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QUARTERLY GROUND WATER MQNITORING REPORT Second Quarter of 1992 4491 West Durham Ferry Road Delta Project No 40-91-732 ' page 4 TABLE 1-Continued ' Ground Water Elevation Data ' Date Elevation of Depth to Ground Water Monitoring Well Measured Top of_Cast n Ground Water ft Elevation(ft)a MW-3 09/04/91 97 93 867 8926 10/13/91 10 10 87 83 10/20/91 1062 8731 ' 04/09/92 1435 83 58 07/10/92 1236 8557 ' a Relative to an assumed elevation of 100 feet * Ground water elevation adjusted due to presence of 0 03 feet of free-phase petroleum hydrocarbons ' 3.2 Ground Water Analytical Results Ground water samples were collected on July 10, 1992, from monitoring wells MW-1, MW-2 and MW-3 and were submitted to a California-certified laboratory for analysis of benzene, toluene, ethylbenzene and xylenes (BTEX) and total petroleum hydrocarbons (TPI-b) as gasoline by Environmental Protection ' Agency (EPA) Method 8260 and extracted by EPA Method 5030 (purge-and-trap) 7 ieId data sheets are presented in Appendix A Ms Mary Mays from the County was on site to observe the sampling ' protocols during the ground water sampling event ' Chemical analyses of the ground water sample collected from monitoring wells MW-1 and MW-2 indicated the presence of TPH as gasoline at concentrations of 45,000 and 8,800 ppb, respectively TPH ' as gasoline in monitoring well MW-3 was below the laboratory detection limit Concentrations of benzene were detected in monitoring wells MW-1 and MW-2 at 57 and 3,300 ppb, respectively(Table 2) ' BTEX was not detected in downgradient monitoring well MW-3 Copies of the certified-laboratory reports are presented in Appendix B ' 3.3 Free-Phase Petroleum Hydrocarbons A sheen of free-phase petroleum hydrocarbons was observed on the surface of the purge water from monitoring well MW-1 on July 10, 1992 RPT029 TA 1