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I ' 13 June 2003 . AGE-NC Project No 97-0249 ' Page 7 of 8 ' in the area of Flag City Chevron well MW-17 at a concentration of 220 p g/l(Figure 11), and from Hydrologic Unit 3 in the area of Flag City Chevron wells MW-11B, MW-15 and MW-18 at concentrations as high as 200 µg/1 • The highest off-site concentrations of dissolved MTBE were detected in the Flag City Chevron samples collected from Hydrologic Unit 1 extraction well EW-8 at 96 gg/l(Figure 10) and from Hydrologic Unit well MW-8A at 900 µg/l (Figure 11) ' • Low concentrations of 1,2-DCA were detected at wells MW-1 OA and MW-11A suggesting that only a minor impact to ground water at the site I • The only detection of dissolved TBA was in the sample collected from well MW-1,however, low concentrations of TBA were previously detected at wells MW-2, MW-3, MW-5 and MW-6 suggesting a minor TBA-impact to ground water at the site • The lateral and vertical extent of the dissolved petroleum hydrocarbon plume is not known toward the south of well MW-6 and toward the north-northeast of well MW-3 (Figures 8, 9, I10 and 11) lie 5.0. RECOMMENDATIONS Based upon the results of the first quarter 2003 investigation, AGE recommends • Continued quarterly groundwater monitoring of wells MW-1 through MW-12,the next two quarterly ground water monitoring event are tentatively scheduled for June 2003 and September 2003 • Conduct future groundwater monitoring events concurrently with the Flag City Chevron site (6421 Capitol Avenue), • Transferring responsibility of well MW-13 (located approximately 20 feet west of the Three B's Truck Plaza above ground tank area) from the Flag City Chevron investigation to the Three B's Truck Plaza investigation I • Additional ground water monitoring wells(screened in Hydrologic Unit 1) are warranted in the area northeast of MW-3 and south-southeast of MW-6, installation of the additional ground water monitoring wells should aid in the preparation of a site conceptual model Based on site data collected, the presence of a local domestic ground water well and due to 1) the high concentrations of contaminants(i e MTBE,BTEX)encountered at the site that are significantly . above the DHS's MCLS, 2)the high mobility of MTBE dissolved in ground water and 3)to prevent impacting the on-site domestic drinking water well, AGE strongly recommends that an active IAdvanced GeoEnvironment8l,Inc I