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• Mr Terry Tarditi <br /> May 17, 2002 <br /> Page 3 <br /> Table 4. Comparison of Groundwater Analytical Results <br /> with Previous Sampling Event <br /> TPH-G Benzene MTBE 8260 B <br /> 01 qtr,01 1qtr,02 40 qtr,01 1,1 qtr,02 4th qtr,01 1•'9tr,02 <br /> Highest concentration L 360 320 90 41 24,000 14,000 <br /> Well with highest concentration MW-3 MW-3 MW-3 MW-3 MW-1 MW-1 <br /> Number of wells with detecuon 1/4 3/4 1/4 1/4 3/4 3/4 <br /> Discussion: <br /> Based on this quarter's data, the groundwater flows hydraulic gradient is basically <br /> flat, as shown in Figure 2 BTEX concentrations remained consistent wrath the <br /> previous quarter in all four wells, except for a decrease in benzene concentrations <br /> in MW-3 TPH-G concentrations were below laboratory reporting limit of 5,000 <br /> gg/L in MW-1,within historical results in MW-3, and were not detected in MW-2 <br /> and MW-4 <br /> . MTBE was not detected in MW-2, and remained consistent with historical results <br /> in MW-3 and MW-4 Due to the elevated concentrations of MTBE in the sample <br /> from MW-1, the method reporting hrrut for BTEX, TPH-G, and MTBE were <br /> increased due to sample dilution The dilution is necessary because the MTBE <br /> concentration is out of the calibration range for the target analyte MTBE <br /> concentrations increased to a historical high result of 24,000 gg/L in MW-1 in the <br /> 4thquarter 2001 and decreased to 14,000 gg/L this quarter The chromatographs <br /> were requested to verify this result <br /> It is not clear why MTBE concentrations elevated so sharply without the common <br /> occurrence of other BTEX components It is possible the rise in groundwater <br /> elevations remobilized MTBE, however,groundwater elevations are not at or near <br /> historical high levels In the 2R1 quarter 2002 sampling event, a second run of the <br /> sample from MW-1 will be analyzed at a lower dilution to determine a better <br /> quantification of BTEX constituents <br /> This report was prepared in acwrdance with the standards of the environmental consulting industry at the ume a was prepared It should not be <br /> rehed upon by parties other than those for whom it was prepared,and then only to the extent of the scope of avrk which was authonZed Tots <br /> rxport does not guarantee that no additional environmental contamination beyond that desmbed in this row exists at the site <br /> P\21000\21417\Reports\1st-02qu doe <br />