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i h4 KLEINFELDER 4 ACTIVITIES CONDUCTED P Kleinfelder conducted the groundwater sampling for the Fourth Quarter 2004 groundwater monitoring. Kleinfelder measured water levels in all of the monitoring wells, and sampled seven monitoring wells (MW-DIS-11s, MW-DIS-Ild, 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 so groundwater gradients could be calculated. Data obtained from the wells was used to evaluate groundwater flow, groundwater impacts and the need for additional assessment. Additionally, Photo-ionization detector (PID) samples were taken from vapor extraction well (VE-1) during the First Quarter 2005. Air inlet and outlet sampling was also conducted on the thermolcatalytic oxidizer. 4.1 MEASUREMENT OF WATER LEVELS In order to assess the groundwater gradient at the time of sampling, water level measurements were made in each of the twenty(20) monitoring wells and three (3)piezometers at the beginning of the sampling round, prior to purging and sampling of the wells (see Record of Water Level Measurements in Appendix B). The depth-to-water was measured in each well according to the i 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. [ The resulting pertinent groundwater elevations were used to assess the direction of the groundwater flow and gradient at the time of sampling. This information was then used to assess which wells represent upgradient and which wells represent downgradient groundwater conditions. See Table 1 for the groundwater elevation data. Plates 2 shows the location of the groundwater monitoring wells. Groundwater elevations for the monitoring wells ranged from—35.72 feet (MW-DIS-6) to —38.00 feet (MW-DIS-15). The depth to groundwater ranged from 46.54 feet below the top of the well casing (MW-DIS-11s) to 57.68 } feet below the top of the well casing (MW-DIS-15). A groundwater gradient and flow direction was calculated based on depth-to-water data collected from the wells on December 20, 2004, using data collected during a survey produced by KSN Inc, on February 14, 2002. Groundwater flow direction at the site is estimated to be generally towards the east/southeast with a relatively flat gradient of approximately 0.0005 ft./ft. This flow direction for the second quarter, continues to show a shift from the previous south/southeast flow directions. A groundwater contour map is included as Plate 3. In areas of relatively flat groundwater gradients such as this site, groundwater flow directions may significantly fluctuate due to rainfall, groundwater recharge, groundwater pumping, etc. Therefore, changes in groundwater flow directions may vary at this site with time, however, past data consistently has suggested a similar groundwater gradient and l flow direction. 12280.MON/ST05R613/7Z:1v Page 7 of 13 2005,Kleinfelder,Inc. May 20,2005 i