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Appendix B. ' TABLE 1 RELATIVE GROUNDWATER ELEVATIONS Western Lift 3430 S. EI Dorado Street, Stockton, CA Relative Depth to Groundwater Relative Groundwater Well No. Casing Elevation Elevation 5-31-94 9-14-94 12-8-94 5-31-94 9-14-94 12-8-94 ' MW-1 101.62 37.57 41.24 40.26 64.05 60.38 61.36 MW-2 101.62+ 37.50 41.08 40.30 64.12 60.54 61.32 MW-3 101.17+ 36.89 40.43 39.62 64.28 60.74 61.55 MW-4 102.02 38.04 41.68 40.70 63.98 60.34 61.32 ' MW-5 101.54 37.35 40.98 40.15 64.19 60.56 61.39 ' •All 111CUSU eulcuts in fret + Revised 2115/4 5.0 CONCLUSIONS & RECOMMENDATIONS Low concentrations of petroleum hydrocarbons continue to be detected in samples from MW-1 and MW-4, which are down gradient of the former UST excavation. Concentrations of TPH as gasoline and benzene were similar to the Sepember monitoring. However, TPH as diesel was again detected in MW-1. As in September 1994, only the concentration of t benzene in MW-1 and MW-4 exceeds the Maximum Contaminant Level (MCL) for drinking water in the State of California. ' Limited groundwater extraction of was performed on MW-1, MW-4 and MW-5 during the December monitoring event. However, concentrations of hydrocarbons in MW-1 and MW-4 remained at previous levels. It appears that groundwater extraction had little effect, if any, ' on concentrations of contaminants in groundwater at the site, and would probably not be a successful remedial alternative for impacted groundwater at the site. ' A well survey should be performed to locate any wells within 2000 feet of the site. The closest downgradient domestic well to the impacted groundater is located on the Cutter Lumber property, approximately 300 feet north of the former UST excavation. We ' recommend that the SESOIL/AT123D modeling program be used to determining if impacted groundwater will reach this well. Ueohynl Audio 1.1w 11e. •'f ' Wane lib QR&k2-9V4.IU /