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5 <br /> GEOCHEMlCAL+GEOTECHNICAL e ENVIRONMENTAL <br /> October 19, 1990 <br /> Ms. Darlene Reuss <br /> San Joaquin County Public Health Services r.•. ;r <br /> Environmental Health Division <br /> P.O. Dox 2009 Rp _ <br /> Stockton, CA 95201 �iQ ��P "`� 1 <br /> Re: 3990 Third Quarter Re ort-Tri <br /> Nowell Road, Thornton, CA, Valley G� 6200 <br /> Dear Darlene: <br /> This letter report updates the activities at Tri-Valley Grower's <br /> Thornton plant during the third quarter of 1990. Activities <br /> during the quarter have included sampling for dissolved <br /> hydrocarbons and monitoring of groundwater. <br /> ' `. Groundwater monitoring conducted in July, August and September <br /> showed the water table dropped approximately 2 feet during the <br /> quarter (Table 1). The groundwater contour maps (Figures 1 and <br /> 2) continue to show a variation in direction and magnitude of the ' <br /> gradient (Table 1) as well as the static water levels (Table 2), i <br /> i <br /> No discernible relationship between the gradient magnitude, <br /> gradient direction or water table elevation is apparent. <br /> # <br /> However, the shallow groundwater system clearly is responding to p <br /> influences other than natural seasonal recharge. Recharge from <br /> irrigation or the effects of pumping in the area are probable <br /> factors. <br /> ? Groundwater samples were collected from the six wells on <br /> f September 18 and 19, 1990, for analysis of benzene, toluene, <br /> ethylbenzene, xylenes (BTEX) and total petroleum hydrocarbons as <br /> gasoline (TPHG), by EPA methods 8015/8020. In addition, Mwl was <br /> sampled for oil and grease by EPA method 503E. Gasoline <br /> hydrocarbons were reported in MW3, MW2 and MW4. A general <br /> decrease in gasoline hydrocarbon concentrations were recorded in <br /> MW1 and MW4 and small amounts of hydrocarbons were again noted in <br /> MW2. Oil and grease concentrations were below detectable levels <br /> in MW1. The results are summarized in Table 3, and the <br /> laboratory reports and chain-of-custody are presented ___as <br /> Attachment--1.- - - <br /> 9790 MAIN STREET + ESCALON,CA 95320 • (209)838-3507 <br /> FRESNO,CA(209)222-3495 • RENO,NV(702)788-6830 <br />