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I - _ 1+J ��9'0'�1 P.03 STATE OF rALIFORMIA i VETE WILSON. Goverrtpr CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— CENTRAL VALLEY REGION °'~µ��_ • 3443 ROUTIER ROAD, SUITE A ` 9ACRAmC-NTC), CA' 95627.3098 r PHONE; jots) 361:5660 "^'' FAX: (9}6) 381.5&86 I r.«r PC 20 July 1992 J U L 2 3 �NVIRONMkN-fAL HEALTH Pf�MIfhCVtga Ms. Diane H?nson San Joaquin; County Public Health Services P.O. Box 2009 Stockton, 0 95211 f NOR-CAL BEYERAGE,11800 E. FREMONT ST. , STOCKTON, SANJOAQUIN COUNTY I have reviewed the file for 1800 Cast Fremont in Stockton. Nor-Calls request for cl'osure' is premature. The file revealed that 3 underground tanks were removed in Januar: 1991 and soil samples from the walls and bottom of the excavation tontained up to 30,000ppb TPIIg 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 6bQO ppb TPHg and 1100 ppb TPHd, Sample #7 contained 27000 ppb TPHg and 9110 ppb; TPHd at 11.5 feet, and Sample #11 contained 23004 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 Gp 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 contaminatibn to impact only a narrow column of soil as the contamination moves downward toward the water table. MW1 was not in an area with high levels of soil contamination. It is not possible to calculate the ' direction of groupd water flow with one well . I At least two moreiwells are necessary to determine the direction of ground water. flow. Additional wells may be needed to deter�ine the extent of ground water containativn. All wells must be sampled quarterly and the results reported as. per Section 2652(d) of the [Underground T4nk Regulations. The soil contamination left in the excavation remains a threat to ground water. Therefore; the-extent of soil contamination ;ust be defined. Once the soil contamination has been defined an appropriate remediation method must be proposed and implemented. i