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�d - PAGE QUARTERLYMONITORING RERORT� - r 5 of 61 QUARTER .�. _ _ � - DATE Third Quarter 2005 19-Oct-2005 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 silt, 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 34 23 feet below ground surface(bgs)in well MW4 to 34 90 feet bgs in well MW-2 The elevation of groundwater in MW-1, MW-2, MW-3, and MW4 was calculated by EI to be at 21 66,21 48,21 76, and 21 88 feet below mean sea leve! (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 decreased approximately three 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 5 1 2 The elevations In wells MWA, MW-3 and MW4 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 51 3 This quarter's measurements of groundwater elevations were contoured and Indicate a delineated line between MWA and MW-4 The area above the delineation line defined directional flow in an southeasterly orientation while the area below the delineation line defined directional flow In an eastern orientation The hydraulic gradient averages 0 0042 feet per foot across the well field (above the delineation line)and 0 0012 feet per foot across the well field (below the delineation line) A groundwater elevation summary and directional flow map for the second 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 1h4s IS04 Y>< 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 1� included as pendix C r 522 TPH-diesel appeared in MWA at a concentration of 5700 ppb,a significant decrease from last quarter All other constituents were below the reporting limits a`sb, 523 MW-2 found continued contamination from DIPS, BTEX,TPH-diesel, and TPH-motor oils J'm' . MTBE again made an appearance TBA,TPH-gasoline, EDB, and ETBE were below the �\4� THIS DOCUMENT AND CONTENTS ARE THE PROPERTY OF ENVIRONEERING, INC