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MW-6, MW-8, and MW-10. 1,2-DCA was detected in groundwater samples collected from wells MW-7 and MW-9 at concentrations of 1.7 4g/L and 7.1 µg/L, respectively. Toluene, ethyl benzene, ETRE, TBA, TAME or EDB were not detected in anv of aroundwater samples. Fiaure 10 r)resents the concentrations of TPHG, benzene and MTBE in all monitoring wells for groundwater samples collected during the second quarter 2003. The concentrations of other parameters such as COD and/or TOC also increased in the observation wells (except MW-5) during the second quarter 2003 correlating to the increase in petroleum hydrocarbon concentrations. During the second quarter 2003, the ORP and nitrate concentrations decreased in all the monitoring wells (both observational and background). A consistent pattern correlating these parameters with DO and/or heterotrophic plate count could not be identified for data collected either during the operation of ozone injection system or prior to the operation (baseline). Stratus will prepare and submit a RAP evaluating various remedial alternatives and recommending a technically feasible and cost effective alternative. In addition the RAP will present details of the C-SpargeTm system operation and evaluate its performance. If C-SpargeTM system is the recommended alternative modification to the existing system, if warranted, will also be presented. LIMITATIONS This report was prepared in general accordance with accepted standards of care that existed at the time this work was performed. No other warranty, expressed or implied is made. Conclusions and recommendations are based on field observations and data obtained from this work and previous investigations. It should be recognized that definition and evaluation of geologic conditions is a difficult and inexact art_ Judgments leading to conclusions and recommendations are generally made with an incomplete knowledge of the subsurface conditions present. More extensive studies may be performed to reduce uncertainties. This report is solely for the use and information of our client unless otherwise . noted. ATTACHMENTS: • Table 1 Groundwater Elevation and Analytical Summary o Table 2 Groundwater Analytical Results for Oxygenates and Additional Compounds o Table 3 Monitoring Plan Summary • Table 4 Physical Parameter Summary o Table 5 Analytical Parameter Summary o Figure 1 Site Location Map o Figure 2 Site Map o Figure 3 Groundwater Elevation Contour Map (Second Quarter 2003) o Figure 4 DO Variation With Time at MW-1, MW-2, MW-7, and MW-9 o Figure 5 TPHG, Benzene, MTBE Variation With Time at MW-4 o Figure 6 TPHG, Benzene, MTBE Variation With Time at MW-5 o Figure 7 TPHG, Benzene, MTBE Variation With Time at MW-6 o Figure 8 TPHG, Benzene, MTBE Variation With Time at MW-7 • Figure 9 TPHG, Benzene, MTBE Variation With Time at MW-8 • Figure 10 Groundwater Analytical Summary (Second Quarter 2003) a Appendix A Field Data Sheets • Appendix B Sampling and Analysis Procedures o Appendix C Certified Analytical Reports and Chain-of-Custody Documentation P:1I3p-Arco for URS154690Quarterly120031Arco_5469_2Q03.doc 6TKA ruoj