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i I KLEINFELDER ' The three piezometers sampled this quarter (NP-70', NP-80', NP-90') all showed decreased or steady concentrations of TPH-g, ethyl-benzene, and xylene compared to last quarter, and further showed a fluctuating pattern of detected concentrations over time. The benzene and 1,2 DCA concentrations increased slightly in NP-90' and NP-70'; whereas in NP-80' benzene decreased and 1,2 DCA decreased. The samples showed non-detectable results for the fuel oxygenates TBA, MTBE, DIPE, ETBE, and TAME. The EDB concentrations in the piezometers decreased this quarter,with the exception of NP-70' where the EDB concentration increased. The seven downgradient well samples (MW-DIS-I Is, MW-DIS-11d, MW-DIS-12, MW-DIS-13, MW-DIS-14s, MW-DIS-14d and MW-DIS-15) all showed non-detectable concentrations of TPH-g, BTEX, TBA, and EDB. Concentrations of 1,2-DCA were detected in MW-DIS-11s, MW-12, MW-DIS-14s, and MW-DIS-15. The 1,2-DCA concentration in MW-DIS-lls decreased approximately 97% from the previous quarterly results (down to 7.6 ug/l). 1,2 DCA was detected in MW-DIS-12 at a concentration of 1.6 ug/l up from a previous quarter of non- detect and 0.64 ug/l. MW-DIS-14s continued to show a decreasing trend during the 2004 monitoring period (down to 1.6 ug/l from 3.2 ug/l, the lowest since monitoring began). It should be noted that the concentration of 1,2-DCA reported for MW-DIS-15 was the lowest since f monitoring began (1.7 ug/l) at this location. The additional oxygenates MTBE, DIPE, ETBE, and TAME in the only sample analyzed (MW-DIS-15). GROUNDWATER TREATMENT SYSTEM OPERATION The soil vapor extraction system installed by CH2M Hill was replaced by Kleinfelder during 2003 with an air sparging (AS)/high vacuum soil vapor extraction(SVE)/ozone injection system. The AS/SVE system consists of a network of two air sparging wells (shallow/deep) and a vapor extraction well positioned at five distinct locations, totaling fifteen wells. The ozone injection system consists of a horizontally directional drilled (HDD) conduit for ozone/air transmitted to a system of wells triple-nested at three different depths below groundwater, at five separate locations, equaling fifteen wells. Active remediation began in May 2003 in the source area (actual Disco site) by means of AS/SVE utilizing a thermal/catalytic oxidizer.unit. Continual operation of the thermal oxidizer began in June 2003. In July 2003, the AS/SVE unit was converted from a thermal oxidizer to catalytic oxidizer thereby optimizing the efficiency through fiiel uptake. The ozone injection system began consistent operation within the downgradient portion of the plume in September 2003. The system has only been inoperable during periods of system maintenance and enhancements. As stated during the Fourth Quarter 2004 a venturi system was installed downstream of the ozone pump, as the mixing point for the dry air and generated ozone. The venturi was designed to help alleviate the high pressures experienced by the ozone pump, which had a working pressure of 75 psi. A %Z-inch Kynar venturi was selected, and designed into the system. During the First Quarter 2005 the venturi system was refined, optimized, and the correct, flow, pressure balance was reached in order to achieve the goal of the reduced pressure on the ozone pump. Thus far the modification appears to be operating as expected. During the first quarter air samples were collected for the performance evaluation of the catalytic oxidizer on March 23, 2005 which revealed TPH-g and benzene at concentrations of 530 ppmv 12280.MON/ST05R613/JZ:1v Page 2 of 13 0 2005,Kleinfelder,Inc. May 20,2005 i