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j kn KLEINFEEDER 1 EXECUTIVE SUMMARY i This is a report of Kleinfelder's First Quarter 2005 groundwater monitoring for the former Disco Facility located at 110 North Filbert Street in Stockton, California. 7 MONITORING EVENT RESULTS On March 21, 2005, twenty (20) monitoring wells and three (3) piezometers were sounded for depth to groundwater. On March, 21, 22 and 23, 2005, nine (9) monitoring wells and three (3) piezometers were sampled by Kleinfelder. The wells included MW-DIS-1, MW-DIS-2, MW- DIS-11s, MW-DIS-I ld, MW-DIS-12, MW-DIS-13, MW-DIS-14s, MW-DIS-14d and MW-DIS- 15. The piezometers included NP1-70, NPI-80, and NP1-90. The monitoring wells and piezometers were sampled in accordance with the "Groundwater Monitoring Frequency Decision Tree'.'developed by CH2M Hill for this project. I The depth to groundwater ranged from 37.29 feet below the top of the well casing (MW-DIS- I Is) to 55.73 feet below the top of the well casing (MW-DIS-15). Groundwater elevations for the monitoring wells ranged from --36.05 feet (MW-DIS-15) to —26.69 feet (MW-DIS-11s). It should be noted that the recorded high and low groundwater elevations were measured from wells which exhibited groundwater mounding and depression respectively. We estimate the remediation activities are the cause of both the mound and depression and a more representative groundwater range for high and low elevations might be characterized by the groundwater r elevations noted in MW-DIS-6 (-34.26) and MW-DIS-13 (-35.00). The wells MW-DIS-I1s and MW-DIS-15 were allowed to further equalize, and on March 25, 2005 re-measured. The subsequent groundwater elevations appeared to have stabilized to groundwater elevations more representative of the surrounding well elevations recorded (-34.54 and -34.65 feet respectively). Groundwater flow direction at the site is calculated to be towards the east/southeast with a relatively flat gradient of 0.0003 ft./ft. near the western portion of the site to 0.0005 ft./ft in the eastern portion of the site. This flow direction continues to show a shift from previously recorded direction toward the south and southeast flow directions. f' jThe 12 groundwater samples were analyzed for the following: Total Petroleum Hydrocarbon as gasoline (TPH-g), benzene, toluene, ethylbenzene, and total xylenes (BTEX), Tert-Butyl Alcohol (TBA), 1,2-Dichloroethane_ (1,2-DCA), 1,2-Dibromoethane (EDB): Only MW-DIS-15 was additionally analyzed for Di-isopropyl Ether (DIPE), Ethyl t-Butyl Ether (ETBE), Methyl tert- Butyl Ether(MTBE), and tert-Amyl Methyl Ether(TAME). Decreases in the concentrations of benzene, toluene, and xylenes were noted in MW-DIS-I, as well as benzene concentrations in MW-DIS-2. Increases were noted in TPH-g, toluene, xylenes, (MW-DIS'2 only), 1,2 DCA, (MW-DIS-1) and ethylbenzene. The 1,2 DCA concentration was approximately 80% increase and has appeared to fluctuate historically. EDB was also detected at 10 ug/1 for the first time since October 2001 in MW-DIS-1. 12280.M0N/ST05R613/JZ:1y Page 1 of l3 ®2005,Kleinfelder,Inc. May 20,2005