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HomeMy WebLinkAbout20141118 Peer Reviews Eggleston Environmental October 16, 2014 North Andover Planning Board 1600 Osgood Street North Andover,MA 01845 Attn: Matthew Egge, Town Planner RE: Stormwater Review 85 Terminal Road,North Andover Dear Mr. Egge and Board Members: Per your request, I have reviewed the September 19, 2014 Special Permit - Site Plan Review Application packet for the above-referenced project. Included in the materials I received and reviewed were the following: ■ Site Development Plans, Map 75 Lot 0000.13, 85 Terminal Road, North Andover MA, (10 Sheets),prepared by Meridian Associates and dated 9/19/14. ■ Stormwater Management Report for 85 Terminal Road, North Andover, MA, prepared for Great Circle Central, LLC by Meridian Associates and dated 9/19/14. ■ Special Permit — Site Plan Review Application for 85 Terminal Road, Great Circle Center, LLC c/o Glovsky& Glovsky, LLC,petitioner, dated 9/19/14. 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 project site is an area of land at the Lawrence Municipal Airport, located to the northeast of the FAA Control Tower and adjacent to the airport runway. The site is currently undeveloped and drainage is overland. The proposed project calls for construction of a 17,388 square foot airplane hangar, a 30 ft wide taxiway and a paved parking area for 10 vehicles on a proposed 48,800 sf leased lot, to be accessed by a new paved driveway off Terminal Road. As proposed, runoff from the parking lot and taxiway will be collected in a closed drainage system with deep sump catchbasins and discharged to a subsurface infiltration system onsite. Roof runoff from the new building will also be discharged to the subsurface infiltration system. Runoff from the new access driveway will drain across turf filter strips to infiltration trenches along the sides of the driveway. 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 f 85 Terminal Road, Stormwater Review 2 October 16, 2014 My comments on the proposed plan are outlined below: 1. Overall, the proposed plan uses a low impact drainage design that maintains existing drainage patterns and controls runoff from the site. While the Site Plan Review regulations require only that the rate and volume of runoff from the site be mitigated, the proposed project also provides for treatment of pavement runoff in a manner consistent with the Massachusetts Stormwater Standards and good design practice. 2. The Site Plan Review regulations require that there be no increase in the rate or volume of stormwater runoff from the post-development site for up to and including the 100-yr design storm event. The hydrologic analysis included in the Stormwater Management Report does indicate that there would be a net decrease in both the rate and volume of runoff to both design points under post- development conditions, however the analysis is based on an assumed.infiltration rate of 1.02 in/hr; at the high end of the range for Hydrologic Soil Group (HSG)B soils. The NRCS soil map indicates that soils on this site are Paxton fine sandy loams, and the soil testing conducted on the site appears to confirm this. These soils are classified as HSG C, thus the design infiltration rate per the Rawls table referenced should be no more than 0.27 in/hr. The proposed infiltration systems are therefore undersized. 3. The roof of the new building should not be modeled as "disconnected" in the HydroCAD analysis since the roof drainage is piped directly and does not run off over pervious surfaces. 4. The test pit elevations for TP14-4 listed on Sheet 10 under "Soils Information" appear to be off by 10 feet; I believe the existing grade at that location should be about 150.3 feet and the ESHGW elevation below 140.4. This should be verified, as TP14-4 is the only test pit conducted in the proposed infiltration system location and the higher groundwater elevation would not be consistent with the proposed design. 5. To the extent that the attenuation of runoff flow from the site is to be provided in subsurface structures it will need to be demonstrated that the conveyance system is sized accordingly, e.g. for the 100-yr storm. Alternatively, the analysis needs to address how flow in excess of the conveyance capacity will be handled. 6. The design detail for the subsurface infiltration facility should show at least two inspection ports brought to grade. 7. I recommend beehive grates on the catchbasins to be located in grassed areas, to prevent clogging. 85 Terminal Load, Stoirnwater review 3 October 16, 2014 8. The Construction Stormwater Pollution Prevention Plan (SWPPP) should include a construction sequence aimed at minimizing the amount of disturbance on the site and protecting proposed infiltration areas. The proposed soil stockpile location should also be shown on the plan. 9. It appears that the proposed project will entail the disturbance of more than an acre of land and will therefore require coverage under the EPA Construction General Permit (CGP). This should be noted on the plan. Coverage will require implementation of the SWPPP and filing of an NOI by the site contractor certifying that they have met the eligibility requirements and will comply with the permit's effluent limits and other requirements. The Planning Board should also be provided with evidence of the filing prior to the start of construction. 10. I have the following comments on the O&M Plan included with the submittal: ■ The Plan lists Windover Construction as the parry responsible for maintenance. It should be clarified whether this is the parry that will be responsible for the long-term (post-construction) maintenance of the proposed BMPs. ■ The subsurface infiltration system should be inspected on a semi-annual (twice per year)vs. bi-annual(once every two years)basis. ■ Deep sump catchbasins should be cleaned a minimum of once per year. ■ The good housekeeping measures outlined in the plan should be specific to the proposed operation of the site and should address issues such as washing and/or deicing of airplanes. I appreciate the opportunity to assist the North Andover Planning Board 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 56 Lisa D. Eggleston, P.E. MERIDIAN ASSOCIATES VIA: HAND DELIVERY November 10, 2014 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Matthew Egge,Town Planner Re: Stormwater Review 85 Terminal Road, North Andover Dear Mr. Egge and Board Members: We have reviewed the letter from Eggleston Environmental dated October 16, 2014 and have made the revisions to the plans and Stormwater Management Report. Please see below for responses to the review comments: 1. Overall, the proposed plan uses a low impact drainage design that maintains existing drainage patterns and controls runoff from the site. While the Site Plan Review regulations require only that the rate and volume of runoff from the site be mitigated,the proposed project also provides for treatment of pavement runoff in a manner consistent with the Massachusetts Stormwater Standards and good design practice. Response: No comment. 2. The Site Plan Review regulations require that there be no increase in the rate or volume of stormwater runoff from the post-development site for up to and including the 100-yr design storm event. The hydrologic analysis included in the Stormwater Management Report does indicate that there would be a net decrease in both the rate and volume of runoff to both design points under post-development conditions, however the analysis is based on an assumed infiltration rate of 1.02 in/hr; at the high end of the range for Hydrologic Soil Group (HSG) B soils. The NRCS soil map indicates that soils on this site are Paxton fine sandy loams, and the soil testing conducted on the site appears to confirm this. These soils are classified as HSG C,thus the design infiltration rate per the Rawls table referenced should be no more than 0.27 in/hr. The proposed infiltration systems are therefore undersized. Response: The exfiltration rate for all the infiltration facilities has been revised to 0.27 in/hr. This substantially increased the size of the subsurface infiltration facility near the existing taxiway. 500 Cummings Center,Suite 5950 Beverly,Massachusetts 01915 P:(978)299-0447 F:(978)299-0567 www.meridiaiiassoc.com 85 TERMINAL ROAD NORTH ANDOVER, MA Page 2 of 3 3. The roof of the new building should not be modeled as "disconnected" in the HydroCAD analysis since the roof drainage is piped directly and does not run off over pervious surfaces. Response: The roof is no longer modeled as "disconnected" in HydroCAD. 4. The test pit elevations for TP14-4 listed on Sheet 10 under "Soils Information" appear to be off by 10 feet; I believe the existing grade at that location should be about 150.3 feet and the ESHGW elevation below 140.4. This should be verified, as TP14-4 is the only test pit conducted in the proposed infiltration system location and the higher groundwater elevation would not be consistent with the proposed design. Response: The test pit information has been verified and revised on sheet 10. 5. To the extent that the attenuation of runoff flow from the site is to be provided in subsurface structures it will need to be demonstrated that the conveyance system is sized accordingly, e.g. for the 100-yr storm. Alternatively,the analysis needs to address how flow in excess of the conveyance capacity will be handled. Response: Storm drain system calculations have been provided that demonstrates no surcharging will occur at any of the manholes or catchbasins for the 100 year storm event. 6. The design detail for the subsurface infiltration facility should show at least two inspection ports brought to grade. Response: The plan view and section view for the infiltration facility on sheet 10 shows two observation ports brought to grade. 7. 1 recommend beehive grates on the catchbasins to be located in grassed areas, to prevent clogging. Response: A note has been added to the catchbasin detail on sheet 9 stating beehive grates shall be installed for the catchbasins in the grass areas. 8. The Construction Stormwater Pollution Prevention Plan (SWPPP) should include a construction sequence aimed at minimizing the amount of disturbance on the site and protecting proposed infiltration areas. The proposed soil stockpile location should also be shown on the plan. Response: A construction sequence has been added to sheet S. 85 TERMINAL ROAD NORTH ANDOVER, MA Page 3 of 3 9. It appears that the proposed project will entail the disturbance of more than an acre of land and will therefore require coverage under the EPA Construction General Permit (CGP). This should be noted on the plan. Coverage will require implementation of the SWPPP and filing of an NOI by the site contractor certifying that they have met the eligibility requirements and will comply with the permit's effluent limits and other requirements. The Planning Board should also be provided with evidence of the filing prior to the start of construction. Response: A note has been added to sheet 5 that states that the project will require coverage under the EPA Construction General Permit (CGP). 10. 1 have the following comments on the O&M Plan included with the submittal: • The Plan lists Windover Construction as the party responsible for maintenance. It should be clarified whether this is the party that will be responsible for the long-term (post construction) maintenance of the proposed BMPs. • The subsurface infiltration system should be inspected on a semi-annual (twice per year) vs. bi-annual (once every two years) basis. • Deep sump catchbasins should be cleaned a minimum of once per year. • The good housekeeping measures outlined in the plan should be specific to the proposed operation of the site and should address issues such as washing and/or deicing of airplanes. Response: Windover Construction will be the party responsible for the post construction maintenance of the proposed BMPs. The subsurface infiltration system will be inspected on a semi-annual basis. Deep sump catchbasins will be cleaned twice per year, or when sediment in the bottom of the sump reaches 24 inches below the bottom of the outlet. A new section has been added for airplane washing and deicing controls. Please feel free to contact me with any questions or comments. Sincerely, MERIDIAN ASSOCIATES, INC. A-- Christopher J. Rokos, PE Senior Project Engineer cc: Lisa Eggleston, PE P:\5659_Windover-Lawrence Airport\ADMIN\Letters_Memos\planning_response141107_Eggleston.doc