The fate and transport of MTBE in three California drinking water reservoirs are simulated with a lake hydrodynamic model. The existing simulation model assumes that a reservoir can be represented as a layered system with only vertical gradients. Up to 200 layers may result from the mixing processes modeled. Forces accounted for in the model that affect the density structure in a lake include heat transfer, solar insolation, evaporation, inflow, outflow, diffusion, and wind mixing. The existing model has been applied to reservoirs around the world experiencing a wide range of conditions.

The existing model has been improved to account for MTBE sources from boats, inflow streams, and atmospheric exchange. Daily inputs of inflow concentration (usually assumed to be zero) and number of boats are taken from local records. The average mass of MTBE emitted per boat per day is also input so that the daily mass flux into the surface layer of water can be obtained from knowing the total number of boats.

A volatilization sub-model has also been added to account for surface loss of MTBE. This sub-model is based on a two-layer film representation of mass exchange across an air-water interface. Flux rate coefficients are taken from published data.

Results from these three lakes will provide a perspective in terms of boat use, climate effects, and MTBE concentrations. The modeled lakes are Donner Lake in the Sierra Nevada mountains, Lake Perris in southern California, and Calero Reservoir in Santa Clara county. Data for temperature and MTBE concentrations with depth during the summer of 1997 are currently being used to evaluate the model�s applicability to modeling MTBE fate and transport.

The three modeled lakes represent a cross section of climates and lake geometries. One goal of the modeling research is to determine if their are any commonalities in these systems that could also be expected in other California lakes. With the paucity of available data on MTBE, the model may be applied to systems where there is no data to provide some level of expected concentrations based on estimated boat use, inflow concentrations, and atmospheric concentrations.

The model will be used to evaluate management alternatives such as artificial mixing, multi-level withdrawal, and restricted boat use. Seasonal effects such as stratification and year-to-year persistence of MTBE will also be assessed.