The document provides the background for EPA's technical support for selecting and developing treatment standards for the constituents to be regulated in these organophosphorous wastes. For the K wastes, Section 2 presents waste-specific information--the number and location of facilities affected by the land disposal restrictions, the waste generating process, and the waste characterization data. Section 3 discusses the applicable and demonstrated technologies used to treat these wastes (or similar wastes). Section 4 presents the available performance data, including data on which the treatment standards are based. Section 5 explains EPA's determination of BDAT, while Section 6 discusses the selection of constituents to be regulated, and Section 7 presents treatment standards for these constituents. The P and U wastes are discussed in Section 8.