In August of 1988, the Environmental Protection Agency (EPA) published new regulations for solid waste disposal known as 'Subtitle D'. These regulations called for expensive landfill improvements, and motivated local government to examine options for solid waste disposal. In 1989, a Solid Waste Planning Group formed in Southern Idaho and met monthly to explore options to meet the proposed EPA regulations.
In 1991, Idaho legislature passed a law authorizing the formation of regional waste districts. In 1992, the Southern Idaho Regional Solid Waste District formed. Sites for the regional landfill were explored with input from the public. Construction at Milner Butte Landfill began in 1993 and opened for operation on April 6, 1994, four days ahead of federal mandate. Prior to this, counties each had their own disposal sites. In June of that year, work began to close and cap the seventeen county-owned landfills.
The SISW system currently features a state-of-the-art municipal solid waste landfill, fourteen waste transfer stations, a waste transportation system, a 3.9 MW landfill-gas-to-energy facility, an effective waste diversion system, a public information and education network, and a special waste management system for problem wastes.