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HomeMy WebLinkAbout2013-07-16 Planning Board Supplemental Materials (42) Eggleston Environmental 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 fax 866.820.7840 July 15, 2013 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tymon, Town Planner North Andover Conservation Commission 1600 Osgood Street North Andover, MA 01845 Attn: Jennifer Hughes, Conservation Coordinator RE: Butcher Boy Marketplace, 1077 Osgood Street Stormwater Management Review Dear Ms. Tymon, Ms. Hughes and Board Members: Per your request, I have reviewed the June 26, 2013 Response to Comments and revised plans and calculations submitted by Lynnfield Engineering for the proposed Pentucket Bank at the Butcher Boy Marketplace (1077 Osgood Street), with respect to stormwater management. My comments on the revised submittal are summarized below: 1. The HydroCAD report for proposed conditions that was included in the revised submittal does not include the invert, structure and pipe size data necessary for me to verify the calculations with respect to the rate and volume of runoff from the site. 2. The proposed plan relies on flow attenuation in subsurface structures for all design storms, however it is not clear that the drainage system delivering the runoff to the subsurface structures has been designed to convey the 100-yr event, or that the drainage system downgradient of the site has the capacity to accommodate the increased flow volume. 3. While the revised plan does call for recharging the roof runoff from the proposed bank building, it does not compensate totally for the loss of recharge r epresented by this project as the roof represents only a fraction of the added impervious cover on the site and the calculations do not account for capture area. The Watershed Protection District regulations (Section 4.136(4)(g) of North Andover Zoning Bylaw) do require that the runoff from impervious surfaces be recharged onsite to the maximum extent practicable. This is particularly important for this site since much of the surface runoff would also be diverted away from the Lake Cochichewick watershed under proposed conditions. While the soils within the project area are relatively poorly draining HSG C soils, the existing topography of the area and the surface detention basin likely enhance the amount of recharge that currently occurs. As stated in my April 10th review comments, consideration should be given to providing compensatory recharge elsewhere on the Butcher Boy site, a Butcher Boy Marketplace, Stormwater Review 2 July 15, 2013 large portion of which is outside of the Zone A but still within the Lake Cochichewick watershed. 4. The proposed roof infiltration systems will be located mostly in fill, and one system within the stone-lined footprint of the existing detention basin. The plans should specify the type of fill to be used on the site and should call for removal of unsuitable material beneath the systems. Confirmatory testing will also be needed to verify the soil type and depth to groundwater in proposed infiltration areas. 5. The roof infiltration units should be set back as far as possible from the retaining walls in order to prevent breakout of infiltrated flow. 6. The architectural plans appear to show metal roof and/or roofing elements on the bank building; runoff from metal roofs (galvanized steel or copper) cannot be infiltrated within the Zone A. 7. Overflow from the roof infiltration systems should not discharge through the proposed CDS units in order to maximize their effectiveness for treating pavement runoff. 8. The proposed treatment train for the pavement runoff on the site is comprised of deep sump catchbasins, in-line hydrodynamic separators, and subsurface “extended detention basins”. The TSS removal calculations claim 80 percent TSS removal in the CDS hydrodynamic separators, based on the predicted removal rates provided by the manufacturer. The DEP Handbook calls for proprietary separators to be used only as pretreatment devices and only in an off-line configuration. Since Massachusetts has not established TSS removal rates for the devices, the Handbook encourages Conservation Commissions to rely on other studies such as the NJCAT one referenced on the MASTEP Technology Review website to determine likely removal rates. The NJCAT study, conducted using modified TARP protocols, resulted in a certified TSS removal rate for the CDS units of 50 percent. Based on my recent conversations with Tom Maguire, the Regional Consistency Coordinator for MaDEP, the expected removal rates for these units in the field may be substantially less than even the 50 percent assigned by NJCAT. 9. The proposed “extended detention basins” appear to be designed specifically for purposes of flow attenuation and not for water quality treatment. As subsurface structures they are not at all consistent with the design guidelines for extended detention basins in the DEP Handbook, which call for above-ground basins with sediment forebays, vegetation and low flow channels to facilitate pollutant removal. The DEP Handbook does not grant any TSS removal credit for subsurface detention structures except when they also provide infiltration. I would also add that the 80 percent TSS removal requirement for this site should be provided upgradient of the proposed subsurface detention structures as any sediment that does accumulate in the subsurface systems will be difficult to remove. Butcher Boy Marketplace, Stormwater Review 3 July 15, 2013 10. DMH3 and DMH5 are outlet control structures and should be labeled as such on the plan (or the OCS detail should identify the structure numbers). 11. Similarly, WQ1 and WQ2 should be labeled as to which model CDS unit they pertain to. 12. The Grading and Drainage Plan (Sheet C-6) needs to show the re-grading of the landscaped area to the northwest of the proposed parking area, where the existing detention basin will be filled in. 13. It is not clear whether the silt fence line on the Erosion & Sediment Control Plan delineates a Limit of Work, as is called for in the Zoning Regulations. I note that the Landscape plan appears to call for tree planting and loaming and seeding in areas outside of the silt fence. 14. New landscaped areas should be constructed in such a manner as to minimize the maintenance that is required, e.g. the soil should be well aerated, it should have a minimum of 6-inches of topsoil and, where possible, native vegetation should be planted to minimize the need for fertilizer and watering. As with similar projects permitted within the Watershed Protection District, both the limits of approved work and the restriction on landscaping chemicals to be used on the site should be permanently recorded on the deed to the property. 15. I did not receive a copy of the Watershed Special Permit application and am unable to verify that a written certification by a professional engineer stating that the project will not cause any significant degradation in the quality or quantity of water in or entering Lake Cochichewick was included. I have also not seen evidence that the applicant has submitted proof that there is no reasonable alternative outside of the Non-Discharge Zone for the proposed project, or components thereof, to occur, as is required by the Zoning Regulations. 16. I have the following comments on the revised O&M Plan:  Other than the name, it is not clear that the revised O&M plan is intended to apply to the entire Butcher Boy Marketplace property, as is suggested in the Response to Comments. The plan should identify all stormwater BMPs to be maintained on the site (including a map showing their locations) and should identify specific measures aimed at improving existing conditions.  Catchbasins and hydrodynamic separator units should be cleaned a minimum of once per year, with a vacuum truck.  It is unclear which detention system the O&M Plan refers to – the roof infiltration systems or the “extended dry detention systems”. The O&M Plan does not call for sediment removal from the systems, as would be required for the “extended dry detention systems, and the attached manufacturers O&M guidelines are for Cultec units, similar to the Stormtech units specified for the roof infiltration systems. Butcher Boy Marketplace, Stormwater Review 4 July 15, 2013  The O&M Plan refers to designated snow storage locations shown on the plan, but I could not find any such locations identified on the plans. To the maximum extent possible, snow storage should be located outside of the Zone A and upgradient of stormwater BMPs; untreated meltwater from plowed snow should not be infiltrated within the Zone A, and particularly not within the Non-Discharge Zone. Once again, I appreciate the opportunity to assist the North Andover Conservation Commission and 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 Lisa D. Eggleston, P.E.