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Geologkal recl"Ics/ttc Page 5 Groundwater Monitoring Report Project No.750.2 November 10,2004 groundwater elevation decreased approximately 1.75 feet since the May 7, 2004 monitoring event. Depth-to-water measurements averaged 65.95 feet AMSL. Groundwater gradients were calculated for the August 2004, groundwater-monitoring event using MW-1, MW-2 and MW-3. Groundwater was flowing N82°W at 0.0022 ft/ft. The elevation, gradient and bearing data are summarized in Table 1 of 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 September 15, 2004, with confirmation number 4632949650. 2.3.3 Vertical Groundwater Gradient For the August 12, 2004, groundwater measurement, the vertical gradient was calculated for the MW-1/MW-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 since February 2001, Figure 2 shows the location of the well cluster used for calculating vertical groundwater gradient in this report, MW-1 and MW-101. Table 2 of Appendix A summarizes the calculated vertical gradients. 2.3.4 Average Groundwater Velocity The lithology at the COE site will be divided into four general layers for the purposes of calculating the average horizontal groundwater velocity. o Layer 1 consists of silts and sands from 5- to 30-feet bgs o Layer 2 is primarily sand with some larger clasts from 30-to 45-feet bgs o Layer 3 is primarily silt from 45- to 50-feet bgs o Layer 4 is primarily sand from 50- to 70-feet bgs. r The average depth to groundwater at the site suggests only Layer 4 will contain groundwater in a saturated state. Laver 1 The average hydraulic conductivity (K), estimated from typical K values for silt and sand mixtures (Driscoll, 1986), 11.98- to 1198-feet per year (ft/yr), and the average hydraulic gradient (i) across the site is approximately 0.0019. Based on the equation v=K i/n, where n is effective porosity estimated at 0.35 (Driscoll, 1986), the average horizontal groundwater velocity(v) of Layer 1 is estimated to be approximately 0.065 to 6.5 ft/yr.