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k� KLEINFELDER 1 EXECUTIVE SUMMARY This is a report of Kleinfelder's First Quarter 2004 groundwater monitoring for the former Disco Facility located at 110 North Filbert Street in Stockton, California. MONITORING EVENT RESULTS On February.17, 2004, twenty (20) monitoring wells and three (3) piezometers were sounded for depth to groundwater. On February 17, 18, and 19, 2003, nine (9)monitoring wells and three (3) piezometers were sampled by Kleinfelder. Source area wells and piezometers sampled included MW-DIS-1, MW-DIS-2, NPI-70', NPI-80', and NPI-90'; and downgradient wells included MW-DIS-I Is, MW-DIS-11d, MW-DIS-12, MW-DIS-13, MW-DIS-14s, MW-DIS-14d and MW- DIS-15. The monitoring wells and piezometers were sampled in accordance with the "Groundwater Monitoring Frequency Decision Tree" developed by CH2M Hill. The depth to groundwater ranged from 42.13 feet below the top of the well casing (MW-DIS- 11s) to 53.97 feet below the top of the well casing (MW-DIS-15). Groundwater elevations for the monitoring wells ranged from —33.47 feet (MW-DIS-6) to —34,50 feet (MW-DIS-12). Groundwater flow direction at the site is estimated to be towards the southeast at approximately 0.001 ft./ft. Localized areas within the project site appear to be affected by the remedial activities and show groundwater mounding and groundwater depressions and local gradients ranging from 0.0005 feet/foot to 0.0007 feet/foot. A localized groundwater mound was noted near the source area wells SVE-N and SVE-S and the water level in MW-1 was depressed below the other nearby source area wells. Another very small groundwater mound was noted from the groundwater elevation data collected in MW-11s. The varying groundwater elevations noted in the source area and downgradient wells near the ozone sparge wells are indicative of the dynamic nature of the remedial system. The 12 groundwater samples were analyzed for the following: benzene, toluene, ethylbenzene, and total xylenes (BTEX), Total Petroleum Hydrocarbon as gasoline (TPH-g), 1,2- Dichloroethane (1,2-DCA), 1,2-Dibromoethane (EDB), and Tert-Butyl Alcohol (TBA). One groundwater sample (MW-DIS-15) was additionally analyzed for the additional oxygenates Di- isopropyl Ether (DIPE), Ethyl t-Butyl Ether (ETBE), Methyl tert-Butyl Ether (MTBE), and tert- Amyl Methyl Ether(TAME). SOURCE AREA SAMPLES TPH-g was detected in each of the 5 source area well/piezometers. The detected concentrations of TPH-g in the source area samples (ranging from 720 ug/I to 200,00 ug/1) all showed increases in the concentration of TPH-g versus the previous date analyzed. This marks the first time TPH- g has been detected in the downgradient well-MW-11s (61 ug/1) since May 2002. 12280.MON/ST04R397 Page 1 of 13 ®2004,Kleinfelder,Inc May 11,2004