Engineering and Implementation Challenges for Chlorinated Solvent Remediation. In: Stroo H, Ward C, editors. In Situ Remediation of Chlorinated Solvent Plumes. New York: Springer; 2010. pp. 109-43. [DOI: 10.1007/978-1-4419-1401-9_5]

An Integrated Approach Supporting Remediation of an Aquifer Contaminated with Chlorinated Solvents by a Combination of Adsorption and Biodegradation

Hydrogeological uniqueness and chemical-physical peculiarities guide the contamination dynamics and decontamination mechanisms in the environmental arena. A single composite geodatabase, which integrates geological/hydrological, geophysical, and chemical data, acts as a “cockpit” in the definition of a conceptual model, design of a remediation strategy, implementation, near-real-time monitoring, and validation/revision of a pilot test, and monitoring full-scale interventions. The selected remediation strategy involves the creation of "reactive" zones capable of reducing the concentration of chlorinated solvents in groundwater through the combined action of adsorption on micrometric activated carbon, which is injected into the aquifer, and degradation of organic contaminants, stimulating the dechlorinating biological activity by the addition of an electron donor. The technology is verified through a pilot test, to evaluate the possibility of scaling up the process. The results of post-treatment monitoring reveal abatement of the concentration of chlorinated solvents and intense biological dechlorination activity. Achieving the remediation objectives and project closure is based on the integration of multidisciplinary data using a multiscale approach. This research represents the first completed example in European territory of remediation of an aquifer contaminated with chlorinated solvents by a combination of adsorption and biodegradation.

Screening houses for vapor intrusion risks: a multiple regression analysis approach

The migration of chlorinated volatile organic compounds from groundwater to indoor air-known as vapor intrusion-can be an important exposure pathway at hazardous waste sites. Because sampling indoor air at every potentially affected home is often logistically infeasible, screening tools are needed to help identify at-risk homes. Currently, the U.S. Environmental Protection Agency (EPA) uses a simple screening approach that employs a generic vapor "attenuation factor," the ratio of the indoor air pollutant concentration to the pollutant concentration in the soil gas directly above the groundwater table. At every potentially affected home above contaminated groundwater, the EPA assumes the vapor attenuation factor is less than 1/1000--that is, that the indoor air concentration will not exceed 1/1000 times the soil-gas concentration immediately above groundwater. This paper reports on a screening-level model that improves on the EPA approach by considering environmental, contaminant, and household characteristics. The model is based on an analysis of the EPA's vapor intrusion database, which contains almost 2,400 indoor air and corresponding subsurface concentration samples collected in 15 states. We use the site data to develop a multilevel regression model for predicting the vapor attenuation factor. We find that the attenuation factor varies significantly with soil type, depth to groundwater, season, household foundation type, and contaminant molecular weight. The resulting model decreases the rate of false negatives compared to EPA's screening approach.

Selective utilization of exogenous amino acids by Dehalococcoides ethenogenes strain 195 and its effects on growth and dechlorination activity

Bacteria of the genus Dehalococcoides are important members of bioremediation communities because of their ability to detoxify chloroethenes to the benign end product ethene. Genome-enabled studies conducted with Dehalococcoides ethenogenes 195 have revealed that two ATP-binding cassette (ABC)-type amino acid transporters are expressed during its exponential growth stages. In light of previous findings that Casamino Acids enhanced its dechlorination activity, we hypothesized that strain 195 is capable of importing amino acids from its environment to facilitate dechlorination and growth. To test this hypothesis, we applied isotopomer-based dilution analysis with (13)C-labeled acetate to differentiate the amino acids that were taken up by strain 195 from those synthesized de novo and to determine the physiological changes caused by the significantly incorporated amino acids. Our results showed that glutamate/glutamine and aspartate/asparagine were almost exclusively synthesized by strain 195, even when provided in excess in the medium. In contrast, phenylalanine, isoleucine, leucine, and methionine were identified as the four most highly incorporated amino acids, at levels >30% of respective proteinogenic amino acids. When either phenylalanine or all four highly incorporated amino acids were added to the defined mineral medium, the growth rates, dechlorination activities, and yields of strain 195 were enhanced to levels similar to those observed with supplementation with 20 amino acids. However, genes for the putative ABC-type amino acids transporters and phenylalanine biosynthesis exhibited insignificant regulation in response to the imported amino acids. This study also demonstrates that using isotopomer-based metabolite analysis can be an efficient strategy for optimizing nutritional conditions for slow-growing microorganisms.