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i kn KLEINFELDER 4 ACTIVITIES CONDUCTED Kleinfelder conducted the groundwater sampling for the Fourth Quarter 2005 groundwater monitoring. Kleinfelder measured water levels in 19 monitoring wells, 2 former soil vapor extraction wells, and 3 piezometers, and sampled seven monitoring wells (MW-DIS-11S, MW-DIS-11D, MW-DIS-12, MW-DIS-13, MW-DIS-14S, MW-DIS- 14D, MW-DIS-15). The wells and piezometers were previously surveyed by Kjeldson, Sinnock, Neudeck, Inc. (KSN, Inc.) of Stockton, California on February 14, 2002 so groundwater gradients could be calculated. Measurements obtained from the wells were used to evaluate groundwater gradient, groundwater impacts and the need for additional assessment. Photo-ionization detector (PID) samples were collected from vapor extraction wells (VE-1, VE-2, VE-3, VE-4, VE-5, and mainline leading to oxidizer). Air inlet and outlet samples were also collected from the thermolcatalytic oxidizer. 4.1 MEASUREMENT OF WATER LEVELS To assess the groundwater gradient at the time of sampling, water level measurements were made in each of the 19 monitoring wells, two former soil vapor extraction wells, and three piezometers at the beginning of the sampling round, prior to purging and sampling of the wells. The depth-to-water was measured in each well according to the protocol described in Appendix A, Section A-4.1. The depth-to-water measurements were then converted to relative groundwater elevations with respect to a surveyed benchmark by subtracting them from the surveyed casing elevations. December 8, 2005 depth to water measurements are included in the Record of Water Level Measurements in Appendix B. The Monitoring Well Construction Detail can be found in Table 1. The resulting groundwater elevations were used to assess the direction of the groundwater gradient at the time of sampling. This information was then used to assess which wells represent up gradient and down gradient groundwater conditions. See Table 2 for the groundwater elevation data. Plate 2 shows the location of the groundwater monitoring wells. The depth to groundwater ranged from 44.60 feet below the top of the well casing (MW-DIS-11S) to 53.82 feet below the top of the well casing (MW-DIS-15). Groundwater elevations for the wells ranged from —32.79 feet MSL (SVE-N) to -34.38 feet MSL (MW-DIS-13). A groundwater gradient direction was estimated based on depth-to-water data collected from the wells. The groundwater gradient was relatively flat on December 8, 2005 towards the east/southeast at 0.0006 ft./ft. A groundwater elevation contour map is included as Plate 3. In areas of relatively flat groundwater gradients such as this site, groundwater gradients may significantly fluctuate due to rainfall, groundwater recharge, groundwater pumping, etc. Therefore, changes in groundwater may vary at this site i with time, however, past data have consistently suggested a similar groundwater 12280.M0N/ST06R0701CD:Iv Page 7 of 14 ©2006 Kleinfelder, Inc. February 16,2006