Georgia

Written By Robin McLamb

Coal Combustion Residuals (CCR)

Large-scale Project

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Variable Depth to Bedrock and Groundwater

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Adaptability During Installation

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Large-scale Project ● Variable Depth to Bedrock and Groundwater ● Adaptability During Installation ●


Special points and unique challenges

  • Variable depth to bedrock, depth to groundwater, and groundwater flux

  • Unanticipated space limitations at installation

    • Narrower than anticipated area of installation due to railroad right of way and delineated wetland area

    • Permit required an exact number of TreeWell Units despite limited space

    • Solution: planted trees based on depth to water, rearranged layout and spacing of units to meet permit requirement and project objectives


Depths: Approximately 15 – 25 ft bgs

Project objective: Reduction of volume of CCR below the potentiometric surface within a closed CCR surface impoundment and reduction of groundwater flux through the same closed CCR surface impoundment.

Implementation

In October 2024, a TreeWell® system was installed consisting of 254 TreeWell units planted with a mix of black willow, eastern cottonwood, American sycamore, loblolly pine, and river birch trees. The system was strategically placed downgradient of a closed CCR surface impoundment to reduce the volume of CCR-impacted groundwater discharging to a nearby stream. River birch were planted in TreeWell units closest to the stream, while other species were distributed throughout the system according to the depth at which fractured limestone was encountered during installation. Groundwater depths targeted ranged from 13 to 28 feet bgs. Five piezometers were installed in individual TreeWell units and equipped with transducers to monitor water levels.

Field implementation often requires flexibility and adaptability as unanticipated conditions arise. In this case, the installation area was narrower than expected due to a railroad right-of-way and the presence of a delineated wetland. At the same time, the project permit required installation of the full number of TreeWell units specified. To address these challenges, the project team adapted the layout by adjusting spacing and arranging TreeWell units based on depth-to-water considerations. This approach maintained compliance with the permit while still meeting the project’s remediation objectives.

TreeWell Units were installed in October of 2024. We are awaiting more detailed data and results.

Robin McLamb
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