Project Abstract

Plant-Assisted Remediation of Soil and Groundwater Contaminated by Hazardous Organic Substances: Experimental and Modeling Studies

Principal Investigators

Lawrence C. Davis
Kansas State University
E-mail: ldavis@ksu.edu

Larry E. Erickson
Kansas State University
E-mail: lerick@ksu.edu

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.