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r1 STATE OF CALIFORNIA 4e � PETE WILSON, Governor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— CENTRAL VALLEY REGION 3443 ROUTIER ROAD, SUITE A s SACRAMENTO, CA 95827-3098 PHONE: (916) 361-5600 FAX: (916) 361-5686 23 July 1991 Ms. Margaret Lagorio San Joaquin County Public Health Services Environmental Health Division P.O. Box 2009 Stockton, CA 95201 HOLT BROTHERS TRACTOR CO. , 1521 WEST CHARTER WAY, STOCKTON, SAN JOAQUIN COUNTY We have reviewed the "Quarterly Report" (QR) , dated 24 January 1991, and the "Progress Report/Remediation Feasibility Study" (PRRFS) , dated 19 April 1991, both prepared by WaterWork. It is our understanding that the contaminated soil that was excavated from the tank pit during tank removal in 1988, was placed back into the pit and then capped with clean fill . The QR indicates that upgradient wells MW3 and MW4 and downgradient well MW6 had and continue to have non-detectable levels of contaminants. However, several things have changed since the last sampling event in February 1990. MW1 had free product again, after one sampling round with no free product in early 1990. Upgradient well MW2 contained non-detectable levels of contaminants for the first time since it was installed in 1988. Downgradient well MW5 contained hydrocarbon and solvent contamination for the first time since it was installed in 1989. In the PRRFS, WaterWork presents information on "a short term step drawdown test and longer term (4 hr) constant rate pumping test using well MW6" . The former product extraction from MW1 and the recent tests on MW6 revealed that MW6 extracts water from a sandy zone which is not present in MW1 and at a higher rate than MWI. The rate of extraction from MWl is too low, due to the clay lithology, to achieve plume control or to install an efficient remediation system. It may be possible to extract ground water from MW6 at an acceptable rate for efficient remediation, however, extraction from MW6 does not have a great impact on the clay layer where MW1 is completed and where the majority of the ground water contamination is found. Recommendations for soil and ground water remediation are also contained in the PRRFS. For soil remediation, WaterWork considered two excavation alternatives, soil vapor extraction, in-situ soil bioremediation, and capping. For ground water remediation they considered a pump and treat system, a pump and bioremediation system, and ground water monitoring as part of the soil capping alternative. They recommended the soil capping and ground water monitoring alternative. Due to the free product in MW1 and movement of the dissolved contaminants into MW5 downgradient of the source, we do not agree with the proposal for soil capping with no soil and ground water remediation and we require submittal of