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t WORK PLAN FOR SOIL BORING SITE ASSESSMENT 2088 Mariposa Road Stockton, California INTRODUCTION In accordance with a request from Mr. Manuel Sanchez of Pacific Gas, Geological Audit Services, Inc. (GeoAudit) has prepared this work plan to perform a soil boring site assessment of the tank pit area at 2088 Mariposa Road, Stockton, California (the site) . The assessment will include the drilling of four (4) soil borings to a depth of 30 feet. However, if field screening of soil samples indicates that contamination is present at depths of greater than 30 feet, at least one boring will be advanced until contamination is no longer encountered or groundwater is reached. This portion of the assessment will only address contamination in the vicinity of the former underground storage tanks (tank pit 1) . Assessment of any contamination associated with the piping or former pumping islands will be addressed in a separate work plan (or work plan addendum) . BACKGROUND The site is located in a flat industrial/commercial area of southeastern Stockton (Figure 1 - Location Map, 7 . 5 Minute Stockton East Quadrangle, USGS Topographic Map Series, 1987) . A building and canopy are currently located on-site. The property was operated as a gasoline station until 1990. The underground storage tank facility consisted of four fuel tanks, one waste oil tank, three fueling islands and their appurtenant piping. The property is currently vacant. In May of 1990, five underground storage tanks (UST's) were removed from the site by Falcon Energy Associates (FEA) . One 5, 000 gallon regular leaded tank, one 2 , 000 gallon diesel tank, one 6, 000 gallon unleaded tank, one 2 , 000 gallon unleaded tank and one 550 gallon waste oil tank were removed. The four fuel tanks were located at the southeast corner of the property (tank pit 1) . The waste oil tank was located on the northwest portion of the property (tank pit 2; see Figure 2 - Site Plan) . Soil samples collected from beneath the UST's indicated that contamination was present and an unauthorized release of hydrocarbons has occurred. Total petroleum hydrocarbons (`.PPH as gasoline) were detected at levels as high as 620 parts per million (ppm) . Volatile aromatics (BTE&X) were detected at levels as high as 458 ppm. Complete soil sample analysis are included in the "Soil Sampling Report - Underground Storage Tanks" dated 1 May 1990, prepared by Water Work for FEA and submitted to the San Joaquin County Public Health Services - Environmental Health Division (PHS/EHD) .