Modeling source area diffusivity of methyl tert-butyl ether (MTBE) in groundwater systems

This research focuses on the development of a laboratory model that will be critical for predicting source area concentration levels of the gasoline additive, methyl tert-butyl ether (MTBE), in the soil atmosphere. Based on the data generated on fate and transport from an experimental laboratory model, it is possible to develop a mathematical model of the movement of MTBE to human receptors in a variety of soil types. Furthermore, the model developed here could be the focal point for risk assessments or exposure studies that would cover effects on human health and environmental health. The model will be able to provide estimations of the unsaturated zone concentration above an MTBE source, such as groundwater contaminated by a leaking underground storage tank. The advantage of the laboratory model is that important parameters can be validated in the laboratory system which reduce uncertainty in mathematical models. Soil column microcosms were constructed in the laboratory in both the horizontal and vertical directions. The soil columns were used to develop and test the hypothesis that a coalescing effect exists in the vertical column, and that free convection is occurring in the horizontal column. These phenomena must be considered when modeling diffusion in the subsurface. The laboratory models also showed that using Fick's law was an effective tool for developing an in-soil apparent diffusion coefficient for MTBE.