ARCHIVED REPORTS XR0001151 - Laserfiche WebLink

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en viroso On May 26, 1995, Fugro submitted a Remediation Summary and Proposal For Final Corrective Action This document stated that the hydrocarbon extraction rate had dropped to less than one-half of 1% of the start-up extraction rate and a cumulative total of 17,449 pounds of petroleum hydrocarbons had been extracted from the subsurface As of November 1996, a cumulative total of 17,628 pounds of petroleum hydrocarbons had been extracted Due to the recent rise in the water table, the SVE system has been idle during 1997 The analytical data indicate that hydrocarbon extraction rates became asymptotic (Plate 3) prior to the rise in the water table in 1995 Therefore, prior to the rise in the water table the SVE system had extracted all of the petroleum hydrocarbons economically achievable by this remediation technique Plume Stability Quarterly ground water chemical analysis at this location began in 1989, providing eight years of ground water data for evaluation Review of these data show that the wells fall into one of three categories those wells in which petroleum hydrocarbon concentrations in ground water have been not detected (ND) since installation (with the exception of an occasional anomalous detection), wells that have shown a pattern of attenuation with concentrations decreasing by one or more orders of magnitude over time, and wells which have shown stable concentrations over time Historic ND petroleum hydrocarbon concentration levels are present in Well MW-1 to the south of the plume,Well MW-6 to the west, and Well MW-10 to the northeast Declining petroleum hydrocarbon concentration levels are present in the central area of the plume in Wells MW-3, MW-4, MW-8, MW-9, and at the eastern edge of the plume in Wells MW-5 and MW-7 Only Well MW-2, located in the area of the former underground storage tanks, has exhibited relatively stable petroleum hydrocarbon concentrations with some decline over time (Table 1) It is difficult to present a definite ground water flow direction due to mounding behavior in the central area of the site (Plate 2) over the last several quarters ND or declining petroleum hydrocarbon concentrations in monitoring wells in every horizontal direction, however, indicates that the dissolved petroleum hydrocarbon plume is stable, and horizontal migration of contaminants from the site is not occurring Based upon the stability of the hydrocarbon plume, the rise in the water table, and the asymptotic hydrocarbon extraction rates exhibited prior to the rise in the water table, Enviros hearby requests permission to end SVE system operation Natural attenuation processes will continue to remediate residual concentrations of petroleum hydrocarbons in soil and ground water Quarterly monitoring, sampling, and reporting will continue on the established schedule to monitor plume stability and natural attenuation r 97375 3