Special Report No. 94-07: Human Perception and Biological Impacts of Kraft Mill Effluent Color

This report contains an analysis of (a) the extent of increases in in-stream color attributable to kraft mill discharges as of 1992, (b) the aesthetic and biological significance of these increases, and (c) the extent to which effluent color discharges are already being addressed by state or local regulatory agencies. The published literature, reviewed in this report, indicates that threshold levels for aesthetic effects are well below those sometimes associated with effects on aquatic life. A mill-by-mill analysis of in-stream color increases indicates that at 30Q5 river flow, only 21 mills are located on rivers where color change due to mill effluent has the potential to be clearly visible (i.e. greater than 50 color unit increase.