U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Use of Simulation to Study Field-Scale Solute Transport and Biodegradation at the Bemidji, Minnesota,Crude-Oil Spill Site

Abstract

A two-dimensional, multispecies solute-transport model that includes aerobic and anaerobic degradation processes was developed and applied to the Bemidji, Minnesota, crude-oil spill site. The model was used as a tool to study the field-scale solute-transport and degradation processes. The simulations included the transport of degradable and refractory dissolved organic carbon, dissolved oxygen, and methane, as well as aerobic and anaerobic (methanogenic) biodegradation. Despite the considerable uncertainty in the model parameter estimates, results of simulations reproduced the general features of the observed ground-water plume. In addition to the kinetics of the biodegradation processes, important factors that affect the distribution of the solutes in the field are the recharge influx and the degree of dispersion and mixing in the ground water system. Recharge influx causes flow lines in the aquifer to be deflected downward from the water table causing downward movement of the plume. Biodegradation results in a narrow plume with sharp gradients at the margins. Spatial variability of hydraulic conductivity increases the amount of carbon degraded by aerobic and anaerobic processes.