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L C ea la$i ca!Tulut ins!�c. Dual Phase Extraction Pilot Test Report Page 9 �-. Project No.723.2 November 5,2004 trail-and-error results in an optimum depth for the stinger to preclude a well from going While using this technology. After the stinger was raised to 47 feet bgs, the well continued o sustain an extraction rate of over 3 gpm for the next twenty four hours. As stated above, depth to water measurements were made in well VEW-1. Table 5 in Appendix A includes the depth to water values and their corresponding eev Figure 4 shows the drawdown measured in well VEW-1 for the first several hours of lation data. groundwater extraction, from EW-1. When extraction starts the depth to water in VEW-1 drops approximately one foot in four hours and then the level stabilizes at 37.68 feet below the top of the well collar. The pumping rate during this period averaged about 4 gallons per minute until the stabilization occurred. The uniform drop in elevation followed by a stable level suggests that the two wells' screens are intercepted by laterally continuous geologic units. As vacuum was applied to EW-1 the well filter pack de-watered and then the vacuum spread out laterally along units of higher conductivity to intercept well VEW-1. Past site investigation efforts identified the geology in the location of the wells as clayey. No sandy or silty layers were encountered but the sample intervals were five feet in the boreholes. It is probable that thin layers of sand or silt layers exist and extraction from these layers produced the decrease in water quantity in VEW-1. After the vacuum stabilized in these layers, they began producing enough water to sustain the 4 gpm rate. V Figure 5 illustrates the cross section relationship of the water drop in VEW-1. After the first 20 hours of extraction, well EW-1 went dry as noted above. This suggests that the cone of depression in EW-1 was very steep as shown in Figure 5. The clayey strata would also suggest-that a steep sloped cone would develop as EW-1 de-watered. Obviously the test did not progress long enough to allow the developing cone to further reduce the groundwater �. elevation in VEW-1. '- 5.0 DISCUSSION The following sections will summarize the results of the pilot test efforts. L 5.1 Vapor Extraction The pressure necessary for demonstrating vacuum influence is generally regarded as at least 0.1 inches of water ("How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites", USEPA, May, 1995). The influence detected in monitoring wells VEW-1, VEW-2 and MW-5 during extraction from EW-1 achieved a minimum of 0.3 inches water vacuum (see Table 3). Well MW-5 is located approximately 46 feet from EW-1 and this distance is used as a conservative estimate as the radius of influence. Figures 5 and 6 indicate the measured vacuum in the wells at 10:00 A.M. and 6:00 P.M. (18:00 hours), respectively on July 26t . The radii of influence in these figures suggest that a soil vapor