Chlorinated solvents and their daughter products are the most common contaminants of groundwater at industrial and military facilities in the United States. Limitations of conventional technologies have intensified efforts to find alternative methods to remediate contaminated sites to regulatory goals set by CERCLA. Natural attenuation of chlorinated solvents is a promising alternative to traditional pump and treat methods but has not been well understood or widely accepted. This modeling study investigated the ability of TCE to completely degrade under various aquifer conditions and rate order constants. It also examined a case study of a former landfill site at Moody AFB. We found unusually high flow of ground water by advection or dispersion inhibits the complete degradation of TCE. High concentrations of sulfate or nitrate inhibit the creation of methanogenic conditions and therefore inhibit reductive dechlorination of TCE. We also found an electron donor co-contaminant a critical factor for the complete destruction of TCE because it creates anaerobic conditions. The model illustrated a possible explanation for the lack of down gradient contaminants at the landfill site may be the coupling of reductive dechlorination and cometabolism naturally attenuation the contaminants.

The lesser chlorinated ethenes, cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC), are produced by anaerobic reductive dechlorination at subsurface sites contaminated by tetrachloroethene (PCE) and trichloroethene (TCE). Accumulation of VC and cDCE under anaerobic conditions limits the application of natural attenuation and enhanced reductive anaerobic biological in-situ treatment technologies (RABITT). Aerobic degradation of lesser chlorinated ethenes has been demonstrated, suggesting that sequential anaerobic/aerobic conditions may result in complete mineralization of PCE/TCE. However, our present understanding of the aerobic transformation potentials of cDCE and VC is limited, thus limiting the reliability of and confidence in natural and enhanced biological alternatives for site remediation. The objective of our project was to determine the prevalence and metabolic capabilities of microorganisms able to derive energy from aerobic oxidation of cDCE and/or VC in subsurface environments. The results help delineate the role of growth-coupled (vs. cometabolic) aerobic oxidation in the natural attenuation of lesser-chlorinated ethenes. Results provide the basis for improved site assessment, improved remedial-action decision-making, and more reliable bioremediation technologies. Our findings indicate that aerobic bacteria (Mycobacterium and Nocardioides strains) capable of growth-linked VC oxidation are widespread in the environment, and commonly found at chlorinated-ethene-contaminated sites. Aerobic assimilation of VC as a carbon source is therefore an ecologically significant phenomenon of equal or greater importance than cometabolic VC degradation. Based on their distribution, growth rates and kinetic parameters, we believe that Mycobacterium strains are most likely to be responsible for the aerobic natural attenuation of VC that has been observed at many sites.

In the past decade, officials responsible for clean-up of contaminated groundwater have increasingly turned to natural attenuation-essentially allowing naturally occurring processes to reduce the toxic potential of contaminants-versus engineered solutions. This saves both money and headaches. To the people in surrounding communities, though, it can appear that clean-up officials are simply walking away from contaminated sites. When is natural attenuation the appropriate approach to a clean-up? This book presents the consensus of a diverse committee, informed by the views of researchers, regulators, and community activists. The committee reviews the likely effectiveness of natural attenuation with different classes of contaminants-and describes how to evaluate the "footprints" of natural attenuation at a site to determine whether natural processes will provide adequate clean-up. Included are recommendations for regulatory change. The committee emphasizes the importance of the public's belief and attitudes toward remediation and provides guidance on involving community stakeholders throughout the clean-up process. The book explores how contamination occurs, explaining concepts and terms, and includes case studies from the Hanford nuclear site, military bases, as well as other sites. It provides historical background and important data on clean-up processes and goes on to offer critical reviews of 14 published protocols for evaluating natural attenuation.

The first comprehensive guide to one of today's most innovative approaches to environmental contamination Natural attenuation is gaining increasing attention as a nonintrusive, cost-effective alternative to standard remediation techniques for environmental contamination. This landmark work presents the first in-depth examination of the theory, mechanisms, and application of natural attenuation. Written by four internationally recognized leaders in this approach, the book describes both biotic and abiotic natural attenuation processes, focusing on two of the environmental contaminants most frequently encountered in groundwater--fuels and chlorinated solvents. The authors draw on a wealth of combined experience to detail successful techniques for simulating natural attenuation processes and predicting their effectiveness in the field. They also show how natural attenuation works in the real world, using numerous examples and case studies from a wide range of leading-edge projects nationwide involving fuel hydrocarbons and chlorinated solvents. Finally, they discuss the evaluation and assessment of natural attenuation and explore the design of long-term monitoring programs. An indispensable reference for anyone working in environmental remediation, Natural Attenuation of Fuels and Chlorinated Solvents in the Subsurface is essential reading for scientists and engineers in a range of industries, as well as state and federal environmental regulators, and professors and graduate students in environmental or chemical engineering.

​This volume provides a review of the past 10 to 15 years of intensive research, development and demonstrations that have been on the forefront of developing bioaugmentation into a viable remedial technology. This volume provides both a primer on the basic microbial processes involved in bioaugmentation, as well as a thorough summary of the methodology for implementing the technology. This reference volume will serve as a valuable resource for environmental remediation professionals who seek to understand, evaluate, and implement bioaugmentation.