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URS <br /> December 22 2005 Z00 <br /> Ms. Victoria McCartney ��It� 05450 <br /> San Joaquin County Environmental Health Department 06.0 <br /> 304 E. Weber Street,Third Floor <br /> Stockton, California 95202 <br /> Re: Site Closure Report <br /> ARCO Service Station 5450 <br /> 1617 West Fremont Street,Stockton, California <br /> Dear Ms. McCartney: <br /> URS Corporation Americas (URS), on behalf of Atlantic Richfield Company (ARCO — a BP-affiliated <br /> company), has prepared this site closure report for the ARCO Station and AM/PM Mini-mart No. 5450 <br /> ' located at 1617 West Fremont Street, Stockton, California (site). This report was prepared at the request <br /> of the San Joaquin County Environmental Health Department (SJCEHD) in the letter dated September <br /> 15,2005 (Attachment A). <br /> This report contains the following information: site background, remediation, contaminant mass <br /> remaining and distribution, future impact on groundwater and maximum plume extent, sensitive <br /> receptors, and conclusions and recommendations. <br /> SITE BACKGROUND <br /> The site is located at 1617 West Fremont Street, near the intersection of West Fremont Street and North <br /> Pershing Avenue, in Stockton, California. The site is an operating gasoline station and AM[PM mini- <br /> mart. Currently, site facilities include three gasoline underground storage tanks (USTs) and associated <br /> product lines and dispensers. <br /> Site Geology and Hydrogeology <br /> As a result of drilling activities at the site, the subsurface geology has been documented to a total depth <br /> of approximately 25 feet below ground surface (bgs). Soil encountered in each of the borings consisted <br /> primarily of silty to sandy clay. A thin layer of fine-grained silty sand approximately i foot thick was <br /> present at MW-2 and MW-1 at approximately 5 feet bgs. A layer ofs oft plastic clay was observed <br /> between 12 to 19 feet bgs at MW-4. First groundwater was encountered in silty clay between 16 and 19 <br /> feet bgs and rose approximately 10 feet bgs in the wells. Boring logs and a geologic cross-section are <br /> presented in Attachment B. <br /> Based on quarterly water-level measurements through the third quarter of 2005, the inferred <br /> groundwater gradient is relatively flat and may be tidally influenced owing to the proximity of the <br /> Stockton Channel to the south of the site. Generally, the groundwater gradient was observed to flow to <br /> URS Corporation <br /> Crown Corporate Center <br /> 2870 Gateway Oaks Drive, Suite 150 <br /> Sacramento, CA 95833 <br /> Tel: 916.679.2000 KAWproccssu5 BP ARCO\054501Soi1 Closure 051Draft of 5450 Closure Report.doc <br /> r� Fax: 916.679.2900 <br /> i <br /> _ f <br />