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k'q KLEINFELDFR i 4 ACTIVITIES CONDUCTED Kleinfelder conducted the groundwater sampling for the Second Quarter 2005 } groundwater monitoring. Kleinfelder measured water levels in all of the monitoring wells and piezometers, and sampled eight monitoring wells (MW-DIS-9, MW-DIS-11s, MW-DIS-11d, MW-DIS- 12, MW-DIS-13, MW-DIS-14s, MW-DIS-14d, and MW-DIS-15). All of 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 i 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). Air inlet and outlet samples were also collected on the thermo/catalytic 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 20 monitoring 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. June 20, 2005 depth to water measurements are included in the Record of Water Level Measurements in Appendix S. The Monitoring Well Construction Detail can be found in Table 1. The resulting pertinent 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 upgradient and downgradient groundwater conditions. See Table 2 for the groundwater elevation data. Plates 2 shows the location of the groundwater monitoring wells. The depth to I groundwater ranged from 43.40 feet below the top of the well casing (MW-DIS-11s) to 52.64 feet below the top of the well casing (MW-DIS-15). Groundwater elevations for the monitoring wells ranged from -32.09 feet MSL (MW-DIS-5 and MW-DIS-6) to -33.16 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 i relatively flat on June 20, 2005 towards the southeast ranging from 0.0006 ft./ft. ? between MW-DIS-6, MW-DIS-10, and MW-DIS-4 to 0.0008 ft./ft between MW-DIS-10, MW-DIS-12, and MW-DIS-13. 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 with time, �- however, past data have consistently has suggested a similar groundwater gradient 12280.M0N/ST05R803/JZ:IV Page 7 of 15 ©2005, Kleinfelder, Inc. July 25,2005 i