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. GT-1 and GT-10 w ere also analyzed for TPH-g and BTEX, and the sample ft om GT-10 was additionally analyzed foi the five gasoline ox)genates 3.0 RESULTS 3 1 Groundvi atcr Gradient and Flow Direction Depth-to-groundwater measurements and calculated groundwater elevations are presented in Table 1 Results tioin pin,ious nionitoiing events are included for comparison The static vatet level is slightIN more than 1 toot dt.eper than it was in Match of this year, and now averages approxim.itely 47 feet in depth It is still within the most contaminated portion of the Modesto Aquifer The present ele'vation (relative to sea level) is slightly less than minus 20 teet The calculated water table elevations were used to construct the gioundwvater gradient map in Figure 3 It appeats that the gradient continues to shift directions, because the present f radient is totally Linlike any of the tour possible maps that wei e presented in the First Quarter 1999 eport At that time "he ele%ation of the eater table was lowest in well GT-10, creating an apparent depression or sink in the vicinit-, of that cell At the present time the water table in this well is higher than in most of the other %�eIls and is lowest in GT-5, which normally has the hig lest water . table eleNation As a result, there is a rela—,elf strong gradient from GT-5 toward G1-7 and a somewhat flatter gradient from GT-9 to GT-7. yielding a groundwatet flow direction to the northwest or north The tendency for the groundwater gradient to change directions has been observed c,n several occasions during the course of this investigation One likely explanation for this tendency is that the direction is partly controlled by pumping of agricultural and other wells in the sit( vicinity Howe%er, with the piesen' data we cannot link the changes in groundwater gradient with changes in season For example, northward, southward and westward gradients have all bee i mapped during the winter months, and no single direction seems to predominate in any season 3.2 Laboratory Results Significant changes in contaminant concentrations also occurred duting the second quaitei (Table 2) Diesel concentrations decreased inarkedly in GT-10, GT-1 and GT-3, while increasing in GT-2 More significantly, diesel was detected for the fir,,t time in the Gillies domestic well (30-1) at a surprisingly high concentration As a result isocontour mapping of diesel concentration, depicts a change in the shape of the diesel plume (Figure 4) Previously, the plume was mapped a, a simple ellipse oriented east-west Now, the plume appears somewhat contorted, and extends co isiderably farther to the south"est and northeast than before Fhis change maybe the result of pumping from G-1, pulling the contaminants to the north . Gasoline and BTFX Compound, were again dejected ,.a GT-10, but at signiftcantl•i n:duced concentrations This, may be due to more thorough purging prior to sampling, but is more likely due 3