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' T GeologicalTechnics inc. Page 2 Groundwater Monitoring Report Project No.750,2 April 12,2004 A vertical groundwater gradient calculation wa&made for the December 2003 groundwater- monitoring event. The vertical gradient was found to be in a downward direction with a slope that is less than the water table horizontal gradient. 1.0 GROUNDWATER MONITORING 1.1 Hydrogeology of Site The dominant soil type in the upper 75-feet of subsurface geologic soils investigated is sand C with fine to coarse-grained texture. Varying amounts of silt, silty sand and laterally discontinuous clay lenses were encountered from borehole to borehole. A thick clay layer was encountered starting at 95-feet in SB-101/MW-101 and continues to at least 115-feet. The average groundwater elevation measured 'during the December 9, 2003, event was 55.47 feet above mean sea level (AMSL), which is consistent with previously measured average elevations at the site. The groundwater elevation has not changed since the I monitoring event of September 6, 2003 Depth-to-water measurements averaged 64.63 feet AMSL. Groundwater gradients were calculated for the December 9, 2003 groundwater-monitoring C' event using MW-1, MW-2 and MW-3. Groundwater was flowing N62°W at 0.0029 ft/ft. The elevation, gradient and bearing data are summarized in Table 1, Appendix A. The groundwater gradient is illustrated on Figure 3: Groundwater Gradient Map. Historical groundwater directions and gradients are presented in Figure 4: Rose Diagram, which shows a historically westerly flow direction. As required under AB2886, the depth to groundwater data was submitted electronically to GeoTracker on February 12, 2004, with confirmation number 8449737370. L Vertical Groundwater Gradients For the December 9, 2003, groundwater measurement, the vertical gradient was calculated for the MW-UMW-101 pair. The vertical gradient was negative (a downward direction). However, it was insignificant as head difference between MW-1 and MW-101 was only 0.02-feet. Generally, the magnitude of the vertical gradient has progressively decreased r since February 2001. L Figure 2 shows the location of the well cluster used for calculating vertical groundwater gradient in this report, MW-1 and MW-101. Table 1 shows a summary of groundwater elevations, bearing and slope. Table 2 shows the calculated vertical gradients.