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Scenarios Evaluation Tool for Chlorinated Solvent MNA

Research Team: Michael J. Truex, Pacific Northwest National Laboratory; Charles J. Newell, Groundwater Services, Inc.; Brian B. Looney, Savannah River National Laboratory (SRNL); Karen M. Vangelas, SRNL

Description: One of the main challenges to implementing MNA is the need to cost-effectively interpret the multifaceted site specific data. To address this challenge, a team of researchers developed a “taxonomic key” to classify contaminated sites into one of thirteen scenarios based on hydrologic setting, geochemistry and a variety of modifying factors. The team developed a guidebook for each scenario to streamline characterization, modeling and monitoring. The result is a practical tool that will assist in environmental decision-making and in developing defensible environmental management strategies.

Report Title: WSRC-STI-2006-00096 R2 Scenarios.pdf
   
  Push-Pull Tests to Determine In Situ Attenuation Capacity at a Field Scale
   
  Research Team: Aaron D. Peacock; Microbial Insights, Inc.; Jack D. Istok and Jennifer A. Field, Oregon State University; Eric Raes, Engineering and Land Planning Associates; and Margaret R. Millings, Savannah River National Laboratory
   
  Description: Measuring the rates of the attenuation mechanisms controlling the destruction, stabilization, and/or removal of contaminants from the subsurface system is a key component to employing mass balance as a means to evaluate and monitor the stability and subsequent shrinkage of a contaminant plume. A team of researchers investigated the use of push-pull tests for measuring rates in situ of reductive dechlorination in settings with low chlorinated solvent concentrations (<1 ppm). These tests have been successfully conducted to support bioremediation at chlorinated solvent sites and transport of metals and radionuclides at contaminated sites. The results of this research indicate this tool will be useful for measurement of in situ reductive dechlorination rates for chlorinated solvents at sites in a state of MNA.
   
 

Report Title: Detecting and Quantifying Reductive Dechlorination During Monitored Natural Attenuation at the Savannah River CBRP Site

 
 
     
 
  Field Testing Passive Flux Meter for Multiple Solute Fluxes
   
  Research Team: Kirk Hatfield, Michael D. Annable and Jaehyun Cho, University of Florida and Margaret R. Millings, Savannah River National Laboratory
   
  Description: The stability of a contaminant plume is a key to initiation of attenuation-based remedies. Measurement of the changes in contaminant flux along a groundwater flow path provides insight into plume stability and contaminant mass balance. Thus characterization and monitoring tools that provide data specifically in terms of mass flux are of great interest. A team of researchers from the University of Florida have developed such a tool, the Passive Fluxmeter, for deployment in groundwater monitoring wells. This tool was developed with support from both the Department of Defense and the Environmental Protection Agency. The results of the research indicate the Passive Fluxmeter provided reasonable measures of local flux for multiple solutes and for water. However, as the researchers noted, unanswered questions remain associated with its use. These questions include upscaling the results into a usable integrated mass flux (the total mass moving through a transect perpendicular to groundwater flow in a given time interval, e.g., Kg/day), deployment logistics, costs, and reliability/robustness.
   
 

Report Title: Passive Fluxmeters: Application as a Characterization/Monitoring Tool for Monitored Natural Attenuation of Chlorinated Solvents

 
 
     
 
  Microsparger for Wellhead Measurements
   
  Research Team: Kirk Cantrell and Tyler Gilmore, Pacific Northwest National Laboratory and W. Keith Hyde, Savannah River National Laboratory
   
  Description: Accurate, timely measurement of chlorinated solvents and other volatile contaminants in groundwater is crucial to support responsible environmental management. Traditionally, two distinctly different paradigms have been explored to meet this need – fixed laboratory analysis and “real-time” sensors. While these alternatives remain important, field based and field screening tools represent a potentially useful intermediate approach that balances some of the advantages and disadvantages of the traditional “end-member” paradigms. The value of accurate, in-field measurements during characterization was recognized in recent sampling/decision methods, such as the TRIAD approach. Strategies that support gathering accurate data on the timescales representative of the rate of change of the system (e.g., months to years, not seconds to minutes) is key for long-term monitoring for chlorinated solvent plumes in which attenuation based remedies are being considered. A team of researchers developed a down-well sampling device that, when used in combination with field gas analysis tools, provides data in the field. The test results indicate this tool, as configured, will provide accurate measurements (as compared with laboratory methods) at concentrations in the hundreds of ppb or higher range, but require confirmatory traditional sampling with laboratory analysis at concentrations approaching 20 ppb and less. The logistics and costs of the sampling device were somewhat complex. The results of the study, while equivocal, generally suggest that future development of this type of in-field technique may be warranted.
   
 

Report Title: A New Device and Method for Measuring Volatile Compounds in Monitoring Wells

 
 
     
 
  Use of Electron Shuttles to Biologically Enhance Abiotic Dechlorination
   
  Research Team: Patrick W. McLoughlin and Robert J. Pirkle, Microseeps, Inc.; John T. Wilson, US EPA; and Barbara J. Wilson, Consultant
   
  Description: Biological anaerobic reductive dechlorination is a robust attenuation mechanism for chlorinated solvents and, under appropriate site conditions, is the dominant attenuation process. When conditions do not favor anaerobic biodegradation, other processes need to be assessed and quantified (EPA, 1998). Abiotic reductive dechlorination is one such mechanism that may contribute to attenuation. A team of researchers conducted studies to develop a method to measure acetylene as an indicator of abiotic reductive dechlorination and to develop a method to enhance this process using electron shuttles. The results of their work indicate additional research is needed to understand and measure this mechanism.
   
 

Report Title: Use of Electron Shuttles to Biologically Enhance Abiotic Dechlorination

 
 
     
 
  Innovative Oxygen Sensor for Remote Subsurface Oxygen Measurements
   
  Research Team: Margaret R. Millings, Brian D. Riha, and W. Keith Hyde, Savannah River National Laboratory
   
  Description:Oxygen is a primary indicator of whether anaerobic reductive dechlorination and similar redox based processes contribute to natural attenuation remedies at chlorinated solvent contaminated sites. Thus, oxygen is a viable indicator parameter for documenting that a system is being sustained in an anaerobic condition. A team of researchers investigated the adaptation of an optical sensor that was developed for oceanographic applications. The optical sensor, because of its design and operating principle, has potential for extended deployment and sensitivity at the low oxygen levels relevant to natural attenuation. The results of the research indicate this tool will be useful for in situ long-term monitoring applications, but that the traditional characterization tools continue to be appropriate for characterization activities.
   
 

Report Title: Evaluating an Innovative Oxygen Sensor for Remote Subsurface Oxygen Measurements

 
     
 
  Advancement of Nucleic Acid based Tools for Monitoring in situ Reductive Dechlorination
   
  Research Team: Frank Löeffler, Georgia Tech. and Elizabeth Edwards, University of Toronto
   
  Description:Regulatory protocols generally recognize that destructive processes are the most effective mechanisms that support natural attenuation of chlorinated solvents. In many cases, these destructive processes will be biological processes and, for chlorinated compounds, will often be reductive processes that occur under anaerobic conditions. The existing EPA guidance (EPA, 1998) provides a list of parameters that provide indirect evidence of reductive dechlorination processes. In an effort to gather direct evidence of these processes, scientists have identified key microorganisms and are currently developing tools to measure the abundance and activity of these organisms in subsurface systems. The research continues the development efforts to Lö effler and Edwards to provide a suite of tools to enable direct measures of biological processes related to the reductive dechlorination of TCE and PCE. This study investigated the strengths and weaknesses of the 16S rRNA gene-based approach to characterizing the natural attenuation capabilities in samples. The results suggested that an approach based solely on 16S rRNA may not provide sufficient information to document the natural attenuation capabilities in a system because it does not distinguish between strains of organisms that have different biodegradation capabilities. The results of the investigations provided evidence that tools focusing on relevant enzymes for functionally desired characteristics may be useful adjuncts to the 16SrRNA methods.
   
 

Report Title: Advancement of Nucleic Acid-Based Tools for Monitoring In Situ Reductive Dechlorination

 
     
 
  Structural Features of VOCS and Contaminant Solid Interactions- Irreversible Sorption
   
  Research Team: Robert G. Riley, James E. Szecsody, A. V. Mitroshkov, and C.F. Brown, Pacific Northwest National Laboratory
   
  Description:Sorption is governed by the physico-chemical processes that partition solutes between the aqueous and solid phases in aquifers. For environmental systems, a linear equilibrium relationship between the amounts of contaminant in the alternative phases is often assumed. In this traditional approach, the distribution coefficient, or K d, is a ratio of contaminant associated with the solid phase to the contaminant in the water phase. Recent scientific literature has documented time-dependant behaviors in which more contaminant mass is held in the solid phase than predicted by the standard model. Depending on the specific conceptualization, this has been referred to as nonlinear sorption, time-variable sorption, or “irreversible sorption.” The potential impact of time-variable sorption may be beneficial or detrimental depending on the specific conditions and remediation goals. Researchers at the Pacific Northwest National Laboratory (PNNL) have been studying this process to evaluate how various soil types will affect this process for sites contaminated with chlorinated solvents. The results described in this report evaluate sorption-desorption of trichloroethylene (TCE) and tetrachloroethylene (PCE) in Savannah River Site (SRS) soils. The results of this study will be combined with ongoing PNNL research to provide a more comprehensive look at this process and its impact on contaminant plume stability and sustainability. Importantly, while the results of the study documented differences in sorption properties between two tested SRS soils, the data indicated that “irreversible sorption” is not influencing the sorption-desorption behaviors of TCE and PCE for these soils.
   
 

Report Title: Desorption Behavior of Trichloroethene and Tetrachloroethene in U.S. Department of Energy Savannah River Site Unconfined Aquifer Sediments
   
 

Development of mRNA-based Dehalogenation Rate Constants
   
 

Research Team: Ruth Richardson, Cornell University
   
 

Description:  The research reported herein describes efforts to develop a molecular method based on mRNA and protein enzymes to determine in situ degradation rates associated with Dehalococcoides.  Because mRNA is produced as needed in response to conditions, mRNA has been identified as a theoretically more direct and quantitative measure of rates than DNA.  Dr. Richardson’s data suggest that, in current practice, mRNA may not be an efficient or effective monitor for instantaneous rates (especially in light of logistics, sampling, handling, reproducibility, and quantitation). Dr. Richardson’s proteomics data (measurements of key proteins/enzymes) suggested that this emerging technology holds promise.  The results of this study when coupled with the results of the Edwards/Loeffler (WSRC-STI-2006-00332) study suggest the value of using a suite of bioindicators in determining the presence and activity of specific microbial populations controlling the destructive degradation of chlorinated solvents. 

   
 

Report ID:  WSRC-STI-2006-00333.pdf
 

 
 

Scenarios Evaluation Tool for Chlorinated Solvent MNA
   
 

Research Team: Michael J. Truex, Pacific Northwest National Laboratory; Charles J. Newell, Groundwater Services, Inc.; Brian B. Looney and Karen M. Vangelas, Savannah River National Laboratory
   
 

Description: One of the main challenges to implementing MNA is the need to cost-effectively interpret the multifaceted site specific data. To address this challenge, a team of researchers developed a “taxonomic key” to classify contaminated sites into one of thirteen scenarios based on hydrologic setting, geochemistry and a variety of modifying factors. The team developed a guidebook for each scenario to streamline characterization, modeling and monitoring.  Included in the guidebook are 12 tables showing the degradation paths of selected chlorinated solvents under anaerobic, aerobic, and anoxic conditions, the likelihood of each pathway occurring, and references supporting those determinations.  The result is a practical tool that will assist in environmental decision-making and in developing defensible environmental management strategies. 

   
 

Report ID:  WSRC-STI-2006-00096.pdf
   
  Developing an MNA Modeling Tool based on RT3D: 3 Reports
1. Natural and Enhanced Attenuation of Chlorinated Solvents Using RT3D RT3D
2. Reaction Modules for Natural and Enhanced Attenuation of Chloroethanes, Chloroethenes, Chloromethanes, and Daughter Products
3. rtFlux: RT3D Flux Plane Utility
   
  Research Team: Christian D. Johnson and Michael J. Truex, Pacific Northwest National Laboratory and T. Prabhakar Clement, Auburn University
   
 

Description:  Integral to the acceptance of MNA and EA as part of a remediation system is documenting the sustainability of the attenuation mechanisms.  As many sites are located in complex hydrogeologic settings, documentation of sustainability will require the use of complex models that have the capabilities to mathematically represent the various attenuation mechanisms.  To address this need a team of researchers developed specific reaction modules for complex chlorinated solvent reactions that occur in the subsurface.  These reaction modules support the RT3D model.  The information provided within these reports provides sufficient detail to adapt these modules to various modeling platforms.

Report ID:  WSRC-STI-2006-00174.pdf
   
 

Decision Tool for Groundwater Cleanup of Chlorinated Solvent Plumes at DOE Sites

Description:  The objective of this project was to develop and test a decision tool and process to support responsible decision-making regarding alternative remedial approaches at sites containing groundwater contaminated with cVOCs. The cVOC Remediation Decision Tool (cVOC Tool) has been designed specifically to be useful at sites with any type of ongoing treatment, and to give fair consideration of all types of alternatives, including EA and MNA.

Report ID: cVOC_Decision_Tool_Final_Report_92906.pdf