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v <br /> O*iarterty Cxar�dwatel MoNtpring Report <br /> 1µB00 West Frontage Road Manteca Caldornia <br /> BACKGROUND <br /> Aegis began a program of monthly monitoring and quarterly sampling of the wells in <br /> January 1991 Work performed at the site by previous consultants included investigations <br /> by Earth Treatment Systems, Inc (ETS), of Merced, California, Delta Environmental <br /> Consultants, Inc (Delta), of Rancho Cordova, California, and Nations Groundwater <br /> Associates of Sacramento, California In August 1988, two soil borings were drilled and <br /> completed by ETS as groundwater monitoring wells MW-1 and MW-2 In April and <br /> May 1989, Delta completed two additional soil borings as groundwater monitoring wells <br /> MW-3 and MW-4 In November 1989, Delta performed soil sampling during the removal <br /> of three 10,000-gallon underground fuel storage tanks Delta completed four more soil <br /> borings as groundwater monitoring wells MW-5 through MW-8 in November and <br /> December 1989 The previous consultants' groundwater data, along with Aegis' data, is <br /> included in Table 1 In November 1991, Aegis supervised drilling and completion of <br /> groundwater monitoring well MW-9 (Figure 2) <br /> GROUNDWATER MONITORING <br /> On April 20, May 18, and June 29, 1992, Aegis personnel collected measurements of <br /> depths to groundwater in wells MW-1 through MW-9 Between March 24 and <br /> June 29, 1992, groundwater levels have risen in all wells (Figure 3) an average of <br /> approximately 3 22 feet, ranging from 2 75 to 4 48 feet (Table 1) Figure 4 is a <br /> potentiometric surface map of the shallow water-bearing zone on April 20, 1992 Figure 5 <br /> is a potentiometric surface map of the shallow water-bearing zone on June 29, 1992 <br /> These maps indicate a reversal in gradient direction during the period reported On the <br /> basis of the June 20, 1992, measurements, groundwater flow direction is to the northeast <br /> with a gradient of approximately 0 008 ft/ft The previous quarter groundwater <br /> measurements indicated a gradient of 0 3 ft/ft to the southwest <br /> Groundwater measurements are summarized in Table 1 All groundwater elevation <br /> measurements were made according to the Aegis standard operating procedures (SOP) <br /> included in Attachment 1 <br /> 90 0978 OMR 2 <br />