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1444 MARIPOSA ROAD WKA No. 2938.05 April 28, 2000 Page 2 Prior to purging and sampling, the water level in each well was measured with an electronic water level indicator and checked for visual signs of free product using new, disposable polyethylene bailers. No free product, sheen or petroleum hydrocarbon odor was observed in the monitoring wells. The depth-to-groundwater measurements were used to calculate the volume of water in each well. Once calculated, approximately three well volumes of water were purged from each well using a two-inch submersible pump until temperature,pH, and conductivity readings stabilized and/or the water cleared of sediment. Groundwater was allowed to recharge to at least 90% at each well prior to obtaining samples. Water samples were then collected through the sampling pump. Sample water pumped from the wells was poured into appropriate sample containers provided by the laboratory. The submersible pump was cleaned with a solution of Liqui-nox and water prior to purging each well to minimize the potential for cross- contamination. In addition, the wells were sampled in order of increasing concentration based on previous sampling results. All water removed during sampling and purging operations was placed in sealed and labeled 55-gallon drums and stored on-site. The samples were immediately placed in an ice-chest with ice and submitted under chain-of- custody to a California-certified laboratory for analysis of Total Petroleum Hydrocarbons (TPH) as gasoline,Benzene, Toluene, Ethylbenzene and Total Xylenes (BTEX)using EPA Method 8260B. The fuel oxygenates Tert-Butanol,Methyl tent Butyl Ether, Di-isopropyl Ether, Ethyl tert-Butyl Ether, Tert-Amyl methyl Ether, Ethanol, and Methanol were additionally analyzed using EPA Method 8260B. Results of laboratory analysis of water samples obtained from wells MW 1 through MW3 and MW5 through MW7 revealed no detectable concentrations of TPH as gasoline or BTEX constituents. TPH as gasoline was detected in the water sample obtained from well MW4 at a concentration of 50 µg/1. A minor concentration of MTBE(0.78 µg11)was detected in well MW2 only. Trace concentrations of Tert-butanol was detected in MW2 and MW7 and ethanol at a concentration of 9.8 µg/1 was detected in MW3. Analytical results for the water samples are summarized in Tables 2 and 3. Chain-of-custody documentation and laboratory analytical reports are appended. Conclusions and Recommendations Groundwater flow direction during the last three monitoring and sampling events has been to the south-southeast with a variable gradient. Petroleum hydrocarbons in groundwater in the vicinity of wells MWI, MW3, MW6, and MW7 have not been detected during the last three sampling events. TPH as gasoline has decreased to nondetectable levels in wells MW2 and MW5 and has INK WALLACE-KUHL r: Er ASSOCIATES INC.