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MEMORANDUM Lal/>✓YA o CALIFORNIA RtGIONAL WATER QUALITY CONTROL BOARD CENTRAL VALLEY REGION (916)255-3000 • CALNET 8-494-3000 • FAX(916)255-3015 Pete Wilson,Governor TO: Gordon L. Boggs FROM: Patricia A. Anderson DATE: 19 December 1997 SIGNATURE: A"- SUBJECT: REVIEW FOR NO FURTHER ACTION,PIE NATIONWIDE, 2007 WILSON WAY, . STOCKTON,SAN JOAQUIN COUNTY Based on my review of the case file concerning the above site, I have noted the following: Background: In August 1991, a 15,000-gallon diesel tank was removed from the above site. Soil samples,collected beneath the tank had 92 to 16,000 mg/kg total petroleum hydrocarbons as diesel (TPH-d). Benzene,toluene, ethylbenzene, and xylene (BTEX) were also detected; however,the concentrations are unknown. In May and September 1997, four soil borings were advanced from 25 to 70 feet below ground surface (ft bgs)near the former underground tank and dispenser island areas. Soil samples from these borings showed a fine sandy silt to silt from the surface to 15 to 25 ft bgs, underlain by a fine to coarse sand extending to 35 ft bgs. This unit is underlain by a fine silty sand to silty clay extending to 70 ft bgs. This highest concentration of contamination occurs in, P-2, near the former dispenser area and product pipeline, Soil samples from this boring show 10,000 mg/kg TPH-d at 25 ft bgs, 12,000 mg/kg at 35 ft bgs 86 mg/kg TPH-d at 45 ft bgs, and 6.1 mg/kg TPH-d at 50 ft bgs. No samples were collected beneath the dispenser area. Soil samples from P-1, the boring near the former underground storage tank area, show contamination occurring with 9,400 mg/kg TPH-d at 20 ft bgs and no contamination at 25 ft bgs. Soil samples from boring P-4 had 1.2 mg/kg TPH-d at 25 ft bgs. The laboratory analysis did not detect BTEX from any soil samples collected from P-4. However, 4.7 mg/kg TPH-d (1.4 mg/kg fluorene, 1.6 mg/kg naphthalene, and 2.4 mg/kg phenanthrene), and 0.22 mg/kg TEX were detected from the boring cuttings,composted and stockpiled on-site. The two borings that extended to 70 ft bgs encountered ground water at 64 ft bgs. However, ground water in this area has occurred from 35 to 70 ft bgs at a nearby site (American Moulding and Mill Works)(12/19/97 phone communication Steve Sasson). According to the map titled Lines of Equal Depth to Groundwater-Spring 1996, the pre-Vailing ground water flow direction in eastern Stockton is generally toward the northeast. Based on this map information, the borings were drilled laterally in a northward direction from the underground storage tank area. However, flow directions may vary locally and seasonally. The borings were not advanced in a triangular arrangement around the sources of contamination, and ground water has not been monitored quarterly. Therefore, the direction of ground water flow has not determined at this site. Crab ground water samples from the two borings had 510 µg/l and 70 µg/1 TPH-d. No BTEX or polynuclear aromatic hydrocarbons were detected. However,the direction of ground water flow has not Our mission is to preserve and enhance the quality of California's water resources,and Recycled Paper ensure their proper allocation and efficient use for the benefit of present and future generations.