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I' QUARTERLY GROUNDWATER MONRORING RI'ORT <br /> 7910 Lower Sacramento Road Stockton California <br /> In January 1992, Emcon was retained by Shell to conduct quarterly monitoring, including <br /> groundwater depth measurements and groundwater sample collection from the three <br /> ' wells on site The data, including the laboratory analytical reports, was then provided to <br /> Aegis for inclusion in this report (Appendices A and B) <br /> ' In June 1992, the monitoring frequency of wells MW-1, and MW-3 was changed from <br /> quarterly to semi-annually <br /> 4.0 GROUNDWATER MONITORING <br /> 41 Groundwater <br /> On June 2, 1992, Emcon personnel collected measurements of depths to groundwater <br /> ' in each of the three wells according to the Emcon sampling report included in <br /> Appendix A Water level measurements collected since the wells were installed are <br /> summarized in Table 1 A groundwater elevation hydrograph is included as Figure 3 <br /> Since February 0 <br /> 2 , 1992 groundwater levels have fallen in all wells an average of <br /> 1 47 feet On the bass of the June 2, 1992, measurements, groundwater is estimated to <br /> flow to the east (Figure 4) at an average gradient of approximately 0 001 ft/ft The <br /> previous estimated direction of groundwater flow was to the east <br /> 4 2 Water Sampling and Analysis <br /> ' On June 2, 1992, Emcon personnel collected a groundwater sample from well MW-2 <br /> The sample was delivered under chain-of-custody to Sequoia Analytical of Sacramento, <br /> California, a state-certified analytical laboratory, for chemical analysis Sample collection <br /> ' was conducted according to the Emcon sampling report included in Appendix A The <br /> sample was analyzed for concentrations of TPH, as gasoline, by EPA Method 8015, and <br /> BTEX by EPA Method 8020 Concentrations of TPH, as gasoline, and benzene were <br /> ' reported to be below the detection limit in MW-2 <br /> The benzene analytical results summarized in Table 2 are also shown on Figure 5 <br /> i Sample handling and chain-of-custody procedures are addressed in the Emcon sampling <br /> report included in Appendix A The laboratory reports and chain-of-custody form are <br /> included in Appendix B <br /> ,i <br /> 91-2316 OMR 2 <br /> i <br />