The U.S. Environmental Protection Agency's (EPA) Office of Toxic Substances (OTS) evaluates submissions to the Premanufacture Notification (PMN) process under section 5 of the Toxic Substances Control Act (TSCA). Azo dyes constitute a significant portion of these submissions. OTE is concerned because some of the dyes, dye precursors or their degradation products such as aromatic amines, which are also dye precursors, have been shown to be, or are suspected to be, carcinogenic. The objective of the study is to dose pilot plant ASP systems with various azo dyes and monitor each dye compound through the system, analyzing both liquid and sludge samples.