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QUARTERLY GFIDUNdWATER MONRORINO FORT 1399 East Yosemite Avenue Manteca,Cafifomfa Aegis began a program of groundwater monitoring in February 1991 Monthly monitoring ' of groundwater levels and quarterly sampling of groundwater was continued until May 1992 On June 20, 1991, Aegis installed monitoring wells MWA B, MW-4, and MW-5 on the site. Wells MW-4 and MW-5 were completed with 4-inch-diameter casing to a depth of 35 feet below grade Well MWA B was completed with 6-inch-diameter casing by 'over-coring" the former MWAA Quarterly monitoring has continued since then ' 4.0 GROUNDWATER MONITORING 4.1 Groundwater On January 19, 1993, Aegis personnel collected measurements of the depths to liquids in wells MW-113, MW-2, MW-3, MW-4, and MW-5 Since October 19, 1992, groundwater levels have fallen in all wells (Figure 3) an average of approximately 1 12 feet (Table 1) On the basis of the January 19, 1993, measurements, groundwater is estimated to flow ' to the northwest (Figure 4) at an average gradient of approximately 0 016 ft/ft Previous groundwater levels are summarized in Table 1 All groundwater elevation measurements were conducted according to the Aegis standard operating procedures (SOP) included as Appendix A 4.2 Water Sampling and Analysis On January 19, 1993, Aegis personnel collected groundwater samples from four of the five monitoring wells at the project site Well MWA B was not sampled due to the presence of floating liquid hydrocarbons The samples were collected according to the ' Aegis SOP included in Appendix A, and submitted under chain-of-custody to Pace, Inc , of Novato, California, a state-certified analytical laboratory The samples were analyzed for concentrations of total petroleum hydrocarbons (TPH), as gasoline, by modified EPA Method 8015, and, • benzene, toluene, ethylbenzene, and total xylenes by modified EPA Method ' 8020 Groundwater analytical results obtained to date, including data reported by previous consultants, are summarized in Table 2 Concentrations of TPH, as gasoline, and benzene reported for samples collected on January 19, 1993, are also shown on Figure 5 Copies of the laboratory analytical reports and chain-of-custody form are included in Appendix B 90-098D QN!R