The Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health (2000) (USEPA, 2000) presented technical guidance and the steps that EPA follows to derive new and revised national recommended ambient water quality criteria (AWQCs) for the protection of human health under Section 304(a) of the Clean Water Act. Water quality criteria define the maximum levels of a pollutant necessary to protect designated uses in ambient waters. For chemicals that bioaccumulate, water quality criteria also describe the maximum advisable concentration of a chemical in freshwater and estuarine fish and shellfish tissue to protect consumers of fish and shellfish among the general population. The 2000 Human Health Methodology included guidance on chemical risk assessment, exposure, and bioaccumulation. To supplement the 2000 Human Health Methodology, EPA is developing a series of Technical Support Documents (TSDs) on Risk Assessment, Exposure Assessment, and Bioaccumulation. The first volume, Volume 1: Risk Assessment (EPA-822-B-00-005), was published with the 2000 Human Health Methodology in October of 2000.