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ENVIRONMENTAlL HEALTH DEPARTMENT <br /> POU'N SAN JOAQUIN COUNTY Unit Supervisors <br /> Donna K.Heran,R.E.H.S. Third Floor Carl Sgins,R. R.E.H.S. <br /> m < Director <br /> 344 East Weber Avenue, Mike Huggins,R.E.H.S.,R.D.1. <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> �•-_`.•'w g <br /> 4�iFORr� Laurie A.Cotulla,R.E.H.S. Fax: (209) 464-0138 Robert McCiellon,R.E.H.S. <br /> Program Manager Mark Barcellos,R.E.H.S. <br /> MAY 3 D 20 <br /> THRIFTY OIL COMPANY <br /> RAYMOND FRIEDRICHSEN <br /> 131.16 IMPERIAL HWY PO BOX 2128 <br /> SANTA FE SPRINGS CA 90670 <br /> RE: Thrifty Gas Station #171 SITE CODE: 1299 <br /> 1250 N. Wilson Way RO#: 0000552 <br /> Stockton, CA. 95205 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed "Additional <br /> Site Assessment Work Plan" (WP) dated February 25, 2003, submitted by Thrifty Oil <br /> Company (TOC) on February 28, 2003. The work plan addresses directives contained <br /> in EHD correspondence dated August 13, 2002. Included in the work plan were TOC <br /> responses to EHD comments. EHD has reviewed the site history and data, and <br /> comments as follows on TOC's responses as numbered in the WP. <br /> 1. Vertical Delineation: Petroleum impacted soil has been encountered at the known <br /> historical greatest depth to groundwater between 75 and 80 feet below ground surface <br /> ('bgs), in borings advanced for installation of monitoring wells MW-3 thru MW-6. Soil <br /> samples from greater depth have not been collected or analyzed for vertical delineation. <br /> TOC cites a 15-foot clay interval (75 to 90 feet bsg) as providing an effective barrier to <br /> deeper contaminant migration. EHD believes the hypothesized barrier has not been <br /> adequately demonstrated. EHD concerns are base on the following data: <br /> • Of the four borings to 90' bgs, only the 90-foot samples were consistently <br /> described as clay; <br /> • 85-foot samples were not collected from any borings, thereby creating a nearly <br /> 10-foot data gap in the purported 15-foot clay interval; <br /> • The four 80-foot samples were described as 1) clay grading to silt, 2) clayey <br /> sand, 3) pebbly clay and 4) silt, and <br /> • While two of the four 75-foot samples are described as clay, the other two are silt <br /> and clayey sand. <br />