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QUARTERLY GROUNDWATER MONITORING FEFORT
<br /> 1605 South 8 Dorado Street,Stockton California
<br /> On July 2 and 3, 1991, Aegis conducted sod borings, sampling, and installation of
<br /> monitoring wells MW-1, MW-2, and MW-3 (Figure 2) Results of soil borings, sampling,
<br /> l' and well installation were reported by Aegis to Exxon in a "Phase I Subsurface
<br /> Investigation Results Report," dated September 13, 1991
<br /> I On December 17, 1991, the top-of-casing well elevations for MW-1, MW-2, and MW-3
<br /> were resurveyed by Tom O Morrow, Inc , of West Sacramento, California
<br /> 4.0 GROUNDWATER MONITORING
<br /> 4.1 Groundwater
<br /> On November 27, and December 19, 1991, and January 17, 1992, Aegis personnel
<br /> collected measurements of the depths to groundwater in wells MW-1, MW-2, and MW-3
<br /> For the first 2 months, since November 27, 1991, groundwater levels had fallen in all three
<br /> wells (Figure 3) The drop ranged from 0 01 to 0 04-feet (Table 1) In the last month,
<br /> December 19, 1991, groundwater levels had risen in the three wells (Figure 3) The
<br /> increase ranged from 0 2a to 0 30-feet (Table 1) On the basis of the November 1991
<br /> through January 1992, measurements, groundwater is estimated to flow to the east-
<br /> northeast at an average gradient ranging from approximately 0 0005 to 0 0007 ft/ft
<br /> Figures 4A, 413, and 4C are the potentiometnc surface maps of the shallow water-bearing
<br /> zones on November 27, and December 19, 1991, and January 17, 1992 Figure 4D Is the
<br /> corrected potentiometric surface map for the measurements collected on October 17,
<br /> 1991, and reported to Exxon in the "Quarterly Groundwater Monitoring Report," dated
<br /> November 11, 1991 The corrected groundwater flow direction is to the east at a gradient
<br /> of approximately 0 001 ft/ft The map was corrected according to the results of the
<br /> December 17, 1991, resurvey by Tom O Morrow, Inc , of West Sacramento, California
<br /> Previous groundwater levels are summarized in Table 1 All groundwater elevation
<br /> measurements were made from the referenced wellhead elevations, measured to the
<br /> nearest 0 01 foot, and conducted according to the Aegis standard operating procedures
<br /> I (SOP) included as Appendix A
<br /> 4.2 Water Sampling and Analysis
<br /> On January 17, 1992, Aegis personnel collected groundwater samples from the three
<br /> wells at the site The samples were collected according to the Aegis SOP included in
<br /> Appendix A, and delivered under chain-of-custody to Pace Laboratories, Inc , of Novato,
<br /> California, a state-certified analytical laboratory The samples were analyzed for
<br /> concentrations of a) TPH, as gasoline, by EPA Method 8015, b) BTEX by EPA
<br /> Method 8020, c) ethylene dibromide and ethylene dichlonde by the AB1803 Method, and
<br /> d) total lead b EPA Met The analytical results are summarized in Table 2 The
<br /> nalytical reports and chain-of-custody forms are included in Appendix B Concentrations
<br /> of TPH, as gasoline, and benzene reported in Table 2 are also shown on Figure 5
<br /> ?4bc'
<br /> 91-0441)RPT s, 2-
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