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t n al" 19 June 2000 AGE-NC Project No 96-0232 Page 4 of 35 Division (PHS-EHD) files for the Flag City Chevron site indicated that three ground water monitoring wells (MW-1, MW-2 and MW-3) were installed on-site in May 1991 to maximum depths of 24 feet bsg, well screens were recorded between 9 and 24 feet bsg Dissolved petroleum hydrocarbons were not detected in initial ground water samples collected from MW-1 though MW-3, however benzene was detected in samples collected from wells MW-1 and MW-3 during subsequent sampling events at concentrations as high as 9 4gg/l,groundwater depths were initially recorded from wells MW-1,MW-2 and MW-3 at approximately 12 feet bsg with a general ground water flow direction toward the north AGE has been informed that monitoring well MW-3 was subsequently abandoned by grouting through the casing to the surface at the time the USTs were removed July 1996- One ground water monitoring well (MW-4) was installed on-site to a depth of 30 feet bsg An as-built well construction diagram of MW-4 is depicted in Figure 5,a boring log of MW-4 is in Appendix B Laboratory analysis of soil samples collected from MW-4 did not detect TPH-g,TPH-d,or BTEX compounds Laboratory analysis of the initial ground water sample collected from MW-4 detected methyl tertiary butyl ether (MTBE) at a concentration of 0 74 gg/l and at concentrations of 310 gg/l and 3 7 µg/1 in the samples collected from MW-1 and MW-2, respectively Ground water depths were recorded from wells MW-1,MW-2 and MW-4 at approximately 15 feet bsg (Table 3), the general ground water flow direction was toward the south-southeast(Figure 6) Analytical results of soil and ground water samples are summarized in Tables 4 and 5 A report of findings (Closure Summary Report-February 1997, dated 30 April 1997)was prepared by AGE and submitted to the PHS-EHD and the RWQCB-CVR • August 1996- Ground water monitoring was performed at wells MW-1, MW-2 and MW-4 Laboratory analysis of ground water samples collected from MW-1 and MW-2 detected MTBE at concentrations of 380 µg/1 and 4 6 gg/l, respectively, TPH-d was detected in a water sample collected from MW-2 at a concentration of 110 gg/l Ground water depths were recorded from wells MW-1, MW-2 and MW-4 at approximately 14 feet bsg (Table 3), general ground water flow direction was toward the southwest at a gradient of 0 006 (Figure 7) Analytical results from the ground water samples are summarized in Table 5 A report of findings (Closure Summary Report - February 1997, dated 30 April 1997) was prepared by AGE and submitted to the PHS-EHD and the RWQCB-CVR • May 1997 - Ground water monitoring was performed at wells MW-1, MW-2 and MW-4 Ground water depths were recorded at approximately 10 feet bsg(Table 3), general ground water flow direction was towards the northeast at a gradient of 0 009 (Figure 8) Laboratory analysis of ground water samples detected MTBE from wells MW-1, MW-2 and MW-4 at concentrations of 440 gg/l, 5 5 gg/l and 2 7 gg/l, respectively Analytical results of ground water samples are summarized in Table 5 A letter report of findings was prepared by AGE and submitted on 20 May 1997 to the PHS-EHD and the RWQCB-CVR Advanced GeoEmironmental,Inc