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. from MW-7 and MW-9 at concentrations of 2.0 pg/L and 6.0 pg/L, respectively. TBA, RIPE, ETRE,TAME, EDB, or ethanol were not reported in any of the groundwater samples collected from the site. During third quarter 2003, the average DO levels in observation wells varied in the range of 1.04 mg/L to 6.64 mg/L while the average DO levels in background monitoring wells were in the range of 1.05 mg/L to 2.22 mg/L. The higher DO levels in observation wells as compared to the background monitoring wells are probably due to ozone injection. The COD concentrations observed in monitoring wells appear to correlate with petroleum hydrocarbon concentrations. During the third quarter 2003, although the nitrate concentrations appear to have increased in both background and observation wells, relatively higher concentrations of nitrate was observed in wells MW-3, MW-5 and MW-7. Stratus will check these monitoring wells for potential filamentous (biofouling) growth that may be caused due to high nitrate concentrations. A consistent correlation of either TOC or heterotrophic plate counts corresponding to petroleum hydrocarbon 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). Based on the field and laboratory data collected to date, the ozone injection system appears to be supplying ozone and oxygen to the subsurface as designed. It is our understanding, based on conversations with Nuel Henderson, that SJCEHD will be requesting a Site Conceptual Model (SCM) to be completed. Upon completion of the SCM, Stratus will prepare a final Remedial Action Plan, which will evaluate the performance of the ozone injection system and provide an evaluation of other commercially available technologies that may be applicable to the site. 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 • Table 2 Groundwater Analytical Results for Oxygenates and Additional Compounds o Table 3 Monitoring Plan Summary • Table 4 Physical Parameter Summary • Table 5 Analytical Parameter Summary • Figure 1 Site Location Map Q Figure 2 Site Map o Figure 3 Groundwater Elevation Contour Map (Third Quarter 2003) • Figure 4 DO Variation With Time at MW-1, MW-2, MW-5, MW-7, and MW-9 • Figure 5 TPHG, Benzene, MTBE Variation With Time at MW-4 a Figure 6 TPHG, Benzene, MTBE Variation With Time at MW-5 • 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(Third Quarter 2003) • Appendix A Field Data Sheets • Appendix B Sampling and Analysis Procedures • Appendix C Certified Analytical Reports and Chain-of-Custody Documentation PABp-Arco for URS\54691Quarterly120031Arco_5469_3Q03.doc5-rRIJT1J5