2003 Progress Report: Incorporating Natural Attenuation Into Design and Management Strategies For Contaminated Sites

EPA Grant Number: R828770C004
Subproject: this is subproject number 004 , established and managed by the Center Director under grant R828770
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: HSRC (2001) - Midwest Hazardous Substance Research Center
Center Director: Banks, M. Katherine
Title: Incorporating Natural Attenuation Into Design and Management Strategies For Contaminated Sites
Investigators: Novak, John T. , Widdowson, Mark
Institution: Virginia Polytechnic Institute and State University
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 2001 through September 30, 2004
Project Period Covered by this Report: October 1, 2002 through September 30, 2003
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management


Monitored natural attenuation (MNA) is recognized as a feasible site remediation approach where MNA is shown to provide a satisfactory level of risk reduction. One of the important uses of MNA is as a plume management strategy for followup to source remediation. The coupling of source remediation with MNA is an approach that can only be addressed by modeling. In effect, this approach seeks to answer the question: Given the natural attenuation capacity of an aquifer, how clean does the source area need to be to use natural attenuation? Once that question is answered, natural attenuation, coupled with source remediation, can be compared to other remediation approaches. Similarly, phytoremediation, as an enhanced natural attenuation process, can be incorporated into models that judge if the degradation and evapotranspiration rates for specific plant systems are adequate at a given site to reduce the risk to acceptable levels. This also can be incorporated into models that incorporate other treatment options. The objectives of this research project are to: (1) monitor the progress of monitored natural attenuation (MNA) at two sites to assess the long-term efficacy of this remediation strategy and to obtain data for the rates of remediation; (2) develop and demonstrate a model protocol and user-interface for MNA with phytoremediation and MNA with source remediation strategies at a number of demonstration sites; (3) obtain laboratory data in conjunction with the field data that help to better clarify the mechanisms associated with the degradation/transformation rates of the contaminants; and (4) develop and improve modules for simulating natural attenuation and phytoremediation in the transport model Sequential Electron Acceptor Model 3-Dimensional (SEAM3D).

Progress Summary:

Assessment of MNA at Chlorinated Solvent Sites

In Year 2 of the project, the main focus of the research at the chlorinated solvent site was the use of SEAM3D to evaluate remediation strategies involving MNA and selection of the remedial strategy by the U.S. Department of Defense (DoD). A bioaugmentation study using laboratory microcosm experiments is nearly completed. This study is using a tetrachloroethene (PCE)-degrading culture obtained from Georgia Institute of Technology researchers. In addition, model validation continued using data provided by the U.S. Geological Survey from U.S. Navy sites.

Figure 1 shows two distinct source areas (PCE "hot spots") identified using a Membrane Interface Probe at the DoD facility. Groundwater flow and solute transport models (modular three-dimensional finite difference groundwater flow model [MODFLOW] and SEAM3D, respectively) were calibrated to simulate the following five remediation alternatives for the chloroethene-contaminated site:

• Monitored Natural Attenuation
• Pump-and-Treat
• Reactive Barrier Wall
• Biostimulation
• Pump-and-Treat with Biostimulation.

Figure 1. Total Chlorinated Ethene Plume (mg/L) and Membrane Interface Probe/Geoprobe Sampling Locations at the Chlorinated Solvent MNA Study Site

The simulations showed that all of these alternatives would be acceptable from the standpoint of preventing discharge of volatile organic compound contamination to a receptor. When judged with respect to aquifer restoration, the pump-and-treat, biostimulation, and combined pump-and-treat with biostimulation options generally were comparable, with the combined alternative providing the fastest overall cleanup. Even so, the time to complete remediation is estimated to extend approximately to the year 2036.

At the creosote-contaminated phytoremediation site, the research team collected two rounds (early winter and early spring) of groundwater samples to assess contamination changes and hydrologic data. Figure 2 depicts the average total polycyclic aromatic hydrocarbon (PAH) concentration in the shallow and deep groundwater from 1999 to 2003 (January sampling events). These results indicate the effectiveness of the phyto system for the shallow groundwater but also indicate that the dense nonaqueous phase liquid (DNAPL) remains for the deeper samples. It can be concluded that the groundwater is being remediated, but removal of the concentrated creosote is not taking place to any great extent. Therefore, it can be concluded that the phytoremediation is protecting groundwater but still has not provided site remediation.

The effect on groundwater can be seen in Figure 3; the concentration of PAHs in groundwater collected at bedrock has changed little during the 6 years of operation (data for 2003 is similar to 2002, so they were not included to avoid clutter). At 5 feet above bedrock, the concentration of PAH (mostly naphthalene) was near zero. For locations near the edge of the site, groundwater has shown an even more dramatic cleaning.

It was thought that the poplar tree system would never remove creosote from the bedrock, but it was expected that the creosote remaining on the bedrock would become enriched in nonmobile PAHs and thereby would become stable. As can be seen in Figure 4, there are some indications that PAH stabilization has been occurring with the depletion of naphthalene from the groundwater.

Figure 2. Total PAH Concentration in the Shallow Groundwater at the Oneida, TN Sites

In summary, the remediation process is progressing. Groundwater is being cleaned, thereby protecting the receiving waters at the site and the creosote is undergoing transformation to higher ringed PAHs that will be less mobile. The major question about the site and other sites using phytoremediation to treat PAH contamination is: How much time is needed before the site can be considered remediated? Much of the research at this site over the next year will be focused on this question.

Figure 3. Groundwater PAH Concentrations Versus Depth Over Time at ML7 in the Plume Center

Figure 4. Depletion of Naphthalene From Groundwater Relative to the Total PAH Concentration at ML 7 Purple (~3 ft above bedrock)

Push-Pull Testing

Inu Year 1 of the project, we indicated that push-pull testing would be a major focus for 2002-2003. Push-pull testing is an attempt to make real-time measurements of contaminant degradation in the field. Push-pull tests consist of injecting a contaminant and a tracer into a well and then, following injection, extracting groundwater from the well. Samples are collected during the injection and the extraction procedures to assess degradation. A series of wells were installed, resulting in a shallow and deep well pair at five locations. Soil samples were collected from each foot and subsequently analyzed on gas chromatography for PAH content. Extra soil was collected from the screened areas and preserved for microcosm experiments. One well pair was a control well outside the plume, and the remaining wells were placed at locations near trees and away from trees to assess the role of trees in degradation. Naphthalene, the most degradable of the PAH compounds found in creosote, was injected along with a bromide tracer.

This method relies on injection of the contaminant of interest into the groundwater over about 4 hours and then removal of the injected water to measure the loss of contaminant or loss of electron acceptor. For our tests, we injected water containing naphthalene, oxygen, and a tracer over 4 hours and then pumped it out over about 6 hours. In Figure 5, the basic operation of the push-pull testing from our field data is shown. The data in Figure 5 are for the "pull" cycle and they show that oxygen is being depleted relative to the tracer.

More importantly, the push-pull tests indicate that the trees are enhancing the degradation of naphthalene. Data in Figure 6 show the difference in locations where trees are present as compared to a non-treed area. Research will continue to assess the real-time field uptake of naphthalene using push-pull testing.

The major goals of the research at Oneida are to: (1) determine the relative contribution of specific degradation mechanisms for PAHs at the site; and (2) develop design tools so phytoremediation systems can be "engineered." Work will continue over the next year in both areas.

Figure 5. Results of Push-Pull Testing

Figure 6. Comparison of Push-Pull Results at Wells in a Control Location (without trees, left) and in a Location Within the Phytoremediation System (right)

Future Activities:

In the coming year, we will continue the activities described earlier, including MNA monitoring at the chlorinated solvent site in Virginia Beach. Depending on the results of the Remedial Investigation/Feasibility Study (RI/FS), biological source treatments will be designed and implemented at the pilot scale. Site models will be validated at several other DoD sites with chlorinated solvents. This approach to the evaluation of MNA will be presented in a number of venues, including at national meetings, in peer-review journals, and at U.S. Environmental Protection Agency Laboratories and Regional Offices. Future research activities at the PAH-contaminated phytoremediation site are described below.

Continued Push-Pull Tests. The initial success of the push-pull tests indicate that this will be a fruitful method for field assessment of in situ degradation rates. We plan to continue to collect field data and especially to compare the rates taken when trees were not active, and compare this to summer push-pull test results to determine if active growth contributes to naphthalene uptake. Based on data collected to date, we believe that this method is new and unique for a PAH-contaminated site and the data are publishable. We will use the method to assess more directly the mechanisms of phytoremediation at the Oneida site.

Radioactive Labeling Uptake Study. Laboratory-scale studies using poplar cuttings and monitoring the fate of C14 labeled PAHs are being planned. The relative contribution to the overall degradation rate then can be quantified for plant uptake and degradation, rhizosphere degradation, and immobilization into the soil humus. Furthermore, this study may be able to characterize PAH metabolites accumulated in plant tissue. Development of methods and an experimental plan for uptake studies using naphthalene, as well as a 2- and 3-ring PAHs, is underway.

Microbial Characterization. Parallel to obtaining degradation rates and quantifying the relative contributions of different mechanisms, we plan to characterize the microbial community in rhizosphere soil versus nonrhizosphere soil. Nonmolecular PAH-degrader screening methods based on enzyme-assays currently are being used. Additional data may be collected using molecular methods.

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Other subproject views: All 6 publications 2 publications in selected types All 2 journal articles
Other center views: All 108 publications 22 publications in selected types All 14 journal articles
Type Citation Sub Project Document Sources
Journal Article Brauner JS, Widdowson MA, Novak JT, Love NG. Biodegradation of a PAH mixture by native subsurface microbiota. Bioremediation Journal 2002;6(1):9-24. R828770 (2002)
R828770 (2003)
R828770 (Final)
R828770C004 (2003)
  • Full-text: Taylor & Francis-PDF
  • Abstract: Taylor & Francis-Abstract
  • Journal Article Robinson SL, Novak JT, Widdowson MA, Crosswell SB, Fetterolf GJ. Field and laboratory evaluation of the impact of tall fescue on polyaromatic hydrocarbon degradation in an aged creosote-contaminated surface soil. Journal of Environmental Engineering-ASCE 2003;129(3):232-240. R828770 (2002)
    R828770 (2003)
    R828770 (Final)
    R828770C004 (2003)
  • Abstract: ASCE-Abstract
  • Supplemental Keywords:

    monitored natural attenuation, MNA, biodegradation, phytoremediation, reductive dechlorination, models, modeling, chlorinated solvents, tetrachloroethene, PCE, trichloroethene, TCE, vinyl chloride, polycyclic aromatic hydrocarbon, PAH, dense non aqueous phase liquid, DNAPL, Hazardous Substance Research Center, HSRC., RFA, Scientific Discipline, Waste, Water, Contaminated Sediments, Remediation, Environmental Chemistry, Hazardous Waste, Environmental Monitoring, Hazardous, Environmental Engineering, contaminant transport, contaminant dynamics, contaminated waste sites, contaminants, contaminated sites, contaminated sediment, transport contaminants, modeling, contaminant transport model, groundwater hydrology models, natural attenuation, groundwater remediation, transport models, contaminated groundwater, monitored natural attenuation, hazardous waste sites, transport modeling, ecological research

    Relevant Websites:

    http://www.mhsrc.org Exit

    Progress and Final Reports:

    Original Abstract
  • 2002 Progress Report
  • Final

  • Main Center Abstract and Reports:

    R828770    HSRC (2001) - Midwest Hazardous Substance Research Center

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R828770C001 Technical Outreach Services for Communities
    R828770C002 Technical Outreach Services for Native American Communities
    R828770C003 Sustainable Remediation
    R828770C004 Incorporating Natural Attenuation Into Design and Management Strategies For Contaminated Sites
    R828770C005 Metals Removal by Constructed Wetlands
    R828770C006 Adaptation of Subsurface Microbial Biofilm Communities in Response to Chemical Stressors
    R828770C007 Dewatering, Remediation, and Evaluation of Dredged Sediments
    R828770C008 Interaction of Various Plant Species with Microbial PCB-Degraders in Contaminated Soils
    R828770C009 Microbial Indicators of Bioremediation Potential and Success