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C, TRIMARK camp APR 2720po. llty GE�'EibF,.iiciq`c Nt. April 26, 2000 Mr. Chandler Martin, Senior Planner SAN JOAQULN COUNTY COMNIUNITY DEVELOPMENT DEPARTMENT Planning Division 1810 East Hazelton Avenue Stockton, CA 95205 -6232 RE: ADT Auto Auction Use Permit - Impacts from Diverted Storm Water Runoff from Existing and Proposed Improvements at the Patterson Pass Business Park, San Joaquin County, California. Dear Chandler: As you are aware, a recently submitted report entitled, Storm Drainage Study, for ADT Automotive Wholesale Auction, Tracy California, dated February 1, 2000, prepared by Kier & Wright, has been submitted to the County and Trimark Communities for review. Our review of the report has raised serious concerns regarding storm water runoff conditions at the South Patterson Pass Business Park. Our concerns stem from the fact that the study shows that Storm water conditions, both existing and proposed, differ from adopted studies and plans done for both the Patterson Pass Business Park project(Site)dating back to 1994, as well as adopted studies and assumptions within the Mountain House Master Plan, Final EIR, Specific Plan I from 1994 and CSD Storm Water Master Plan, approved in 1999. Specifically, the ADT Storm Drainage Study indicates that the existing peak flow leaving the Site in the approved initial development (80 acres) exceeds the Site pre-development peak flow, and diverts additional watersheds toward Mountain House. According to the Lion & King Storm Water Study (Bissell &Kams, 1994), development of the initial 80-acre business park would not increase off-site peak flow. The ADT Storm Drainage Study shows that an existing detention basin was modeled as a pass- through basin, since it currently does not have a low flow outlet as proposed in the Lion & King Storm Water Study. The ADT study proposes to increase the basin to 30-acre feet, but does not include a low flow outlet. This lack of low flow outlet does not allow the basin to be used as a BMP basin for storm water treatment. Based on our direct discussions with Kier & Wright, a portion of the auto action site will use grass-lined swales to provide BMP storm water treatment. Such treatment methods should be reviewed to determine whether they are suitable for the proposed development. We strongly urge the County to require existing, proposed, and future development of the business park to bring the peak flows leaving the Site back down to their pre-development rate, and to meet the same level of BMP storm water treatment required of the Mountain House Community, by the County. Failure to address and resolve these issues will cause significant storm drainage, water quality and economic impacts to the Mountain House Community, as well as substantial delays in 3120 Tracy Boulevard Suite A Tracy,California 95376 209 836-1560 Telephone 209 836-1759 Fax