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February 6, 1996 <br /> n36 <br /> Michael Infurna, Sr. RENS j�{VC Es <br /> San Joaquin County PHS <br /> Environmental Health Division <br /> P. o. Box 388 <br /> Stockton, CA 95201-0388 <br /> Re: Eighth Quarterly Groundwater Monitoring Report, 1500 Shaw Road, Stockton, CA; Site <br /> Code 1727 <br /> Dear Mr. Infurna: <br /> This report summarizes the monitoring and sampling event conducted on December 19, <br /> 1995. Field activities at the above referenced Canteen facility include monitoring and sampling <br /> of the seven monitor wells onsite and the two offsite monitor wells (MW-8 and MW-9 from the <br /> U.S. Chemical property), which were monitored and sampled and included with these data for <br /> the second time. <br /> Based on the groundwater elevations from the monitor wells, the groundwater gradient <br /> • was 0 52 feet pqr 100jecuad the general direction of groundwater flow was to the uth. Fluid <br /> level measurements for this event and historical events are summarized in Table 1 and the <br /> Potentiometric Surface map is included as Figure 1. <br /> Free product was not detected in any of the monitor wells, nor has it ever been. <br /> The groundwater elevation was approximately 12 feet higher during this monitoring event <br /> than during the initial gauging (06103193) due apparently to an increase in the rainfall. The <br /> groundwater elevation for this event was higher than the first six events and above the top-of the <br /> screened intervals in each well. The two offsite wells (MW-8 and MW-9), which were <br /> contoured with the Canteen monitor wells, were consistent with the established groundwater flow <br /> direction (south) and gradient. <br /> Benzene, toluene, ethylbenzene, total xylenes (BTEX), and TPH-G concentrations <br /> continued to decrease or remained the same in monitor wells MW-1, MW-2, MW-3, MW-4, <br /> MW-5, and MW-7. Monitor well MW-6, the monitor well upgradient of the former tank hole, <br /> had an increase in benzene concentration from non-detect to 1 µg/L and in BTEX concentrations <br /> from non-detect to 9.6 ,ug/L both of which are at or below drinking water standards. The two <br /> monitor wells on the U.S. Chemical property, MW-8 and MW-9, had benzene, total BTEX, and <br /> TPH-G concentrations below method detection limits, with the exception of the toluene <br /> concentration in MW-8, which increased from non-detect to 0.5 pg/L. <br /> 16415 Addison Road, Suite 700• Dallas, Texas 75248-2460 9 Tel (214) 380-9555 • Fax (214) 380-5553 <br />