Estimating natural attenuation rates for a chlorinated hydrocarbon plume in a glacio-fluvial aquifer, Schoolcraft, Michigan.

摘要

A plume of chlorinated hydrocarbons in Schoolcraft, Michigan, that has undergone abiotic and biotic degradation processes, was examined using numerical modeling techniques. The flow field was simulated with a three-dimensional steady state heterogeneous plume scale model that incorporated natural hydrologic boundaries through a Telescopic Grid Refinement of a three-dimensional steady state regional scale model that was extended to natural hydrologic boundaries. Contaminant plume evolution was examined using an RT3D model that includes aerobic and anaerobic biodegradation of the source compounds PCE, TCE, TCA, and their daughter byproducts, as well as the simultaneous abiotic degradation of TCA. The model was used to estimate the degradation rates of the plume species by comparing the calculated ratio of a species to its daughter byproduct for observed data and simulated results in a well transect downgradient of the source. The ratio approach should be applicable to any field site in which contaminants degrade to form a byproduct, thus circumventing the source term problem. The plume compounds degraded at a rate between 10−2 day−1 and 10−5 day −1, which is similar to natural attenuation rates at the RTDF Dover Site. The rates are too slow to allow natural attenuation process alone to remediate the plume in a reasonable time frame.