Raymond Hozalski, Principal Investigator

Modeling Perchloroethene Degradation in Anaerobic Aquifers

Chlorinated solvents are among the most common contaminants detected in groundwater. This is a public health concern because chlorinated solvents are known or suspected carcinogens. This research group is currently involved in a large project investigating the feasibility of promoting biodegradation of chlorinated solvents by using gas-permeable membranes to deliver hydrogen to contaminated aquifers.

As a sub-objective of this research, the group has developed a complex mathematical model to simulate the transport and microbial transformation of chlorinated solvents and hydrogen in groundwater. The model accounts for the fate of seven solutes (perchloroethene and its four dechlorination daughter products, plus hydrogen, and methane) and also simulates the growth of three different microbial populations that compete for hydrogen. One of the microbial populations is undesirable because it rapidly consumes hydrogen, but does not degrade chlorinated solvents. However, these researchers have hypothesized that pulsing hydrogen into the groundwater will inhibit the undesirable microbial population while stimulating growth of microbial species capable of degrading chlorinated solvents.

The mathematical model involves ten interdependent second-order nonlinear parabolic partial differential equations. The governing equations are applied to two adjacent physical domains: an aquifer and soil-free trench in which the H₂-supply membranes are installed.

The domains have different contaminant transport and biotransformation properties and are thus linked by appropriate boundary conditions. A Crank-Nelson finite-differences program has been written in fortran90 to solve the initial value problem.

In order for the group to meet its research objectives, they will perform the following tasks using Supercomputing Institute resources:

• Perform rigorous finite-differences grid analyses to confirm convergent solutions are attained
• Conduct sensitivity analyses to evaluate the most critical parameters in the model
• Evaluate the system performance under a range of hydrogen pulsing times
• Investigate the potential of using groundwater pumping to increase the hydrogen “zone of influence”

Research Group

Lee Clapp, Research Associate