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f <br /> ZI <br /> RiAoua Market <br /> Fourth Quarter Groundwater Sampling Report November 2004 <br /> Page: 2 <br /> • <br /> Groundwater flow direction was to the northeast with a very shallow gradient (North 21 <br /> East / 0 003) similar to past monitoring events The groundwater elevations and <br /> groundwater flow direction are shown on Figure 2 Site Map / Groundwater Flow <br /> Groundwater Elevations 11/01/04 <br /> Well Collar Elev—a-777 DTW GW Elevation <br /> MW-1 6328 2721 3607 <br /> MW-2 6359 275 3609 <br /> MW-3 638 2772 3608 <br /> MW-4 6352 2745 3607 <br /> The analytical laboratory reported groundwater contamination by MTBE in well MW-2, <br /> located at the edge of the tank basin Trace concentrations (below drinking water <br /> standards) of aromatic hydrocarbons were detected in the deep well, MW4 Groundwater <br /> chemistry for the November 1, 2004 event is presented in Figures 3, 4, and 5 An Oxygen <br /> low is present at MW1 with higher oxygen concentrations measured in the down gradient <br /> wells Dissolved oxygen distribution for the November 1, 2004 event is shown in Figure <br /> 6 <br /> Laboratoa Groundwater Sample Results Petroleum Com ounds 11/01/04 <br /> SMEle I D I Gasolme I Benzene Toluene I E-Benzene I Xylenes I MTBE I t-Butanol I 1,2DCA I DO <br /> MW-1 <0 05 <0 3 <0 3 <0-3 <0 6 <0 5 <5 <0 5 7 14 <br /> MW-2 007 <0 3 <0 3 <0 3 <0 6 362 <50 <5 0 106 <br /> MW-3 <0 05 <0 3 <0 3 <0 3 <0 6 <0 5 <5 <0 5 422 <br /> MW4 <0 05 1 5 43 1 4 71 <0 5 <5 <0 5 539 <br /> ND=Non Detect NA=Not Analyzed <br /> Mg/L for gasoline&Dissolved Oxygen µg/L for BTEX,MTBE,and 8260 Oxygenated Compounds <br /> The lateral and vertical extent of MTBE, the contaminant of concern has been defined <br /> laterally and vertically to be restricted to the immediate vicinity of the former <br /> underground storage tanks A survey of potential contamination plume receptors within <br /> 2,000 feet of the point of release identified water well approximately 2000 feet from the <br /> former underground storage tanks <br /> It appears that the release does not pose a risk to the identified water wells in the vicinity <br /> of Ripona Market Quarterly monitoring of all wells will continue An evaluation of the <br /> potential long term threat of the impacted groundwater and corrective action pian was <br /> submitted on October 28, 2004 to the San Joaquin County Environmental Health <br /> Department <br />