Date of Award

Spring 2000

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Civil and Environmental Engineering

First Advisor

Zanoni, Alphonse E.

Abstract

Naturally occurring processes in soil and ground water can, without human intervention, reduce the mass, mobility, toxicity, volume, or concentration of contaminants released in soil and ground water over time. For some releases of hazardous material, this "natural attenuation" may sufficiently reduce mass, mobility, toxicity, volume, or concentration of contaminants to acceptable levels of risk to human health and the environment. In 1996, United States Environmental Protection Agency (USEPA) released data showing that natural attenuation is the most common treatment option at sites with contaminated ground water. n the last few years, several organizations published technical approaches for evaluation and implementation of natural attenuation. These procedures have adapted the National Research Council 's suggested strategy for demonstrating in-situ bioremediation to the demonstration of natural attenuation. The strategy is to establish the following lines of evidence: I) Documented loss of contaminants from the site, 2) Laboratory assays showing that microorganisms in site samples have the potential to transform the contaminants under the expected site conditions, and 3) One or more pieces of evidence showing that the biodegradation potential is actually realized in the field. These approaches place significant emphasis on using site-specific biodegradation rate constants to document mass removal of contaminants. USEPA advocates the use of one of three approaches to estimate site-specific biodegradation rate constants from ground water concentration data: 1) Exponential regression of "corrected" concentration data, 2) Buscheck and Alcantar's method of exponential regression using an analytical solution of the general one-dimensional solute transport equation to correct for dispersion and sorption effects, and 3) Extracting degradation rate constants from a calibrated solute transport model. This paper presents a critical evaluation of the application of the three site-specific degradation rate estimation methods advocated by USEPA to a chlorinated ethene (trichloroethene) plume.

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