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t 0 Nv.'eGEFS ES M1EAS CLWS iI1Ni$ 1.0 INTRODUCTION ' The purpose of this corrective action plan work pian is to address the remediation of petroleum hydrocarbon impacted soil at San Joaquin County Mosquito and Vector Control District ' (SJCMVCD) property located at 200 North Beckman Street, Lodi, California The impacted soil has resulted from the activities associated with three underground storage tanks (USTs), which were removed from the site in August 1986 The location of the subject property is shown on Figure 1. This corrective action plan is being submitted in response to the request of the San Joaquin County, Public Health Services, Environmental Health Division (EHD) 2.0 ENVIRONMENTAL SETTING The site is located within the Central Valley Geomorphic Province in central California The ' topography of the area is generally flat. Soil boring and monitor well lithologic logs from the site indicate the area is underlain with silty sand to a depth of approximately 30 ft below ground surface (bgs), and silt with sand and clay below the 30 ft depth A sand layer 5 to 10 ft thick is present at the approximate depth of 55 ft bgs iGroundwater flow, as identified in previous site investigation reports, is to the northeast Depth to groundwater at the site has been increasing since the site was first investigated in 1986. Depth to groundwater in December 1986 was approximately 38 ft bgs, and by 1994 the groundwater level had dropped to approximately 59 ft bgs Water level measurements collected in May of 1995 indicate the depth to groundwater at the site is approximately 52 to 55 ft bgs. The water table rise may be the result of heavy rainfall from the winter season Average annual rainfall at the site is approximately 16 inches, however, rainfall to "date" in the 1994-1995 season is approximately 23 inches 3.0 PREVIOUS INVESTIGATIONS RESULTS SUMMARY Three phases of removals and investigations have occurred at the UST site since August 1986. The first phase, which occurred between August 1986 and December 1986, consisted of removing the three USTs from the site and excavating petroleum hydrocarbon contaminated soil associated with those tanks This phase also included the installation of monitor wells and collection of groundwater samples from monitor wells at the site in January 1987 The second phase was conducted between December 1991 and January 1993, and included quarterly monitoring of the three existing monitor wells on site, and the installation and monitoring of an additional monitor well This additional monitor well, MW-4, was installed L\M0JECTS\SA 10Q"01 ncr 15 May Ivqs