Project no.: 92-05

Goals: Research objectives are to investigate suitability of deep-planted poplars as a vegetative remediation strategy for heavy metal-contaminated sites; to determine effects of poplar tree cultivar on survivability and growth when deep-planted at a heavy metal-contaminated site; to investigate effects of soil amendments on poplar tree survival and growth; to determine heavy metal concentrations in poplar leaves, roots, and wood when grown in a heavy metal-contaminated environment; to investigate optimum depth of soil cover for establishment of a perennial grass cover; and to extend a current mathematical model that simulates fate of heavy metals in a vegetated soil and to use the model to develop a protocol for determining the most effective vegetative planting strategies for immobilizing heavy metals in contaminated soil.

Rationale: Abandoned sites associated with old heavy metal mining and smelting activities often have a large proportion of their area without vegetative cover. This allows erosional forces to proceed at a maximum rate, and materials with high heavy metal concentrations are dispersed by wind and water. Little research has addressed use of poplar trees in such a situation.

Approach: This study will focus on an abandoned zinc and lead smelter site in southeast Kansas. The investigators propose to begin investigations whose ultimate goal is to immobilize the metals in place. This would be accomplished with grading to 3-5% slope, to encourage runoff without excessive erosion, and the use of rapid-growing poplar trees that have a high water demand. This strategy would minimize net percolation through mine spoil material, thus minimizing impact on groundwater. Surface erosion would be effectively controlled once the trees are established. A thin soil cover would be employed to establish a perennial grass cover to prevent surface erosion until the trees had become established.

Status: This project has utilized an abandoned zinc/lead smelter site near Dearing, Kansas, for its investigation. Poplar trees were first planted in June 1994, but survival as of September of that same year was only 7%. This was attributed to the late planting date (which was necessary because of extremely wet conditions), a reduction in tree viability due to storage, and drought conditions following planting. The trees were replanted in March 1995, a more appropriate planting time, in a split-plot design with the main plots being the in-trench treatments with or without manure and the subplots being poplar cultivar. Height and trunk diameter of each tree were measured to serve as a baseline to which all future measurements could be compared. Survival measurements and leaf samples have also been taken. As of September 1995, 400 out of the original 576 trees were alive for an overall survival rate of 69.4%. Addition of manure to the trenches significantly increased growth via increases in height and trunk diameter. The data clearly show that tree cultivar and soil amendments can influence survival and growth parameters. Soil samples have been collected from eight different areas and analyzed for lead concentration. Soil lead concentrations will be compared to leaf tissue lead concentrations after those analyses are complete. This project is in its fourth, and final, year.

Clients/Users: This research is of interest to the mining industry and regulatory community.

Keywords: heavy metals, soil, poplar trees, zinc, lead.

Project no.: 92-08

Goal: The goal of this project is to quantify the process of heavy metals removal by binding to biopolymers from dilute aqueous solutions containing more than one metal.

Rationale: Extracellular polymers extracted from living microorganisms constitute an attractive alternative for heavy metals removal from dilute aqueous solutions. However, demonstrated technologies do not offer any rational means of predicting the process kinetics as a function of water chemical composition. Thus far the documented research effort is largely related to binding single metals from aqueous solutions. Such convenient simplification is unacceptable for most technical applications of the process. For example, it is a rare exception that a water is contaminated with a single heavy metal. In frequently encountered situations when more than one heavy metal is present in the solution, existing models do not apply, and the result of the process cannot be predicted.

Approach: Investigators propose describing the kinetics and thermodynamics of metals binding to biopolymers from solutions of many metals. Relevant parameters for process modeling will be obtained from measurements of binding constants, binding capacities, selectivity coefficients, diffusion coefficients, and rates of metal binding reaction. Predictive value of the models will be experimentally verified.

Status: In mixtures of the metals of interest, investigators determined binding constants and binding capacities under competition, and included participation of hydrogen ion as a cation. A multiequilibrium binding model that predicts final concentrations of divalent cations in solutions comprised of mixtures of the metal ions and protons in the presence of alginate biopolymer gel beads was developed. Investigators found that bead regeneration was more efficient using equilibrium shifting plus electrodeposition than either technique alone. The model and technology were tested in the field at a mine pit, and the results confirmed that the technology works. A larger-scale field test under different temperature and hydrodynamic operating conditions is needed. This project has ended.

Clients/Users: Results are of interest to other researchers, private industry, and regulatory personnel.

Keywords: heavy metals, water, biopolymers, sodium alginate.

Project no.: 93-12

Goal: This project will attempt to demonstrate an alternative, cost-effective, permanent mine tailing reclamation methodology through the marriage of mineral processing and land reclamation techniques. The approach to be used, Clean Tailing Reclamation (CTR), utilizes potentially field deployable mineral separation technologies to remove dense sulfide minerals from tailing material by gravimetric separation, followed by vegetative stabilization of the cleaned tailing material with native plants. CTR will allow for removal of environmental contaminants and acid-forming materials.

Rationale: Mine waste is a widespread and pervasive problem in EPA Regions VII and VIII. Historical mining activity has contaminated many thousands of acres of soil by uncontrolled waste disposal practices resulting in resource degradation that will cost billions of dollars to remediate. One of the principal problems associated with reclamation of hardrock mine sites is tailing reclamation. Tailing materials cover tens of thousands of acres of land in the region pair. This research specifically compliments research being conducted in Anaconda, Montana, on tailing reclamation and will provide comparisons on the relative strength of this technology, through plant performance, geochemical distribution of contaminants, and cost of implementation. Upon completion of this research, the findings will be useful to Superfund Managers and Potentially Responsible Party decision makers and to operational mines and regulators.

Approach: Research will be implemented at Montana State University. Outside expertise will be solicited from other experts in mineral separation in conjunction with the use of experimental equipment housed at Butte, Montana. Contract laboratories will be solicited and appropriate sample analyses will be submitted for analysis. Sample material used in research will be collected from three locations in coordination with regulatory personnel. Representative samples of tailings materials will be collected from each of the three locations and chemically characterized to identify the elemental and mineralogical distribution of the heavy metal and acid-generating contaminants. Subsequent to sample characterization, mineralogical separation of the dense sulfide minerals will be performed using gravimetric techniques. For bench-scale work, mineral separation technologies considered will include technologies developed through the Superfund Innovative Technology Evaluation (SITE) Program. Following tailing material reprocessing activity, subsamples will be chemically characterized to determine the efficacy of the reprocessing/tailing cleaning technologies. Greenhouse studies will be implemented in the cleaned tailing material to compare performance of the cleaned tailing material with conventional reclamation approaches. The native grass species selected for use are Red top (Agrostis alba) and Basin wild rye (Leymus cinereus).

Status: During the first phase of this study, significant effort was expended to collect samples and initiate the project. Three tailing materials were collected and transported to the laboratory, and characterization was completed. Bench-scale and subsequent pilot-scale separation of sulfides from silicates in tailings was performed. Soluble chemistry evaluation of various treatments was initiated, as was literature-review activity. Much of the research conducted during the early phase of the project has been completed. Samples were submitted for acid-base account analysis for characterization of the acid-generating potential of all three tailing materials both before and after reprocessing. Metal analysis of the initial tailing material, high-grade concentrate, and cleaned tailing material has been performed. The greenhouse study began May 31, 1996, and has been completed. The soluble chemistry study is complete and data reduction efforts have been initiated. A technology transfer seminar was hosted with participants from industry and government attending. Further inquiry of mineral separation effectiveness is planned. The potential for metal recovery and reuse will also be evaluated upon receipt of the final metal analyses, which are underway. Field visits will be conducted to evaluate the potential for conducting field-scale tailing cleaning in a mining environment. Data summary, interpretation, and write-up will follow completion of data collection. This project has ended.

Clients/Users: This research will be of interest to those in the mining industry and regulatory agencies.

Keywords: vegetation, reclamation, metallic minerals, mining, tailings.

Project no.: 93-22

Goal: The goal of this project is to assess the full potential of chelating extraction technology in removing and/or recovering heavy metals from contaminated media, e.g., soils and mine tailings ponds. A large number of chelators will be examined, and those chelators which are suitable for selective removal or recovery of various heavy metals will be identified.

Rationale: Heavy metal contamination of soil is a common problem encountered at many hazardous waste sites. Lead, chromium, cadmium, copper, zinc, and mercury are among the most frequently observed metal contaminants. They are present at elevated concentrations at many National Priority List sites, are toxic to people, and threaten groundwater supplies. Once released into the soil matrix, most heavy metals are strongly retained and their adverse effects can last for a long time. Chelating extraction of heavy metals from contaminated soils is a relatively new treatment method. There exists a need to assess the full potential of this technology in removing and/or recovering heavy metals from contaminated media. A methodology is needed to examine a large number of chelators and identify those suitable for the selective removal or recovery of various heavy metals. Chelators that are identified, studied, and recommended as a result of this project could be used in on-site soil washing processes following excavation.

Approach: Investigators will assess the potential of extracting and recovering heavy metals from contaminated soils using chelators. Results of assessment of a large number of chelators will provide a guide to select suitable chelators for different metals. Equilibrium chemical modeling/calculation and connectivity index modeling will be performed to choose about ten chelators from the initial list for detailed experimental study. Study will be conducted on the extraction and recovery of the seven target metals from collected contaminated soils using ten selected chelators. Investigators will also demonstrate that through a proper choice of functional groups in a chelator, the selectivity of the chelator can be greatly enhanced and that through a proper choice of chelator, extracted mixed metals can be recovered separately through sequential treatment stages. Finally, stability of about six chelators will be evaluated with respect to biodegradation.

Status: Characterization of soil samples was completed for two uncontaminated soil samples and seven samples contaminated with various types and amounts of metals. Chemical equilibrium modeling and connectivity index modeling were completed. The results of chemical equilibrium modeling were published, and the connectivity index modeling work has been accepted for publication. Five target heavy metals were extracted using eight chelating agents. Investigators were able to separate and reuse the reclaimed chelating agents using only pH adjustment for those chelating agents of moderate strength. They were also able to effectively recover the strongest chelators using cationic and/or anionic precipitants. The mechanisms of loss of the chelators were investigated with ion chromatography. Optimal precipitant dosages to enhance recovery and minimize loss were studied. Investigators were able to recover a single metal at a time from mixed metals extraction solutions. The biodegradation of DTPA and ADA was evaluated. This project has ended.

Clients/Users: This research will be of interest to public agencies such as U.S. Environmental Protection Agency, U.S. Department of Defense, and industry.

Keywords: heavy metals, chelators, extraction, lead, copper.

Project no.: 93-06

Goals: The overall objective of this research is to determine whether establishment of vegetation in heavy metal- and radionuclide-contaminated soil will significantly affect retention of metals in soils and to mathematically predict the results using a calibrated model.

Rationale: Vegetation is often the primary method of reclamation in mining areas to stabilize waste with respect to wind and water erosion and to minimize downward translocation of contaminants. Plants reduce the possibility of metal leaching through decreased water infiltration, adsorption of metals to root surfaces, plant uptake of metals, and stimulated microbial immobilization in the rhizosphere. Plants may increase metal leaching through complexation with rhizosphere organic acids exuded by roots, produced by microbial activity, or generated by decomposition of soil organic matter. Field and laboratory determinations are needed to quantify effects of vegetation on the leaching of metals. Models that attempt to predict the fate of heavy metals in soils have focused primarily on the geochemical aspects of the problem and have not considered the effect of a plant’s geochemistry. The difficulty associated with using models to simulate the fate of a heavy metal in the root-soil environment is properly accounting for all interactions among water movement, contaminant transport, uptake of water and metals by plant roots, and geochemistry.

Approach: Impact of vegetation and revegetation schemes on the mobility of metals (lead, cadmium, zinc, barium, etc.) is being investigated on contaminated soil and/or mine waste from zinc and lead mining regions of southeast Kansas, lead mines of Montana, and a paint-producing industry in southern Kansas. The series of experiments will be employed to pursue the following objectives: a sequential extraction procedure for determination of various fractions and mineral associations of the metals; batch (laboratory-scale equilibrations) and column experiments to directly assess impact of organic acids on heavy metal mobility; large soil columns to determine effects of vegetation overlying soil depth on mobility of metals and metal uptake by plants; sorption/desorption and determination of potential or existing solid phases of the metals to quantify the soil chemical aspects of metal retention; and integration of geochemical and solute transport modeling to predict and analyze the fate of metals as influenced by the presence of vegetation.

Status: In the first year of this project, soil columns were constructed and leaching studies begun. Transport models for metals were developed and studied. Results from experimental equilibrium studies were incorporated into mathematical models. Plant/column studies also were begun, and estimation of root characteristics were incorporated into transport models. Column studies with organic acid were completed. Investigators also identified metal uptake and adsorption characteristics and estimated related parameters for incorporation into a numerical model. Metal uptake and metal adsorption to the soil have been quantified for Pb, Zn, and Cr under several sets of circumstances. A series of batch experiments were performed for solutions containing strong chelating acids and cadmium, lead, and zinc. The investigators have finished plant column/studies on the effect of vegetation on metal leaching from mine tailings, and the effect of tall fescue on the fate of Cr(VI) in soil. A mathematical model has been developed for understanding the fate of lead in a metal-contaminated soil. In the final phase of the project, hypothetical field site simulations will test the model. This project is in its third year.

Clients/Users: This project is intended to be of interest to any group that is involved in restoration of land contaminated by heavy metals, including U.S. Environmental Protection Agency, U.S. Department of Energy, Kansas Department of Health and Environment, and U.S. Department of Defense.

Keywords: vegetation, heavy metals, radionuclides, soil, fate and transport.

Project no.: 93-07

Goals: This research has two purposes. First, the efficacy of different plant and microbial regimes in reducing surface water contamination from revegetated plots will be assessed. To determine the ability of various vegetation/microbial regimes to act as buffer strips, after the first year of the project the design of the experiment will be altered. Half of the plots will remain as non-interceptor strips, while half will receive surface runoff from contaminated tailings uphill from the plots. In this way the ability of the various vegetation strips to limit heavy metal-contaminated runoff can be quantified.

Rationale: In southeastern Kansas where heavy metals were mined until the middle of this century, the presence of large piles of gravel tailings with extremely high levels of cadmium, lead, and zinc pose a serious environmental and health risk which led the U.S. Environmental Protection Agency to designate this area as a Region VII Superfund Site in 1985. In areas not designated as Superfund sites, a need also exists for development of economic strategies for containment of heavy metal contamination. While vegetation interceptor strips have been used extensively in agricultural settings to reduce surface water contamination by agricultural herbicides and pesticides, the ability of vegetation buffer strips to limit spread of heavy metal contamination in surface water has not been studied, but could represent an economical alternative with broad application to mine spoils and areas of acid mine drainage as well.

Approach: Revegetation of Superfund and non-Superfund areas will be undertaken to stabilize the sites and reduce wind and water erosion from the tailings. Previous research by these investigators and that of the Bureau of Mines has suggested that certain soil microorganisms, the mycorrhizal fungi, contribute significantly to and may be mandatory for survival and establishment of vegetation on mine spoils. Both the ability of various vegetation regimes to limit surface water erosion and spread of heavy metal contamination, and the ability of these vegetation regimes to act as interceptor strips for contamination uphill from the vegetation strips will be studied in this project.

Status: Although investigators experienced significant difficulties collecting water samples due to flooding of the collection basins, they were able to obtain 21 samples, which were analyzed for sediment concentrations and total and soluble metal concentrations. A rainfall simulator was constructed for collecting water samples with accurate volume estimations from field plots. It was installed at a test site in Kansas and yielded useful data. Soil samples collected during the fall of 1995, at the initiation of the experiment, were analyzed for total metal concentrations. These concentrations were higher than expected for chat material. Fall 1995 soil samples were also analyzed for KC1-extractable ammonium and nitrate concentrations and for soil pH. Soil samples were again collected in the spring of 1996 and analyzed for extractable ammonium, nitrate, phosphorus, potassium, and soil pH. Soil samples gathered at this time were analyzed with the sequential extractable scheme of Tessier et al. (1979). Plant tissue samples were collected in May 1997 and analyzed for cadmium, lead, and zinc. There were no treatment effects on tissue composition. Root samples were also collected in April 1997 to assess the extent of mycorrhizal colonization, and mycorrhizae have been characterized. Techniques for evaluating the usefulness of commercially available mycorrhizal fungi designed for environmental restoration are being developed. Evaluation of vegetation as a means of slowing the migration of contaminated sediments has been completed. Work on modeling has included a review manuscript, which was completed and submitted for publication. Work is also in progress to develop models applicable to the experimental sites, as well as larger field sites. Future plans include increasing output of water from the rain simulator to collect more data from all test plots. This project is in its third year.

Clients/Users: This research will interest those in the mining industry, regulatory community, U.S. Environmental Protection Agency, and U.S. Department of Defense.

Keywords: heavy metals, interceptor zones, mycorrhizal fungi, Superfund, vegetation.

Project no.: 94-05

Goal: The primary goal of this project is to design and develop a hydrometallurgical flow sheet to treat waste zinc residues containing iron and other heavy metal impurities such as lead and cadmium. The resulting flow sheet will be used at Big River Zinc Co., or any other industry desiring to treat similar wastes.

Rationale: A major problem faces the minerals industry in the form of huge tonnages of environmentally unacceptable zinc residues. Previously these oxidized dusts, which contain high iron and zinc contents with lead, cadmium, and other heavy metals, were precipitated in chemical forms acceptable for standard landfills. Under current laws, this practice will not be allowed and costs of compliance are expected to increase dramatically. In fact, it may even be necessary to reprocess all the wastes that have been stored and accumulated over the years. The technical challenge is to develop metallurgical and chemical processes to treat these hazardous wastes in an economically viable manner. The most serious technical impediment preventing treatment of these wastes is the inability to separate the iron from the zinc. The investigator on this project has developed a process, galvanic stripping, to separate the iron from the zinc. As the next step, it is important to develop unique in-line processes specifically for handling diversity in feedstock, particularly when certain categories of impurities are present in low concentrations. Many existing processes are basically sound, but supplementary unit processes must be developed to make them more amenable to treat impure metal wastes and residues in an economic fashion.

Clients/Users: This research will interest those in the mining and metals industry, U.S. Department of Defense, and regulatory community.

Keywords: heavy metals, extraction, flow sheet, galvanic stripping, zinc.

Project no.: 94-15

Goal: The purpose of this research is to develop air-sparged hydrocyclone (ASH) technology for treatment of water contaminated by volatile organic compounds, especially chlorinated hydrocarbons.

Rationale: The air-sparged hydrocyclone technology offers the opportunity to achieve efficient removal of chlorinated hydrocarbons from water at high specific processing capacity. Thus, the equipment will require a much smaller operating space compared to conventional equipment.

Approach: The work will include the fundamental basis for the design and operation of the process, volatile organic carbon transport between water and air phases, and field testing.

Status: Volatile organic compounds’ (VOCs) removal from contaminated water by air stripping with the air-sparged hydrocyclone is the first such application of the ASH technology. The results obtained during this investigation demonstrate the applicability of the ASH technology in this field. Features such as short residence time, large interfacial area between water and air, and turbulent transport of air through the swirl layer give the ASH technology a distinct advantage over other stripping technologies, which are known for the poor economy of the aeration process resulting from the rapid saturation of air bubbles with VOCs. Experimental results with respect to 1) changes in the air flow rate, water flow rate, and the air-to-water flow rate ratio; 2) changes in the contaminant concentration; and 3) changes influencing Henry’s constant, particularly temperature and contaminant type, have been given preliminary analysis in terms of the steady state solution to the traditional mass transfer equation. This research is part of an investigation designed to establish detailed, fundamental information that will provide the basis for application of the ASH technology. Basic research is complete and construction of the mobile ASH unit is finished.

Clients/Users: Government agencies such as the National Science Foundation, U.S. Department of Energy, and U.S. Department of Defense are interested in this project.

Keywords: remediation, chlorinated hydrocarbons, volatile organics, air-sparged hydrocyclone.

Project no.: 93-05

Goal: The primary objective of this project is to determine the role of herbicide-tolerant plants and commodity plants in facilitating microbial degradation of herbicide wastes in soils. This information can then be used in defining the potential role of vegetation, under specific types of chemical contamination (herbicides, insecticides, industrial chemicals) in the bioremediation process.

Rationale: With the increase in pesticide usage since the early 1950s has come a rapid growth in the numbers of agrochemical dealerships. Unfortunately, many of these dealerships have, through normal operating procedures, contaminated the soil and water at these sites, creating one of the most ominous issues facing the agrochemical industry. The expense of most of the current technologies for cleanup of contaminated soil and water preclude their use at agrochemical dealership sites. Biological restoration of contaminated surface soils using indigenous microbial populations is potentially an effective remediation strategy, provided that a sufficient consortium of microorganisms capable of degrading contaminants are present, and that their activity is not limited by existing environmental conditions. Environmental conditions can be altered to enhance microbial populations and/or their activity, such as through nutrient additions or aeration.

Approach: Experimental procedures will utilize pesticides from different chemical classes and with different properties as model compounds in studies to identify critical environmental and biological variables affecting rate of degradation in the root zone. Experiments will be carried out using soils and plants collected from a pesticide-contaminated site in Iowa. An initial sampling trip to the site was used to document type and percent cover of vegetation as well as to collect soil and vegetation samples from the site. Initial studies in the laboratory have developed suitable extraction and analysis techniques for quantifying pesticide wastes in soils. Experiments on influence of vegetation on microbial degradation of pesticides were conducted utilizing sterile, nonvegetated, and rhizosphere scenarios in an environmental chamber. Results of these preliminary tests indicated enhanced degradation of atrazine, metolachlor, and trifluralin in the rhizosphere of Kochia sp., an herbicide-tolerant plant compared with nonvegetated soils and sterile control soils. In addition, Kochia sp. seedlings have emerged from rhizosphere soils spiked with additional concentrations of the three test chemicals, indicating the ability of these plants to survive in soils containing high concentrations of herbicide mixtures. In addition, radiotracer experiments will be conducted to provide further evidence for biodegradation of pesticides in root zones of plants from contaminated sites, as well as allow for mass balance calculations. Finally, small-scale field trials will be conducted.

Status: Site description and characterization have been completed, along with soil collection. Nearly all radiotracer experiments, degradation studies, and field trials are finished. A study of the bioavailability of pesticide residues vs. residence time in soil is still in progress. This project has been completed.

Clients/Users: This research will interest agrochemical dealerships, consulting and remediation companies, and federal agencies such as U.S. Department of Defense.

Keywords: vegetation, bioremediation, pesticides, agrochemicals, rhizosphere.

Project no.: 94-08

Goal: The goal of this project is to develop a slurry biotreatment process for soils contaminated with Pentachlorophenol (PCP) and creosote.

Rationale: PCP and creosote polyaromatic hydrocarbons (PAHs) are found in most contaminated soils at wood-treatment sites. Treatment methods currently being used for such soils include soil washing, incineration, and biotreatment. Soil washing involves removal of hazardous chemicals from soils using solvents, but the solvent stream must still be treated for destruction of contaminants. Incineration is an effective tool for destruction of contaminants but is costly and lacks public acceptance. Bioremediation has been considered and used for treatment of soils contaminated with wood-treatment chemicals, but bioremediation may leave regulated chemicals in the soil. Slurry-phase biotreatment of contaminated soils and sediments is an innovative treatment technology. Its advantages include easy manipulation of physicochemical variables and operating conditions to enhance rates of biodegradation and ease of containment of exhaust gases and effluent. Bioslurry technology is currently hampered by some bottlenecks that need to be relieved.

Approach: Engineering and process development aspects of bioslurry treatment of PCP- and creosote-contaminated soils from a Superfund site will be studied in this project in shake flasks and in 14-liter well-instrumented fermentors. Use of surfactants and cosolvents will be explored in order to enhance aqueous solubility of hydrophobic and sparingly soluble contaminants. The effect of cosolvents on microbial activity will be studied. Kinetic studies for biodegradation of PCP and PAHs will be carried out in sealed bioreactors so that accurate material balances can be taken. Experiments are planned to investigate the role of surfactant/cosolvent, temperature, carbon source, and oxygen delivery by sparging of pure oxygen in reduction of concentrations of PAHs and PCP in the contaminated soil slurry. Reactors with power measurement devices will be used to investigate several different types of mechanical agitators in order to keep the solids in suspension. The power requirement under aerated and unaerated conditions will be correlated with geometrical and system parameters such as particle size, nature of soil, solid density, and physical dimensions in the reactor. Oxygen transfer rate and oxygen transfer efficiency in the slurries with sufficient power input for minimal and complete suspension will also be studied in this reactor. All of the information will be used to develop a flow diagram of the bioslurry treatment process for cleanup of contaminated sites and to generate cost data that may be used to determine cost-effectiveness of this process for field-scale treatment.

Status: Work on the effect of solubility on microbial growth has been accepted for publication, and a manuscript related to work on the biodegradation of surfactants has been prepared for publication. Adsorption data for the non-ionic surfactants on three different clean soils at three different temperatures were previously reported. Experiments with adsorption of Dowfax 8390D at the three different temperatures have been completed. As expected, it is least adsorbed on sand. Investigators also conducted solubility enhancement studies. Biodegradation studies were conducted based on the results of solubility enhancements and surfactant biodegradation was tested, too. A bioslurry reactor has been constructed and is being used to determine the correlation between Power number and Reynold number for a specific impeller under different conditions. An economic analysis of slurry bioreactor operation was performed for three site scenarios. Biodegradation studies for creosote-contaminated soil are complete but some data remains to be analyzed. Research plans for the duration of the project mostly center around the reactor kinetics. This project is in its third year.

Clients/Users: This project will interest those in the wood-treatment industry and federal agencies such as U.S. Environmental Protection Agency and U.S. Department of Defense.

Keywords: soil, PCP, creosote, slurry bioreactor, wood treatment.

Project no.: NCIBRD 1

Goal: This project will address the possibility of using sodium salts of organic acids from two to 10 carbons in length to support dehalogenation of chlorinated hydrocarbons.

Rationale: Previous work has demonstrated anaerobic biotransformation of chlorinated solvents both in laboratory settings and in field demonstrations. However, there has been no investigation of the addition of organic electron donors to both increase solubility and to act as the electron donor for dehalogenation. Also, there is no clear delineation of the upper concentrations at which reductive dechlorination is possible. This study will provide information regarding the potential for use of medium-length fatty acids for bioremediation of chloroethenes. Applications of these results could facilitate development of technologies for in situ bioremediation of dense, nonaqueous-phase liquid (DNAPL)-contaminated aquifers.

Approach: The project will consist of four phases: (1) evaluating different concentrations of the sodium salt of each acid on the solubility and diffusion rate of tetrachloroethene (PCE) and trichloroethene (TCE) into water; (2) delineating the concentrations of each acid which can support dehalogenation of PCE or TCE in slurries made using aquifer solids from an anaerobic zone in chloroethene-contaminated aquifer and site groundwater; (3) determining the microbial community tolerance to high levels of PCE or TCE; and (4) modeling of the predicted movement of selected chloroethene, added electron donor, acetic acid, and partially dechlorinated chloroethene intermediates which are formed in the aquifer.

Status: The presence of many peaks in samples forced a modification in the analytical protocol. After 170 days of incubation, there was no evidence for PCE dechlorination. Solubility experiments were conducted to select surfactants for further use in the column experiments. The batch studies of the impacts of the Brij series surfactants on the solubility of PCE in synthetic site water indicated a linear increase in PCE solubility over the range of surfactant doses examined (up to 1 mM). Based on relative performance of the surfactants, Brij 56 and Brij 58 were selected for use in column studies Column effluent PCE concentration profiles were obtained through controlled feed experiments in which 2 mM Brij 56 and Brij 58 in synthetic site water were fed to columns containing number 30 and number 40 Ottawa sand loaded with PCE to residual saturation. PCE concentration profiles were affected by surfactant type and pore velocity, with higher pore velocities resulting in lower PCE concentrations. Work on the first modeling milestone has been completed. This involved the development of a theoretical model as a basis for describing the transient dissolution of DNAPL. This project is completed.

Clients/Users: This project will be of interest to other researchers and federal agencies.

Keywords: organic acids, bioremediation, dense nonaqueous-phase liquids, aquifers.

Project no.: 93-02

Goal: This research will investigate the hypothesis that both microbial and abiotic processes contribute to reductive dechlorination of xenobiotics in methanogenic incubations with elemental metals, such as iron, serving as an ultimate electron donor.

Rationale: Polychlorinated compounds such as carbon tetrachloride (CT) are known to be transformed via sequential reductive dechlorination by both abiotic and microbial mechanisms under aerobic conditions. However, existing treatment processes which utilize reductive dechlorination suffer from several drawbacks including inefficient transfer of electrons from the ultimate electron donor to the chlorinated compound and slow rates of reaction, thereby resulting in possible accumulation of transformation products of equal or even greater toxicity. Elemental metals in aqueous solution can act as an energy source for methanogens via production of hydrogen. Reductive dechlorination of chlorinated compounds could then proceed by three mechanisms: (1) abiotic processes whereby electrons are transferred directly from the elemental metal to the chlorinated compound, (2) microbial processes whereby electrons from H₂ that are involved in biosynthetic processes are diverted to the chlorinated compound, and (3) microbial-catalyzed abiotic processes whereby electrons from the elemental metal are transferred to the chlorinated compound via biological electron carriers.

Approach: Experiments will be conducted in batch and column-reactor systems. Initial studies will investigate iron and carbon tetrachloride (CT). Other metals, such as aluminum, tin, and zinc will be used in later studies. Various chlorinated organics will also be assayed. A hydrogen-utilizing, mixed, methanogenic culture will be developed as an inoculum source for all experiments. Initial batch studies will be performed to determine the general time-course that the reactions will follow. Inhibition studies using 2-bromoethanesulfonate (BES), a specific methanogenic inhibitor, will address the role of methanogens. Analytes to be measured in headspace gas samples include CT, chloroform (CF), dichloromethane (DCM), chloromethane (CM), hydrogen, and methane. Subsequent, detailed, batch kinetic studies will be performed and, where appropriate, analytes will include ferrous iron, total soluble iron, CT, CF, DCM, CM, hydrogen, methane, and oxidation-reduction potential. The stoichiometry and kinetics of all pertinent reactions will be determined. Electron balances will be conducted to provide insight into important abiotic and biotic processes. Flow-through column experiments using adjustable-bed-length, glass chromatographic columns packed with steel wool will be conducted to simulate long-term in situ treatment and to validate the kinetics determined in batch studies. A one-dimensional, finite-difference, numerical model will be developed to simulate the performance of the column reactors. The model will include advection, dispersion, and sorption, and the appropriate degradation kinetics as determined from batch experiments.

Status: Investigators have established stock-mixed-culture reactors and two pure cultures of methanogens, conducted a variety of batch, serum-bottle experiments with iron alone, and with iron in combination with pure and mixed cultures. Experiments suggest it is possible to control the rate and direct the products of contaminant degradation. They have also constructed four new column reactors that have been operating for more than a year. Two pilot-scale steel-wool columns were installed at Dover Air Force Base in Delaware to field test the technology. The study is complete but data is still being analyzed. Modeling studies will probably not be completed because a budget cut caused a reduction in the project’s scope. However, experiments with perchloroethylene and 1,1,1-trichloroethane are complete, as are the nitrate studies. This project is in its third year.

Clients/Users: This project will be of interest to other researchers and to U.S. Department of Defense.

Keywords: dechlorination, xenobiotics, heavy metals, iron.

Project no.: 93-24

Goal: The goal of this project is to advance understanding of anaerobic and mixed-electron acceptor bioremediation of chlorinated aliphatics to a level that full-scale evaluation of these processes is possible. If successful, field-scale evaluation of technologies developed in this research will be pursued.

Rationale: The U.S. EPA Hazardous Substance Research Centers and national agencies such as the Department of Defense and Department of Energy have identified research on remediation processes for chlorinated aliphatic-contaminated subsurfaces as a high priority. A promising technique is use of in situ bioremediation, and full-scale evaluations of this process are ongoing at trichloroethene-contaminated sites. All of these efforts have focused on use of aerobic bacteria, particularly methanotrophs. However, several of the chlorinated aliphatics of greatest concern are not degraded by aerobic bacteria. Unlike aerobic biological processes, anaerobic biotransformations of all chlorinated aliphatics occur. This lack of specificity, coupled with the fact that most contaminated aquifers are anaerobic, may make anaerobic bioremediation an alternative or supplement to aerobic processes.

Approach: This research will focus on three chlorinated aliphatics that are not degraded by aerobic bacteria: perchloroethene, 1,1,1-trichloroethane, and carbon tetrachloride. If successful, field-scale evaluation of technologies developed in this research will be pursued. In order to accurately assess potential for anaerobic or combined electron acceptor bioremediation technology, all experimental systems will be operated under conditions similar to those observed in contaminated aquifers. Additionally, soil cores will be obtained from contaminated sites as a source of organisms that are indigenous to contaminated areas. These cultures may be considerably different than those obtained from anaerobic digesters and may contain organisms particularly suited for chlorinated aliphatic degradation.

Status: All the necessary equipment has been updated and all experimental systems are functioning properly. Preliminary kinetic experiments have been completed and detailed experiments are continuing. Preliminary studies using only anaerobic biofilm columns have essentially been completed. Aerobic columns have been attached to anaerobic columns and chlorinated compounds have been fed to these systems for more than six months. A change in the anticipated funding has made it uncertain if the investigators will be able to complete studies on identification of organisms that are able to convert chlorinated aliphatics to nonobjectionable products or on the effects of nonaqueous phase chlorinated aliphatics on the extent of degradation and toxicity. This project is in its third year.

Clients/Users: Results from this research will be of interest to other researchers, U.S. Environmental Protection Agency, U.S. Department of Defense, U.S. Department of Energy, and others.

Keywords: anaerobic, bioremediation, chlorinated aliphatics, mixed-electron acceptor.

Project no.: 94-07

Goal: The goal of this project is to develop a bench-scale, fluidized-bed bioreactor (FBBR) to degrade TCE in extracted groundwater. This study of FBBRs is expected to yield the high performance necessary for pilot or field testing.

Rationale: Our knowledge of organic contaminant biodegradation has advanced from fundamental biochemical/microbiological studies to a stage of active treatment process development. Trichloroethene (TCE), once considered to be nonbiodegradable, can be cometabolized by microorganisms with oxygenase enzymes. The phenol-degrading organisms selected for this work readily form cohesive biofilms, which is a prerequisite for their use in biofilm reactors such as the fluidized-bed bioreactor (FBBR). Development of FBBRs for cometabolizing trace contaminants in extracted groundwater is attractive because they are compact, relatively simple to operate, and their use is widespread in several industries. Biological oxidation of TCE should be less costly than advanced chemical oxidation techniques that use combinations of ultraviolet light, ozone, and hydrogen peroxide. Ongoing research with bioreactors continues to yield improvements in performance as better operating strategies and configurations are tested. Studies with FBBRs, which will be conducted under this project, are expected to yield the high performance necessary for pilot or field testing.

Approach: A mixed-culture of phenol-utilizing microorganisms enriched from domestic wastewater will be grown on sand to form bioparticles in a bench-scale FBBR. Reactor inlet conditions will be varied and TCE removal will be measured. Concentrations of phenol, oxygen, and TCE will be determined at various points in the reactor to select inlet conditions or design variations that improve TCE removal. Several sizes and types of sand will be evaluated to increase biomass holdup and control biomass thickness. Facilitating spatial sequencing of bioparticles between growth and degradation zones will be an important factor in designing high performance FBBRs. High and low dispersion conditions in the reactor will be obtained by modifying the reactor inlet distributor. Periodic pulsing of phenol will be used in some experiments to increase TCE removal by temporal sequencing of substrates. A draft tube reactor will allow greater control over internal sequencing (via circulation) of bioparticles between phenol and TCE degradation. Performance of this innovative reactor type will be characterized in the same manner as the conventional type of FBBR.

Status: All controllable operational problems related to the bioreactor have been solved. Investigators have completed and evaluated abiotic TCE loss rates, oxygen delivery, and dechlorination effectiveness of the new reactor configuration and feed system. Work has also included the characterization of the phenol growth period for fresh and reused 30/35 garnet sand to determine the duration of the start-up and regrowth period, start-up procedures and substrate requirements, and the resulting biomass. Conductivity tracer test data has also been obtained, completed, and evaluated for the 1995 FBBR experiments, including the effect of effluent recirculation on TCE removal and quantification of detention times and dispersion numbers for representative experiments. Investigators have completed and tested a numerical biofilm reactor simulation model for cometabolism. Time-course TCE feeding experiments have been completed for evaluating TCE removal with 30/35 garnet and for verification of variable phenol loading effects observed in prior experiments. Work has also included development of a technique for in-bed sampling of bioparticles and water, which resulted in obtaining phenol and biomass profiles within the bed. Dominant microorganisms in the reactor effluent have been identified. In batch studies, the abiotic reaction rate of various reactor sands with TCE and PCE under oxic and anoxic conditions was assessed. Future plans include design, fabrication, and troubleshooting of a dual-chamber reactor, as well as reactor operation and measurement removal. This project is in its third year.

Clients/Users: This project will be of interest to other researchers, U.S. Department of Defense, and others.

Keywords: trichloroethene, cometabolism, fluidized-bed bioreactors, chlorinated solvents, water.

Project no.: 94-25

Goal: The goal of this research is to determine feasibility and efficacy of vegetative bioremediation, specifically poplar trees, at sites contaminated with benzene, toluene, ethylbenzene, and xylene (BTEX) compounds.

Rationale: Vegetative remediation has become a promising, inexpensive, publicly accepted, and innovative technique for cleaning contaminated hazardous waste sites. This technique is best suited for sites of shallow contamination that are in the zone of impact for deep-rooted poplar trees. BTEX contamination is ideally suited for vegetative remediation. Being light, nonaqueous phase liquid (LNAPL) contaminants, BTEX compounds are often located near the surface at hazardous waste sites. BTEX contamination is also ubiquitous in today’s environment, and many of these sites are located at rural and abandoned sites where little money is available for more expensive traditional remediation techniques.

Approach: This research will attempt to determine whether vegetative remediation with poplar trees is a fundamental approach for remediation of BTEX-contaminated sites. Poplar uptake of BTEX compounds will be monitored and translocation within plant tissues will be studied. Plant tissues and aerial compartments will be examined to measure accumulation in plant tissues and volatilization from leaf surfaces, respectively. Poplars are widely adapted to a wide variety of temperate and boreal environments; they are fast growing, hardy, and easily reproduced from parental cuttings; they are easily rooted at variable and great depths; and they have been successfully grown from tissue cultures.

Status: Work has centered on experimental apparatus design, method development, and experiments utilizing various compounds. Investigators have conducted uptake studies with the majority of these compounds in the reactors designed for this project. These reactors have been designed to contain the individual poplar cuttings and can accommodate growth of the cutting in either hydroponic growth solution or in soil media. The reactors are constructed to contain and collect any VOCs released from the above-ground plant components. Reactors have proven to perform as expected in the laboratory setting. Mass balances for VOC experiments utilizing vigorously-growing cuttings in the reactors have consistently been over 85%. The further improvement of mass balances is a point of focus in future research. Studies to determine structure activity relationships for the leaf volatilization of VOCs by poplar trees are also ongoing, and investigators are examining the impact soil processes have on phytoremediation of VOCs. The overall focus has been the quantification of volatilization, storage, and possible metabolization of specific compounds in poplar tree phytoremediation systems. A study to investigate the impact of soil processes on phytoremediation of VOCs has been started. This project is in its third year.

Clients/Users: This research is of interest to the city of Houston, Texas, which has a petrochemical spill site. It will also be of interest to U.S. Department of Defense and for petrochemical "land farming" sites, U.S. Department of Energy sites, and agricultural locations.

Keywords: vegetative remediation, poplar trees, BTEX, soil, plants.

Project no.: 94-27

Goals: Objectives of this project are to develop experimental systems to improve oxygen availability for enhanced aerobic biodegradation; monitor transfer of contaminants through plants; apply a mathematical model to describe fate of water, contaminant, root exudes, plants, microbes, and oxygen in laboratory and field systems; and work with professionals elsewhere to apply this technology to one or more field sites.

Rationale: Much of the population in U.S. EPA Regions VII and VIII relies on groundwater for its potable water, but many groundwater aquifers within this region have been contaminated with hazardous organic chemicals. Such chemicals may be by-products of agricultural and industrial production or may have leaked from fuel storage tanks or ruptured soil liners at disposal sites. Soil contamination involved in these types of problems is often very dispersed so that conventional soil and groundwater remediation techniques would be very expensive or, in some cases, impractical. Plants can play an important role in remediating soil and groundwater contaminated with organic substances. To put this new technology to effective use, we need to better understand and predict effects that plants have on soil and groundwater remediation, so that effective planting and management plans can be developed.

Approach: Previously a prototype system has been built by these researchers and used for study of bioremediation of groundwater assisted by plants. Based on experience with the prototype system, a new system has been constructed with more but shorter path length channels and a depth of 60 cm. It will permit introduction of controlled amounts of air into the soil, either above or below the water table, in two of the channels. By use of evolutionary operation design, performance of the system will be optimized to minimize air input and maximize degradation of target substances. Material balance measures will be used to determine the fate of target substances. Potential intermedia transfer will be monitored by FTIR measurements on the gas phase above the growing plants, while changes in contaminant concentration in the groundwater will be monitored by headspace gas chromatography or FT-IR of aqueous samples. The groundwater flow and transport model will be used to model behavior of contaminants in the new system under several experimental conditions. The model will be further refined to improve the fit of predicted and observed behavior. It will then be applied to field situations where monitoring wells are in place, such as near landfills.

Status: Experiments with alfalfa in growth chambers are yielding much data, with the flow properties characterized and dissolution of TCE from the nonaqueous phase measured. A Gasmet FT-IR instrument is used for highly sensitive analysis of soil gas composition, except for O₂, which is infrared inactive. Investigators have introduced a nonaqueous-phase TCE below the water table and determined the extent to which it is solubilized by the flow of groundwater. Soil surface fluxes are monitored with the Gasmet. PCR-based techniques have been developed for detection of specific bacteria. Good success has been had in modeling the distributions of reactants and products through the prototype plant growth chamber under steady state conditions. Other modeling studies are underway. As originally proposed, investigators will study the fate and transport of other contaminants. Pilot-scale studies were done to determine the ability of higher plants to degrade TNT and the sensitivity of alfalfa to soluble TNT. The original prototype chamber was switched to a combination TCE and toluene to examine cometabolism. Other contaminants with different volatilities and degradabilities are being introduced into the chamber. Results of both experiments and simulations indicate the crucial role of soil aeration in contaminant degradation and flux. Investigators now need to determine optimum oxygen supply rates for various contaminants in the presence of plants. In terms of modeling, they need to describe in precise terms the relative fluxes of contaminant through gas-filled and water-filled pores of soil. The Gasmet FT-IR will continue to be used to routinely monitor fluxes to the atmosphere in the six-channel system. We will continue to develop PCR and selective plating techniques to rapidly monitor microbial populations in planted soils. We have applied for funding to do a field application of plant-based bioremediation for VOCs near airports, where contamination from deiceing agents is a problem, and one county landfill is already preparing a remediation plan with advice from the investigators. This project is in its third year.

Clients/Users: Contractors, regulators, professionals with manufacturing companies and government agencies, and researchers have expressed interest in this research. Riley County Public Works officials have also expressed interest in using this technology at the Riley County Landfill. This research is also of interest to U.S. Department of Defense and U.S. Department of Energy.

Keywords: plants, soil, groundwater, alfalfa, poplar trees.

Project no.: 94-29

Goal: The primary goal of this research is to develop and implement systematic procedures for applying, in the field, treatment and remediation technologies that have been developed in the laboratories, taking into consideration the complexities which are encountered in the field.

Rationale: The primary hypothesis is that natural heterogeneities of soil and heterogeneities due to nonaqueous phase liquid (NAPL) entrapment result in preferential flow of water and treating agents. These constraints to flow and delivery of treating agents alter effectiveness of treatment schemes in the field. This research will attempt to identify the basic processes that are affected by these complexities and determine the parameters that control the behavior at the field scale.

Approach: A systematic procedure to extend to the field the knowledge gained through experimentation at the laboratory scales of pore, cell, column, and soil flumes will be developed. Laboratory, modeling, and field investigations will focus on issues related to transport, entrapment, recovery, dissolution, fingering, and physical chemical and thermal mobilization, blob dispersion to increase dissolution, etc., that are of fundamental importance in developing remediation technologies. Laboratory experiments in cells, columns, and large tanks will be continued to identify basic parameters which need to be upscaled to field problems. Some of the parameters that have been identified for study include hydraulic conductivity, capillary pressure versus saturation, relative permeability, entry pressure, pore-size distribution, dispersivity, sorption coefficient, mass transfer coefficients, and dissolution parameters. Investigators will use chemical mixtures to look at multicomponent mass transfer and realistic field soils. Sites in Kansas, Colorado, Wyoming, and Louisiana will be selected for field studies. Once effective parameters are identified, techniques will be developed to obtain these in the field.

Status: One report on enhanced dissolution using surfactants and another on thermal mobilization were completed. Research on development of analytical and computer modeling techniques required to interpret solute breakthrough curves in terms of effective parameters continues. Investigators have identified tracers as one of the most promising methods of determining scale-dependent parameters in heterogeneous systems. They also found that interphase mass transfer from entrapped NAPLs can be greatly enhanced with the use of surfactants. All column LNAPL experiments showed an increase in recovery efficiency with an increase in water flood temperature. Overall, however, hot water flooding was unable to produce the significant amounts of LNAPL recovery found during the column experiments when applied to a more realistic multi-dimensional, heterogenous system. Investigators identified that subsurface heterogeneity, low-permeability zones, and relative-permeability reductions caused by the presence of NAPL can all prevent surfactants from making contact with the NAPL -- leading to its failure of enhancing remediation. Considerable progress was made to find field sites for testing, with three sites identified and evaluated so far. Future plans include laboratory investigations on alternative remediation technologies, investigations to determine parameters for upscaling to field, development of systematic procedures to extend laboratory information to field, development and adaptation of models for field-scale applications, development of field characterization techniques, and field testing and applications. This project is in its third year.

Clients/Users: The developed technologies will be of use to environmental scientists, environmental engineers, geologists, and hydrogeologists who are employed by U.S. Environmental Protection Agency and other federal and state regulatory agencies; U.S. Department of Defense; U.S. Department of Energy; nvironmental consulting firms;and the manufacturing industry.

Keywords: aquifers, organic chemicals, nonaqueous phase liquids, remediation.

Project no.: 89-26, 92-03

Goal: Investigators are attempting to develop a new technology for one-step destruction of hazardous substances, including chlorocarbons, chlorofluorocarbons, organophosphorus, nitrogen, and sulfur compounds. This new technology is based on ultrahigh surface area metal oxides with reactive surfaces that behave as "destructive adsorbents" (surfaces that adsorb and break chemical bonds in the hazardous adsorbate). Research objectives are (1) to develop the best ways of synthesizing destructive adsorbents, (2) to understand the surface chemistry going on during the adsorption/destruction process, and (3) to develop a second generation of better destructive adsorbents based on multilayer oxide/oxide composites. Destructive adsorbent technology has promise as an alternative to incineration and for air purification systems.

Rationale: Organic compounds containing halogens can be completely destroyed under mild conditions using metal oxides. Destructive adsorbent technology has promise as an alternative to incineration and for air purification systems. Further research is needed to develop this technology so that it can be used in field applications.

Approach: Research work on the production of magnesium oxide, ferric oxide on magnesium oxide, and calcium oxide in nanoscale particle size and reactivity studies is being carried out. Adsorption and transformation of chlorinated hydrocarbons, phenols, and phosphorous compounds are being investigated.

Status: Work has involved synthesizing the best destructive adsorbents, understanding the surface chemistry, designing and testing a continuous reactor, and training students. Efforts have also included new preparative approaches to nanoparticles and their chemistry, the use of metal particles to destroy contaminants in groundwater, scaleup experiments, and applications. A small company called Nantek has been established to manufacture and market nanoparticles for environmental remediation and other purposes. This project is concluded.

Clients/Users: Results of this research are of interest to other researchers and to those in private industry. Representatives from several government agencies have expressed interest in the research.

Keywords: magnesium oxide, carbon tetrachloride, adsorption, calcium oxide.

Project no.: 92-24

Goals: Goals are to establish accurate predictions of desorption kinetics of munitions residues by elucidating changes in sorption characteristics over time; to characterize transport properties of both freshly added and aged RDX, TNT, and principal degradates; and to predict the fate and transport of munitions residues over time with a computer transport model.

Rationale: Past disposal practices of munitions production facilities have resulted in contamination of terrestrial and aquatic ecosystems. Efforts to date have documented the extent of contamination and estimated potential migration routes. To predict the fate and transport of munitions in soils, an accurate description of the adsorption-desorption process is critical.

Approach: Investigators hypothesize that munitions residues residing in soils for extended periods may be more tightly bound into a soil organic fraction and that this bound fraction may be more important in predicting the long-term fate and transport of munitions residues. The proposed research will elucidate the transformations, mechanisms, and reversibility of munitions residues in soils with traditional sorption experiments and diffuse reflectance (FTIR) spectroscopy. The validity of using transport equations that assume instantaneous equilibrium, isotherm linearity, and adsorption-desorption singularity in field-contaminated soils will also be tested. The proposed research will characterize the sorption of munitions residues in soil and provide improved predictions on desorption kinetics.

Status: TNT transport, degradation, and long-term sorption characteristics were determined in soil. In all experiments, a significant fraction of added TNT was recovered as amino degradates of TNT. Most of the unaccountable TNT was hypothesized to be unextractable. Investigators’ observations illustrate that TNT sorption and degradation are concentration-dependent and the assumptions of linear adsorption and adsorption-desorption singularity commonly used in transport modeling may not be valid for predicting TNT transport in munitions-contaminated soils. Non-linear transport codes were successfully used to model observed TNT breakthrough curves obtained in column transport experiments. We have established that the chemical (abiotic) treatments of Fenton oxidation and treatment with iron metal (Fe) have an excellent potential to remediate munitions-contaminated soil and water. This technique was demonstrated in situ. Microbial populations in TNT-contaminated soils have been identified and characterized. Other work included the study of long-term TNT sorption and bound residue formation in soil, and experiments were also conducted with uncontaminated and munitions-contaminated subsurface soils. These experiments were conducted to determine the effects of prior contamination and organic matter content on long-term availability of TNT residues. Rate constants were determined for TNT sorption and desorption on a Sharpsburg soil and thermodynamic parameters were calculated. Researchers also studied long-term sorption and degradation of RDX in soil. These experiments indicated limited RDX sorption and degradation in the Sharpsburg soil. Most of the sorbed RDX was potentially available for transport, which indicated the importance of remediating RDX-contaminated soil to protect groundwater. This project has ended.

Clients/Users: This research will be of use to those in munitions production facilities, U.S. Department of Defense, and others.

Keywords: fate and transport, munitions, soil, adsorption, diffuse reflectance spectroscopy.

Project no.: 93-20

Goal: The goal of this project is to conduct a detailed investigation of air sparging systems operated in a pulsed mode to provide a fundamental framework from which to evaluate the applicability and effectiveness of biosparging technology for a given set of site, soil, and waste constraints.

Rationale: Air sparging represents a highly attractive remediation alternative for contaminants located below the groundwater table. It has been shown through anecdotal evidence that contaminant emission rates increase and groundwater concentrations are greatly reduced at groundwater monitoring well points. Specific mechanisms of air sparging system performance are yet to be investigated, and adequate monitoring of field scale systems to quantitatively document their performance throughout affected areas of injection well influence are yet to be developed.

Approach: The proposed research project will involve two integrated components, companion field scale and laboratory scale studies. The field study will be utilized to provide mass transfer and contaminant biodegradation rates resulting from a field scale biosparging system, as affected by media property and heterogeneity limitations inherent at field sites. The laboratory component of the proposed research will provide detailed analysis of mass transfer and contaminant degradation rates under controlled conditions. Laboratory investigations will include an evaluation of the effect of bubble size, air injection rate, air injection depth, media properties, and contaminant properties on observed mass transfer and contaminant degradation rates. Air injection versus inert gas injection will allow the separate evaluation of mass transfer and degradation, while air injection in clean water systems will allow an evaluation of system mass transfer relationships independent of effects due to contaminant properties and/or contaminant/media interactions.

Status: Significant progress has been made in the design, testing and construction of a field instrumentation bundle capable of representative sampling of dissolved oxygen, pressure and contaminant concentrations within the contaminated aquifer below the Layton field site. A spacially-dense, three-dimensional sampling grid consisting of driven gravel points at five vertical depths and four horizontal radii from the injection well has also been installed. Instrumentation bundles have been installed at the field site. A data acquisition system has been configured and is operational. Initial air-injection trials have been completed. It was necessary to remove the asphalt and reinstall a new piping system to provide a means of remote data collection. Conduit originally installed in surface trenches did not support the surface activity at the site. Two sets of laboratory studies began in May 1996- one to evaluate oxygen transfer in air sparging versus in-well aeration systems, and the other to evaluate tracer methods for monitoring air-injection remediation systems. Initial "clean water" oxygen transfer/mixing studies are complete. Future plans include air-sparging tests, in-well aeration tests, clean water tests, dirty water tests, media clean water tests, and media dirty water tests. This project is in its third year.

Clients/Users: Results from this project will be of interest to other researchers, the U.S. Department of Defense, private industry, and regulatory personnel.

Keywords: biosparging, biodegradation, mass transfer.

Project no.: 93-21

Goal: The overall goal of this research effort is to provide new information concerning the distribution of polycyclic aromatic hydrocarbon (PAH) biotransformation products among humic materials associated with the solid fraction of soil and the water soluble extract (leachate) fraction, and the effect of environmental variables and amendments on humification and leaching.

Rationale: There is a lack of information concerning transformation intermediates regarding their reactions, measurement, and management in soil bioremediation systems. Specifically, the role of the humification process is currently unknown in prepared bed systems. Disappearance of compounds within soil treatment systems does not necessarily indicate mineralization or detoxification of toxic and hazardous compounds. The formation of intermediates and the fate of those intermediates with regard to association with the soil solid phase in the process of humification is an area where information is needed in order to fully assess the treatment effectiveness of soil bioremediation systems. Development of information addressing behavior of transformation intermediates with an emphasis on characterizing humification of target organic chemicals would increase our understanding of soil bioremediation processes with regard to protection of public health and the environment. Based on information developed in this project, techniques for management of the humification process may be identified and applied to soil bioremediation systems.

Approach: The approach in this project is to use samples of soil taken from field-scale bioremediation systems treating creosote- and creosote/PCP-contaminated soil. Soil samples have been taken from the Champion International Superfund site. The first activity involves identification of PAH and PCP transformation products that occur in soil systems and that can be extracted. The second activity involves chemical mass balance and toxicity determinations during treatment and development of instrumental approaches for evaluating humification. The approach is used to generate information concerning: (1) chemical bonding of PAHs and PCP/intermediates with the soil solid phase, humic and fulvic acid fractions, and with leachate; (2) effects of environmental variables (light, temperature, soil moisture) on the humification process; and (3) effects of amending soil with electron acceptors on humification, mineralization, and volatilization.

Status: Researchers are reviewing work regarding sorption processes of highly hydrophobic chemicals. They are also conducting work involving extraction and fractionation procedures for evaluating the binding of target chemicals to solid phase components of the soil. A new work plan for obtaining samples at the Libby site was prepared, submitted, and approved. An interim report was submitted to the U.S. EPA summarizing the work researchers have conducted. Microcosms have been implemented to evaluate the effect of electron acceptor addition, including manganese and iron, temperature, and moisture. Biological intermediates of pyrene metabolism by microorganisms have been identified through literature searches. Researchers have completed all of the planned experiments with regard to PCP reactions with manganese oxides as a function of pH and redox potential. They are currently involved in data generation and collection with regard to effects of electron acceptor addition and environmental variables. Future research plans are consistent with the schedule presented in the proposal, except that the project was extended over a three-year period, instead of two, with the original budget. The project has been expanded to include cooperation with the USEPA Cincinnati NRMRL concerning treatability and technology transfer of "presumptive remedies" for soil contaminated with wood preservative. This project is in its third year.

Clients/Users: Information generated from this project will be useful for regulators and the wood preserving industry. The U.S. Environmental Protection Agency has expressed interest in this project. The U.S. Department of Defense is also interested in this project.

Keywords: bioremediation, humification, mineralization, leaching, volatilization, intermediates.

Project no.: 94-02

Goal: Through use of prompt gamma ray neutron activation analysis (PGNAA), the goal of this project is to develop analytical procedures for "de-convolution" of measured gamma ray spectra to yield contaminant concentration profiles.

Rationale: The prompt gamma ray neutron activation analysis (PGNAA) methodology is ideally suited to measurement of soil concentration profiles of the heavy-metal contaminants associated with mining and metallurgical enterprises. This project will lead to improved precision in site characterization, thereby minimizing quantities of soil to be decontaminated.

Approach: This project is concerned with in situ hazardous-waste site characterization for and diagnosis of the need for decontamination. This project will deal with analysis of factors affecting speed and accuracy of the PGNAA method and how both soil conditions and neutron-source/gamma-ray detector geometry need to be accounted for in optimization of data collection and analysis. The work output of this project will be documentation of methodology. Investigators will make every effort to work directly with commercial and government enterprises in implementation of optimization methods developed for data collection and analysis.

Status: Literature reviews, TORT code problem specification, Gamma-ray transport code preliminary tests, Gamma-ray response function development, and complete preliminary calculations were completed. Representative thermal and fast neutron fluence profiles of five representative soils were established through Monte Carlo and/or discrete ordinates transport calculations. These profiles were used to generate a library of gamma ray fluences above the soil resulting from neutron capture in the soil. Methods for estimating contaminant profiles from simulated capture gamma ray observations were developed using inversion or deconvolution methods applied to idealized contaminant profiles to assess their robustness for the soil contamination problem. In addition, investigators were able to devote more staff-months of effort than originally budgeted, at no additional cost to the sponsoring organization. Also, instead of one graduate student assigned as a research assistant, there were four. This project has ended.

Clients/Users: This research is directed toward meeting technology needs of the U.S. Department of Energy. This project will also be of interest to those in mining and metallurgical enterprises and the U.S. Department of Defense.

Keywords: prompt gamma ray neutron activation analysis, remote sensing, characterization, monitoring, sensor technology.

Project no.: 94-09

Goal: This project is designed to improve understanding of fundamental relationships between surfactant chemistry, contaminant solubilization, and subsequent biodegradation rates in soils, while developing novel methods which may be useful in the bioremediation of nonpolar organic compounds in soils.

Rationale: During the past decade, much discussion has centered on the unavailability of sorbed compounds to soil microorganisms; it is generally now assumed that desorption and diffusion of bound contaminants to the aqueous phase is required for microbial degradation. Furthermore, with aging, many nonpolar contaminants form irreversibly bound residues which are difficult to extract with nonpolar solvents and are essentially unavailable to indigenous microbial communities or to those added as an inoculum to stimulate biodegradation. In a recent workshop convened to discuss major research needs in bioremediation, the bioavailability of soil-bound contaminants was consistently identified as a fundamental limitation in enhancing rates of contaminant biodegradation in soils. One of the strategies for enhancing desorption rates and subsequent biodegradation rates of nonpolar contaminants in soils is the use of surfactants.

Approach: A series of contaminant partitioning studies using a wide range of surfactants with varying structures will be performed. Functional relationships between surfactant concentration, surfactant structure, and extent of contaminant solubilized will be established using batch and column studies. Effects of surfactants on subsequent biodegradation rates of phenanthrene, PCP, DDT, and PCB will be studied under batch and column conditions using two representative bioremediation strategies: indigenous microbial populations and addition of white-rot fungi. Degradation rates will be determined under batch and flow conditions in previously uncontaminated soils with and without contaminant aging. In addition, contaminant degradation in soil samples from several field sites contaminated with PCP and polyaromatic hydrocarbons will be compared to controlled laboratory experiments.

Status: Investigators have completed additional experiments on the relationship among surfactant solubilization of phenanthrene, aqueous phase surface tension, and phenanthrene degradation. We have now moved to experiments on the degradation of phenanthrene during transport conditions in the presence and absence of surfactants and hexadecane. Future research plans include continued column experiments and the study of aging effects as they relate to the effectiveness of surfactants in enhancing degradation and transport of phenanthrene. Data from column experiments will be used for testing transport models in which biodegradation kinetics are coupled to the advective dispersion equation. We also plan to study the effects of pore-water velocity on the degradation rates of surfactants and organic contaminants during transport conditions to better understand the potential use of surfactants in transport applications. Investigators also plan to publish three manuscripts. This project is in its third year.

Clients/Users: This research will be of interest to members of industry and to the U.S. Department of Defense.

Keywords: surfactants, bioavailability, biodegradation, nonpolar organic compounds.

Project no.: 94-11

Goal: The goal of this research is to understand contaminant binding to soil organic matter, particularly the fraction known as humin.

Status: This project is on schedule, although the time line had to be adjusted to reflect the unexpected amount of time needed to complete the ultrafiltration of samples. To speed completion of this portion of work, an additional ultrafiltration cell is being purchased. A portion of the contaminant mass balance has been completed and a manuscript describing the distribution of PAHs and PCBs between the humic fractions and components of humin has been submitted. Studies on how organic components in humin affect binding capacity for different target compounds had to be modified when it became clear it might not be possible to get this information as the experiment was originally conceived. This work and the ultrafiltration studies should be completed in year three of the project. The analytical protocol for the BET soil analysis and the soil organic matter fraction surface area has been developed. The method for examining the binding of the target compounds to humin and its components has been refined. Delays in spending authorization have held up much of the project for year three but future research plans include describing the nature of bound contaminant residues and their chemical environment in order to begin to develop an understanding of the binding phenomena and the parameters that control it. This project is in its third year.

Clients/Users: Results of this project could be used by regulatory agencies, individuals conducting research into the fate and transport of environmental contaminants, or those attempting to produce more effective herbicides or pesticides. The U.S. Department of Defense will also be interested in this research.

Keywords: contaminant binding, humin, soil organic matter, binding mechanisms.

Project no.: 94-12

Goal: The goal of this project is to develop a systematic approach to the design and management of vegetative remediation schemes and to implement this approach in a decision support system that can be used by environmental professionals to evaluate the potential use of vegetative systems for remediating a contaminated site.

Rationale: Several previous and current research projects have investigated the potential for vegetation to aid in remediation of soils and groundwater that are contaminated near the soil surface. One of these projects produced models that can predict the fate of hazardous organic substances in the root zone of a soil. Preliminary comparisons between developed models and laboratory experiments were favorable, yet two significant modeling limitations were observed. First, the models could only simulate a limited number of contaminant degradation processes. Second, the models require a large amount of information about a site where vegetation is being considered as a remediation option. These limitations could prevent use of the models in predicting potential benefits of a vegetative remediation system designed by environmental professionals involved in soil and groundwater remediation projects. To overcome these limitations requires development of a methodology that can synthesize the required modeling data from information that is available about a remediation site and use the model to systematically arrive at an efficient remediation design.

Approach: Objectives of this project related to the efficient design of vegetative remediation systems will be achieved by developing a general methodology based on systems theory. This involves forming a systems statement that includes the quantitative definition of goals of the remediation project, design variables that can be manipulated to attain these goals, and practical and legal constraints that limit attainment of these goals. Several conventional and heuristic solution procedures will be used to solve the systems statement. The most robust and computationally efficient procedures will be selected for continued use in this project. Once developed, the design procedure will be applied to a field site within U.S. EPA Regions VII and VIII that has near surface soils and groundwater contaminated with hazardous organic substances. Then a graphically-based decision support system will be developed from this design experience for future use by environmental professionals.

Status: Development and analysis of conventional gradient programming solutions to solve the design systems statement, and development and analysis of heuristic solution methods to solve the design systems statement are essentially completed. Existing vegetative remediation models have been modified to incorporate a wider range of field conditions and these models are being validated. Investigators will also study the use of the modified models and design methodology to develop a pump-and-treat style vegetative remediation system. A Windows-based interface for the design and operation support system has been developed and has been applied to two field sites contaminated with hazardous organic contaminants. Preliminary results are very promising and potential applications of the program are being vigorously pursued. This project is in its third year.

Clients/Users: This project will be of interest to government agencies, such as the U.S. Department of Defense and U.S. Department of Energy, and to industry.

Keywords: modeling, vegetation, phytoremediation, plant remediation.

Project no.: 94-24

Goal: This research will explore the possibility of using sonic pulse propagation, combined with advanced signal processing techniques, to determine the depth of coherent cement plugs in abandoned wells.

Rationale: Each year many wells are plugged and abandoned throughout the United States. These include water wells, mineral exploration wells, and oil and gas production wells. Many wells penetrate one or more aquifers. The wells also pierce formations containing oil and gas reservoirs, mineral deposits such as uranium and lead, and water contaminated with salt, iron, selenium, sulfates, and radon. The well borehole provides a mechanism for communication of fluids and gasses between formations. When aquifers are involved, this poses a severe pollution threat. For example, if the borehole passes through both an aquifer and a brine-bearing formation, the brine can invade the aquifer and compromise the quality and purity of the water. The problem escalates if the brine layer is pressurized with respect to the aquifer, causing continuous flow of brine into the fresh-water formation. Conversely, water will escape from the aquifer if its hydrostatic pressure exceeds the pressure in other porous layers. Improperly plugged wells can compromise the integrity of the aquifer layer since this natural isolation is destroyed, allowing water to come in contact with these potentially toxic materials.

Approach: In this project, investigators will develop, instrument, and test a borehole scale model. Research will be undertaken to understand wave propagation and plug reflections in the model. Investigators will simulate responses for selected borehole scenarios and evaluate various models and receiver configurations. They will develop a sensor system, analog-to-digital conversion, and portable computer-based analysis system for measuring plug reflections; develop signal processing methods to extract plug information from reflection data; and conduct field tests to characterize performance of the prototype system.

Status: Original plans called for equipment and signal analysis techniques to be tested using a water well. However, high ambient noise levels from nearby car traffic and underground steam tunnels made the site unsuitable. The tests were shifted to an artificial borehole test bed developed over the past year. Tests using the artificial borehole have shown standard commercial geophones to have adequate bandwidth and sensitivity for use in this project. Additional advantages include ruggedness and low cost. The structure of received geophone signals is very complex, comprising both primary reflections from plug surfaces, and secondary reverberations from energy reflecting back and forth between plugs. To help understand the nature of various reflection events, two computer modeling programs have been developed. Limited site testing was performed but efforts were shifted to troubleshoot and improve performance of the transducer system. New data acquisition software was written for recording data from the modified transducers and this has yielded excellent signal-to-noise ratios. Future work includes testing the transducers at the artificial borehole to resolve problems, then to test them on at least one plugged well. Computer modeling studies will also continue. This project is in its third year.

Clients/Users: This project will be of interest to agencies responsible for protecting subsurface aquifers. It will also be of interest to the Department of Justice, U.S. Environmental Protection Agency, and U.S. Department of Defense. Private oil and gas exploration companies may also be interested.

Keywords: boreholes, aquifers, oil wells, gas wells, cement plugs.

Project no.: 94-26

Goal: The principal objective of this project is to determine—through a series of carefully controlled bench-scale tests designed to measure changes in hydraulic conductivity of soils treated with ultramicrobacteria compared to untreated soils—the feasibility of using biologically modified soils as waste containment barriers.

Rationale: The U.S. Environmental Protection Agency (EPA) is responsible for developing standards and regulations governing design, operation, and maintenance of landfills, surface impoundments, and waste piles used to treat, store, or dispose of hazardous wastes. A good deal of EPA effort, therefore, is focused on design and performance of waste containment systems. All such systems include one or more barriers to prevent transport of contaminants into the environment. Performance of contaminant barriers depends upon many factors, including type of wastes being contained, materials used to construct the barrier and their compatibility with the waste materials, quality of construction, and long-term durability under adverse environmental conditions. Materials used for barriers should be inexpensive, have low hydraulic conductivity and low molecular diffusivity, and must be durable enough to last for tens and possibly hundreds of years. This project will involve developing new, low-cost barrier materials bioengineered for waste containment.

Approach: In order to determine the feasibility of using biologically modified soils as waste containment barriers, a series of bench-scale tests will be performed to measure changes in hydraulic conductivity of soils treated with ultramicrobacteria (UMB) compared to untreated soils. The project will investigate the range of biological conditions under which UMBs have the ability to reduce soil hydraulic conductivity. Based on results of bench-scale tests, investigators will establish the range of physical and biological parameters most likely to result in successful application of biofilm technology to the design and construction of field-scale waste barriers. Finally, feasibility of using biofilm barriers at the prototype scale will be tested.

Status: Investigators have completed work regarding the development of procedures for preparing bacterial and nutrient solutions. The design of a large-scale test program utilizing the Environmental Simulation Laboratory was completed in August 1995. Hydraulic conductivity testing was completed and indicated that biofilm containment barriers were feasible and should be investigated further at a larger scale to simulate field conditions. If their pending proposal is funded, investigators plan to pursue the next step in the development of this technology, which is to construct and test biofilm barriers in the Environmental Simulation Laboratory. Internal funding from the University of Wyoming has allowed graduate students to investigate the effects of biofilm on diffusion of organic chemicals in the soil, the genetic mechanisms controlling the production of biofilm by B. indica, and the mechanisms of adhesion between biofilm and soil particles. This project is completed.

Clients/Users: Results of this project will be of interest to the U.S. Environmental Protection Agency, U.S. Department of Defense, environmental contractors, regulators, and the mining and agriculture industries.

Keywords: biofilms, hydraulic conductivity, ultramicrobacteria, waste containment, barriers.

Project no.: 94-28, 93-11

Goal: The overall goal of this project is to understand factors which promote or retard biomass accumulation in porous media with an intent to apply such understanding toward prediction and beneficial manipulation of permeability and mass transport properties.

Rationale: A concept which appears promising in the manipulation of biological and chemical processes for remediation of subsurface hazardous waste sites is the creation of biobarriers for containment and remediation of soil and groundwater contaminated with organics and heavy metals. Biobarriers are formed by stimulating growth of microbial biomass so as to plug the free pore space flow paths through porous media, thereby reducing permeability and mass transport. Selective plugging of permeable strata is currently being explored as a means of preventing contaminant migration of groundwater contaminants from hazardous waste sites. Penetration of bacteria through porous media varies between extensive penetration of ultramicrobacteria and formation of plugging biofilms on the proximal formations by well-fed cells of the same organisms. Investigators will attempt to use simple nutritional differences to deliver bacteria to any location in the subsurface environment to resuscitate and either plug the formation or carry out specific biodegradation.

Approach: Test organisms will include a Klebsiella pneumoniae as well as these same bacteria starved for ultramicrobacteria size. Experimental objectives will be carried out using a series of flowing packed- bed reactors including flat plate flow cells and packed columns. Procedures will be developed for applying bacterial inoculum, along with subsequent resuscitation with nutrients, so as to produce controlled reduction of porous media permeability and dissolved oxygen transport. Researchers will quantify and model temporal and spatial variability in the biofilm accumulation (and mass transport) using bioluminescence. Finally, a mathematical model for biofilm accumulation and corresponding permeability and dissolved oxygen gradients in porous media will be developed and evaluated.

Status: This project is on schedule and no major difficulties are anticipated. Investigators have determined quantitative relationships that describe biomass accumulation and corresponding mass transport properties in saturated porous media. Methods for controlling biobarrier thickness, longevity, and degree of permeability reduction have been established. The efficacy of using biobarriers to create and maintain anaerobic conditions has been assessed. Funding from a major oil company has been obtained for a pilot project that will test the feasibility of installing a biobarrier at a field site to control hydrocarbons leaching from the groundwater system into a nearby river. A radial flow lysimeter was constructed to simulate field conditions in preparation for this demonstration project. Efforts to refine our modeling techniques will continue. This project is in its third year.

Clients/Users: This project will be of interest the U.S. Department of Energy, U.S. Department of Defense, environmental contractors, regulators, and those in the petroleum industry.

Keywords: biofilms, hydraulic conductivity, ultramicrobacteria, waste containment, barriers.

Project no.: 95-10

Goal: The goal of this research is to 1) investigate the fate of TCE and other chlorinated ethenes in plant/soil systems through a combination of laboratory experiments and mathematical modeling and 2) to evaluate the applicability of a plant-based bioreactor for the remediation of groundwater contaminated with TCE.

Rationale: Chlorinated solvents, such as TCE, are among the most frequently found groundwater contaminants at military installations, due to their widespread use in degreasing operations. Understanding the fate of these contaminants is critical in performing risk assessments and evaluating remediation options. Development of less costly remediation alternatives for contaminated groundwater are also of considerable importance. The uptake into plants is a potentially important fate process that has not been adequately evaluated for TCE and other chlorinated solvents. Determination of uptake rates, plant/water and plant/air distribution coefficients, and degradation rates would greatly improve fate modeling and risk assessment efforts. In addition, the literature indicates that conditions in the rhizosphere may favor co-metabolic transformation of TCE. Phytoremediation has shown promise, but its implementation has been limited, in part due to the difficulties associated with non-engineered systems. The plant-based bioreactor proposed in this study may provide a cost-effective approach for remediating groundwater contaminated with TCE and other hazardous organic chemicals. The bioreactor approach enables the control of key environmental variables, such as moisture, nutrients, pH, and oxygen in order to maximize plant growth and remediation efficiency.

Approach: Laboratory studies will evaluate the fate of chlorinated ethenes in hydroponic systems. Specifically, these studies will determine plant/water/air distribution coefficients and plant uptake rates. This approach will be extended to laboratory and field plant/soil systems. Based on the results, a plant-based bioreactor for the remediation of contaminated groundwater will be constructed. Environmental conditions will be managed to optimize plant growth and microbial activity.

Status: Funding for the project was received in September 1996. Three closed-chamber systems have been constructed. We expect to complete the hydroponic and plant/soil microcosm studies, as well as the modeling phase, this year. This project is in its second year.

Clients/Users: Successful completion of this project will provide information of value to state and federal government agencies, environmental consulting firms, and the U.S. Department of Defense.

Keywords: chlorinated solvents, trichloroethylene, TCE, contaminated groundwater, remediation, soil systems, plant systems.

Project no.: 95-29

Goal: The goal of this project is to determine the feasibility of using plants to remediate soils contaminated with chlorinated aliphatic compounds by studying their uptake, translocation, and resulting metabolites and by investigating plant enzyme capabilities to degrade these compounds.

Rationale: Based on our previous research, we understand that there are several potential mechanisms for the uptake and transformations of TCE in a plant-soil system.

Approach: Investigators will research potential mechanisms and the feasibility of phytoremediation to enhance the cleanup of TCE-contaminated sites. Studies will examine the uptake of TCE or its metabolites into the roots, the xylem transfer of the compounds to the leaves, volatilization from the leaves, foliar uptake of TCE from air, phloem transfer, and bound residue formation throughout the plant.

Status: Progress has been made on determining uptake, translocation, and accumulation of TCE in plants. Volatilization rates of TCE through poplar cuttings compared to soil volatilization were determined. Potential metabolites contained in soil, poplar tissues, and volatilized air are being investigated and phytotoxicity studies will continue. This project is in its second year.

Clients/Users: Anyone involved with the cleanup of sites contaminated with TCE. The U.S. Air Force has shown particular interest.

Keywords: plant enzyme systems, chlorinated aliphatic compounds, TCE, phytoremediation.

Project no.: 95-32

Goal: The objectives of this project are to 1) develop and test zero-valent iron-promoted processes for simultaneous remediation of atrazine and nitrate in contaminated ground and surface water, sediment, and soil; 2) investigate the technical and economic feasibility of the iron-promoted systems for above-ground and in situ remediation of ground and surface water, sediment, and soil contaminated with atrazine and nitrate; and 3) elucidate mechanisms of transformation and determine kinetics associated with the proposed processes.

Rationale: Preliminary studies demonstrate the potential use of iron-promoted processes to remediate ground and surface waters contaminated with atrazine and nitrate.

Approach: Investigators are using zero-valent iron-promoted processes, employing fine-grained iron metal as a reducing agent, to simultaneously transform atrazine- and nitrate-contaminated water, sediment, and soil.

Clients/Users: Investigators anticipate the results of this project will be of interest to the U.S. EPA and others working in the field of ground and surface water remediation.

Keywords: atrazine, nitrate, groundwater, surface water, contamination, zero-valent, iron-promoted processes.

Project no.: 95-04a

Goal: The goal of this project is to develop a one-step process that uses ultra-high-surface-area metal and metal oxide particles for destroying hazardous substances, including chlorocarbons, chlorofluorocarbons, organophosphorus, nitrogen, and sulfur compounds.

Rationale: Zinc is an effective metal in the dehalogenation of chlorocarbons that contaminate groundwater. This reagent can help efficiently remove chlorinated hydrocarbons with high capacity. Trichloroethylene (TCE), one of the most common pollutants, was found to be degraded by zero-valent Zn in aqueous solutions under neutral pH conditions.

Status: During the past year, high surface area zinc metal particles were used to destroy chlorocarbon contaminants in water. We now understand a great deal about the reactions of Al, Zn, and Sn zero-valent particles with chlorocarbons in water but these reactions must be cataloged for all reactive metals in order to extend the technology to field applications. In the future we hope to test a variety of core/shell nanoparticles with shells of transition metal oxides and cores of MgO and CaO. This will help determine which combinations of metal oxides are most effective overall for treating contaminated water, and whether larger and less expensive microparticles can substitute for nanoparticles. A fixed-bed reactor for destructive adsorption of air pollutants has been constructed and experiments continue. Later, we will consider converting this fixed-bed unit into a flow reactor for treating contaminated water.

Clients/Users: United States Department of Defense and other government agencies.

Keywords: nanoscale, nanoparticle, DAT, destructive adsorption technology, metal oxide.