Over a 21 year period, several remediation methods were used for the cleanup of chlorinated solvents dissolved in groundwater at an oilfield pump manufacturing facility in Claremore, Oklahoma. These methods included soil excavation and off-site disposal, air sparging/soil vapor extraction, groundwater circulation wells, high vacuum multiphase extraction, carbohydrate injection and throughout the project’s history, the current pump-and-treat system. The primary chemicals of concern (COCs) include trichloroethene (TCE); 1,1,1 trichloroethane (TCA); and associated degradation products. Due to challenging hydrogeologic conditions and the nature of the contaminants, only a modest improvement in groundwater quality has been achieved. Even with the significant historical remediation efforts and considerable expenditures, there was no foreseeable end point. The company objective is to reduce the contaminant concentrations and to assure that no off-site contaminant migration can occur which might impact sensitive receptors. The company sought a sustainable solution that would not involve continued expensive remediation system operations and maintenance.

The remediation strategy was evaluated and revised to include engineered phytoremediation as a primary component. In March 2012, 52 trees were installed within large diameter boreholes for groundwater hydraulic control and in situ treatment.

This paper presents the challenges and solutions for drilling and completing the tree installations in highly variable fractured shale and sandstone within the constraints of tight spaces at a busy operating plant. Preliminary data concerning tree health, growth and hydrologic effects are presented. This evaluation includes the varying mortality of bare root versus potted trees and the importance of staking the trees in the strong Oklahoma winds. During the first growing season, the tree roots reached and began using groundwater, enabling them to survive an unusually hot and dry summer.

Once the trees are more fully established, phytoremediation is expected to provide a sustainable and cost effective remedial alternative to the long-term groundwater pump-and-treat system. Its successful application at this site opens up the possibility for using phytoremediation at other challenging fractured rock sites.

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