Phytoremediation of PAH-Contaminated Groundwater: Contaminant Remediation and Hydrologic Control

Problem:

The usefulness of phytoremediation as a remedial strategy to clean-up groundwater contamination has not been rigorously identified. This research effort provides the opportunity to evaluate phytoremediation as a remedial tool. A potential solution that could help resolve this dilemma would be the application relatively low-cost but effective remediation technologies that would be restorative of contaminated groundwater and protective of surface waters. The use of phreatophytes, or plants that use subsurface sources of water, has been shown to be a relatively low cost and low maintenance technology (phytoremediation). Phreatophytes, such as grasses, shrubs, or trees, can specifically be installed to affect the site groundwater hydrology and to take up contaminants dissolved in groundwater (Landmeyer, 2001). Thus, using phreatophytes in this manner could be a cost-effective strategy to remediate contaminated groundwater and be protective of downgradient surface-water systems.

Objectives and Scope:

Objectives of this study are to:

1. Determine hydraulic containment of planted trees
2. Determine if planted trees reduce contaminant levels

Approach:

1. Use pressure transducers to evaluate changes in water and air pressure caused by trees
2. Measure contaminants in wells upstream and downstream of planted poplars

The approach of this proposed investigation consists of determining if phreatophytes can (1) decrease groundwater contamination, and (2) decrease unsaturated zone contamination to reduce the risk of transport to adjacent surface water. Although phreatophytes that use copious quantities of groundwater are most frequently associated with the arid deserts of the states of the Southwestern US, they also are found naturally along floodplains in the more humid Southeast (such as river birch and sycamore). In such areas, their influence of local water budgets is more prominent during times of drought. As would be expected, trees in these areas also can use surface water and recent rainfall to meet evapotranspirational demands. At sites characterized by the potential for contaminated groundwater discharge to surface water, the existing plants are typically not dense enough to achieve significant reductions in groundwater contaminant concentrations or flow necessary to reach remedial goals within realistic timeframes. The engineered installation of phreatophytes, however, permits sufficiently dense plantations of phreatophytes to affect groundwater flow, contaminant concentrations, and subsequent reduction in the potential for contaminants to be discharged to surface water.

The most important aspect of this proposed investigation is the collection of the performance data necessary to document the affect of plants on groundwater and unsaturated zone contaminant levels.