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kn KLEINFELDER 4 ACTIVITIES CONDUCTED Kleinfelder supervised the activities conducted for the Third Quarter 2002 groundwater J monitoring. Del-Tech Geotechnical Support Services of Oakdale, California measured water levels in, and sampled the existing monitoring wells (NP-1-70', NP-1-80', NP-1-90', MW-DIS- 1, MW-DIS-2, MW-DIS-9, MW-DIS-11s, MW-DIS-11d, MW-DIS-12, MW-DIS-13, MW-DIS- 14s, and MW-DIS-14d). All of the wells 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. 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 20 monitoring wells and 3 piezometers at the beginning of the sampling round, prior to purging and sampling of the wells (see the attached Del Tech Monitoring Well Field Summary Log 2002). The depth-to-water was measured in each well according to the jprotocol described in Appendix A, Section A-4.1. The depth-to-water measurements were then converted to relative groundwater elevations with respect to mean sea level or a local.benchmark f by subtracting them from the surveyed casing elevations. I 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. Plate 2 shows the location of the groundwater monitoring wells. Groundwater elevations for the monitoring wells ranged from --32.67 feet (MW-DIS-5) to -33.16 feet (MW-DIS-14d). A groundwater gradient and direction was calculated based on depth-to-water data collected from these wells on August 12, 2002, and by data collected during a survey produced by KSN Inc. on February 14, 2002. The groundwater flow direction is estimated to be towards the south at a relatively flat gradient of approximately 0.0002 ft./ft. A groundwater contour map is included as Plate 3. In areas of 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 flow direction. l 12280.MON 1 ST02R519 Page 6 of 14 ©2002,Kleinfelder,Inc September 19,2002