02/24/2004 ZONING BOARD OF APPEALS Minutes

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41kCharles L. -Rowley & Associates CIVIL EN13INEERS & SURVEYORS SITE EVALUATION LAND SURVEYING SITE DESIGN ENVIRONMENTAL CONSTRUCTION LAYOUT TITLE 5 DESIGN 9 CRANBERRY HIGHWAY TEL:(508)295-0545 •OFFICE BOX 9 FAX:(508)295-1 192 aST WAREHAM,MA 02576 May 12, 2004 Town of Mashpee Zoning Board of Appeals Town Hall 16 Great Neck Road North Mashpee, MA 02649 Re: Site Plans for Volta Oil Co. 414 Nathan S. Ellis Highway Dear Board Members: I am in receipt of a set of site plans and drainage calculations prepared by Norfolk Ram Group, LLC, Engineers, Plymouth, MA dated 4/25/03 and December 2003 respectively. You have requested a review of the documents and an opinion of the scope of the project. The project is a reconstruction of an existing service station on Route 151. An existing building is to be demolished and removed and will be replaced by a new structure in the location shown on the plans. The existing gasoline dispensing island and storage tanks are to remain. The site impervious cover will be extended and site drainage has been included with the design. The extent of increase in impervious surfaces is approximately 46%, from 14,995 s.f. to 21,825 s.f. Drainage Calculations A set of drainage calculations was completed for the project using acceptable methods, however there are some basic concerns about the calculations and some assumptions that were made that may influence the end result. Assumptions made: 1. That the underlying soil has a percolation rate of 2 minutes per inch. No percolation tests were done on the site. 2. That the ground water depth at the site is 13 feet below the ground surface. The depth of 13 feet is an average depth that is cited on page 2 of a Phase III Remedial Action Plan dated June 29, 2001. The Action Plan was prepared by Corporate Environmental Advisor, Inc. of West Boylston. Ground water depths below grade varied from a minimum of 10.38 in April of 1998 to a maximum of 15.34 in August of 1999. According to the report monitoring wells were installed to check the ground water levels. Both of these assumptions may influence the design in a negative way if actual testing of conditions show other results. A 3' separation was used between the average ground water depth and the bottom of the proposed leaching facilities of the stormwater system. If the minimum ground water depth is used, the facilities would be sitting at or in the ground water. A wetland line is shown on the plans to the east of the site. Is there any correlation between the ground water depths and seasonal high ground water that may be in this wetland area? The plan also indicates that test pits were dug in this area. Are they available to substantiate the assumption of a percolation rate of 2 minutes per inch?