HR: 0830h
AN: H21D-0883    [PDF]
TI: Benzene and MTBE Sorption in Fine Grain Sediments
AU: * Leal-Bautista, R M
EM: rlb@geol.niu.edu
AF: Northern Illinois University, Geology and Environmental Geosciences, DeKalb, IL 60115 United States
AU: Lenczewski, M E
EM: melissa@geol.niu.edu
AF: Northern Illinois University, Geology and Environmental Geosciences, DeKalb, IL 60115 United States
AB: The practice of adding methyl tert-butyl ether (MTBE) to gasoline started in the late 1970s and increased dramatically in the 1990s. MTBE first was added as a substitute for tetra-ethyl lead then later as a fuel oxygenate. Although the use of MTBE has resulted in significant reduction in air pollution, it has become a significant groundwater contaminant due to its high solubility in water, high environmental mobility, and low potential for biodegradation. A recent report (1999-2001) by the Metropolitan Water District of Southern California in collaboration with United State Geological Survey and the Oregon Health and Science University found that MTBE was the second most frequent detected volatile organic compound in groundwater. In Illinois, MTBE has been found in 26 of the 1,800 public water supplies. MTBE has also been blended in Mexico into two types of gasoline sold in the country by the state oil company (PEMEX) but is not monitored in groundwater at this time. Early research on MTBE considered it unable to adsorb to soils and sediments, however, by increasing the organic matter and decreasing the size of the grains (silts or clays) this may increase sorption. The objective of this study is to determine if fine grained materials have the potential for sorption of MTBE due to its high specific surface area (10-700 m $^{2}$/g) and potentially high organic matter (0.5-3.8%). The experiment consisted of sorption isotherms to glacial tills from DeKalb, Illinois and lacustrine clays from Chalco, Mexico. Experiments were performed with various concentrations of MTBE and benzene (10, 50, 100, 500 and 1000 ug/L) at $10\deg$C and $25\deg$C. Results showed a range of values for the distribution coefficient (Kd, linear model). At $10\deg$C the Kd value for MTBE was 0.187 mL/g for lacustrine clay while the glacial loess had a value of 0.009 mL/g. The highest Kd values with MTBE were 0.2859 mL/g for organic rich lacustrine clays and 0.014 mL/g for glacial loess at $25\deg$C. The highest values with benzene were 0.323 mL/g for organic rich lacustrine clays and 0.119 mL/g for glacial loess at $10\deg$C. At $25\deg$C the organic rich lacustrine clays the Kd value was 0.332 mL/g, while Kd value for glacial loess was 0.114 mL/g. Sands with no organic matter (Ottawa sand) had a value of $<$ 0.001 mL/g for both temperatures $25\deg$C and $10\deg$C and both organic compounds. The retardation factor (R) for MTBE was 1.559 at $10\deg$C and 1.855 at $25\deg$C for lacustrine clays; while the glacial tills R was 1.058 at $10\deg$C and 1.095 at $25\deg$C. The retardation factor for benzene was 1.967 at $10\deg$C and 1.996 at $25\deg$C for lacustrine clays; while the glacial tills R was 1.039 at $10\deg$C and 1.037 at $25\deg$C. These results indicate higher retardation values than previously determined for a clayey sand; therefore show that sorption can occur in fine grain materials especially with high organic matter. This study contributes to the understanding of the sorption of MTBE and improves the knowledge to implement the optimal remediation method for sites contaminated by MTBE.
DE: 1803 Anthropogenic effects
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2003 Fall Meeting