In August 1988, the U.S. Environmental Protection Agency proposed Solid Waste Disposal Facilities Criteria (40 CFR Part 258) for municipal solid waste landfills. The background document 'D' - Design Criteria of Part 258. The document contains a discussion of background information leading to the development of the categorical rule option, and provides detailed information on the revised design criteria. The document discusses the general development of the design criteria while specifically addressing the following items; the various design options considered by the Agency, how the design standard was selected and alternatives considered, how location specific considered ions are involved in the design standard, and what methodologies are available for meeting the design performance standard. The document also provides a discussion of landfill designs, specifically addressing such items as liners, leachate collection systems, and final covers.