Excavation, Closure By Removal, and Reconstruction of Ash Ponds

SITUATION
In 2016, to meet changing regulatory requirements, a Mid-Atlantic utility was required to excavate, close by removal, and reconstruct ash ponds but needed an innovative solution to complete the first closure by removal of ash ponds in that utility.

INNOVATIVE SOLUTIONS
In order to execute this Closure by Removal (CBR) impoundment project, Charah Solutions provided a turnkey solution, meeting engineering and regulatory challenges, including all construction and QA/QC engineering.

The project had three primary components – the excavation of five unlined coal combustion residuals (CCR) ponds, construction of three new larger lined ponds within the same footprint, and construction of a state-of-the-art effluent filtration system. Construction of the new CCR ponds featured a 2’ gradient control system (underdrain system), general fill layer, 8” Soil Graded Layer, Geocomposite Clay Liner, 60-mil HDPE liner, 32 ounce geotextile, and 10” concrete paved surface. The filtration system included design, procurement, and installation of multi-disc filters, chemical feed, pumps and piping as needed to convey wastewater from the CCR basins and plant effluent through the system. The filtration system was housed in a building to protect the system from weather and enhance operation and maintenance.

CCR Removal from these ponds was accomplished by utilizing both mechanical and hydraulic dredging methods. These methods proved effective and allowed Charah Solutions to maintain both schedule and budget while also providing recovery from multiple delays associated with weather and unforeseen changes in scope.

RESULTS
The construction of the new ponds and filtration system allows the power plant to continue compliant operations for the foreseeable future. Upon completion, over 130,000 cubic yards of CCRs were successfully excavated. Furthermore, in 2017, the utility partner recognized the team for working over 150,000 manhours without a recordable or lost time incident.