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' Rpona Market Vertical Groundwater Investigation II Report Page 9 The upper 15 feet of sediments explored at the site consist of medium dense to dense, fine to medium, angular, arkosic sands A fine-grained unit is present from depths 21 to 30/35 ft This unit consists of interbedded predominately moderately consolidated low plasticity, clays, silts, and poorly sorted silty sands The consolidated nature of the fine-grained unit provided a solid foundation for the installation of the conductor casing Shallow unconfined groundwater was present ' at an approximate depth of 25 feet The basal portion of the borings below the fine-grained unit is composed of fine to medium grained moderately sorted unconsolidated sands The sands are unstable and often flowed into the borehole under hydraulic pressure The "heaving sands" flowing into the open augers restricted the insertion of the dull bit and sampling ' tools As noted on the logs "heaving sands" prevented the collection of soil and water samples at several of the planned intervals ' 3.2 Soil Contamination Soils contamination was not detected in any of the soil samples collected in the ' boring (Table of Laboratory Soil Sample Results — August 24, 2005), Fuel oxygenates were previously detected in soil samples collected at depths of 25 and 30 feet in a boring located adjacent to the former underground storage tanks An MTBE contamination cross section is shown as figure 4 3.3 Groundwater Contamination 1 Groundwater contamination by gasoline, BTEX, and MTBE was not detected in the new deep down gradient well, MW-5 Low concentrations of MTBE were detected ' in a water sample collected from well MW-2 located adjacent to the former underground storage tanks and trace concentrations of MTBE were detected in a water sample collected from the deep well, MW-4 during the July 2005 quarterly ' monitoring event A report of the July 2005 quarterly monitoring event was submitted to the San Joaquin County Environmental Health Department under separate cover MTBE groundwater contamination is shown in map view in figure 6 and in cross section in figure 4 MTBE groundwater contamination is limited to the vicinity of well MW-2 and defined vertically at a depth of 55 to 60 feet vertically 4.4 CONCLUSIONS AND RECOMMENDATIONS O MENDATIONS ' The lateral and vertical extent of MTBE, the contaminant of concern has been defined laterally and vertically and is restricted to the immediate vicinity of the former underground storage tanks A survey of potential contamination plume receptors within 2,000 feet of the point of release identified water a well approximately 2000 feet from the former underground storage tanks It appears that the release does not pose a risk to the Iidentified water wells in the vicinity of