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KLEINFEL©ER
<br /> r I EXECUTIVE SUMMARY
<br /> This is a report of Kleinfelder's Third Quarter 2004 groundwater monitoring for the former Disco,
<br /> Facility located at 1.10 North Filbert Street in Stockton, California.
<br /> MONITORING EVENT RESULTS
<br /> On September 13, 2004, twenty (20) monitoring wells and three (3) piezometers were sounded
<br /> J for depth to groundwater. On September 13, 14, and 15, 2004, ten (10) monitoring wells and
<br /> three (3) piezometers were sampled by Kleinfelder. The wells included MW-DIS-1, MW-DIS-2,
<br /> MW-DIS-9, MW-DIS-lls, MW-DIS-lld, MW-DIS-12, MW-DIS-13, MW-DIS-14s, MW-DIS-
<br /> 14d and MW-DIS-15; and the piezometers included NP-70', NP-80', NP-90'. The monitoring
<br /> wells were sampled in accordance with the "Groundwater Monitoring Frequency Decision Tree"
<br /> developed by CH2M Hill for this project.
<br /> The depth to groundwater ranged from 46.74 feet below the top of the well casing (MW-DIS-
<br /> 11 s) to 55.97 feet below the top of the well casing (MW-DIS-4). Groundwater elevations for the
<br /> monitoring wells ranged from --36.00 feet (1\4W-DIS-1) to —36.24 feet (MW-DIS-13).
<br /> Groundwater flow direction at the site is estimated to be generally towards the east to southeast
<br /> with a relatively flat gradient of approximately 0.0002 ft./ft. There appeared to be a
<br /> groundwater mound near the central portion of the subject site, most likely due to the affects of
<br /> remediation taking place.
<br /> The 13 groundwater samples were analyzed for the following: benzene, toluene, ethylbenzene,
<br /> and total xylenes (BTEX), Total Petroleum Hydrocarbon as gasoline (TPH-g), 1,2-
<br /> Dichloroethane (1,2-DCA), 1,2-Dibromo ethane (EDB), Tert-Butyl Alcohol (TBA), Di-isopropyl
<br /> Ether (DIPE), Ethyl t-Butyl Ether (ETBE), Methyl tert-Butyl Ether (MTBE), and tert-Amyl
<br /> Methyl Ether(TAME).
<br /> Significant decreases in the concentrations of TPH-g, 1,2-DCA, and the BTEX compounds were
<br /> noted in the source area wells MW-DIS-1 and MW-DIS-2 (excluding benzene). Many of the
<br /> decreases were in excess of 50% and as high as 79% (1,2-DCA in MW-DIS-1). The benzene
<br /> concentration noted in MW-DIS-2 had increased slightly from 1.7 ug/l in 2/19/04 to 2.3 ug/l,but
<br /> still remained well below the previously recorded concentration of 4 ug/1 in March 5, 2003.
<br /> f
<br /> The three piezometers sampled this quarter (NP-70', NP-80', NP-90') all showed decreased
<br /> concentrations of TPH-g, ethyl-benzene, and xylene compared to last quarter, and further showed
<br /> a fluctuating pattern of detected concentrations over time. The benzene and toluene
<br /> concentrations increased slightly in NP-70' and NP-80'; whereas in NP-90' benzene.decreased
<br /> ` and .toluene remained the same. The samples showed non-detectable results for the fuel
<br /> oxygenates TBA, MTBE, DIPE, ETBE, and TAME. The 1,2-DCA and EDB concentrations in
<br /> r the piezometers increased this quarter, with the exception of NP-80' where the EDB
<br /> concentration decreased. The increased concentrations of benzene, toluene, 1,2-DCA, and EDB
<br /> 12280.M0N/ST04R1610/JZJv Page 1 of 13
<br /> 0 2004,Kleinfelder,Inc. December 10,2004
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