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1 <br />' 31 March 2005 <br /> AGE-NC Project No 97-0249 <br />' Page 7 of 8 <br />' Chevron wells MW-11B and MW-18 at concentrations as high as 150 µg/l (Appendix A) <br /> On-site MTBE-impacted ground water from Hydrologic Units 1 and 2 are depicted on <br /> Figures 11 and 12, respectively <br />' The highest off-site concentrations of dissolved MTBE were detected in monitoring wells <br /> toward the east and northeast, in water samples collected from Flag City Chevron wells <br /> MW-8A (290 pg/l, Hydrologic Unit 2), MW-19A (900 µg/1, Hydrologic Unit 1) and <br />' MW-20A (180 pg/l, Hydrologic Unit 1) Off-site MTBE-impacted ground water from <br /> Hydrologic Units 1 and 2 are depicted on Figures 11 and 12, respectively <br />' Low concentrations of TBA and 1,2-DCA have been detected from wells MW-1, MW-2, <br /> MW-3, MW-5, MW-6, MW-8A, MW-l0A and MW-11A, suggesting that only a minor <br /> TBA-impact and 1,2-DCA-impact to ground water in Hydrologic Unit 1 is present at the site <br />' The lateral and vertical extent of the dissolved petroleum hydrocarbon plume is not known <br /> toward the northeast of Three B's Truck Plaza well MW-2, toward the south of Three B's <br />' Truck Plaza well MW-6 and toward the south of Flag City Chevron wells MW-16/17/18 <br /> (Figures 9, 10, 11 and 12) <br /> 5.0. RECOMMENDATIONS <br /> Based upon the results of the fourth quarter 2004 investigation, AGE recommends <br /> • Continued quarterly ground water monitoring of wells MW-1 through MW-12, the next <br /> quarterly ground water monitoring event is tentatively scheduled for 28, 29 and 30 March <br /> 2005, <br /> • Continue to conduct future ground water monitoring events concurrently with the Flag City <br /> Chevron site (6421 Capitol Avenue), <br />' • Additional ground water monitoring wells are warranted in the area northeast of Three B's <br /> Truck Plaza well MW-3, south-southeast of Three B's Truck Plaza well MW-6 and <br /> southwest of MW-16/17/18, installation of the additional ground water monitoring wells <br />' should aid in the preparation of a site conceptual model A monitoring well installation work <br /> plan will was approved by the SJCEHD on 22 March 2005, AGE has tentatively scheduled <br /> drilling activities to commence by 15 May 2005 <br /> • The higher concentrations off-site at Flag City Chevron well MW-19 represent an additional <br /> release and source of dissolved MTBE and should be assessed <br />' Advanced GeoEnvkronmeatal,Inc <br />