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SITE ASSESSMENT WORK PLAN (OVBREXCAVATION) <br /> Pacific Gas <br /> 2088 Mariposa Road <br /> Stockton, California <br /> INTRODUCTION <br /> In accordance with a request from our client, Mr. Manuel Sanchez of <br /> Pacific Gas, Geological Audit Services, Inc. (GeoAudi.t) has <br /> prepared this work plan to perform overexcavation procedures at <br /> 2088 Mariposa Road, Stockton, California (the site) . The location <br /> of the site is illustrated in Figure 1. A plan of the site is <br /> illustrated in Figure 2 . <br /> BACKGROUND <br /> The site is located in a flat industrial/commercial area of <br /> southeastern Stockton (Figure 1 - Location Map, 7 . 5 Minute Stockton <br /> East Quadrangle, USGS Topographic Map Series, 1987) . A building and <br /> canopy are currently located on-site. The property was operated as <br /> a gasoline station until 1990. The underground storage tank <br /> facility consisted of four fuel tanks, one waste oil tank, three <br /> . fueling islands and their appurtenant piping. The property is <br /> currently vacant. <br /> In May of 1990, five underground storage tanks (UST's) were removed <br /> from the site by Falcon Energy Associates (FEA) . One 5, 004 gallon <br /> regular leaded tank, one 2, 000 gallon diesel tank, one 6, 000 gallon <br /> unleaded tank, one 2 , 000 gallon unleaded tank and one 550 gallon <br /> waste oil tank were removed. The four fuel tanks were located at <br /> the southeast corner of the property (tank pit 1) . The waste oil <br /> tank was located on the northwest portion of the property (tank pit <br /> 2 ; see Figure 2 - Site Plan) . <br /> Soil samples collected from beneath the UST' s indicated that <br /> contamination was present and an unauthorized release of <br /> hydrocarbons had occurred. Total petroleum hydrocarbons (TPH) as <br /> gasoline were detected at levels as high as 6200 parts per million <br /> (ppm) . Volatile aromatics (BTE&X) were detected at levels as high <br /> as 458 ppm. Complete soil sample analysis are included in the "Soil <br /> Sampling Report - Underground Storage Tanks" dated 1 May 1990, <br /> prepared by Water Work for FEA and submitted to the San Joaquin <br /> County Public Health Services - Environmental Health Division <br /> (PHS/EHD) . <br /> In March 1993, a soil boring site assessment was conducted to <br /> determine the extent of contamination. Nine borings were drilled <br /> . around the tank pit and piping areas. A total of 27 samples were <br /> analyzed for petroleum hydrocarbon contamination. Only two samples <br /> had detectable concentrations of hydrocarbons. TPH as gas was <br /> detected in sample B7-10 (south of tank pit #1, 10 foot depth) at <br /> 12 ppm; xylenes were detected in sample B9-10 (product line north <br />