ENERCON recently completed the clean-closure of a Coal Combustion Residual (CCR) impoundment at the Oklahoma Gas and Electric (OG&E) Muskogee, Oklahoma Power Plant. The CCR impoundment was approximately 15 acres in size and was constructed with earthen dike walls integrated with a concrete liner. Phase I of the project was initiated in November 2018, and consisted of impoundment dewatering, blending and conditioning wet CCR with cement kiln dust and dry fly ash, and followed by excavation and off-site disposal. Approximately 73,760 tons of ash material was excavated, transported, and disposed to the Muskogee landfill, which is state-approved to accept non-hazardous industrial and solid wastes. ENERCON developed a traffic management plan to manage the 2,700 trailer-loads of CCR transported at an average rate exceeding 100 trucks per day through the facility to the landfill. Significant periods of rainfall during this first phase of the project required ENERCON to implement a near continuous dewatering effort of the impoundment into the plant’s water treatment system.
Phase II of the project consisted of removing the impoundment liner, which was specified as a crushed stone subbase, cement stabilized aggregate, and underlain with a bentonite clay liner. Although the original project scope required excavation and disposal of the liner to the off-site landfill, ENERCON identified an alternative approach of utilizing a concrete crusher to provide crushed aggregate (beneficial re-use) for a portion of the liner material for use within the on-site plant roads. ENERCON prepared a pollution prevention plan for the beneficial re-use and assisted OG&E with obtaining regulatory approval for changes to the closure plan. A portion of the liner that could not be beneficially re-used resulted in the transport and disposal of approximately 59,500 tons of liner material, while approximately 38,250 tons of crushed aggregate (commercial value of more than $500,000) was provided to the plant for spreading on plant roads. The revised approach resulted in a cost reduction of more than $151,000 for OG&E.
Following removal of the liner material, ENERCON performed a land survey to develop a refined estimate of the cut-and-fill needed to backfill the project site to grade. ENERCON’s proposal included importing offsite fill material for the final grade, however, the revised grading and fill plan determined that offsite fill material would not be needed. ENERCON informed OG&E that a cost reduction of more than $45,000 could be expected based on the revised grading plan.
Phase III of the project involved demolition of the dikes and concurrent backfilling / grading. Grading was nearing completion in mid-May when significant rain events in northeast Oklahoma caused historic flooding conditions at the plant site. ENERCON and subcontractor equipment was moved to high ground or moved offsite prior to flooding reaching the project area. It is estimated that the project area was flooded by more than five feet of water and the project field office was significantly flooded.
Work to complete the site grading was restarted on June 13, 2019 and was completed on June 25, 2019. The project area was then hydroseeded to facilitate vegetation growth. ENERCON conducted weekly inspections to monitor the vegetation growth and on August 21, 2109, the project area was deemed to be 80% covered in vegetation. ENERCON removed the storm water controls and reported the project complete on August 22, 2019.
The project presented several unique challenges and was a first of a kind project for ENERCON. The coordination and collaboration between OG&E, ENERCON, and ENERCON’s subcontractors was critical to ensuring the success of the project. After reporting to OG&E that the project was complete, OG&E’s Project Manager provided the following feedback:
“I have been nothing short of amazed at how your team has handled this job from start to finish. You guys knocked this out of the park. Thank you for all your efforts. Hope to be able to work with you guys in the future.”