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STATE OF CALIFORNIA GEORGE DEUKMEJIAN,Governor <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— <br /> CENTRAL VALLEY REGION tl� <br /> 3443 ROUTIER ROAD <br /> SACRAMENTO,CA 95827-3098 <br /> ✓ r <br /> 6 March 1990 ! G. <br /> Ms. Diane Hinson llIAR - (j <br /> Supervising REHS 1990 <br /> San Joaquin County <br /> Public Health Services <br /> Environmental Health Division <br /> P.O. Box 2009 <br /> Stockton CA 95201 <br /> SHELL SERVICE STATION, 7910 LOWER SACRAMENTO ROAD, STOCKTON - <br /> HYDROGEOLOGIC ASSESSMENT REPORT <br /> We have reviewed the 20 October 1989 Phase I Hydrogeologic Assessment <br /> Report prepared for this site by Delta Environmental Consultants (Delta) . <br /> The investigation included installation and sampling of three ground water <br /> monitoring wells and three additional soil borings on-site. <br /> According to the report, petroleum hydrocarbons detected in ground water <br /> beneath the site may have originated from an off-site source. Because the <br /> levels of petroleum hydrocarbons detected in ground water were below the <br /> Department of Health Services action levels, Delta recommends that no <br /> further action be taken, and requests closure of this site. <br /> Based on the information provided in the report, it cannot be reasonably <br /> concluded that the petroleum hydrocarbons either originated from an off- <br /> site source, or that the extent of contamination has been adequately <br /> assessed. The hydrocarbons detected in the upgradient well (MW-1) could <br /> also have originated from an on-site source in the vicinity of the <br /> adjacent pump islands, or the tank pit located approximately 15 feet away. <br /> In general , it is not appropriate to conclude that a site should be closed <br /> based on the results of the initial round of sampling. <br /> At this time we do not believe it is appropriate to request closure for <br /> this site. Hydrocarbons detected in soil adjacent to the pump islands and <br /> beneath the former tank pit have not been adequately addressed. If future <br /> sampling of the on-site monitoring wells continues shows hydrocarbons in <br /> ground water, additional investigation may be necessary to define the <br /> extent of the ground water pollution. <br /> If you have any questions, please call me at (916) 361-5731. <br /> THOMAS D. PELTIER <br /> Engineering Geologist <br /> TDP:tdp <br />