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pTS <br /> PUBLIC AL <br /> SAN JOAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DIVISION P <br /> Health Officer ;t� c'c,Foa <br /> M.D., ' <br /> Karen Furst, ., M.P.H., <br /> Third Floor • Stockton, CA 9520 <br /> 304 East Weber Avenue, <br /> 209/468-3420 � U <br /> SEP 0 21997 <br /> THOMAS JNOKES <br /> 1650 PARK ST <br /> } ALAMEDA CA 94501 <br /> RE: DISCOVERY CHEVROLET SITE CODE: 2595 <br /> { 1615 WEST 11TH STREET <br /> TRACY CA 95376 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has <br /> recently reviewed the June 6, 1997 "Report of Additional Subsurface Investigation" prepared by <br /> { Horizon Environmental and the July 7, 1997"Second Quarter 1997 Status Report" prepared by <br /> GeoStrategies Inc. for the above referenced site. <br /> i The June report summarizes the results of a workplan implemented on April 3, 1997, to comply <br /> 1I with the recommendations in the PHS/EHD correspondence of September 9, 1996. In this letter <br /> PHS/EHD requested a complete soil and groundwater assessment of contamination at the site. <br /> The required data was to include the lateral and vertical extent of soil contamination in the former <br /> common tank location, the downgradient extent of the groundwater plume, an evaluation of natural <br /> i attenuation and a well survey. <br /> Hand auger borings were used to define the extent of soil contamination around the former tank pit. <br /> The boring logs from the hand augered borings were not included in the report. The hand augered <br /> borings were unable to identify the lateral or vertical extent of soil contamination to the west. The <br /> lateral extent of soil contamination east of the former tank pit appears to have been identified. <br /> None of the hand augered samples were able to identify the vertical extent of the contamination. <br /> During the September 10, 1994, installation of monitoring well 1 soil samples were taken from 6.5', <br /> 10.5', 15' and 20' below ground surface(bgs). Only the 10.5' sample was submitted for analysis. <br /> The Photo Ionization Detector(PID) reading from this sample was 1149 ppm. The analytical results <br /> of this sample confirmed the presence of gasoline contamination. PID readings from the 15'and <br /> the 20' sample were 356 ppm and 449 ppm respectively. MW-1 was installed near the dispenser <br /> lines. The vertical extent of contamination in this area has not been defined. <br /> j The September 10, 1994, boring log for MW-2 recorded the PID readings as 1281 ppm at 10.5', <br /> I 11.5 ppm at 15', 1.3 ppm at 17.5' and 2.4 ppm at 20'. Although only the 10' sample was analyzed, <br /> based on the PID readings, gross contamination does not appear to extend beyond 15 feet on the <br /> i' north side of the former tank excavation. <br /> { <br /> Laboratory analyses of samples obtained from the hand augered borings combined with the <br /> monitoring well data implicate the former dispenser and lines as a source of contamination. <br /> Obtaining soil data from beneath the former dispenser and lines is necessary to determine the size <br /> of the soil plume. The size of the soil plume is necessary to determine the probability of <br /> i groundwater impact and to determine the feasibility of various cleanup options. It may be <br /> I necessary to obtain samples from soil deeper than static water to define the vertical extent of soil <br /> contamination in this area. Since gradient is north west additional monitoring wells may be <br /> necessary north west of the building to monitor the groundwater plume that would have resulted f <br /> A Division of San Joaquin County Health Care Services <br />