Integrating Phytoremediation, Wetlands, Spray Irrigation, and Prairie Restoration
to Treat Carbon Tetrachloride Contamination in a Rural Community  

Lorraine M. LaFreniere*, M. Cristina Negri †, Y. Eugene Yan*, and Robert A. Sedivy*,
*Environmental Research Division and †Energy Systems Division, Argonne National Laboratory;
Steve Gilmore and Don Steck, U.S. Department of Agriculture;
Peter Kulakow, Stacy Hutchinson, and Larry Erickson, Kansas State University

Grain fumigation activities in the 1950s and 1960s at a former U.S. Department of Agriculture (USDA) grain storage facility in Nebraska resulted in carbon tetrachloride contamination in public water supply wells and in groundwater that exits to surface water in a downgradient creek tributary. Contaminant levels in both groundwater and surface water exceed regulatory limits and require mitigation. Contamination extends to approximately 75 feet below ground level, with the highest concentrations at the base of a sandy aquifer unit.

Investigation of a number of remedial technologies led to an integrated approach combining (1) seasonal groundwater extraction and treatment by a modified spray irrigation system near the source with (2) phytoremediation augmented with a constructed wetland and other features downgradient. The contaminant plume emanating from the former storage facility is now under the town and adjacent fields and is moving into the creek tributary. Extensive modeling indicates that the integrated approach will be effective in mitigating the contamination with little disruption to the community — and with actual benefits.

Immediate technical objectives are as follows:

• Conceptual Design. Develop a conceptual design that
• Is technically defensible — because it reflects the current hydrologic characteristics of the aquifer, the patterns of groundwater flow, and the contaminant distribution in groundwater and surface water;
• Benefits the community — by enhancing wildlife habitat, stabilizing the stream, and restoring a local prairie; and
• Achieves compliance and protection — by reducing contaminant levels to the accepted standard and protecting the water resource from further degradation.
• Extraction and Spray Irrigation. Apply a modified spray irrigation-extraction well system to mitigate the high-concentration, deeper parts of the plume, with beneficial reuse of the treated water for irrigation of recreational lands.
• Phytoremediation. Design an engineered phytoremediation system for further mitigation of groundwater contamination in the downgradient, shallower parts of the plume.
• Purposes:
• Augment current natural plant uptake of water and entrained carbon tetrachloride.
• Promote contaminant breakdown to prevent further degradation of surface water quality in the creek tributary.
• Features:
• Deep-rooting plantings that act as individual pumps, drawing water from target zones in the contaminant plume and intercepting the contaminated groundwater at approximately 20–25 feet below ground level, before it reaches the creek.
• Riparian buffer along creek banks that prevents or retards mixing of contaminated groundwater with uncontaminated surface water.
• Augmented wetland for additional polishing of contaminated water, as well as to contain and treat flow from major precipitation events.
• Stabilized stream bank.
• Surface vegetation cover (native prairie plants) to capture uncontaminated soil moisture in the vadose zone

Guiding the conceptual design are computer flow modeling and mass transport modeling to simulate the current distribution of carbon tetrachloride, characterize contaminant migration pathways, estimate water budgets, and establish criteria for eventual testing of the selected design for expected performance. Implementation of the remedial design will occur in a phased approach in collaboration with the USDA, the U.S. Environmental Protection Agency, and the Nebraska Natural Resources Conservation Service, beginning in the spring of 2005.