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iQ _ a _ ON B1-Anal Ground-Hater Monitoring Report 1 13475 Highway 88-E leekeford, California RGA Project No. 10-40-104 Page 2 summa of Rrevious Work Previous work performed by Applied Geosystems (AGS) at this site include the installation of four ground-water monitoring wells in June, 1987; issuance of a report evaluating the extent of petroleum hydrocarbons in soil and ground water at the site in July, 1987; and preparation of ground-water monitoring reports in October, 3987; April, 1988; July, 1988; and August, 1989. NGA prepared a previous bi-annual ground-water monitoring report for this site in October, 1990. QL,TS NgteX Table?310vations Water table elevations were measured by a representative of NGA for this report in April, 1991. The depth to the ground-water surface was measured from the north side of the casing of each well with an electric tape. Water table elevations are reported in Table 1. Water table elevations range from a low of 26.01 feet above mean . i sea level (msl) at monitoring well MW-2 to a high of 27.54 feet msl - at. monitoring well MW-4. A water table contour map (Figure 2) , depicting the elevation of tha ground-water surface at the site, has bean prepared in order to determine the. direction .of ground- water flow. Examination of Figure 2 shows the direction of-ground- water flow at the site to be in a southwesterly direction. The hydraulic gradient of the water table at. the site is calculated to a be .about 0.007 foot/foot. TABLE 1 Ground-Water Elevations e Depth to Water & patCasing Elevation Water Table Elevation (feet below surface) (mean sea levels (mean sea, eve]] MW-1 4/16/91 72.20 99.62 27.42 MW-2 4/16/91 72.45 : 99.26 26.81 i . i MW-3 4/16/91 72.61 100.00 27.39 6 MW-4 4/16/91 71.30 95.84 27.54 ----- 11-elevations-are-referenced-relative---to--an arbitrary--elevation -of--100.00--feet----- mean of--100.00--feet--lean sea level (msl) assigned to monitoring well MW-3.