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CALIFORNIA GEOPHYSICAL GROUP, INC. _ <br /> O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 <br /> Fax (209) 527-4810 <br /> December 5 , 1995 - <br /> Public Health Services <br /> San Joaquin County <br /> I P.O. Box 388 <br /> Stockton, Ca 95201 <br /> RE: Technical Review Committee Report <br /> Darpetro Service Station <br /> 749 E. Charter Way <br /> Stockton, Ca. <br /> Site # 1060 <br /> INTRODUCTION <br /> The Preliminary Site Assessment phase of this site began in <br /> January, 1990. To this date 11 monitoring wells have been <br /> installed and sampled along with 1 boring and 2 hydropunch <br /> borings. During the site assessment, anomalies of the <br /> groundwater contamination were noted after the installation of <br /> wells BM-6 and BM-7 . The hydraulic gradient at this site is <br />' mainly to the northeast with occasional gradients to the north <br /> and east southeast. Because of these anomalies, well BM-9 was <br /> installed west of the site. This well contained much higher <br /> amounts of groundwater contamination than well BM--7 located 50 <br /> feet east (down gradient of well BM-9) . <br /> Based upon this information we believe another plume exists to <br />' the west of well BM--9 . We presented this information in our Site <br /> Assessment Report dated October 10 , 1994 . <br /> The San Joaquin County Environmental Health Division (EHD) <br /> requested we obtain hydropunch information to the east of well BM- <br /> 9 , which was done in June, 1995. The results of this testing <br /> I were reported in our Activity Report dated June 30, 1995. The <br /> hydropunch groundwater sampling again suggested another plume to <br /> the west of BM-9 . <br /> In a meeting on November 14, 1995, we met with Ms. Diane Hinson <br /> and Mr. Steve Sasson of the EHD and presented our rationale for <br /> our belief that another plume exists. <br /> iThe EHD has informed us that a Technical Review Committee meeting <br /> is scheduled for December 21 , 1995, to review the data in this <br /> case. The purpose of this report is to discuss our rationale for <br />' our belief that another plume exists. <br /> HISTORY <br /> On November 14, 1989 four underground gasoline storage tanks were <br /> removed from this site. Soil sampling under the tanks indicated <br />' Page 1 <br />