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• elevation was near its 24 May 2002 level was on 14 February 2001, during an extended period of the DPE unit operation on the Chevron site. During this event, when ground water flow was presumably toward the west, TPH-g concentrations increased from 679 ppb to 2,520 ppb in KF-3. The data from this one event would clearly contradict the model proposed by UEC if only data from single monitoring events are considered An example of using long-term trends would be EHD's interpretation of the sudden decrease of contaminant concentrations between November 1997 and May 1998 as a result of a ground water elevation increase of approximately 8 feet, with•the water table going over the well screens. Drowning of the wells may have been the most important factor in the apparent cleaning up of the dissolved hydrocarbons. Data from a number of sampling events must be obtained to show data trends and associate the trend with controlling factors." Upgradient Environmental does not agree that drowning of the well screens was the most important factor in cleaning up the wells_ Data from several wells disprove that conclusion, as discussed below. It is true that it is necessary to consider sustained trends to document the operative processes and prove cause and effect relationships. Upgradient Environmental began graphing hydrocarbon concentrations at this site in 2001, and a graph documenting the parallel decline in TPH-g concentrations in KF-3 and Chevron, well MW-6 was presented in the Problem Assessment Report for the Kwikee site (July 2001). Figure 9 of this report is a modified version of that graph, and the sustained downward trend in gasoline concentrations exhibited by the graph was discussed in section 2.4.3. In addition, it was pointed out in section 4.9 that the concentration increase that was observed in KF-3 in May 2002 was not from a single well, but was a phenomenon that was observed in several wells concurrently. It must therefore be regarded as,significant, and its temporal correlation with the sudden increase in eastward hydraulic gradient does not appear coincidental. The data from Chevron well MW-6, which is screened over the same interval as KF-1, 2, and 3, are clearly inconsistent with the interpretation that the decrease in hydrocarbon concentrations between November 1997 and May 1998 was due to a rise in the water table above the well screens. The water table rose above the screens in MW-6 in early 1996 and has remained above the screens since then, yet as Figure"9 shows, concentrations had been decreasing in MW-6 since at least 1993. Furthermore, the sharpest decline observed in that well took place in mid-1996, notin early 1998. Equally contradictory data are available from MW-7; from 1992 through the end of 1995, the static water level was within the screened interval and TPH-g concentrations ranged from 2,700 to 24,000 ppb. In 1996 and 1997, the water level was 3-8 feet above the screens, and concentrations ranged from 9,900 to 22,000 ppb (Appendix B). If anything, concentrations may have been slightly higher—but not lower—after the water level rose above the screen. . 22