This study summarizes the state of Idaho's approach to determine the suitability of reusing used tires for drainfield aggregate (drainrock) in standard subsurface sewage disposal systems and as a substitute for gravelless domed chamber systems. The used tire industry has developed alternative uses for used tires such as: a fuel supplement in incinerators, playground equipment, road building materials, marina boat dock bumpers, and for alternative daily cover at municipal solid waste landfills. Used tires are prohibited in Idaho from being disposed of in municipal solid waste landfills. The need exists to find several methods to reuse used tires because of the prohibition of landfilling tires and as an alternative to other more expensive methods of used tire disposal.
Researchers report that shredded tires do not release any significant amounts of priority pollutants. These reports provide a general indication that the use of used tires as road bed materials does not pose a risk to ground water. The use of chipped tires and half tires in drainfields has not been evaluated as to the potential for ground water contamination. This study addresses the information gap for use of waste tires in subsurface sewage disposal applications. Used tire chips as a substitute for drainrock release sulfer and zinc from the rubber, and iron from the reinforcing wire. This release of metals was not observed for the half tires placed in the gravelless domed chamber design.