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STATE OF CALIFORNIA I%kd PETE WILSON, Governor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— 4% CENTRAL VALLEY REGION m g 3443 ROUTIER ROAD, SUITE A , SACRAMENTO, CA 95827-3098 PHONE: (916) 361-5600 FAX: (916) 361-5686 HE ' %E . b 20 July 1992 J UL 2 3 1992 �NVIRONMWAL HEALTH PERM ITMOYIOO Ms. Diane Hinson San Joaquin County Public Health Services P.O. Box 2009 Stockton, CA 95201 NOR-CAL BEVERAGE, 1800 E. FREMONT ST. , STOCKTON, SAN JOAQUIN COUNTY I have reviewed the file for 1800 East Fremont in Stockton. Nor-Cal 's request for closure is premature. The file revealed that 3 underground tanks were removed in January 1991 and soil samples from the walls and bottom of the excavation contained up to 30,000 ppb TPHg at a depth of 10.5 feet. The tank pit was reexcavated in March 1991 . Sample #6, collected at a depth of 21 feet, contained 6000 ppb TPHg and 1100 ppb TPHd, Sample #7 contained 27000 ppb TPHg and 9100 ppb TPHd at 11 .5 feet, and Sample #11 contained 23000 ppb TPHg and 2000 ppb TPHd at 16 feet. One monitoring well , MW1, was installed through the tank pit in May 1991 . Depth to ground water was approximately 69 feet and soils consist predominantly of sands and silty sands. Only 100 ppb benzene was found in one , soil sample from the bore hole. In the ground water sample, 100 ppb TPHg and 1 .6 ppb benzene were detected. The well was sampled again in September 1991 and it contained up to 220 ppb TPHg and 0.8 ppb benzene. In a ground water sample collected in January 1992, no hydrocarbons were detected. Depth to ground water was again about 69 feet. Because of the extremely high levels of soil contamination left in place and the sandy nature of the soils, one well is not adequate to complete the ground water investigation. In sandy soils it is common for hydrocarbon contamination to impact only a narrow column of soil as the contamination moves downward toward the water table. MW1 was not installed in an area with high levels of soil contamination. It is not possible to calculate the direction of ground water flow with one well . At least two more wells are necessary to determine the direction of ground water flow. Additional wells may be needed to determine the extent of ground water contamination. All wells must be sampled quarterly and the results reported as per Section 2652(d) of the Underground Tank Regulations. The soil contamination left in the excavation remains a threat to ground water. Therefore, the extent of soil contamination must be defined. Once the soil contamination has been defined an appropriate remediation method must be proposed and implemented.