ARCHIVED REPORTS XR0008637 - Laserfiche WebLink

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I OuARZERLY GROUNDWATER MowmRING RERORf 1605 South EI Dorado 5treet.Stockton Callforma On December 17, 1991, the top-of-well casing elevations were resurveyed by Tom O Morrow, Inc , of West Sacramento, California 4 0 GROUNDWATER MONITORING 4.1 Groundwater On March 25, 1993, Aegis personnel collected measurements of the depths to groundwater in wells MW-1, MW-2, and MW-3 Since December 17, 1992, groundwater has risen in all the wells an average of 2 61 feet (Figure 3), ranging from 2 59 to 2 64 feet (Table 1) On the bass of the March 25, 1993, measurements, groundwater is estimated to flow to the east at an average gradient of 0 001 ft/ft This is the same gradient and flow direction estimated in December 1992 Figure 4 is a potentiometric surface map of the shallow water-bearing zone on March 25, 1993 Previous groundwater levels are summarized in Table 1 All groundwater elevation measurements were made from the referenced wellhead elevations, measured to the nearest 0 01 foot, and conducted according to the Aegis standard operating procedures (SOP) included as Appendix A 4 2 Water Sampling and Analysis On March 25, 1993, Aegis personnel collected groundwater samples from the three wells at the site The samples were collected according to the Aegis SOP included in Appendix A, and delivered under chain-of-custody to Pace Laboratories, Inc , of Novato, I California, a state-certified analytical laboratory The samples were analyzed for concentrations of a) TPH, as gasoline, by modified EPA Method 8015, and b) BTEX by modified EPA Method 8020 The analytical results are summarized in Table 2 The analytical reports and chain-of-custody form are included in Appendix B Concentrations of TPH, as gasoline, and benzene reported in Table 2 are also shown on Figure 5 5 0 SCHEDULED ACTIVITIES Quarterly monitoring will continue at the site The next quarterly sampling event is scheduled for June 1993 IAegis has received approval on a workplan for the installation of two vapor extraction wells and four or five additional groundwater monitoring wells, including one or two off-site y3 n766 I wells Data from the monitoring wells will be used to determine the extent of dissolved petroleum hydrocarbons in groundwater on and off site A vapor extraction pilot test will be performed to assess the feasibility of this technology for remediating soil within and beneath the former UST basin The work will be completed when the open UST excavation has been backfilled The backfilling has been delayed by weather However, the work is expected to be conducted in April 1993 91-044D GMR 2