Enid, OK — 2012-Present
Benzene; as well as lower concentrations of several other petroleum hydrocarbons dissolved in groundwater (0 to approximately 25 feet below ground surface).
To evaluate the potential for utilizing phytoremediation to prevent further off-site migration of VOCs by achieving groundwater hydraulic control.
The TreeMediation implementation consisted of five on-site plots of closed-liner TreeWell units which were installed in March, 2012 at approximately 20 feet below ground surface. Three weeks later, alternations of hybrid poplar, sycamore, and willow trees were planted in each unit. Root cameras were installed in the main plot, background plot, and hydrocarbon north plot to monitor the root systems of each species of tree. Fifteen piezometers and monitoring wells were installed within individual TreeWell units in the area immediately upgradient and downgradient of the plot, 12 of which were equipped with pressure transducers to measure water and barometric pressure.
Results to Date:
In the 2012 growing season, herbicide was sprayed in the field where the TreeWell plots were located, resulting in the destruction of a large number of trees, willows in particular being negatively affected. In the following years, tree growth and viability were observed to be “very good” for the entire TreeWell study. The tree health assessments do not show any significant indicators of plant stress. The height and canopy of most of the trees in the TreeWell units have continued to increase. Trees are displaying vigorous growth and, based on hydrogeologic monitoring data, are providing hydraulic capture. Preliminary hydrogeologic data suggest they are on track to perform as designed.