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ill DISCUSSION: • Groundwater flow direction and hydraulic gradient are consistent with previous results Groundwater sampling results are consistent with previous results Wells W-lA, W-2, W-2B, W-5, W-9, W-10, W-11, and W-12 contain low concentrations of xylenes and/or toluene Additionally, wells W-1A, W-2B, and W-5 contain low concentrations of benzene and/or total petroleum hydrocarbons as gasoline Petroleum hydrocarbons have not been detected in these wells for at least one year, and in most cases for more than one year Sampling efforts conducted this quarter (by PEG) at this and other ARCO sites show low concentrations of petroleum hydrocarbons in wells that are historically non-detect for petroleum hydrocarbons Therefore, the occurrence of petroleum hydrocarbons in the site wells this quarter is suspect, and may be the result of laboratory or sampling equipment contamination BC will evaluate the validity of the reported low concentrations of petroleum hydrocarbons after the second quarter groundwater sampling event has occurred ATTACHMENTS: 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 Appendix B O&M Report BROWN AND CALDWELL 6t7l Joel Coffman 4Cafomia cas v , Project Manager Registered Geologist#4301 JC PYD vm Enclosures cc/enc. Ms Margaret Lagono, San Joaquin County Public Health Services, Environmental Health Division Ms Elizabeth Thayer, California Regional Water Quality Control Board, CVR • Use or disclosure of data continued on this sheet is subject to the restriction specified at the beginning of this document 3392\RF.i'ORMi sTQTR96 DOC