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f <br /> • <br /> INTERIM WORK PLAN <br /> Pacific Gas <br /> 2088 Mariposa Road <br /> Stockton, CA <br /> 1. 0 INTRODUCTION <br /> Geological Audit Services, Inc. (GeoAudit) has been retained by Mr. <br /> Manuel Sanchez of Pacific Gas to continue the assessment of soil <br /> and groundwater contamination at 2088 Mariposa Road. This work plan <br /> details the work outlined in GeoAudit's proposal dated June 4 , <br /> 1993 . <br /> 2 .0 BACKGROUND <br /> Located in a rural, low-density commercial area in southeastern <br /> Stockton (Figure 1) , the site was occupied by a Pacific Gas service <br /> station until 1990. The five underground storage tanks and their <br /> associated piping were removed by Falcon Energy Associates in May, <br /> 1990, and hydrocarbon contamination was detected in all 17 soil <br /> • samples collected beneath the tanks and piping. GeoAudit was <br /> subsequently retained to assess the lateral and vertical extent of <br /> contamination, and drilled nine borings in March 1993 . <br /> The results were presented in GeoAudit ' s Preliminary Investigation <br /> and Evaluation Report (April 1993) . Borings drilled around the <br /> margins of the fuel tank pit (tank pit #1) and in the waste oil <br /> tank pit (tank pit #2) did not encounter any soil contamination. <br /> Minor contamination was detected in borings B7 and B9, near the <br /> former pipelines. GeoAudit recommended further excavation of tank <br /> pit #1 to remove any contamination that might be present below a <br /> depth of 15 feet. In subsequent verbal communication, San Joaquin <br /> County Public Health Services - Environmental Health Division <br /> (PHS/EHD) notified GeoAudit that, due to seasonal high groundwater <br /> of approximately 45 feet, a groundwater investigation involving the <br /> installation of three monitoring wells would be required. <br /> 3. 0 SCOPE OF WORK <br /> In September, 1992 , the depth to first groundwater at the USA <br /> gasoline station, across the street to the south, was 75 feet. <br /> Regionally, groundwater levels rose several feet during the 1992- <br /> 1993 rainy season, but have since fallen slightly. We anticipate <br /> encountering groundwater near 70 feet and completing the wells at <br /> • a depth of approximately 80 to 85 feet. Figure 2 shows the proposed <br /> well locations, and Figure 3 shows the anticipated well design. <br /> Soil samples and auger returns will be screened for evidence of <br /> contamination as drilling proceeds. If no evidence of vadose-zone <br /> 1 <br />