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' Ripona Market <br /> Groundwater Monitoring Well Installation Report <br /> Page: 7 <br />' This unit was deposited in a predominately lacustrine environment Permeability <br /> and porosity in this unit can be expected to be considerably less than those found in <br /> the upper, sandier unit <br />' 3.1b — Groundwater Groundwater is found at a depth of 25 ft beneath the site <br /> Shallow ground water is found under water table conditions Gradient is to the <br />' ENE at 0 009 ft /ft This is typical for shallow groundwater in the Modesto area <br />' 3.2 Soils Contamination <br /> Soils contamination appears to be limited to the area around MW-2 at a depth of <br />' 25 ft (at the water table) This sample returned 1700 gg/l for MTBE Previous <br /> sampling at the site showed minor soils contamination at the water table in the <br /> vicinity of the former tank nest <br /> 3.3 Groundwater Contamination <br /> Relatively high levels of Benzene and MTBE were found in the groundwater <br /> samples collected from MW-2, the up gradient well Low levels of MTBE and <br /> ND for Benzene was found in the sample collected from MW-3, the down <br /> gradient well Both Benzene and MTBE were ND for the sample collected from <br /> MW-1, another up gradient well <br /> This indicates that the ground water contamination plume is rather small in size <br /> and that it may be remediating itself by natural attenuation in the subsurface <br /> However, it is possible that higher contaminate concentrations might be found to <br /> I the 15 to 20 feet due south of MW-3, directly down gradient from the high <br /> concentrations found in MW-2 An additional monitoring well placed directly <br /> down gradient from MW-2, on the NE side of the market would test the natural <br /> attenuation hypothesis <br /> 4.0 CONCLUSIONS AND RECOMMENDATIONS <br /> Contaminants of concern have been identified as gasoline range petroleum hydrocarbons, <br /> benzene, toluene, ethyl benzene, and xylenes probably sourced from the former <br /> Iunderground storage tanks and related piping MTBE at moderately high levels has been <br /> detected in this investigation <br /> ISoil contamination appears to be restricted to the immediate vicinity of the former fuel <br /> tanks However, high concentrations of contamination by MTBE and low levels of <br /> gasoline and gasoline components were detected in all of the groundwater samples The <br /> lowest concentrations of groundwater contamination by gasoline and gasoline <br /> components were detected in MW-1 The highest concentration of groundwater <br />