Ash Pond In-Situ Stabilization CCR Field Pilot

This project was a field-scale pilot study of in-situ stabilization (ISS) for subsurface media within a coal ash residuals surface impoundment. In the ISS process, we perform reagentless drilling with various drilling fluids, until we reach the target depth interval. At the target depth, we then inject reagents, which reduces permeability and increases compressive strength.
 
To ensure the correct drilling fluid was applied at the right time and switched as needed, the project engineer, driller, and batch plant operator needed to coordinate and plan meticulously. The objectives for the pilot-scale study included evaluating reagentless drilling methods, managing the transition from reagentless drilling to grout injection, and assessing productivity and treatment effectiveness for ISS. These steps were crucial for identifying the best practices for environmental remediation.

To complete the project, we began with mobilization and site preparation. We mobilized the necessary equipment, set up project trailers, and installed access roads and decontamination pads. We then cleared, grubbed, and graded the three pilot study areas and prepared the batch plant area.

To improve site stability, we installed erosion and sedimentation controls around the pilot study areas and the batch plant area. We also installed HDPE piping for water and grout and set up the batch plant and drill rig.

For the reagentless drilling phase, we utilized a Delmag RH-28 hydraulic drill rig, which was capable of reagentless drilling and ISS treatment using both 8-foot and 10-foot augers. This advanced drill rig featured a monitoring system that could track crucial parameters such as depth, rotational speed, torque, grout pressure, flow and volume, inclination, and column deviation. 

Our system also had the capability to monitor and record the auger tip depth, verticality, as well as x and y deviations, ensuring precise and effective drilling operations. Using this equipment, we installed and sampled 30 columns with a 10-foot diameter and 15 columns with an 8-foot diameter to assess the conditions for drilling through ash without reagents.

Next, we focused on productivity by installing and sampling five sets of three overlapping 10-foot diameter columns, each with a 1-foot overlap. This allowed us to determine the production sequence and timing for efficient operations and further refine our approach to ISS soil mixing.

To evaluate treatment effectiveness, we installed and sampled three sets of seven overlapping 10-foot diameter columns. This step was crucial for assessing the effectiveness of the in-situ solidification process, a key aspect of CCR remediation.

In the site restoration phase, we removed the erosion and sedimentation controls, as well as the access roads and decontamination pads. These measures were integral to ensuring the long-term success of the environmental remediation efforts.

Lastly, we prepared a comprehensive final report. This report included detailed data from the pilot study and provided recommendations for transitioning to full-scale ISS construction, emphasizing the significance of hydraulic control and surface impoundment closure.

The success of the pilot test was instrumental in validating the effectiveness of in-situ stabilization for the project. This initial phase demonstrated that ISS could be applied efficiently and safely under site-specific conditions, achieving the desired outcomes in terms of containment and stabilization of materials.

The comprehensive data collected from the pilot test confirmed that ISS is not only a viable option but also an optimal solution for the in-place closure of coal combustion residuals (CCR) surface impoundments. 

This success highlights the project’s contribution to effective CCR remediation and underscores its significance in the broader context of environmental remediation and hydraulic control.