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Uns Ms Lori Duncan Page 5 San Joaquin County Environmental Health Department March 25, 2004 Groundwater Monitoring Fourth Quarter 2003 During the fourth quarter 2003 groundwater monitoring event, depth to groundwater in the site wells ranged from approximately 14 39 feet bgs to 25 24 feet below top of casing Based on monitoring data collected on December 23, 2003, groundwater flow beneath the site was to the northeast at an average hydraulic gradient of 0 017 feet/foot A groundwater elevation contour map is presented as Figure 4 Groundwater samples were analyzed for gasoline range organics (GRO) by EPA Method 8015, benzene, toluene, ethylbenzene, and total xylenes (BTEX), fuel oxygenates (including MtBE), and halogenated volatile organic compounds were analyzed by EPA Method 8260B In the groundwater sample collected from new deep monitoring well MW-12D, GRO was reported at 52 µg/L, benzene was reported at 18 lig/L, MtBE was reported at 2 2 µg/L, and cis-1,2-dichlorethene was reported at 2 9 Ag/L GRO, BTEX, and MtBE were reported above method detection limits in groundwater samples collected from site wells during the fourth quarter 2003 groundwater monitoring event Additionally, the volatile organic compounds isopropylbenzene, n-propylbenzene, n-butylbenzene, naphthalene, sec- butylbenzene, 1,2,4-trimethylbenzene, tert-butylbenzene, cis-1,2-dichloroethene, and trichloroethene (TCE) were reported above method detection limits in groundwater samples collected from site wells this quarter Analyte concentrations were generally consistent with previous quarterly monitoring events Groundwater elevations in the site wells generally decreased relative to the previous quarter The inferred groundwater flow direction and gradient were consistent with previous quarters Groundwater monitoring data are summarized in Tables 1, 2, 3, and 4 Sampling field data sheets are included in Attachment D Attachment E presents detailed groundwater sampling and analysis procedures Laboratory analytical reports and chain-of-custody documentation are included in Attachment F A summary of groundwater analytical data for the fourth quarter 2003 sampling event is presented on Figure 5 Waste Disposal A composite soil sample was collected from the SO-I and SO-2 soil cuttings and submitted to the Sequoia Analytical Laboratory in Petaluma, California, for analysis of GRO, BTEX, and total lead Upon receipt of laboratory results, Dillard Environmental Services hauled the 20 drums of soil to the Republic Services Vasco Road landfill in Livermore, California, where it was disposed of as non- hazardous waste Waste sample soil analytical data are summarized in Table 5 The laboratory analytical report is included as Attachment F Waste water generated during the well installation was contained in 10 55-gallon drums On December 17, 2003, the waste water was transported by Dillard to • K IWprocessV5 BP ARC01044931Well Install14493 well installation report04 doc