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i + • Fage 2 2.0 INTRODUCTION • This report discusses the results of groundwater monitoringfor the period from e pe February 20 to April 18, 1996 The project was conducted in accordance with proposal #96021 and approved by the San Joaquin County Public Health Services Environmental Health Division (PHS/EHD), the lead regulatory agency for the project 3.0 BACKGROUND INFORMATION The Teresi Trucking yard is located east of U S highway 99 in Lodi, California (Figure l) On December 1, 1995, three underground storage tanks were removed by Jim Thorpe Oil from the rear portion of the facility(Figure 2) The tanks stored diesel and unleaded gasoline and had been used to fuel company trucks In accordance with regulatory guidelines, eight soil samples were collected from beneath the tanks when they were removed Samples were also collected from the dispenser island, piping trench, and soil stockpiles GeoAnalytical Laboratories analyzed the samples for the presence of petroleum hydrocarbons in the diesel and gasoline ranges, for volatile aromatic hydrocarbons, and for total lead Contamination, primarily in the diesel range, was detected in several'samples Thorpe performed additional excavation on December 6 in order to remove the remaining contaminated soil from the excavation PHS/EHD instructed Thorpe to cease excavating at a depth of 25 feet and collect two bottom samples Figure 2 shows the approximate locations of samples OE-1 and OE-2, in which diesel was detected at concentrations of 3,000 and 6,000 mg/kg and gasoline was detected at concentrations of 60 and 800 mg/kg The stockpile of excavated soil was covered with plastic sheeting and the excavation was allowed to remain open During the tank removal, a 12-inch diameter domestic well was discovered within the fueling facility On February 1, 1996,a representative of Welenco performed down-hole television survey of the domestic well The groundwater interface was penetrated at a depth of approximately 54 feet, where a thin black layer or film of hydrocarbon product was observed floating on the water surtace The groundwater remained cloudy or turbid to a depth of 69 feet, where the camera revealed that the casing walls had collapsed inward Because the camera could not pass the obstruction, the survey was terminated at this depth No other irregularities in the casing were noted above this depth On February 12, five borings were drilled by V& W Drilling of Rio Vista, California, under contract to Upgradient Three of the bongs were converted to monitor wells Twenty-five soil samples, two hydropunch water samples, three samples from the newly installed monitor wells and one sample from the domestic well were obtained and sent to Excelchern Laboratories of Roseville Only one soil sample and two groundwater samples detected hydrocarbons above detectable limits Based on the further assessment results and previous remedial work, the site appeared to pose a low risk to public health No further work was recommended other then periodic monitoring