The coal ash and sludge pond at the Apache Generating station near the Willcox Playa has a liner designed to keep any materials from flowing down an earth fissure into underlying ground waters. [right, location of earth fissure, pond, and power plant. Credit, Keaton et al, AEG SP 8]
Ever since the collapse of the TVA coal ash impoundment in Tennessee a few weeks ago, Congress and others are looking at increasing regulations on these facilities. News stories report that ash ponds in many locales are not regulated or done so, minimally.
The earth fissure was discovered in 1993 and subsequent geotechnical studies convinced AZ Dept. of Environmental Quality that a proposed ash sludge pond could be constructed safely. The original pond design was for a geomembrane under the entire pond. Subsequently, that was modified to add a second geomembrane liner over the earth fissure and extending across the pond site. It was built in 1994.
The geotech study (Geomechanical Analysis of an Earth Fissure Induced by Ground-Water Withdrawal for Design of a Proposed Ash and Sludge Impoundment, Southeastern Arizona) was published by Jeff Keaton, Mike Rucker, and Suange Cheng in:
Land Subsidence Case Studies and Current Research; Proceedings of the Dr. Joseph F. Poland Symposium on Land Subsidence, - Association of Engineering Geologists Special Publication No. 8, 1998.