0286 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 1.77 sf #4 Discarded 128.00' 0.270 in/hr Exfiltration over Surface area from 128.00'-129.10' Excluded Surface area= 1,476 sf #5 Primary 131.80' 8.0' long x 7.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 Coef. (English) 2.40 2.52 2.70 2.68 2.68 2.67 2.66 2.65 2.65 2.65 2.66 2.65 2.66 2.68 2,70 2.73 2.78 tscarded OutFlow Max=0.00 cfs @ 8.10 hrs HW=129.10' (Free Discharge) =Exfiltration (Exfiltration Controls 0.00 cfs) Primary OutFlow Max=8.83 cfs @ 12.20 hrs HW=131.28' TW=0.00' (Dynamic Tailwater) -Culvert (Passes 8.83 cfs of 21.41 cfs potential flow) E1=Orifice/Grate (Orifice Controls 1.31 cfs @ 6.69 fps) 2=06fice/Grate (Orifice Controls 7.51 cfs @ 4.25 fps) 5=Broad-Crested Rectangular Weir ( Controls 0.00 cfs) Proposed-R3r EXFILTRATION Type 11124-hr 100 yr Ralnfall=8.60" Prepared by tenter your company name here) Printed 3/14/2016 H droCAD®10.00-15 s/n 06611 ©2015 M droCAD Software Solutions LLC Page 3 Summary for Pond 2P: Forebay Inflow Area = 67,975 A 75.45% Impervious, Inflow Depth = 7.64" for 100 yr event Inflow - 12.49 cfs @ 12.09 hrs, Volume= 43,291 of Outflow - 12.55 cfs @ 12.09 hrs, Volume= 42,855 of, Atten= 0%, Lag= 0.1 min Primary - 12.55 cfs @ 12.09 hrs, Volume= 42,855 of Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.05 hrs/2 Peak Elev= 131.29' @ 12.19 hrs Surf.Area= 448 sf Storage= 440 cf Plug-Flow detention time= 12.0 min calculated for 42,855 of(99% of inflow) Center-of-Mass det. time= 5.5 min ( 772.0-766.4) Volume Invert Avail.Storage Storage Description #1 128.00' 440 of Custom Stage Data (Prismatic) Listed below(Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 128.00 151 0 0 129.00 336 244 244 129.60 448 196 440 Device Routing Invert Outlet Devices #1 Primary 129,50' 9.0' long x 2.0'breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 Coef. (English) 2.54 2.61 2.61 2.60 2.66 2.70 2.77 2.89 2.88 2.85 3.07 3.20 3.32 Primary OutFlow Max=12.33 cfs @ 12.09 hrs HW=131.08' TW=131.05' (Dynamic Tailwater) At-I=Broad-Crested Rectangular Weir (Weir Controls 12.33 cfs @ 0.87 fps) Summary for Pond 11 P: Stormtech Inflow Area = 14,845 sf,100.00% Impervious, Inflow Depth = 8.36" for 100 yr event Inflow - 2.81 cfs @ 12.09 hrs, Volume= 10,342 of Outflow = 2.42 cfs @ 12.14 hrs, Volume= 9,193 of, Atten= 14%, Lag= 3.0 min Discarded = 0.01 cfs @ 1.60 hrs, Volume= 634 of Primary - 2.41 cfs @ 12.14 hrs, Volume= 8,559 of Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt=0.05 hrs/2 Peak Elev= 133.68' @ 12.14 hrs Surf.Area= 961 sf Storage= 1,919 of Plug-Flow detention time= 119.3 min calculated for 9,177 of(89%of inflow) Center-of-Mass det. time=66.1 min ( 806.5-740.3 ) Proposed_R3_EXFILTRATION Type 11124-hr 100 yr Rainfall=8.60" Prepared by{enter your company name here) Printed 3/14/2016 Hy droCAD®10.00-15 s/n 06611 ©2016 HydroCAD Software Solutions LLC Page 4 Volume Invert Avail.Storage Storage Description #1A 130.60' 880 of 25.25'W x 38.041 x 3.50'H Field A 3,362 of Overall - 1,163 of Embedded = 2,199 of x 40.0% Voids #2A 131,00' 1,163 of StormTech SC-740 x 25 Inside#1 Effective Size=44.6"W x 30.0"H => 6.45 sf x 7.121 = 45.9 of Overall Size= 51.0"W x 30.0"H x 7.56'L with 0.44'Overlap Row Length Adjustment= +0.44'x 6.45 sf x 5 rows 2,042 of Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Discarded 130.50' 0.270 in/hr Exfiltratlon over Surface area #2 Primary 132,42' 10.0" Round Culvert L= 81.0' CPP, square edge headwall, Ke= 0.500 Inlet/Outlet Invert= 132.42'/ 124.00' S= 0.1040'/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 0.55 sf Discarded OutFlow Max=0.01 cfs @ 1.60 hrs HW=130.54' (Free Discharge) t--1=Exfiltration (Exfiltration Controls 0.01 cfs) Primary OutFlow Max=2.38 cfs @ 12.14 hrs HW=133.66' TW=0.00' (Dynamic Tailwater) t-2=Culvert (inlet Controls 2.38 cfs @ 4.36 fps) Summary for Pond 12P: Rain Garden Inflow Area = 18,357 sf, 9.48% Impervious, Inflow Depth = 5.35" for 100 yr event Inflow = 2.58 cfs @ 12.09 hrs, Volume= 8,177 of Outflow - 0.20 cfs @ 13.50 hrs, Volume= 4,138 of, Atten= 92%, Lag=84.3 min Discarded = 0.03 cfs @ 13.50 hrs, Volume= 2,597 of Primary = 0.16 cfs @ 13.50 hrs, Volume= 1,641 of Routing by Dyn-Stor-Ind method, Time Span= 0.00-30.00 hrs, dt= 0.05 hrs/2 Peak Elev= 141.77' @ 13.50 hrs Surf.Area= 5,431 sf Storage=4,853 of Plug-Flow detention time= 364.4 min calculated for 4,132 of(51% of inflow) Center-of-Mass det. time= 252.4 min( 1,067.8-815.4 ) Volume Invert Avail.Storage Storage Description #1 139.25' 6,732 of 139.25(Prismatic) Listed below(Recalc) Elevation Surf.Area Voids Inc.Store Cum.Store (feet) (sq-ft) M (cubic-feet) (cubic-feet) 139.25 5,110 0.0 0 0 141.50 5,110 30.0 3,449 3,449 142.00 5,713 100.0 2,706 6,155 142.10 5,835 100.0 577 6,732 Proposed_R3_EMLTRATION Type /1124-hr 100 yr Rainfall=8.60" Prepared by{enter your company name here) Printed 3/14/2016 HydroCAD®10.00-15 s/n 06611 02015 HydroCAD Software Solutions LLC Page 5 Device Routing Invert Outlet Devices #1 Device 2 141,75' 2.0"x 2.0"Horiz. Orifice/Grate X 36.00 C= 0.600 Limited to weir flow at low heads #2 Primary 137.00' 12.0" Round Culvert L= 51.0' CPP, square edge headwall, Ke= 0.500 Inlet/Outlet Invert= 137.00'/ 133.00' S= 0.0784 T Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 0.79 sf #3 Discarded 139.25' 0.270 in/hr Exfiltration over Surface area Phase-In= 0.01' Qiscarded OutFlow Max=0.03 cfs @ 13.50 hrs HW=141.77' (Free Discharge) 'c--3=Exfiltration (Exfiltration Controls 0.03 cfs) Primary OutFlow Max=0.16 cfs @ 13.50 hrs HW=141.77' TW=0.00' (Dynamic Tailwater) t--2=Culvert (Passes 0.16 cfs of 7.81 cfs potential flow) t-1=Orifice/Grate (Weir Controls 0.16 cfs @ 0.42 fps) Operation &Maintenance Plan #2302 Turnpike Street North Andover, Massachusetts November 4,2015 Revised December 29,2015 This Operation&Maintenance Plan has been prepared to comply with the provisions set forth in the Massachusetts Department of Environmental Protection(DEP) Stormwater Management Standards. Structural Best Management Practices (BMPs) require periodic maintenance to ensure proper function and efficiency in pollutant removal from stormwater discharges that would otherwise reach wetland resource areas untreated. Maintenance schedules found below are as recommended in Department of Environmental Protection's Massachusetts Stormwater Handbook and as recommended in the manufacturer's specifications. The stormwater management system owner and the party responsible for maintenance of the stormwater management system shall be Earth Works,Inc. and its designated employees. The following BMPs shall be utilized for pollutant removal from stormwater discharge as well providing additional groundwater recharge on site: • Deep-Sump Catch Basin w/hood • Sediment Forebay • Surface Infiltration Pond (1P) • Subsurface Infiltration Pond (11P) • Rain Garden Deep-Sump Catch Basins w/Hood&Outlet Control Structure: • Inspect or clean at least once per year with special consideration given to the end of foliage and snow removal seasons. • Sediments must also be removed once per year or whenever the depth of deposits is greater than or equal to one half the depth from the bottom of the sump or one half the depth of the invert of the outlet pipe. • Clarnshell buckets and/or vacuum trucks are typically used to remove sediment in Massachusetts. • Cleanings may be taken to a landfill or other facility permitted by MassDEP to accept solid waste, without any prior approval by MassDEP. However,some landfills require catch basin cleanings to be tested before they are accepted. For information on all of the MassDEP requirements pertaining to the disposal of catch basin cleanings go to www.Mass.gov/dep/recycle/lawsZcafacts.doc Sediment Foreba : • Inspect the forebays monthly with special consideration given to the end of foliage and snow removal seasons and clean them out at least four times per year. Operation &Maintenance Plan #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 • Frequently removing accumulated sediments will make resuspension less likely, • Stabilize the floor and sidewalls before making it operational to avoid excess amounts of suspended sediments. • Keep the grass in the sediment forebay no lower than three(3) to four(4) inches but no higher than six (6)inches. • Inspect the sediment forebay for signs of Tilling and gullying and repair as necessary. • Replace any vegetation damaged during the clean-out by either reseeding or resodding. • If reseeding,utilize practices such as hydroseeding with a tackifier,blanket,or similar practice to ensure that no scour occurs in the forebay and allow the seeds to germinate and develop roots. Surface Infiltration Pond (1P): • Infiltration basins are prone to clogging and failure so it is imperative to develop and implement aggressive maintenance plans and schedules. Installing the required pretreatment BMPs,e.g. deep- sump catch basins and sediment forebays,will significantly reduce the maintenance requirements for the basin. • The infiltration basin should be inspected during and after several storms(e.g.0.5-inch or greater) and maintenance performed if necessary during the first year of operation.Thereafter,inspections and preventative maintenance shall be performed at least twice a year,and after every time drainage discharges through the high outlet orifice or a major storm event which is defined as a storm that is equal to or greater than the 2-year,24-hour storm(3.1 inches in a 24 hour storm) • After the basin is on line,inspect it after every major storm for the first few months to ensure that it is stabilized and functioning properly. Take corrective action if necessary. • Note the time that water remains standing in the basin after a storm event. Standing water within the basin 48 to 72 hours after a storm indicates that the infiltration capacity of the basin may have been overestimated or the bottom has been clogged. • If the reason is clogging,determine the cause,e.g.erosion,excessive compaction,or low spots and take the necessary corrective action. Thereafter,inspect the infiltration basin at least twice per year. • Important items to check during the inspections include; Signs of differential settlement, Cracking, Erosion, Leakage in the embankments, Tree growth on the embankments, 2 Operation& Maintenance Plan #2302 Turnpike Street, North Andover, MA November 4,2015 Rev. December 29, 2015 Condition of riprap, Sediment accumulation and, Health of the turf. • At least twice a year the buffer area,side slopes,and basin bottom shall be mowed. Remove the grass clippings and accumulated organic matter to prevent an impervious organic mat from forming. Remove trash and debris at this time as well as using deep tilling to break up any clogged surfaces, revegetate immediately. • Remove sediment from the basin as necessary only when the floor of the basin is completely dry. Use light equipment to remove the top layer to prevent compacting the underlying soil. Deep till the remaining soil and revegetate as soon as possible. Subsurface Infiltration Pond (1" • Chamber maintenance is not generally required.However,recharge systems are prone to failure due to clogging. Regulating the sediment and petroleum product input into the proposed recharge system is the priority maintenance activity.Sediments and any oil spillage should be trapped and removed before they reach the chambers.Any upstream devices connected to the infiltration system(catch basins,deep sump manholes,proprietary devices) shall be inspected and cleaned at least once per year to prevent sediments and debris from entering and clogging the recharge system. • Sediments must also be removed whenever the depth of deposits is greater than or equal to one half the depth from the bottom of the sump or one half the depth of the invert of the outlet pipe. • The contractor shall verify that the required washed crushed stone and geotechnical fabric materials are clean and free of sediments and petroleum residue prior to,during and after chamber system installation. • Inspections of the chamber system shall be made by after every major storm for the first few months after construction to verify that proper functioning has been achieved.During the initial inspection the water level should be measured and recorded in a permanent log over several days to check the drainage duration and verify that sediments are not accumulating.If ponded water is present after 24 hours or an accumulation of sediment or debris is noted within the chambers the owner or designated property manager and engineer shall determine the cause for this condition and devise an action plan to improve system functionality. • Once the chamber system has been verified to perform as designed,interior chamber conditions shall be inspected at least annualy.Post construction inspections(to be conducted through inspection ports) shall consist of documenting interior and stone bed conditions,measured water depth and presense of sediment.Should inspection indicate that the system is clogged(ponding water present after 24 hours and/or sediment accumulations)replacement or major repair actions may be required as determined by a professional engineer.Should the system require replacement or major repair actions the owner or designated property manager and engineer shall determine the cause for this condition and devise an action plan. 3 Operation& Maintenance Plan #2302 Turnpike Street, North Andover, MA November 4,2015 Rev. December 29, 2015 • The inspection and maintenance of the subsurface infiltration system shall belong to the owner or designated property manager. Rain Garden (1M- • Inspect and remove trash monthly throughout the year. • Remove and replace dead vegetation annually in the spring. • Prune the shrubs annually in the spring. • Replace mulch annualy in the spring. • Remove any accumulated sediment from mulch areas and from the pretreatment sideslopes annually in the spring. • Mow the pretreatment sideslopes once a month during the growing season. • When areas of erosion are identified,repair areas of erosion and revegetate as needed as soon as possible. • Inspections shall be performed at least twice a year,or after a major storm event which is defined as a storm that is equal to or greater than the 2-year storm event. • During these inspections,record and map the following information; -The presence of accumulated trash and/or debris, -The presence of dead vegetation and/ or invasive species (invasives must be removed), -Stability of the sideslopes and berms, -Accumulation of sediment, -SurvivaI rate of plantings(dead plantings must be replaced) The following BMPs shall be utilized to minimize impacts to wetland resource areas: Grassed Drainage Channel: • Inspect the grass channel semi-annually the first year and at least once a year thereafter. • Frequently removing accumulated sediments will make resuspension less likely. Sediment build-up in the grass channel reduces the capacity to treat and convey the water quality event,2-year and 10-year 24-hour storm. • Stabilize the floor and sidewalls before making it operational to avoid excess amounts of suspended sediments. Check on a yearly basis and clean as needed. Use hand methods when cleaning to minimize disturbance to vegetation and underlying soils. 4 Operation &Maintenance Plan #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 • Keep the grass no lower than three (3) to four (4) inches but no higher than six (6)inches. Remove accumulated trash and debris prior to mowing. • Inspect for signs of rilling and gullying and repair as necessary. • Replace any vegetation damaged during the clean-out by either reseeding or resodding. If grass grown is impaired by winter road salt or other deicer use,re-establish grass in the spring. • If reseeding,utilize practices such as hydroseeding with a tackifier,blanket,or similar practice to ensure that no scour occurs in the forebay and allow the seeds to germinate and develop roots. Parking Lot Street Sweeping • Street sweeping will be conducted four times annually within the parking lot area. Special attention will be given to the spring(March or April) and late fall (November or December). Snow Removal: • Snow will be removed from the parking area and sidewalks during snow events. The snow will be stockpiled in the designated"Snow Storage Area"locations as shown on the site development plan set. • Provisions will be made to remove snow from the site when the designated areas have reached their capacity. Rain Garden Outlet: • The rain garden outlet will be inspected during and after several storms(e.g. 0.5-inch or greater) and maintenance performed if necessary during the first year of operation. Thereafter,inspections and preventative maintenance shall be performed at least twice a year or after a major storm event which is defined as a storm that is equal to or greater than the 2-year,24-hour storm (3.1 inches in a 24 hour storm). Rip Rap Emergency Spillway&Level Spreader: • The emergency spillway and level spreader will be inspected during and after several storms (e.g.0.5- inch or greater) and maintenance performed if necessary during the first year of operation.Thereafter, inspections and preventative maintenance shall be performed at least twice a year,and after every time drainage discharges through the high outlet orifice or a major storm event which is defined as a storm that is equal to or greater than the 2-year,24-hour storm(3.1 inches in a 24 hour storm). • Any detrimental sediment accumulation shall be removed. • If rilling is present downgradient or adjacent to the emergency spillway or level spreader the damage shall be repaired. • Leaf litter shall be removed from the emergency spillway or level spreader area. 5 Operation & Maintenance Plan #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev, December 29, 2015 • Vegetation in the vicinity of the emergency spillway and level spreader shall be inspected periodically and if needed,fertilized to maintain healthy,dense growth. The estimated annual budget for maintenance of the BMP's is approximately$2000. 6 Operation& Maintenance Plan #2302 Turnpike Street, North Andover, MA November 4,2015 Rev, December 29, 2015 INSPECTION AND MAINTENANCE REPORT FORM #2302 TURNPIKE STREET NORTH ANDOVER, MA 01846 TO BE COMPLETED FOR REQUIRED INSPECTIONS AND MAINTENANCE SEE ABOVE FOR FREQUENCY OF INSPECTIONS AND MAINTENANCE Name of Inspector: Date: Inspector's Company/Affiliation: Days Since Last Rainfall: Amount of Last Rainfall: gg,, :y •�; d� o%r..` t., e ati " �` �,,, '�..���„�,,g x�z t -_�: �, '. .��ix hc��,. , s�. `' poor r yes - no yes - no fair ra good poor yes - no yes - no fair ._ good poor .r S yes - no yes - no fair good u. poor yes - no yes - no fair _ :rgood 3 poor ' yes - no yes - no fair Rood a - poor yes - no yes - no T __ fair good Maintenance Required: To Be Performed By: On or Before: 7 Operation& Maintenance Plan #2302 Turnpike Street, North Andover, MA November 4,2015 Rev. December 29, 2015 INSPECTION AND MAINTENANCE REPORT FORM #2302 TURNPIKE STREET NORTH ANDOVER, MA 01845 TO BE COMPLETED FOR REQUIRED INSPECTIONS AND MAINTENANCE SEE ABOVE FOR FREQUENCY OF INSPECTIONS AND MAINTENANCE Name of Inspector: Date: Inspector's Company/Affiliation: Days Since Last Rainfall: Amount of Last Rainfall: .\� � .""L� . =r` ���.� i�..2. q� ,� '�� .se�A]�.�� yr r`�{,a7�' },...i� � �Y f .v-ov �♦ m;. �i,�.}}' tw 1; -Yqy � �i-i FS , M � �a, ,u -L_4 •ahp { L'x ,�• � t' Y sF •�,T _ ti� � x"�iT r� �1 �.} '� F�'r'x�ySS �!��5�� � ��1��' -,. \..2� �5.'U}•'�'� },. >.. S- A•� •�C';e.�s'z,+'z� s' .. �<a\''9raNi ^,"", r'`-,. ,.zt:,.,,R ux O7' .� .Y{ �Ha X.• Ohl if_i minor/moderate/major sc� 1-M minor/moderate/major minor/moderate/major minor/moderate/major 1. 11001 �v Maintenance Required: To Be Performed By: On or Before: 8 Operation & Maintenance Plan #2302 Turnpike Street, North Andover, MA November 4, 2015 Rev. December 29, 2015 INSPECTION AND MAINTENANCE REPORT FORM #2302 TURNPIKE STREET NORTH ANDOVER, MA 01845 TO BE COMPLETED FOR REQUIRED INSPECTIONS AND MAINTENANCE SEE ABOVE FOR FREQUENCY OF INSPECTIONS AND MAINTENANCE Name of Inspector: Date: Inspector's Company/Affiliation: Days Since Last Rainfall: Amount of Last Rainfall: f. '� 3����.. � c2y1s'''yR[•i ._v�A?i4fi .�,. �� �, �{y�•- A,- ..>.,,g i�.aH-�,��1�$f �''`- "?'u'}�e'�"x t'lti=,�,�' t.,�'�;ki?,ter 1-:,zx \. y� } �„ � � �'•ty' ,ram ••-�+ �� ry-`a F'"2 w*�'F.-. >:�wa� 'f�, -• ..� ,��.^.e{., -_...K !�� t � .r. �gy�v ;� ti. i� 1 •ij{Ch n n�:f ��"3t��`i 5+t�`'y`"r��� poor/fair/good minor/moderate/major poor/fair/good minor/moderate/major a��A` `i ..h 4 L's^�•0 4.t�� �.. poor/fair/good minor/moderate 1 major F _ poor/fair/good minor/moderate/major • s Maintenance Required: To Be Performed By: On or Before: 9 Operation &Maintenance Plan #2302 Turnpike Street, North Andover, MA November 4,2015 Rev. December 29, 2015 INSPECTION AND MAINTENANCE REPORT FORM #2302 TURNPIKE STREET NORTH ANDOVER, MA 01845 TO BE COMPLETED FOR REQUIRED INSPECTIONS AND MAINTENANCE SEE ABOVE FOR FREQUENCY OF INSPECTIONS AND MAINTENANCE Name of Inspector: Date: Inspector's Company/Affiliation: Days Since Last Rainfall: Amount of Last Rainfall: { p ' '#. k z ff r x E._` •., rr ay:.. ''si h� °may i _ �, � ��'` � ,�..-&ice g � _'��° .� .i -•, �� C� , ;�.,2�i5� Y,�C�`a�� �+<;"�i E.f ��. "' •} - ' �L* � ° . 1t .� } _ �- �I �.a 4' �` tc#= a� '� :-;•' ` .'�'�} u ��k�i±R'�,�k�-x�?F1;+ s%� ::����A � .,irk. ,..b�i,���„`�L-a M-i'i'.R"�_�C».y?.�� ` Em Al WI .. - minor/ moderate/major . minor/moderate/major minor/moderate/major minor/moderate/major w. 4F Maintenance Required: To Be Performed By: On or Before: 10 CKWta �_ - .a SKETCH PLAN 1 1 1 I IN IDDLET SCALE: 1"=20' DATE:JANUARY 11,2016 Rev.March 8,2016 - "SHOWING BMF5 TO BE MAINTAINED" DHIIN�CE \ cwwrm. + r 6 _ 4 z Siq SfOPtGE } RD RD �d r _ -�'o ; I D_ W - EL Z ID I _ � 1 t � NEFLS p p JBUC� k 3/21/2016 Town of North Andover Mail-2302 Turnpike St .... 7,4f ._.. __ NORTH A D,C0VER Massachusetts Rebecca Oldham <roldham@northandoverma.gov> 2302 Turnpike St Lisa Eggleston <lisa@egglestonenvironmental.com> Fri, Mar 18, 2016 at 1:21 PM To: "Enright, Jean" <JEnright@townofnorthandover.com>, Jennifer Hughes <Jhughes@townofnorthandover.com>, Rebecca Oldham <roldham@northandoverma.gov> Cc: Chris Sparages <csparages@wsengineers.com> Jean, Just letting you know that I have received and reviewed the March 3rd response letter and March 8th revised plan set and drainage analysis for the proposed Earth Works project at 2302 Turnpike Street. I also had a telephone conversation on March 9th with representatives of Williams & Sparages to discuss my March 2nd comments and their response. The March 8th plans reflect only minor revisions to the outlet design for the proposed rain garden. The revised drainage analysis uses a more conservative design infiltration rate consistent with the mapped soils, and satisfactorily demonstrates compliance with Stormwater Standard #2. An O&M sketch plan was also included in the response. At this time, all of my previous comments have been satisfactorily addressed and I have no further comments on the stormwater design. Please let me know if you have any questions or need anything else. Lisa D. Eggleston, P.E. Eggleston Environmental 32 Old Framingham Rd, Unit #29 Sudbury, MA 01776 Tel 508.259.1137 https:Hmail.googl e.com/mail/?ui=2&i k=ab4f3cb798&view=pt&search=i nbox&m sg=1538a8881572f506&si m l=1538a8881572f506 1/1