INVESTIGATION OF NONEQUILIBRIUM PHYSICAL, CHEMICAL, AND MICROBIOLOGICAL TRANSPORT PROCESSES FOR EMERGING ORGANIC CONTAMINANTS USING MODELS AND LABORATORY TRACER TESTS

Laboratory column tests were conducted to assess the relative importance of nonequilibrium physical, chemical, and microbiological transport on pharmaceuticals and other organic contaminants. Field soils and natural waters spiked with dissolved organic contaminants are used in laboratory column experiments at different flow rates that are realistic for ground-water systems. Breakthrough curves are analyzed with mathematical models to elucidate the important transport processes. The following transport processes are examined: physical nonequilibrium (diffusion into low-permeability materials), nonequilibrium sorption; irreversible sorption, two-site sorption; first- and zero-order biodegradation; degradation in the soil versus aqueous phase. Results indicate that site soils do not exhibit physical nonequilibrium. The relevance of nonequilibrium sorption and the type of biodegradation varies among contaminants. The study demonstrates that different models may be necessary for specific contaminants when a suite of contaminants are of concern.