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Third-Quarter Groundwater Monitoring Letter Report January 15, 1992 Tri-Valley Growers, Thornton, California W2102 petroleum hydrocarbons as gasoline (TPHG), by EPA methods 8020 and modified 8015, respectively In addition, monitoring well MW 1 was sampled for total oil and grease (TOG) by EPA method 5520 B&F. No dissolved gasoline hydrocarbon constituents were reported above detection limits in monitoring wells MW1, MW3, or MWb Oil and grease was not reported above detection limits in MW1 (Table 2). The zero line for total petroleum hydrocarbons in the groundwater is plotted on Figure 5. Influent and effluent samples from the pumping well (MW4) were also analyzed for BTEX, TPHG, and TOG on October 9 and December 19, 1991. Analytical results indicate an increase in TPHG and the gasoline constituents benzene, toluene, and xylenes in the influent samples - collected on December 19 from the October 9 sampling round Ethylbenzene levels are shown to have decreased since the October 9 sampling round. The influent sample recorded nondetectable levels of TOG Analytical results indicated break-through in carbon filter 1 (CFTC), but not in carbon filter 2 (CF2C) during the October 9 sampling round. 'Carbon filter 1 was replaced on November 11, 1991 No break-through from carbon filter 1 (EFFC1) or 2 (EFFC2) was evident during the December 19 sampling round Laboratory analyses were performed by Applied Analytical Laboratory (DHS certification #1211) The analytical results are sum manzed in Table 2, the laboratory reports and chain-of- custody documentation are presented in Attachment 2 As previously approved, monitoring wells MW2 and MW5 have been changed to a biannual sampling schedule. Sampling of weIls MW2 and MW5 will be included in the next quarter's activities. RESNA personnel will continue with the quarterly monitoring program which will include a report detailing system performance The first quarterly monitoring event of 1992 will include analysis for BTEX and TPHG from all monitoring wells, and remediation system influent (MW-4) and effluent The sample from MW-1 and Influent will also be analyzed for TOG We will continue to monitor system performance and adjust pumping rates as necessary QUO10692 SAY 2