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A plot of partitioning for TBA and MTBE between gasoline and water is shown in Figure 4 1 This plot indicates that, for water in contact with MTBE-gasoline, in approximately less than one out of twenty instances (cumulative probability, P=0 95 or greater), aqueous TBA concentrations can be similar or greater than the MTBE concentration levels in water 150000 1000 P=0 99 ► 12 3%MTBE c o 4l r+ = 100000 — —►10 2%MTBE �, y I C N N C � O _"" P=0 95 500 P CD Y rW � a � m c 50000 ` �I I c WE � " CO CO P=0 5 � I ~ P=0 OS V —0—MTBE 0 0 —O.-TBA 0 2000 4000 6000 8000 water concentration (mg1L) Figure 4 1 Estimated partitioning of MTBE and TBA from gasoline to water A large gasoline to water ratio is presumed The 10 2% to 12 3% range for MTBE is based on the reported range of MTBE in oxygenated gasoline The plotted values for TBA, P = 0 05, 0 5, 0 95, and 0 99 refer to the confidence levels of finding TBA in gasoline at or lower than the referred concentration, in unweathered MTBE- gasoline Actual occurrence of TBA concentrations in groundwater at a remediation site would depend on a number of factors dependent on site conditions, geology, and hydrogeology At the sites listed in Table 3 1, preliminary review shows nominal high-range measured TBA concentrations in groundwater that are (in some cases) of the same order as the calculated gasoline/water equilibrium-partitioning estimates of Figure 41 These estimates, based on ranges of TBA concentration, indicate that some fraction of TBA in groundwater may possibly originate from gasoline MTBE and TBA are soluble and volatile constituents of gasoline that, in a release, are depleted as the gasoline mixes with increasing volumes or water or air (or both) Concentrations in the water (or air) phase will decrease with increasing dilution of the gasoline, and will be less than the equilibrium partitioning estimates of Figure 4 1 11