This paper summarizes some of the information obtained during research projects sponsored and directed by the U.S. Environmental Protection Agency's (EPA) Storm and Combined Sewer Research Program. The first phase of the project investigated typical toxicant concentrations in stormwater, the origins of the toxicants, and rain and land-use factors that influenced the toxicant concentrations. All metals investigated were found in all samples, including most filtered sample fractions. Thirteen of the base-neutral and pesticide organic compounds were found in at least ten percent of the samples. The most frequently detected organics were 1,3-dichlorobenzene (maximum concentration of 120 µg/l) and fluoranthene (maximum concentration of 130 µg/l). Both of these compounds were detected in 23 percent of the samples.

The second phase of the project investigated the control of stormwater toxicants (measured using the Microtox® screening test) through treatment unit processes. The benefits of the treatment processes varied for different samples. However, some of the treatment processes consistently provided the greatest benefits. The most beneficial treatment tests included settling for at least 24 hours (generally 40-90% reductions), screening through at least 40 µm screens (20-70% reductions), and aeration and/or photo-degradation for at least 24 hours (up to 80% reductions).

The current project phase, which is just beginning, is testing a prototype treatment device that would be useful for controlling runoff from automobile service facilities, probably the most widespread and significant toxicant source in urban areas. This device is also intended for pretreatment before infiltration of source area runoff from other areas.