ARCHIVED REPORTS_XR0010751 - Laserfiche WebLink

Home Browse Search

lie 16 December 2005 AGE-NC Project No 97-0249 ' Page 7 of 8 ' from the area of Three B's Truck Plaza wells MW-8C, MW-10C and MW-11C at concentrations as high as 8 5 pg/l, and from the area of Flag City Chevron wells MW-11B, MW-15 and MW-18 at concentrations as high as 170 µg/1 (Appendix A) ' • The highest off-site concentrations of dissolved MTBE were detected in monitoring wells toward the east and northeast, in water samples collected from Flag City Chevron wells MW-8A (610 µg/1, Hydrologic Unit 2), MW-19A (100 µg11, Hydrologic Unit 1) and ' MW-20A (460 µg/1, Hydrologic Unit 1) Off-site, MTBE-impacted ground water from Hydrologic Units 1 and 2 are depicted on Figures 10 and 11, respectively ' • Low concentrations of TBA and 1,2-DCA have been detected from wells MW-1, MW-5, MW-8A and MW-10(A-C), suggesting that only a minor TBA-impact and 1,2-DCA-impact to ground water in Hydrologic Unit 1 is present at the site ' • The lateral and vertical extent of the dissolved petroleum hydrocarbon plume is not known toward the northeast of Three B's Truck Plaza well MW-2, toward the south of Three B's Truck Plaza well MW-6 and toward the south of Flag City Chevron wells MW-16/17/18 (Figures 8 through 11) 5.0. RECOMMENDATIONS Based upon the results of the second quarter 2005 investigation, AGE recommends I Continued quarterly ground water monitoring of wells MW-1 through MW-12, the third quarter 2005 ground water monitoring event was performed on 26 and 27 September 2005 and a report of findings is forthcoming An interim ground water remediation program should be implemented at the site as soon as possible to establish hydraulic controls,inhibit potential off-site migration of the contaminated ground water plume, and to protect the on-site domestic water from the on-site ground water plume Additional considerations justifying interim ground water remediation include • The high concentrations of contaminants(i e BTEX and MTBE and 1,2-DCA)encountered at the site that are significantly above the DHS's MCLs • The high mobility of the above contaminants dissolved in the First Water Zone (30 to 50 feet) and Second Water Zone (70 to 85 feet) • The apparent southeastward migration (down-gradient) of the Three B's Truck Plaza dissolved hydrocarbon plume towards the Flag City Chevron dissolved plume Advanced GeoEnvironmentel,Inc i I