ARCHIVED REPORTS_XR0007213 - Laserfiche WebLink

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BACKGROUND ' The subject site was previously a gasoline service station with four (4) underground storage tanks (UST's) (1-10, 000 gallon tank containing unleaded gasoline, 1-8,000 gallon tank containing unleaded gasoline, 1-6, 000 gallon tank containing regular gasoline, ' and 1-250 gallon tank containing waste oil) . The three (3) gasoline tanks were buried in a common excavation in the central portion of the subject site and the waste oil tank was buried in a separate ' excavation within the building. On 10 July 1990, the four UST's were decommissioned and removed ' from the property. ETS Environmental & Associates (ETS) observed the tank removals and obtained confirmatory soil samples beneath the tanks. ' On 12 July 1990, the product lines were excavated and removed from the property. ETS observed the removal of the product lines and obtained confirmatory soil samples in the excavation. ' In October 1991, ETS submitted a Preliminary Investigation and Evaluation Report (PIER) which included soil sampling in the bottom of the open excavations, the drilling of three (3) 100' deep borings, and the conversion of the three borings into 2-inch diameter monitoring wells (Figure 2) . Elevated concentrations of Total Petroleum Hydrocarbons (TPH) and purgeable aromatic hydrocarbons (BTE&X) were detected in soil samples obtained from the gasoline tank excavation, the product ' line excavation, and in each of the three borings. The highest TPH concentration, 3, 300 mg/kg was detected in the soil sample obtained from boring B3 at a depth of 65. 5 feet (Table 1) . Free product was also encountered in the product line excavations. Elevated concentrations of Total Petroleum Hydrocarbons (TPH) and purgeable aromatic hydrocarbons (BTE&X) have been detected in ground-water samples obtained from monitoring wells MW1, MW2 , and MW3 (Table 3) . The highest TPH concentration, 18, 000 gg/l was detected in the water sample obtained from MW1 (ETS report dated ' May 1992 and AC reports dated 10 October 1992 and 11 January 1993) . TPH and BTE&X have not been detected in the ground water samples obtained from MW2 and MW3 in the last two quarters (AC report dated 11 January 1993 and 9 April 1993) . The depth to ground-water is approximately 83 feet below the subject site. According to Mr. Michael Infurna of the San Joaquin Public Health Services, the ground-water elevation in this area fluctuates as much as 20 feet, seasonally. The hydraulic gradient, calculated in March 1993 is <. 01 to the southwest. The hydraulic gradient has fluctuated over time (Figure 2) .