Closure of a Wastewater Treatment Impoundment Using Ash and Multi-Layered Geogrid, 2002 Environmental Conference Proceedings

P. Dohney, K. Nilsson, L. Growney and A. Zhao -- The Mead Corporation has considered closing unlined wastewater treatment impoundments, including a 2.8-hectare (7.acre) strong waste pond at the Mahrt, Alabama, mill. The Mahrt strong waste pond contains a mixture of spent liquor, fiber and some ash. In addition to receiving the occasional liquor spill material, the pond receives some storm water. The pond is frequently covered with some depth of water, and any exposed solids are typically weak and unstable.

The pond would be closed under guidelines promulgated by the Water Division of the Alabama Department of Environmental Management (ADEM). One requirement stipulates that any cap should maintain a minimum slope of 5 percent.For the 2.8-hectare (7-acre) impoundment, this would require significant earth fill volumes. However, the guidelines allow some variance in the stipulated closure approach, provided that the closure method used will achieve equal or better protection of the groundwater than Alabama Department of Environmental Management’s (ADEM.s) prescribed closure method. Mead.s proposed concept involved the use of ash as a construction material in covering the solids in place. Ash would be used as a fill to allow the landfill operator to construct the cover incrementally, without double handling of material. This would save significant construction costs and preserve valuable landfill airspace.

A demonstration project for the closure concept was performed using ash and a multi-layer geogrid for bridging the soft solids. The closure strategy was demonstrated successfully, and a closure concept was developed.