We've Moved!
Visit SDSU’s new digital collections website at https://digitalcollections.sdsu.edu
Description
Gasoline components pose contamination threats to groundwater on many levels. Four column tests were designed to evaluate the order and nature of MTBE and BTEX elution. These four tests had different initial saturations of the soil, as well as changing flow rates. The order of elution for all tests was MTBE, benzene, toluene, ethylbenzene, m-p xylene, and o-xylene. The effective solubilities of MTBE and BTEX were different for each test. Several batch tests were run during the column tests, and some diluted batch tests were run after to determine the equilibrium concentrations of the gasoline components. MTBE concentrations were much higher in batch test results than column test results, possibly due to its high solubility, and removal during initial flushing of the column prior to each test. Column tests results revealed that for the first two column tests, lower elution pore volumes were observed with lower saturations. When the velocity was increased, however, this was not always the case. Due to possible effects of biodegradation and nonequilibrium conditions during the later tailing stages, tests with lower saturation levels took longer to elute than those with higher saturations in these higher velocity tests. A new technique for analyzing the gasoline remaining in the column at the end of each test was incorporated. For each test, the column was divided into ten 3 cm sections, and analyzed for gasoline content. This showed the tendency for the gasoline to pool in certain sections of the column, while other sections were virtually devoid of any gasoline at the end of the test. A mass-balance model and equilibrium retardation factor were used to predict the order of elution and concentrations of the contaminants, with separate input parameters being put in. corresponding to each column test. The predicted order of elution was the same as the ones in this research, however, the pore volumes and concentrations were overestimated. Certain input parameters, such as weight percentages of gasoline components, and initial residual saturation were required to obtain comparable results.
