As part of the U.S. Environmental Protection Agency's Nationwide Urban Runoff Program, the Municipality of Metropolitan Seattle (METRO) studied the sources and presence of toxic substances in urban stormwater runoff, as well as their potential adverse effects on local freshwater receiving environments. Sampling and analysis were designed to provide concentration data for the Clean Water Act's priority pollutant metals and organics. Sampling of potential sources to stormwater runoff included airborne particles, street dust, and catchbasin sediments. Both urban and control environmental samples were taken from interstitial streamwaters, stream sediments, and Lake Washington bottom sediments. Evaluations of toxicant control measures focused on currently available removal techniques, such as street sweeping, detention basins, and oil separators. The report incorporates a thorough literature review and includes an extensive bibliography.