SREL research in the remediation and restoration can be assigned to one of three general categories: (1) engineered remediation, (2) biologically-based remediation, and (3) restoration. Fundamental to these efforts is a multidisciplinary approach that bridges the span between basic and applied environmental research to provide a scientific basis for the development, evaluation, and stakeholder acceptance of remediation and restoration efforts that are protective of human as well as ecosystem health.
Engineered remediation processes include the controlled alteration of impacted ecosystems in such a manner as to reduce contaminant migration, bioavailability, and receptor exposure. Laboratory-, intermediate- and field-scale studies examine the migration of contaminants within complex heterogeneous geologic systems containing various reactive mineral and organic components to identify the major physicochemical and biogeochemical mechanisms controlling contaminant transformations and mobility in environmental systems relevant to the DOE. Studies include detailed chemical speciation of contaminant metals and radionuclides and an examination of contaminant organic transformations utilizing a number of advanced analytical methods being developed in other programs.
Examples of engineered remediation efforts include:
- redox manipulation to enhance biodegradation of organic contaminants and/or the solid phase partitioning of redox sensitive inorganic contaminants,
- addition of contaminant-specific sorbents or stabilizing amendments to soils/sediments,
- development and evaluation of physical and/or institutional barriers to contaminant migration and receptor exposure.
The aim of this research is to provide a framework for screening a range of remediation strategies that enable us to recommend management alternatives that increase the efficiency and identify potential problems associated with field-scale implementation of remediation systems. Such studies are critical for developing accurate models that predict contaminant migration and consequently, accurate quantification of exposure vectors and hazards for risk assessment, which promote stakeholder confidence. Additionally, such studies are important for designing remediation strategies that target specific biogeochemical controls to either enhance mobility under various contaminant extraction scenarios (e.g. pump-and-treat, soil washing, etc.) or decrease mobility (e.g., in situ stabilization) to reduce potential exposure hazards.
Biologically-based remediation approaches, including engineered and native biological systems, utilize biological, rather than mechanical or chemical, processes to remediate environmental pollutants. Our research involving these systems focuses on bioremediation, phytoremediation, and monitored natural remediation.
Bioremediation, which emphasizes the roles of microorganisms in remediation, has been used successfully at many sites for organic contaminants; however, optimal conditions for successful implementation are not well understood. Bioremediation of metals requires a better understanding of fundamental interactions between microbes and metals, and how these interactions affect the bioavailability and mobility of the metals. Our goals are to:
- develop new ways to stimulate endogenous organisms and effectively introduce known degraders into contaminated systems to remove organic contaminants,
- understand the microbes that affect speciation of heavy metals and radionuclides in situ,
- evaluate the long-term stability of such transformations in the field.
Phytoremediation involves the metabolism of contaminants in the plant rhizosphere, uptake and degradation within plant tissue, as well as uptake and sequestration of contaminants. Plants can degrade or enhance degradation of certain organic compounds; however, lack of a fundamental understanding of how plants perform these processes limits our capacity to manipulate plants and their metabolic pathways to enhance phytoremediation effectiveness. One of our goals is to utilize genetic maps that are currently being generated for plants such as poplar and Arabadopsis, to identify functional genes involved in degradation of organic contaminants or transformation of heavy metals or radionuclides. Identifying those genes will allow native plant species to be selected by screening for the genes, or specific genes to be manipulated to enhance the degradation capacity of plants. Additionally, we are examining native plants to determine their possible role in both remediation and restoration of impacted sites.
Monitored natural attenuation (MNA) involves the interactions between plants, microbes inhabiting the rhizosphere as well as free-living microorganisms, and the physical and chemical nature of the soils and evaluates how these interactions affect the fate of both organic and inorganic contaminants. Effective techniques and methods need to be developed to successfully characterize biogeochemical systems for predicting the potential success of MNA on any given site.
Restoration, which we consider to be the process of revitalizing degraded ecosystems, is an integral part of remediation. It can be a component of engineered remediation systems, monitored natural attenuation, or other remediation efforts. Restoration involves the return of ecosystem attributes, including species composition, structure, and ecosystem functions. This process requires us to identify and characterize reference systems, describe differences between reference and impacted systems, design a restoration plan, and monitor return of the system to reference conditions. All of these activities are integral to effective stewardship of DOE lands.
An understanding
of basic ecological processes and their application in restoration of desirable
engineered or natural systems may be the key to cost-effective and sustainable
restoration efforts. One goal of our research is to determine if we can accelerate
or direct natural processes, such as succession, to restore sustainable vegetation
on focal remediation sites, including closure caps, floodplains, and isolated
wetlands.
SREL researchers associated with the Remediation and Restoration theme include:
