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Ground-Water Sampling Senior Specialist Steve Sasson of the San Joaquin County Environmental Health Division was on-site to witness monitoring activities. Prior to normal well-sampling procedures, ground-water sampling equipment was steam-cleaned and/or washed in Liquinox® prior to sampling and 1 between sampling each well. Water-condition parameters of temperature, electrical conductivity, and pH were measured and logged during well-purging prior to sampling the wells. Purging was continued until at least three well-volumes of water were removed from each well, and <' water condition parameters had stabilized. The Well Sampling and Monitoring Logs are included as Appendix A. _. Each ground-water sample was collected within a clean, disposable, polyethylene bailer lowered to just below the water surface. Each ground-water sample was brought to the surface and immediately transferred to two-to-six, 40-m1 capacity, glass, Volatile Organic Analysis (VOA) vials and fitted with Teflon's-lined screw caps. Care was taken to ensure that no air space existed in the vials by inverting, tapping, and checking for bubbles. Each container was F-; properly labeled in the field and refrigerated for transport to Sherwood Labs in Hilmar for TPH- g by EPA Method 503018015-mod and BTEX analytes by EPA Method 602. TRPH-d analysis by EPA Method 351018015-mod was not required for this fourth quarter-1995 activity because diesel analytes have not been detected in past sampling activities. Appropriate chain-of-custody procedures were adhered to at all times during sample procurement and handling. The samples were extracted and analyzed within the lifespan Iimits set forth by EPA guidelines for the specified analyses. Analytical Results r=a Ground-water samples collected from the five wells were received at Sherwood Labs on October 19, 1995. The analytical results revealed continuing nondetectable concentrations of TPH-g and BTEX in samples collected from wells MW-4, MW-5, and MW-7. The results of the analyses of the samples collected from MW-6 indicate that the ground water underlying that vicinity remains impacted with TPH-g and benzene analytes above the Maximum Contaminant Levels 'j (MCLS) set by the California Department of Health Services; the analytes are less prevalent this quarter. With the exceptions of benzene, detected at 0.4 µg1 f, and xylenes, detected at just 0.6 pgl f, the sample collected from MW-8 revealed nondetectable analytes; these results are slightly '._ higher than the laboratory detection limit of 0.3 I,gLE. The analytical results for these sampling activities are summarized in Table 4. The Sherwood Labs analytical reports and chain-of- custody are included as Appendix B. W.W.Irwin,Inc. Prajmt No.33016.06 to 1 - October 1995 _J .I