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Groundwater Research
Milestones
Contaminated groundwater is a major problem at contaminated property across the country, including Superfund sites; those needing corrective action under the Resource Conservation and Recovery Act (RCRA); leaking underground storage tanks; and Brownfield sites. Conventional groundwater cleanup remedies are taking much longer than originally anticipated, and operation and maintenance costs are substantial.
Research activities, primed with input from EPA's Office of Solid Waste and Emergency Response, EPA's Regional Offices, and other federal and state agencies, address the need to characterize subsurface contamination and develop more cost-effective and efficient remedial options.
Emerging Innovative Technologies
In-Situ Chemical Reduction: In-Situ chemical reduction research efforts have led to the development of an innovative technology for remediating dissolved phase chromium [Cr(VI)] in groundwater. Field studies at Macalloy Corporation Superfund Site in Charleston, South Carolina, have reduced risk to human health and the environment and saved an estimated $1 million in remedial costs. ORD researchers have received a U.S. patent for this innovative remedial technology.
Nanotechnology/Emulsified ZVI: ORD researchers are conducting research on the treatment efficiency and cost-effectiveness of injecting nano-scale, emulsified zero-valent iron (EZVI) to treat Dense Non-Aqueous Phase Liquid (DNAPL) source areas. Anticipated benefits of this research: reduction in duration and cost of remediation at DNAPL sites, and support for regulators and site managers on selection and implementation of EZVI technology
Permeable Reactive Barriers (PRBs) Research
Results of the permeable reactive barriers (PRBs) long-term performance study treating chlorinated organics have been published in a synthesis of research report entitled, Capstone Report on the Application, Monitoring, and Performance of Permeable Reactive Barriers for Ground Water Remediation (EPA/600/R-03/045). This report represents a synthesis of 10 years of research and development on PRBs.
PRB technology has expanded rapidly in its use and acceptance as a viable approach for achieving site cleanup and closure. Over 100 applications of the technology are documented in the U.S. and worldwide. The primary reason for this expansion is that technology results in cost savings over other alternative methods.
Researchers investigate the geochemical, hydrogeological, and microbiological factors that govern the performance and functioning of PRBs. Understanding these factors is necessary in order to predict the longevity of PRB systems and to optimize the implementation of this technology for a wide variety of hazardous compounds.
Use of PRBs over traditional pump and treat methods resulted in an operation and maintenance savings of $12 million at two field study sites at the Denver Federal Center in Colorado and the Elizabeth City Coast Guard Support Center in North Carolina.
Monitored Natural Attenuation (MNA) of Inorganic Contaminants Research
Inorganic contaminant research focuses on identifying attenuation mechanisms and the stability of the immobilized species under anticipated geochemical conditions and evaluating the long-term performance and efficiency of remedial strategies
Arsenic attenuation and immobilization research at the Industri-plex Superfund Site in Massachusetts has saved an estimated $13 million in remedial expenses
Research activities have generated technical framework documents on MNA of inorganic contaminants in ground water for EPA's Office of Solid Waste and Emergency Response.
Dense Non-Aqueous Phase Liquid (DNAPL) Source Removal Research
DNAPL research focuses on characterization, sampling, and analytical methods to reduce the uncertainty in fate and transport models that improve exposure estimates supporting risk assessments. Research efforts include evaluating innovative and cost-effective technologies for cleaning up DNAPL source zones, as well as assess the benefits of partial source removal.
Flux-based DNAPL site management activities provide data for optimization of remedy selection and design and for establishment of appropriate remedial objectives (for example, contaminant flux data are used to optimize allocation of resources between source and plume treatment, to target remediation on high flux zones and to establish short-term remedial goals required for long-term protection of human health and the environment.
In-Situ Chemical Oxidation (ISCO) Research
ISCO is a rapidly developing remediation technology currently used or under consideration that targets a wide range of contaminants in multiple phases under a variety of hydrogeologic conditions at a large number of hazardous waste sites in all EPA Regional Offices across the country.
ORD research and technical support have improved ISCO-related project planning and implementation, avoided expensive and time-consuming setbacks through misuse of this technology, and accelerated remediation schedules and site closures.
Vapor Intrusion Research
In 2005, ORD evaluated and reviewed the literature on vapor intrusion and published the report entitled, Review of Recent Research on Vapor Intrusion A follow-up report is planned for journal publication in 2008.
The report citation is: Tillman, Fred D, and James W. Weaver, Review of Recent Research on Vapor Intrusion, U.S. Environmental Protection Agency, Washington DC, 2005, EPA/600/R-05/106.
ORD undertook more detailed evaluation of uncertainties associated with the results from the Johnson and Ettinger model in vapor intrusion assessment. Researchers determined, when all parameters were considered simultaneously, that the uncertainties in the model results were greater than previously appreciated. From these analyses, researchers developed a set of upper and lower-bound parameters for use in bounding vapor intrusion assessments. The purpose of this work was to establish sets of parameters that could be assured to generate best or worst case exposure assessments, given uncertainty in the parameter values.
The research is reported in the journal publications:
Tillman, F. D. and Weaver, J.W. Uncertainty from Synergistic Effects of Multiple Parameters in the Johnson and Ettinger (1991) Vapor Intrusion Model, Atmospheric Environment, 2006, 40(22) 4098-4112.
Tillman, F.D. and Weaver, J. W. Parameter Sets for Upper and Lower Bounds on Soil-to-Indoor-Air Contaminant Attenuation Predicted by the Johnson and Ettinger Vapor Intrusion Model, Atmospheric Environment, 2007, 41(27), pp 5797-5806.
ORD researchers developed calculation tools LINK http://www.epa.gov/athens/onsite to for use in assessing uncertainties in the Johnson-Ettinger model. These calculators are being used by states and consultants for assessing transport of environmental contaminants in the subsurface. A publication on a version of these calculations is:
Tillman, F., Weaver, J.W. Johnson and Ettinger (1991) Vapor Intrusion Model With Sub-Slab Concentration. U.S. Environmental Protection Agency, Washington, DC, 2005, EPA/600/C-06/002.
ORD outfitted a research building in Athens, Georgia, with instrumentation for measurement of soil moisture content and gas phase pressure. The experimental facility has been used to show the impacts of using various assumptions concerning the degree-of-dryness of soil beneath and outside existing buildings. The results showed that the moisture content beneath a newly constructed building situated on a heavy clay soil was unchanged after a year's worth of monitoring and that usage of moisture content that represented conditions outside the building footprint would cause vapor impacts to be over estimated. Vapor intrusion research is continuing.
More information on vapor intrusion at this research facility.
Tillman, F.D. and Weaver, J. W. Temporal Moisture Content Variability Beneath and External to a Building and the Potential Effects on Vapor Intrusion Risk Assessment, The Science of the Total Environment, 2007, 379(1) 1-15.
The Land Research Program recently synthesized vapor intrusion research in the document entitled, Assessment of Vapor Intrusion in Homes Near the Raymark Superfund Site Using Basement and Sub-Slab Air Samples. The method and associated quality control measures developed for sub-slab sampling are being used at EPA regional offices across the United States. Several states, including California and Colorado, have incorporated many of the report's recommendations into state guidance documents on vapor intrusion.