SITE INFORMATION AND CORRESPONDENCE_CASE 1

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'IEMORANDUM Cal/EPA CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD' CENTRAL VALLEY REGION ' 3443 Routier Road,Suite A,Sacramento,CA 95827-3003 (916)255-3000 • CALNRT 8-494-3000 • FAX(916)255-3015 Pete Wilson,Governor TO: Gordon L. Boggs FROM: Patricia A. Anderson x DATE: 26 May 1998 SIGNATURE: SUBJECT: REVIEW FOR NO FURTHER ACTION REQUIRED CONCURRENCE, FRANK'S EXXON#4, 14800 W. FRONTAGE ROAD. (HWY. 99),MANTECA,SAN JOAQUIN ,. .1., �.4� ..�.COUNTY-t --------- An - _An investigation of the lateral and vertical extent of petroleum contamination was initiated in response to the detection of petroleum hydrocarbons in the soil adjacent to the underground storage tanks. In 1988 and 1989, four soil borings were advanced between 40 to 49 ft bas and completed as monitoring wells. The highest concentrations of soil contamination occurred in MWA and MW-2 at 15 to 25 ft below ground surface (ft bgs)with 88 mg/kg total purgeable (gasoline)petroleum hydrocarbons (TPPH) 0.26 mg/kg benzene, 0.53 mg/kg toluene 0.31 mg/kg ethylbenzene, 1.9 mg/kg xylene (BTEC 0.01 mg/kg ethyldibromide, and 0.003 mg/kg 1,2 dichloroethane (1,2-DCA). This contamination extends beyond 30 ft bgs with lower concentrations of contamination. -Ground water samples from these wells had 200 9g/1 TPPH,4 µg/1 xylene, and 8.4 µg/l ethyldibromide. In November 1989,three 10,000 gallon underground storage (regular, unleaded and diesel) tanks (USTs) were removed and contaminated soil was excavated to 17 ft bgs. All soil samples, collected from the pit, confirmed contamination. In November 1989 and June 1992, five additional monitoring wells were installed. Quarterly ground water sampling of the monitoring wells from April 1992 to January 1995 showed that contamination occurred consistently in MW-1 through MW-4, occasionally in MW 5 through MW-8, and was nondetect in MW-9. During this period, the maximum concentration of contamination occurred in MW-3 with�14,000 µg/1 TPH-g, 5,200µg/I-TPH=dx3;700;110,1' 00,-I;900 µg/I BTEx`MW- '-had-the.--u- highest concentration (770 µg/1) of 1,2-DCA, and 280 µg/l methyl tertiary-butyl ether(MTBE/EPA R Method 8020). it The excavated soil was stockpiled on site and aerated to nondetect. This soil was used for landscaping. Remedial action was initiated in October 1990 with the installation of soil venting components in the tank basin after the USTs were removed. Two 25 ft casings were installed at 10 ft bgs beneath the product lines and two 25 ft casings were installed 17 ft bgs beneath the USTs. Soil vapor and ground water extraction systems were operated from January 1995 to November 1996. During this period, these systems extracted 2,391.8 lbs of TPH-g and 8.17 lbs of benzene. When the 3 remediation systems were shut-off, the quarterly ground water sampling showed that the plume of ' contamination had diminished in size with contamination being detected in MW-1 through MW-4 and Recycled Paper Our mission is to preserve and enhance the quality of California's water resources,and ensure their proper allocation and efficient use for the benefit of present and future generations.