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QUARTERLY MONITORING REPORT PAGE PAGE 5 of 58 QUARTER DATE First Quarter 2006 26-Jun-2006 several thousand feet of terrestrial and marine sedimentary rocks The northern San Joaquin Valley has been a lowland area subject to marine intrusion, flooding and incremental sedimentation for millions of years The uppermost 1000 feet of sedimentary strata consist of Holocene, Pleistocene and Pliocene sediments, including the Laguna Formation,the Mehrten Formation and the Valley Spring Formation The sediments are interbedded mixed- fluvial and deltaic sediments, dominated by medium-grained sand and silts Generally, thin beds of unconsolidated clayey sift, silty clay and sandy clay are abundant in this upper zone, which are laterally discontinuous over distances of several tens of feet 4 0 Hydrogeology 41 Description 41 1 Depth to water during this quarter's sampling event vaned from 29 88 feet below ground surface (bgs)in well MW-4 to 31 21 feet bgs in well MW-2 The elevation of groundwater in MW-1, MW-2, MW-3, and MW-4 was calculated by El to be at 17 45, 17 79, 17 65, and 17 53 feet below mean sea level (MSL) respectively, based upon casing elevation data from Kier&Wright Civil Engineers and Surveyors All groundwater elevation data including the historical data is summarized in Table 1 5 0 Results 51 Groundwater Level Measurements 51 1 Figure 5 shows groundwater elevations at various dates The groundwater elevations have increased approximately four feet since last quarter and decreased over six feet since the corresponding season in 2000 The elevations fluctuate over very significant ranges(up to 5 feet in 9 months),which will affect contamination levels,flow direction, gradient, etc 51 2 The elevations in wells MW-1, MW-3 and MW-4 move in tandem,with MW-2 generally following the same trend, but, moving higher or lower somewhat randomly This is due to the difficulty of measuring groundwater elevations in MW-2 because of free product in this well 5 1 3 This quarter's measurements of groundwater elevations were contoured and indicate a delineated line between MW-1 and MW-4 The area above the delineation line defined directional flow in a northerly orientation while the area below the delineation line defined directional flow in a southeasterly orientation The hydraulic gradient averages 0 0038 feet per foot across the well field (above the delineation line)and 0 0042 feet per foot across the well field (below the delineation line) A groundwater elevation summary and directional flow map for the first quarter groundwater measurements are shown on Figures 4 and 5 5 1 4 The groundwater elevation data collected during this event is typical of the site, and is consistent with historical data and seasonal trends 52 Groundwater Sample Analysis 5 2 1 This section presents the results of the most recent groundwater sampling event, and synthesizes these data with other data previously collected Table 2 summarizes the groundwater monitoring well analytical results from the most recent groundwater monitoring event Certified analytical laboratory reports and chain-of-custody documentation are included as Appendix C 522 TPH-diesel appeared in MW-1 at a concentration of 4100 ppb, consistent from last quarter All other constituents were below the reporting limits 523 MW-2 found continued contamination from DIPE, BTEX,TPH-diesel, and TPH-motor oils TBA, MTBE, EDB, DCA12, ETBE,TAME, and TPH-gasoline were below the reporting limits CONFIDENTIAL