48. Impact of In Situ Chemical Oxidation on the Biogeochemistry of a Sand and Gravel Aquifer

An increasingly common choice for remediation of groundwater contaminated with organic compounds, particularly for treatment of dense non-aqueous phase liquids (DNAPLs), is in situ chemical oxidation, or ISCO. This approach utilizes the delivery of strong chemical oxidants, such as permanganate, Fenton’s reagent, or hydrogen peroxide, to the subsurface to completely oxidize (and therefore eliminate) target contaminants. A key advantage of the approach is circumventing the need for pump-and-treat technology, which can be problematic when DNAPLs are present because of the need to pump very large quantities of water to remove compounds with limited aqueous solubility. The ISCO approach involves pumping solutions of an oxidant into an affected aquifer and utilizing the oxidant’s non-specific reactivity to degrade a variety of contaminants, or mixtures of contaminants, in place within the aquifer.

As might be expected, the studies pertaining to ISCO have primarily focused on timing and delivery of the oxidant, laboratory studies on contaminant-oxidant reaction mechanisms, and case studies evaluating efficacy of contaminant removal. It is well recognized that the oxidant will react with more than just the target contaminant(s). Indeed, in many or most cases, natural oxidant demand (NOD) greatly exceeds what is required to oxidize the contaminant(s). A great deal of the NOD is associated with aquifer solids in the form of microorganisms, sorbed organic material, and inorganic minerals. This results in the need to pump large quantities of oxidant into the aquifer to ensure that a sufficient supply is present to accomplish the desired remediation. In short, what might be considered nuisance or secondary reactions because they do not involve oxidation of the contaminant(s) are in fact the primary result of an ISCO remediation.

These secondary effects of an ISCO treatment are usually ignored or presumed to be benign. However, an integrated, in situ-oriented study of the secondary effects has not been conducted, even though such a study could simultaneously provide valuable information about the big-picture effect of the ISCO approach and the general nature of inherent aquifer processes. The latter could have important implications regarding the fate and transport of a variety of contaminants (organic, inorganic and microbial).

We are most interested in postdoctoral proposals for research to be conducted at the U.S. Geological Survey (USGS) Cape Cod Toxic Substances Hydrology site.  Proposed studies at other sites may be considered.  The Cape Cod study site features a sand and gravel aquifer that has been contaminated by the long-term disposal of treated wastewater. The contaminant plume has been the focus of integrated studies on the fate and transport of wastewater constituents. Many of these studies have included in situ tests that utilize the large array of field instrumentation (wells and multilevel samplers) available at the site. Natural-gradient injection tests with a variety of tracers (organic, inorganic, and microbial) are a hallmark of this study site. Also present in the immediate vicinity of the USGS site are a large number of solvent and fuel-spill contaminant plumes resulting from past military activity on the Massachusetts Military Reservation (MMR). ISCO remediation of one of these solvent plumes with permanganate has been attempted by the MMR on a pilot scale basis.

Research proposals should include a combined field and laboratory approach to study secondary effects of ISCO remediation with permanganate. Remediation of a targeted contaminant need not be the focus of the study. Rather, elucidation of the net effect of the remediation approach on aquifer biogeochemical processes would be the goal. Laboratory studies could include experiments with aquifer core material under controlled conditions to determine key parameters to monitor and to gain experience handling and quantifying samples that contain permanganate. Field studies could include injection experiments with permanganate with close-interval sampling (both spatial and temporal). The Cape Cod site offers the potential to compare the response in contaminated vs. uncontaminated locales, or to compare different geochemical conditions (for example, oxic versus anoxic or solvent versus wastewater contamination).

There is significant room for individual creativity in this Opportunity. The ideal applicant would have a strong background in biogeochemistry and be able to function well in an interdisciplinary environment. Proposals that address overlapping aspects of microbiology and geochemistry are preferred. Suggested topics could include, but are not limited to, the following areas:

1. Characterization of the microbial community before, during and after an ISCO injection, both at and downgradient from the injection site.
2. Reaction of sorbed organic carbon with permanganate, and fate, transport, and microbial degradation of incomplete organic carbon oxidation products.
3. Role of manganese oxides on microbial re-colonization, sorption of new carbon, and hydraulic permeability after an ISCO injection.
4. Fate and generation of nutrients (primarily N and P) during and after an ISCO injection.
5. Impact on adsorption, ion exchange, and redox properties of sediments, and how these impacts influence the composition of ground water flushing through the affected zone.
6. Impact on naturally occurring toxic constituents like arsenic and uranium in reduced forms (for example, sulfide minerals).

Proposed Duty Station: Boulder, CO

Areas of Ph.D.: Hydrology, geochemistry, biogeochemistry, geology, microbiology

Qualifications: Applicants must meet one of the following qualifications: Research Hydrologist, Soil Scientist, Research Chemist, Research Geologist, Research Biologist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): Richard Smith, (303) 541-3032, rlsmith@usgs.gov; Doug Kent, (650) 329-4461, dbkent@usgs.gov; Denis LeBlanc, (508) 490-5030, dleblanc@usgs.gov

Human Resources Office contact: Vanessa Chambless, (303) 236-9584, vchambless@usgs.gov

Summary of Opportunities