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v o A S S O C I A T E S I N C The average hydraulic gradient on June 23, 2004 was calculated to be 0 00008 ft/ft or approximately 0 4 ft/mile A summary of groundwater monitoring data is presented in Table 1 CONCLUSIONS Concentrations of TPHg, toluene, ethylbenzene, and total xylenes Increased in the groundwater sample collected from MW-2 during the second quarter 2004 with respect to the previous quarterly monitoring event conducted in October 2003 Concentrations of TPHg, toluene, ethylbenzene, and total xylenes decreased in the groundwater sample collected from MW-3 Concentrations of petroleum hydrocarbons remained at nondetectable levels in groundwater samples collected from MW-1, MW-4, MW-5, and MW-6 The direction of groundwater flow and magnitude of the hydraulic gradient are generally consistent with previous quarters RECOMMENDATIONS Based on the following, ATC recommends the site be considered for closure • Petroleum hydrocarbon constituents have never been detected in samples collected from MW-4, MW-5 Petroleum hydrocarbon constituents have not been detected in MW-6 (downgradient monitoring well) since 1997 • Benzene has not been detected in any of the groundwater samples collected during the last two • quartetly sampling events Benzene has never been detected in samples collected from MW-1 and has not been detected in samples collected from MW-2 since September 1994 a MTBE has not been detected in samples collected from MW-1 and MW-2 since February 2001, , yri 6t and July 200 , respectively The concentrations of MTBE detected in samples collected from q�l�l these wells have not exceeded the Maximum Contaminant Level for this constituent • Laboratory analytical results of groundwater samples collected from MW-3 indicate a decreasing trend in petroleum hydrocarbon concentrations MTBE has not been detected in samples collected from this well since April 1998 • It is ATC's understanding that the nearby municipal supply well has been taken out of service and therefore reduces the potential for impacted groundwater from the site to impact the local drinking water supply Please contact our office at(209) 579-2221 if you have any questions or comments Respectfully submitted, ATC Associates Inc Todd C Ha her Je ne Homsey, P E Project Geologist CA Registered Civil Engineer No1r cc Gerald Thiemann Jim Barton, RWQCB Q-s " slenvironmenta11626051quartlyl2QK-2004 doe 3 Y .0 F' P 14 r t 4 SMT :SyRw