Handbook of Solvents - George Wypych - ChemTech - Ventech!

23
Contamination Cleanup: Natural
Attenuation and Advanced
Remediation Technologies
23.1 NATURAL ATTENUATION OF CHLORINATED SOLVENTS IN
GROUND WATER
Hanadi S. Rifai
Civil and Environmental Engineering,
University of Houston, Houston, Texas, USA
Charles J. Newell
Groundwater Services, Inc., Houston, Texas, USA
Todd H. Wiedemeier
Parson Engineering Science, Denver, CO, USA
23.1.1 INTRODUCTION
Chlorinated solvents were first produced some 100 years ago and came into common usage
in the 1940’s. Chlorinated solvents are excellent degreasing agents and they are nearly nonflammable
and non-corrosive. These properties have resulted in their widespread use in
many industrial processes such as cleaning and degreasing rockets, electronics and clothing
(used as dry-cleaning agents). Chlorinated solvent compounds and their natural degradation
or progeny products have become some of the most prevalent organic contaminants found
in the shallow groundwater of the United States. The most commonly used chlorinated solvents
are perchloroethene (PCE), trichloroethene (TCE), 1,1,1-trichloroethane (TCA), and
carbon tetrachloride (CT). 1
Chlorinated solvents (CS) undergo the same natural attenuation processes as many
other ground water contaminants such as advection, dispersion, sorption, volatilization and
biodegradation. In addition, CS are subject to abiotic reactions such as hydrolysis and
dehydrohalogenation and abiotic reduction reactions. While many of the physical and
chemical reactions affecting chlorinated solvents have been extensively studied, their
biodegradation is not as well understood as perhaps it is for petroleum hydrocarbons. Researchers
are just beginning to understand the microbial degradation of chlorinated solvents
with many degradation pathways remaining to be discovered. Unlike petroleum hydrocarbons,
which can be oxidized by microorganisms under either aerobic or anaerobic condi-