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I * %TC A S S O C I A T E S 1 iN C . The concentration of TPHg in MW5 increased from <50 ug/L on June 3, 2004 to 360 ug/L on December 13, 2004. The concentration of TPHg increased from 120 ug/L on September 13, 2004 to 360 ug/L on December 13, 2004 in MWS. DO increased from 0.81 mg/L on June 3, 2004 to 1.11 mg/L on September 13, 2004. TPHg was not detected at method detection limits of 50 ug/L in MW8. The successive decline of TPHg in EW1 from 85,000 ug/L on June 3, 2004 in each of the monitoring events following was significant. During the December 13, 2004 event, TPHg was reported at 1300 ug/L for a removal efficiency of 98.5% after approximately 6 months of operation. TPHg maps were also plotted using data from March 17, 2004, June 13, 2004, September 13, 2004 and December 13, 2004. The March 17, 2004 and June 3, 2004 sampling data were obtained prior to system start-up. The September 13, 2004 and December 13, 2004 sampling data was information obtained, respectively, approximately three and six months after system operation start-up. Although there are not apparent reductions in the areal extent of TPHg, significant reductions of TPHg concentrations are apparent along the injection well corridor (Figure 23). 5.0 CONCLUSIONS Petroleum hydrocarbons and associated COCs detected in the groundwater samples collected from MW6a and MW7a indicate the hydrocarbon plume extends offsite in the shallow aquifer. Petroleum hydrocarbons and COCs detected in groundwater samples collected from MW6b, MW6c, MW7b, MW7c, and MW10b indicate the hydrocarbon plume extends offsite to the east in deeper groundwater. DO increased significantly after system start-up in MW1, MW2, MW4, MW8 and EW1. Although DO has increased it has not increased significantly in MW3 and MW5 after system start-up. During the fourth quarter monitoring event, benzene levels in on-site wells, MW1, MW2, MW3, MW4 and EW1 declined. Benzene concentrations in MW5 and MW8 remain non-detected at method detection limits. TPHg concentrations appeared to decrease significantly in MW 1 and EWL During the fourth quarter, benzene in MW4 was reduced to non-detected at method detection limits (<0.5 ug/L). The reasons for the decrease in benzene in MW3 are not as clear. MTBE levels in MW1, MW2, MW4, MW5, MW8 and EW1 also declined. MTBE in MW3 remains undetected. Concentrations of MTBE have fluctuated considerably. The reasons for the fluctuations in MTBE are unclear at this time. They may be due to a combination of seasonal conditions or due to mixing if the trends are related to remediation system activities. S:1268231QM reports12004 4QR.doc 12