Ash Pond Closure

Phillips Contribution

Phillips was responsible for bulk dredging using cutter suction equipment in the main ash pond, re-handling the material in the surge pond, and redirecting the dredgeate to the ATP operated by Southern Company Services and Alabama Power. The scope of work also included pond water management related to the overall pond water elevation and miscellaneous cleaning and removal of ash around the pond perimeter. A floating barge platform with long-reach excavator was utilized for the following:   

• Removing obstructions (clay roads, geotextiles, trees, rocks, and other foreign materials) within the pond.

• Clean ash from the slopes while directing the material to the dredge for final removal. 

• Excavation of 6:1 design slopes for ash stability in the closure area. 

CHALLENGES & SOLUTIONS  

The ATP is designed for specific ranges (total flow rate and solids density) of slurry delivered to the plant. Providing slurry to the ATP plant at the specified feed rate and density range is challenging. Phillips initially worked with our dredge manufacturer to provide automated slurry delivery to the ATP using densitometers and flow meters. These instruments were incorporated into our new dredge pumping system to control the pumping flow rate (gpm) automatically and automatically raise/lower the pump within the ash column to provide the correct percentage of solids in the slurry feed at the designated flow rate. This automation should have provided more accurate control of the feed matrix and enabled the ATP to operate as efficiently as possible; however, the CCR material in the surge pond did not react to the pumping as we had forecasted. We anticipated the ash would “flow” to the pumps as material was removed, and the slopes would remain relatively gentle. The material was not loose and did not run towards the pumps. Steep vertical walls were created in the process, which meant much more movement was necessary, and we realized the Dragflow pumping system would not consistently fluidize the ash as we thought. The Dragflow pumps could not provide consistent production to the ATP because the material had to be “attacked” to fluidize. Things would have worked out as planned if the material had been loose and “run” to the pump. We abandoned the surge pond concept and hooked the main dredge(s) directly to the ATP. 

Much work was done to reconfigure the surge pond for direct feed from the main pond dredges to the plant. We removed both booster pumps from the Dragflow dredges (surge pond) and placed them on land to boost the dredge feed up to the plant. HDPE piping was relocated, and the electrical feed system was modified, all while continuing to run material to the plant. One major drawback to direct feeding the ATP was that we had to limit the dredge feed volume since the ATP was limited to about 10,000 gpm. Our main dredges can provide up to 16,000 gpm at standard capacity. 

Another challenge Phillips faced was with the ATP operational time. There were several plant components that have failed to provide adequate service life. These maintenance issues led to numerous plant outages over the life of the project. To circumvent downtime, we were allowed by the client to dredge directly to portions of the closure area (F1) that were submerged. This allowed us to continue working even when the plant was not operational. At the end of 2023, Southern Company stopped running the ATP and developed dredge cells in the ash closure area. Ultimately Southern Company abandoned the ATP and used dredge cells located on the ash pond closure footprint to place the dredged ash material. From January 2024 until the end of our contract, Phillips dredged another 1,998,000 CY of ash to dredge cells (provided by others).