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f <br /> Quarterly Groundwater Monitoring Results <br /> This report summarizes results of the quarterly groundwater monitoring conducted on <br /> November 11,1998 at the Disco property in Stockton,California. The results include water <br /> level measurements and laboratory analytical results.Water level measurements and <br /> groundwater sample collection were performed by Del Tech of Oakdale,California. <br /> Field data sheets,chain-of-custody and laboratory analysis reports for this sampling event <br /> are included as attachments to this summary. Figure 1 shows a map of the Disco property <br /> and vicinity. The Disco property is located southeast of the intersection of Myrtle Avenue <br /> and Filbert Street in Stockton,California. <br /> Groundwater Elevation Data-Groundwater elevation data for the period between <br /> September 1991 and November 1998 are summarized in Table 1. Shallow groundwater <br /> elevation contours for the November 1998 sampling event are presented on Figure 1. Table 2 <br /> presents the groundwater gradient direction and magnitude for each quarter since July <br /> 1993. Figure 2 graphically presents the variation in flow directions at this site since July <br /> 1993. <br /> Groundwater elevations measured within monitoring well MW-DIS-8S were not used for <br /> drawing groundwater contours from August 1997 through July 1998 because they were <br /> unusually high. This is most likely due to changes in the elevation of the top of the well <br /> casing,i.e. the well casing may have settled. Monitoring well MW-DIS-3 may have also <br /> settled,since recent groundwater elevations measured in this well have also been unusually <br /> high. Construction on the street and sidewalk is currently occurring around wells MW-DIS- <br /> 8S and-8D,and the dirt area surrounding MW-DIS-3 may have become compacted due to <br /> heavy truck traffic. Also,groundwater elevations measured in AS/SVE wells and nested <br /> fpiezometers were not used in drawing these gradient maps because the top of the well <br /> casings have not yet been surveyed. <br /> j The groundwater levels have risen about 30 feet at this site since measurements began in <br /> September 1991.Groundwater flow directions were west to northwest in 1993 and 1994. <br /> Groundwater flow directions were not calculated during 1995 due to SVE system operation <br /> (Flow directions were determined in October 1995 when the system was temporarily turned <br /> off). The groundwater flow direction has been consistently towards the southeast at a <br /> magnitude of approximately 0.001 ft/ft since October 1995. <br /> fAnalytical Results-Analytical results are presented in Tables 3 and 4.Table 3 presents <br /> groundwater sample analysis for TPH-gasoline and benzene,toluene,ethyl benzene,and <br /> xylenes(BTEX).Table 4 presents analytical results for MTBE and other oxygenate <br /> compounds. <br /> 1 <br /> f <br /> f <br /> fOTFLREP 12-98.00C <br />