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Quik Stop Markets, Inc. RA �MA Project No. F7132.32 Rei store Working To Restore Nature Page 2 Quarterly Well Pumping ' As agreed upon with the San Joaquin County Public Health Services (see Background Section-- Appendix A),monitoring well MW-5 is pumped out on a quarterly basis. This quarter, pumping was conducted on October 26, 1992. Prior to pumping a groundwater sample was obtained from the well and labeled MW-5. The well was then pumped for about three hours and approximately 200 gallons of water was removed from the well. After pumping was complete, another groundwater sample was collected and labeled MW-5A. Laboratory Analyses The groundwater samples were transported to RESNA Environmental Laboratories, a state- , certified laboratory, located in Fremont, California. Samples were analyzed for the presence of TPHG following Environmental Protection Agency (EPA) Method 8015 modified and BTEX following EPA Method 8020/602. The laboratory analytical report and chain-of-custody document are attached in Appendix D. Summary of Results ' A summary of the analytical results from current and past well samplings is presented in Table 1. - Plate 2 shows the groundwater elevation contours based on the water level data in Table 1. In the local aquifer, groundwater elevations declined an average of 3.13 feet since last quarter. In the perched aquifer, a groundwater elevation decline of 0.48 foot_was noted since last quarter. The apparent groundwater flow directioniremains to the`east-southeast at a gradient of approximately 0.001. _.. ' Results of September laboratory analysis found that TPHG, and BTEX were not detected in groundwater samples from-monn nitog viwells MW-1 R, MW-3,.and MW-4.,-TPHG was also no[ detected in monitoring well,MW-2but'trace amounts of benzene [0.70 parts per billion (ppb)] and toluene (1.5 ppb) were detected. MW-5 contained detectable levels of TPHG (310 ppb), and ethylbenzene (0.63 ppb). In the June 1992 analysis, unknown solvent peaks_were,reported by the laboratory for groundwater-samples-from_MW--.1R..and_MW-5.. _, n examination of the ' ".chromatograms revealed that these solvent peaks closely resembled those associated with methyl lent=butyl ether (MTBE). MTBE is a non'-metallic (lead-free) antiknock compound used lead; free gasolineFln•this sampluig and analysis, theamples.from.MW.s1R and_MW_-5 wer,_analy?xd for MTBE:^MTBE was detected in the groundwater samples from MW .1R and.MW-S at 61 ppb and 920.ppb,respectively. JMTBE is a very light and highly mobile compound. In light of the past history of excavation of this site, the presence of such a compound is not unexpected. The next quarterly groundwater sampling will be conducted in December 1992. Analysis of the samples collected before and after the October 26, 1992 pumping of MW-5 resulted in TPHG at concentrations of 330 ppb prior to pumping and 340 ppb after the pumping was completed. Benzene concentrations increased from t0.5 to 2.3 ppb prior to and after pumping, respectively (See Table 1). Recommendations ` Monitoring wells MW-3 and MW4 have not had detectable TPHG or BTEX since they were fust sampled in September 1990. MW-3 is located upgradient of the spill location.and�MW 41iis located, ' approximately 50 feet laterally from the spill location. ilii vim ew of these factors and in compliance