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C U UMNLY G IOUNDWATER KION K011INO REPOlir 1605 South EI Dorado Street,Stockton California On December 17, 1991, the top-of-well casing elevations were resurveyed by Tom O Morrow, Inc , of West Sacramento, California 4.0 GROUNDWATER MONITORING 4.1 Groundwater On December 17, 1992, Aegis personnel collected measurements of the depths to groundwater in wells MW-1, MW-2, and MW-3 Since September 1992, groundwater has fallen in all the wells an average of 0 19-feet (Figure 3), ranging from 0.17 to 0 22-feet (Table 1) On the basis of the December 17, 1992, measurements, groundwater is estimated to flow to the east at an average gradient of 0 001 ft/ft Figure 4 is a Ipotentiometric surface map of the shallow water-bearing zone on December 17, 1992 Previous groundwater levels are summarized in Table 1 All groundwater elevation measurements were made from the referenced wellhead elevations, measured to the nearest 0 01 foot, and conducted according to the Aegis standard operating procedures (SOP) included as Appendix A 4.2 Water Sampling and Anal sis P 9 -Y On December 17, 1992, Aegis personnel collected groundwater samples from the three wells at the site The samples were collected according to the Aegis SOP included in E Appendix A, and delivered under chain-of-custody to Pace Laboratories, Inc , of Novato, California, a state-certified analytical laboratory The samples were analyzed for concentrations of a) TPH, as gasoline, by modified EPA Method 8015, and b) BTEX by modified EPA Method 8020 The analytical results are summarized in Table 2 The analytical reports and chain-of-custody form are included in Appendix B Concentrations of TPH, as gasoline, and benzene reported in Table 2 are also shown on Figure 5. I 5.0 SCHEDULED ACTIVITIES 1 Quarterly monitoring will continue at the site The next quarterly sampling event is scheduled for March 1993 IAegis is currently preparing a workplan for the installation of two vapor extraction wells and four or five additional groundwater monitoring wells, including one or two off-site wells Data from the monitoring wells will be used to determine the extent of dissolved petroleum hydrocarbons in groundwater on and off site. A vapor extraction pilot test will be performed to assess the feasibility of this technology for remediating soil within and beneath the former UST basin This work is expected to be completed by March 1993 91-044C LMR -2-