Environmental Behavior of Me- Thyl Tert-butyl Ether: a Study of Henrys Law Constant and the Dispersion of Mtbe through River Bottom Sand and Soil

The Henry’s Law constant was determined for methyl tert-butyl ether (MTBE) at four temperatures through a new, accurate, and experimentally simple method, based on the work of Gossett (Environ. Sci. Technol. 21:202-208, 1987). The constant was calculated to be 0.032 at 25 °C, suggesting that MTBE is more volatile than previously reported. Analysis of unpublished data collected earlier, using the method of Gossett, is consistent with the most recent estimate, giving median estimates of 0.046 and 0.032 in two series. The value of H was also determined by consecutive additions of water to a single bottle containing a solution of MTBE. Duplicate bottles gave median values of 0.030 and 0.036 at 25 °C. The only published measures of H are 0.022 at 25 °C and 0.048 at 30 °C, but neither value lies very close to the regression line determined for the range 25 to 50 °C [each value deviates from the line by the equivalent of ~2 °C] (Robbins et al.; Anal. Chem. 65:31133118, 1993). The dispersion of MTBE through course and fine river bottom sands and silty sand was also analyzed. A simulated MTBE spill on the three materials was studied for a seven-day period by sampling of the headspace gas of effluent collected daily after application of measured amounts of water to simulate precipitation. Core samples at precise depths were taken at the fifth, sixth, and seventh days for replicate columns. It was determined that for the more porous material, MTBE traveled through the material rapidly and with lower recovery in the effluent water. No MTBE remained in the coarse, freely draining sand after five days; while in the silty sand, a significant portion remained in the soil even after seven days. The loss of MTBE mass is presumably due to volatilization, and this work indicated that rapidity of loss of MTBE to the atmosphere will vary greatly with soil properties. INTRODUCTION Methyl tert-butyl ether (MTBE) is a colorless, flammable liquid with a strong distinctive odor. MTBE has been the number one oxygenate to lower emission levels since the Clean Air Act Amendment (CAAA) was established in 1990. MTBE makes up about 85% of the oxygenates used nationally. Gasoline in the U.S. is composed of levels between 5% and 15% MTBE. Most refiners have chosen MTBE because it can be produced at the refinery (ease of production and lower cost), and it blends easily with gasoline. The introduction of MTBE to gasoline may pose significant wastewater treatment and groundwater remediation problems because of accidental release of gasoline into the environment (Johnson et al., 2000). Possible sources of MTBE in groundwater include point sources such as leaking tanks and nonpoint sources such as recharge of soil water by precipitation carrying MTBE in storm water runoff. MTBE is volatile and would typically be expected to volatilize rapidly from soil surfaces or water, but because MTBE is soluble in water and highly mobile in soils, it poses a particular environmental threat (Squillace et al., 1997). The EPAhas