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L Harding Lawson Associates August 5, 1997 r ' 38737 001 Ms Mary Meays San Joaquin County Public Health Services Environmental Health Division 304 East Weber Avenue, Third Floor Stockton, California 95202 Analysis of SECOR Investigation and Recommendations for Additional Work Tn Valley Growers Plant T 26200 Nowell Road ` Thornton, California Site Code 1920 Dear Ms Meays On behalf of Tri Valley Growers (TVG), Harding Lawson Associates(HLA) submits to San Joaquun County Public Health Services, Environmental Health Division(PHS/EHD), this letter report that summarizes the recent field investigation performed by SECOR, and proposes additional work to pursue site closure at TVG's facility in Thornton, California (Site Code 1920) In light of the recent changes regarding the alternatives for mitigation of petroleum hydrocarbon impacted sites,TVG requested that HLA analyze the SECOR investigation, review the existing site data, and provide recommendations Of particular concern to TVG were the SECOR sampling techniques used and analytical results from the recent investigation Presented in this report are a summary of the previous investigations associated with the underground storage tanks (USTs), a review of the SECOR results, and recommendations to collect additional data from the site to evaluate possible alternatives for closure Preparations are currently being made to sample the monitoring wells at the site As requested, to facilitate PHS/EHD's review of the report, HLA will submit the results of the sampling when completed SITE DESCRIPTION Site Location and Topography TVG owns and operates Plant T, a tomato cannery, located at 26200 Nowell Road in Thornton, California (Plates 1 and 2) The area of investigation occurs within the northern part of Plant T, adjacent to the forklift repair shop (Site) as shown on Plate 3 The Site has an elevation of approximately 11 feet above mean sea level (USGS, 1978) with very little topographic relief ' The surrounding land use is mainly agricultural with some residential areas A private residence borders the Site on the immediate north Agricultural fields occur to the northwest, northeast, and southeast of the Site the city of Thornton occurs to the west and southwest of the Site Located approximately 40 feet to the northwest on the adjacent Lopez parcel, another UST site is under investigation with oversight by ' the PHS/EHD (Henry, Personal Communication, 1997) Hydrogeologic Framework The nearest major surface water body is the Mokelumno River,located approximately one-half mile northeast of the Site The Mokelumne River flows to the northwest at this location and is subject to periodic flooding The regional groundwater flow direction is northeast, toward the Mokelumne River Engineering and ' Environmental Serv,ces 10265 Rockingham Drive Suite 150 Sacramento CA 95827 9161364 0793 Fax 916!364-5633