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so that the static water level is presently within the screened interval, and the well is locate d close to the axis of the Modesto Channel, in an area of high soil contamination The present extent of diesel-range hydrocarbons in the groundwater is interpreted in figure 12 Although the overall shape of the plume is open to interpretation, one thing appears clear all of the highest TPH-d concentrations that have been measured in groundwater samples have c Mme from bonngs and/or wells that are located east of the UST excavation Based on this, it is fai,ly certain that the center of the groundwater plume is located east of the excavation, rather than west This is significant when the groundwater flow direction is considered (see next section) 3.6 Groundwater Gradient and Flow Direction Depth-to-groundwater measurements and calculated groundwater elevations for both March 22 and April 9 are presented in Table 4 Results from previous monitoring events are included for comparison Based on the survey of April 9, the casing elevations of most wells were i evised by 0 01 to 0 03 feet relative to GT-3 (the reference point well) The static water level is slightly more than 2 feet shallower than it was last year at this time, and now averages approximately 46 feet in depth,placing it within the most contaminated porgy ion of the Modesto Aquifer The present elevation(relative to sea level) is slightly less than minus 1')feet . The calculated water table elevations were used to construct the groundwater gradien maps in Figures 13 and 14 These maps are divided into four quadrants,and each quadrant shows a different] but possible interpretation of the data Maps 13A and 14A present the interpretation that the primary flow direction is to the south, but is interrupted by a linear, southeast-trending groundwater ridge extending from GT-3 toward GT-1, which creates a groundwater depression near GT-10 Presumably, the primary gradient is reestablished somewhere south of the Gillies property Maps 13B and 14B illustrate an alternative interpretation in which a groundwater depression is located northeast of GT-10 and the local flow direction is highly variable West of GT-2, the flow direction is east or southeast, whereas south of GT-6 it vanes from northwest (toward the depr--ssion) to southwest (toward a possible second depression south of the Gillies property. Figures 13C and 14C illustrate yet another interpretation in which the primary gradient is to the southeast, but a groundwater trough forms an arc from GT-9 through GT-3 to GT-10 and interrupts the primary gradient The fourth interpretation (Figures 13D and 14D) depicts a pnmary gradient to the northeast, created by a linear groundwater trough that trends in that direction from GT-9 through GT-10 None of these maps bears a close resemblance to the maps that were constructed in 1995 through 1998, prior to the drilling of GT-10 The maps constructed in October 1996 and November 1997 depict a wes 7trenduig _oundwater trough between GT-6 and GT-2, such a trough ,annat be accommodated by the present data and none of the maps in Figures 13 and 14 shove s a west- trending trough The map constructed in December 1996 depicts an`east4rending groundwater ridge in this same location, a somewhat similar ridge is shown in Figures 13B and 14B All other • 8