ARCHIVED REPORTS XR0000679 - Laserfiche WebLink

Home Browse Search

1 z 1 August 2003 • AGE-NC Project No 96-0232 ' Page 14 of 15 ' The vertical extent of MTBE-impacted ground water at the Flag City Chevron site appears to lie between 14 feet bsg (estimated depth to ground water) and 50 feet bsg (Figure 8) Relative to the inferred source area near the Flag City Chevron UST area (EW-1), the Flag City Chevron plume ' appears to have extended approximately 200 feet to the west at depths as great as 75 feet bsg,the full westward extent of the Flag City Chevron plume appears to be the former area of the Rocky's Restaurant domestic drinking water well (RDW-1), and comingled with the Three B's Truck Plaza ' plume in the area between Three B's Truck Plaza well MW-4 and Flag City Chevron wells MW-11, MW-14 and MW-15 The Flag City Chevron plume appears to extend approximately 130 feet to the south (MW-6B) at depths as great as 48 feet bsg, and at least 60 feet to the east(between EW-9 and ' MW-2) at depths as great as 35 feet bsg (Figure 8) The northern extent of the Flag City plume is uncertain at the present time because of the high concentrations of MTBE (up to 290 µg/1)detected in northernmost Flag City Chevron well MW-8 during the June 2003 monitoring event Figures 9 and 10 depict Flag City Chevron wells EW-1, EW-4, EW-5, EW-7 through EW-10, MW-8,MW-9,MW-11 and Three B's Truck Plaza wells MW-1,MW-2,MW-4,MW-6 and MW-8 through MW-12 to be located within two,dissolved MTBE-impacted plumes that converge near the vicinity of the former Rocky's Restaurant domestic well RDW-1 � . It is not clear at this time why substantial MTBE is present in on-site well MW-8A after nine consecutive quarters(between May 2000 and December 2001)of being non-detect Since initiation I of ground water extraction activities at the site,First and Second Zone ground water flow direction in the area of MW-8 has generally been towards the south-southeast, and should draw on-site contaminants away from MW-8(Figure 5) The most intense MTBE detections were reported during the March 2002 and the March 2003 sampling events, which could be related to the seasonal high ground water levels observed at the site each year near March(Table 4) However,intermediate well MW-4, located between MW-8 and the UST area, have no detection of MTBE, albeit screened in the First Zone, and three soil borings (P-36 through P-38) advanced in October 2002 to assess the area near MW-8(Figure 2)did not detect MTBE in grab ground water samples collected from`First Water'and `Second Water' AGE has tentatively concluded that the MTBE detections in MW-8 is a separate dissolved MTBE plume(Figure 10) AGE estimates the arithmetic average concentration of MTBE in ground water extracted between 25 March 2003 and 25 June 2003 at 34 µg/1 During this time, the volume of water processed through the ground water pump and treat system was recorded at 2,090,669 gallons (equivalent to 17,429,907 pounds), yielding 0 74 pounds of MTBE (equivalent to 335 grams) from the plume of impacted ground water (Appendix D) In general, decreasing MTBE concentrations were reported in Second Quarter 2003 water samples collected at the pump-and-treat influent sampling port and at extraction wells EW-1, EW-4,EW-5, EW-7,EW-8,EW-9 and EW-10 Previously,AGE had observed a`spike' m MTBE concentrations at extraction wells EW-4, EW-5, EW-7 through EW-10, and may have been related to some of the Advanced GeoEnvironmental,inc