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4• DISCUSSION: See attached tables for historical data Sampling efforts conducted during the first quarter of 1996 (by PEG) at this and other ARCO sites showed low concentrations of petroleum hydrocarbons (notably toluene and xylenes) in wells that were historically non-detect for petroleum hydrocarbons During the first quarter of 1996, concentrations of petroleum hydrocarbons were detected in ARCO Facility 434 wells WAA, W-2, W-2B, W-5, W-9, W-10, W-11, and W-12 This quarter, petroleum hydrocarbons were not detected in wells W-1 A, W-2, or W-9 The occurrence of petroleum hydrocarbon constituents in these wells during the first quarter of 1996 is probably the result of laboratory or sampling equipment contamination Petroleum hydrocarbons were detected in well W-5 during the second quarter of 1996 Wells W-2B, and W-10 through W-12 are on a semi-annual sampling schedule and were not sampled this quarter The presence or absence of petroleum hydrocarbons in wells W-2B, and W-10 through W-12 will be confirmed in the next quarterly sampling event Appendix A of this report presents operation and maintenance data for this quarter The remediation system at the site was shut down in February 1996 A Risk Based Corrective Action (RBCA) Report will be prepared for this site j ATTACHMENTS: �J Figure 1 Groundwater Elevation Map Figure 2 Constituent Concentration Map Table 1 Water-Level Elevations Table 2 Historical Flow Directions and Gradients Table 3 Analytical Results Appendix A Field Data Sheets, Laboratory Reports, and Chain-of-Custody Documentation BROWN AND CALDWELL 9f Xtow"_\ Joel Coffman Pat Cullen Project Manager California Registered Geologist#4932 JCPYDvm Enclosures Use or disclosure of data continued on this sheet is subject to the restriction specified of the beginning of this document 33821REPORTSUNDQTR96 DOC