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r r4.2 Analytical Results of Groundwater Samples TPH as gasoline and diesel were detected in MW-1 at concentrations of 1,800 ppb and 300 ppb, respectively. Benzene, toluene, ethylbenzene and xylenes were also detected in MW-1 r at concentrations of 52 ppb, 8 2 ppb, 72 ppb and 220 ppb, respectively r No petroleum hydrocarbons were detected in MW-2, MW-3 or MW-4.The analytical results of the groundwater samples are summarized in Table 2 The laboratory report and chain-of- custody are included in Appendix B r 5.0 CONCLUSIONS & RECOMMENDATIONS r5.1 Groundwater FIow Direction and Gradient Since March 1993, the groundwater flow direction and gradient have remained consistent at the site During the same period, groundwater depth has remained within 15 feet of rsurface grade at the site 5.2 Petroleum Hydrocarbon Impacted Groundwater Concentrations of petroleum hydrocarbons in MW-I increased between June and September 1994, from 560 ppb to 1,800 ppb, but are still below concentrations detected in March 1994 Concentrations of BTE&X also showed similar fluctuations. Low concentrations of some petroleum hydrocarbon compounds were detected in MW-2 and MW-3 dunng the June 1994 sampling However, these hydrocarbons were not detected dunng the September 1994 sampling It is unlikely that the hydrocarbon plume is migrating towards MW-2 or MW-3 The petroleum hydrocarbon plume continues to be sufficiently defined at the site and does not appear to be migrating significantly The down-gradient well (MW-4) remains uncontaminated The concentrations of toluene, ethlybenzene or xylenes detected at the site do not exceed ' the State of California Maximum Contaminant Levels (MCL's)or Action Levels (AL's) The AL for toluene is 100 ppb, the MCL for ethylbenze is 680 ppb, the MCL for xylenes is 1,750 ppb No MCL's or AL's have been established for TPH as gasoline or diesel Only the ' concentration of benzene in MW-1 (52 ppb) exceeds the MCL (1 0 ppb) 53 Petroleum Hydrocarbon Impacted Soil ' Since impacted soil still remains at the site, remediation systems that target both soil and groundwater should be considered We propose to install three additional borings to assess the extent of impacted soil A workplan for the installation of soil borings is included in Appendix C After the additional soil bonngs have been dnlled, possible soil and groundwater remediation methods can be considered 1 Geological Audht Seances,Iac_ 10 STEWARTS BEACON QR5/661-5/10 94 1 1 l IS y }