The document provides the background for EPA's technical support for selecting and developing the proposed treatment standards for the constituents to be regulated in K043 waste. Section 2 presents waste-specific information--the number and location of facilities affected by the land disposal restrictions, the waste generating process, and waste characterization data. Section 3 discusses the technologies used to treat the waste (or similar waste), and Section 4 presents available performance data, including data on which the proposed treatment standards are based. Section 5 explains EPA's determination of BDAT, while Section 7 discusses the selection of constituents to be regulated. The proposed treatment standards are determined in Section 7.