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HomeMy WebLinkAbout2012-09-04 Planning Board Supplemental Materials (25) Eggleston Environmental 32 Old Framingham Rd Unit 29 Sudbury MA 01776 tel 508.259.1137 fax 866.820.7840 August 20, 2012 North Andover Planning Board 1600 Osgood Street North Andover, MA 01845 Attn: Judy Tymon, Town Planner RE: Watershed Special Permit Review 0 Great Pond Road Dear Ms. Tymon and Board Members: Per your request, I have conducted a technical review of the August 7, 2012 Watershed Special Permit Application packet for the above-referenced project, prepared by Sullivan Engineering Group, LLC on behalf of David and Corliss Paolino. The proposed project entails the construction of a single family home on a presently undeveloped lot, a portion of which is in the Non-Disturbance Zone of the Watershed District since it is within 100 ft of a wetland resource area within the watershed. The lot was created prior to October 24, 1994. My comments on the application are outlined below: 1. The only soil data included with the application was the log from a single test pit excavated at the proposed roof drywell location, which indicated that the subsurface soil is a sandy loam. The design of the infiltration structures should therefore be based on the hydraulic conductivity characteristic of sandy loam, or about 1.02 in/hr per the DEP Stormwater Handbook and 1982 “Rawls” table. Percolation tests tend to underestimate the saturated hydraulic conductivity and should not be used to design stormwater systems. 2. Additional soil tests will be needed in the vicinity of the porous pavement driveway prior to installation to verify soil suitability in that location, and the area where the old stone foundation is to be removed will need to be filled with suitable subgrade material. 3. The stone surround for the drywell should be modeled as a 12’D x 4’H cylinder, not a 12’ x 12’ x 4’ bed. 4. The proposed roof drywell is to be set partially in fill, and is less than 10 feet away from a 3.5 foot drop in grade at the retaining wall. The design plans should specify the nature of the fill material to be used, and a means to prevent breakout of infiltrated flow. 5. Filter fabric should be used on the top and sides only of the roof infiltration system. Placement of the fabric on the bottom of the excavation can lead to system failure. 0 Great Pond Rd, Technical Review 2 August 20, 2012 6. The application indicates that the roof drainage from the front portion of the house will be directed to the stone reservoir beneath the porous pavement, and that is how the system is modeled. However there is no roof drain connection shown on the plans and it is not clear how this roof drainage would be distributed within the driveway subbase. 7. The limit of work, including vegetation clearing, should be shown on the site plan per the Special Permit requirements, and the proposed landscaping should be described. I recommend that the creation of new lawn area be limited to that which is absolutely necessary, and that any new landscape area 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 clearing and the restriction on lawn care products should be permanently recorded on the deed to the property. 8. The porous asphalt should specify polymer modified performance grade asphalt binder (PGAB). 9. The O&M Plan for the porous pavement should call for regular (e.g. annual vacuuming) in order to prevent clogging. It should also specifically prohibit sealcoating. 10. In order to preserve the infiltration capacity of the porous asphalt driveway and provide stormwater management during construction, I recommend that the sequencing plan developed by the UNH Stormwater Center be utilized. This would entail installing the driveway subbase with a two-inch overfill at the outset of construction, then removing the overfill (and the sediment and fines trapped within it) once the site is stabilized. The subbase should then be inspected for compaction and infiltrative capacity and, if necessary, scarified to the depth required prior to placement of the porous asphalt layer. 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 Lisa D. Eggleston, P.E.