ARCHIVED REPORTS_20100427 ATC 1Q2010 GWMR COMPLETE

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Ms.Amy Terrell April 27,2010 Page 3 of 10 GROUNDWATER ELEVATIONS AND GRADIENT Table 3 summarizes groundwater levels measured during the current and previous sampling events. Well locations and top of casing (TOC) elevations were surveyed for all Site monitoring wells on August 31, 2007 as part of the Expanded Pilot Test. TOC elevations are presented in Table 2 and historical groundwater elevations presented in Table 3 reference. Groundwater levels beneath the Site in March 2010 ranged from 59.74 to 60.24 feet above mean sea level (ft MSL). Groundwater elevation contours from the First Quarter 2010 sampling event are shown on Figure 3. The groundwater flow direction for the First Quarter 2010 groundwater monitoring event was to the east-northeast with a gradient of 0.0007 foot/foot (ft/ft), which is consistent with historical trends. Historical groundwater gradient and flow direction is tabulated on Table 4. Figure 4 graphically displays groundwater elevation for all monitoring wells at the Site since their respective installation date. The groundwater elevations typically display seasonal variability with a generally decreasing groundwater level trend since 1998. Groundwater elevations were observed to be at an all time low during the March 2010 groundwater monitoring and sampling event. ANALYTICAL RESULTS The samples collected during the March 2010 semi-annual groundwater monitoring and sampling event were analyzed by Southern Petroleum Laboratories, Inc. (SPL), of Houston, Texas. Specific constituents were subcontracted by SPL to Argon Laboratories of Ceres, California, APPL Lab of Clovis, California and TestAmerica of Irvine, California. Analytical results are presented in Tables 5 and 6 and on Figures 5 through 11. The analytical laboratory report is provided as Attachment 2. Table 5 provides historical data for the past eight years. Table 6 provides data from the pre-injection baseline monitoring event for the initial pilot study conducted in June 2002. A complete historical dataset is provided in Attachment 3. The following discussion of analytical results is organized according to the position of the monitoring wells relative to the Site: on-Site (MW-2, MW-3, MW-6R and MW-7) and downgradient of the Site (MW-5). Upgradient monitoring well MW-4 is sampled annually during the third quarter. On-Site: MW-2, MW-6R,MW-7 and MW-3 Monitoring wells MW-2, MW-3, MW-6R, and MW-7 are located along the eastern boundary of the Site (Figure 2). MW-2 and MW-7 are located immediately downgradient of the Expanded Pilot Test area and MW-6R is located within the Expanded Pilot Test area. The results of the Expanded Pilot Test performance monitoring are discussed later in this report. The following is a summary of the analytical results for the 2010 groundwater sampling event.