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GeorogiCdl T"h lcs Im Page 2 ' Groundwater Monitoring Report Project No 425 2 November 8,2005 The analytical results from the July 20, 2005 monitoring event show that TPH-G, BTEX ' and/or MtBE constituents are present in 6 monitoring wells (MW-1, MW-2, MW-4, MW-5, MW-8 and MW-106) The three domestic wells sampled dunng this event did not contain petroleum hydrocarbon contaminants above laboratory reporting linuts ' A summary of groundwater analytical findings include MW-1 shows the presence of TPH-G, BTEX and MtBE constituents Overall there ' appears to be a decrease in contaminant concentrations • MW-2 shows the presence of TPH-G and BTEX constituents MtBE is likely present but not detected due to elevated detection limits The plume appears stable around ' MW-2 Y MW-4 shows the presence of TPH-G and BTEX constituents The plume appears to be stable around MW-4 MW-4 likely represents the southern edge of the plume ' ® MW-5 shows the presence of TPH-G, BTEX and MtBE constituents Overall there appears to be a decrease in contaminant concentrations ' i MW-8 shows the presence of TPH-G and BTEX constituents The plume appears to be increasing in concentration around MW-8 MW-8 likely represents the eastern edge of the plume e MW-106 shows the presence of MtBE and is non-detect above laboratory reporting limits for all other analyzed constituents G Samples were collected from three domestic wells during the July 2005 monitoring event The domestic wells were non-detect above laboratory reporting limits suggesting contamination has not migrated to the monitored domestic wells ' 1.0 HYDROGEOLOGIC SYSTEM 1.1 Regional Structure ' George's Service (Georges) is located in the northeast quarter of the northeast quarter of the northeast quarter of Section 20, T3S, R6E, related to the Mount Diablo B&M, on the United ' States Geological Survey (USGS) Topographic Map, Vernalis Quadrangle, California, 7 5 minutes series A review of the USGS Topographic Map reveals that the elevation of this site is approximately 83 feet above mean sea level (AMSL) The site is located on the gradually sloped floor of the northern San Joaquin Valley The geologic composition of the area is characterized as fluvial deposits of the San Joaquin - Sacramento River delta system that overlay continental rocks and deposits derived from erosion of the Sierra Nevada Mountain Range located approximately 50 miles northeast of ' Modesto The southwest tilting Sierra Nevada fault block underlies the northern San Joaquin Valley area Overlying the consolidated rocks are unconsolidated sediments The lower consolidated I