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- Ground-Water Sampling �I Senior Specialist Steve Sasson of the San Joaquin County Environmental Health Division was again 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 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. I 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' 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 properly labeled in the field and refrigerated for transport to Sherwood Labs in Hilmar for TPH- :: g by EPA Method 5030/8015-mod and BTEX analytes by EPA Method 602. TRPH-d analysis by EPA Method 351018015-mod was again not required for this first quarter-1996 activity because diesel analytes have not been detected in past sampling activities. Appropriate chain-of- `i custody procedures were adhered to at all times during sample procurement and handling. The samples were extracted and analyzed within the lifespan limits set forth by EPA guidelines for the specified analyses. Analytical Results Ground-water samples collected from the five wells were received at Sherwood Labs on January 16, 1996. The analytical results revealed continuing nondetectable concentrations of TPH-g and BTEX in samples collected from wells MW-4, MW-5, and MW-7. Also, no detectable gasoline analytes were detected in the sample collected from MW-8. The results of the analyses of the sample collected from MW-6 indicate that the ground water underlying that vicinity remains impacted, though favorably, to a lesser degree. TPH-g and benzene analytes still impact the ground water at concentrations exceeding the Maximum Contaminant Levels (MCLS) set by the California Department of Health Services. TPH-g and benzene have declined approximately 33% between October 18, 1995 and January 16, 1996. Concentrations of toluene, ethylbenzene, and total xylenes have also declined dramatically, falling further below their respective MCLS. The analytical results are summarized in Table 4. The Sherwood Labs analytical report and chain-of-custody are included as Appendix B. I W.W. IrvWn, Inc. Project No. 33016.06 February 1996 10