About 860 communities in the US have combined sewer systems, serving about 40million people. Pollutants from CSO discharges can include bacteria and other pathogens, toxic chemicals, and debris. These pollutants have also been linked with antimicrobial resistance, posing serious public health concerns. The U.S. Environmental Protection Agency (EPA) issued a policy in 1994 requiring municipalities to make improvements to reduce or eliminate CSO-related pollution problems. The policy is implemented through the National Pollutant Discharge Elimination System (NPDES) permit program. The policy defined water quality parameters for the safety of an ecosystem; it allowed for action that are site specific to control CSOs in most practical way for community; it made sure the CSO control is not beyond a communitys budget; and allowed water quality parameters to be flexible, based upon the site specific conditions. The CSO Control Policy' required all publicly owned treatment works to have "nine minimum controls" in place by January 1, 1997, in order to decrease the effects of sewage overflow by making small improvements in existing processes. In 2000 Congress amended the Clean Water Act to require the municipalities to comply with the EPA policy.