Jon E. Hodge

Date of Award


Document Type


Degree Name

Master of Science


Department of Engineering Physics

First Advisor

Kirk A. Mathews, PhD


Many try modeling groundwater contaminant transport to predict it. Is this possible with rate-limited processes, and under what conditions? On occasion, cleanups go slower than predicted (tailing) and hazardous concentrations reappear after cleanup is thought complete (rebound). Rate-limited transport is blamed by many. When immobile water is present, diffusion from varied sizes and shapes of immobile regions can cause varied rate limitations (due to varied diffusion path lengths). Although known, most modelers represent these varied rate-limiting processes with a single 'representative' rate-parameter. This can yield poor predictions for long-term experiments, and the parameter is generally time and pump-rate dependent. This model employs a distribution of first-order rate parameters to investigate the effects of using a single rate-parameter. Spatial effects are ignored by using volume-averaged concentrations (a point, well-mixed model) and dilutive pumping and rate-limited transport are modeled to isolate rate-limited transport for study. A three-parameter Gamma distribution defines the rate parameter continuum. A clean flow approximation is used extensively, and pulsed pumping is examined briefly. An effective time and pump-rate dependence is seen in the average rate. Long-term soil and contaminant transport characteristics along with uptake history or good experimentally-derived initial contaminant presence are concluded as necessary for accurate predictions.

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