A large number of pharmaceuticals and personal care products (PPCPs) have been found in U.S. surface waters. These compounds are part of a growing class of pollutants known as emerging contaminants, chemical compounds or organism only recently found in significant proportion in surface and groundwaters. Research has shown that these compounds can enter the environment, disperse and persist to a greater extent than first anticipated (Kolpin et al. 2002, 1202-1211).Wastewater treatment plants are a common source of emerging contaminants in waterways because some emerging contaminants are difficult to remove in conventional wastewater treatment systems. Stormwater runoff is known to carry some of these emerging contaminants, such as pesticides and PAHs from non-point sources, plus pharmaceuticals from pet wastes, and possibly other PPCPs. In most areas, some runoff enters sanitary sewer lines through inflow or infiltration and consequently enters the wastewater treatment system. This additional stormwater increases the volumes and flow rates and changes the characteristics of the influent to the wastewater treatment plant, factors that may detrimentally affect treatment plant performance. This EPA-funded research is focusing on wet weather flow contributions of emerging contaminants, including their treatment, at municipal wastewater treatment plants during wet weather when the flows are substantially greater than during normal dry weather conditions.