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USING SCIR TO PREDICT THE RATE OF BIOREMEDIATION OF MTBE
Citation:
Wilson*, J T., P. M. Kaiser*, J W. Weaver*, T. Kuder, P. Philp, AND S. Daugherty. USING SCIR TO PREDICT THE RATE OF BIOREMEDIATION OF MTBE. Presented at Battelle Conference, Baltimore, MD, 06/6-9/2005.
Description:
The 13C of MTBE was determined in ground water from four wells at a gasoline spill site in Orange County California. The natural logarithm of the fraction of MTBE remaining after biodegradation was estimated by subtracting the 13C of MTBE in gasoline from the 13C of MTBE in the ground water sample, then dividing the difference by the isotopic enrichment factor. The heaviest reported value of 13C in gasoline (?27.4o/oo) and a conservative value of (-12) were used to estimate the faction of MTBE remaining. This approach puts a conservative boundary on the extent of biodegradation of the MTBE. Biodegradation was at least as extensive as estimated. This estimate of MTBE biodegradation is not influenced by dispersion in the aquifer or by dilution in the monitoring well.
The MTBE concentration in the most contaminated well was 11,000 g/L. The concentration in three down gradient wells was 869, 47, and 19 g/L. The 13C of MTBE in the most contaminated well was -22.88o/oo. The extent of biodegradation was minimal, 75% of the MTBE remained after biodegradation. The 13C of MTBE in the down gradient wells was 6.84o/oo, 9.83o/oo, and 19.11o/oo respectively , corresponding to a fraction remaining that was no more than 5.8%, 4.5% and 2.3% of the MTBE originally released, or 7.7%, 6.0% and 3.0% of the MTBE in the most contaminated well. The average hydraulic conductivity based on slug tests of monitoring wells was 36 feet per day. The average hydraulic gradient was 0.0023 feet/feet based on thirteen rounds of water table elevations. Assuming an effective porosity of 0.25, the travel time from the most contaminated well to the down gradient wells was 0.26, 0.37 and 0.31 years. The corresponding first order rate of natural biodegradation of MTBE between the most contaminated well and the three down gradient wells was 9.8, 7.4 and 11 per year. These rates are consistent with rates of anaerobic biodegradation in microcosm studies at other sites.