What is a stormwater outfall and how does it affect water quality?
A. Stormwater is runoff water from rain or snow. Stormwater flows into underground sewers (typically a Municipal Separate Storm Sewer System, or MS4) that outfall into a waterway (e.g. river, stream) or in certain cases to a sewage treatment plant. In a wet weather event, when flow volume exceeds the capacity of the treatment plant, the stormwater overflows into the receiving water. While stormwater overflows do not include sanitary waste, they carry high levels of floatables and can also include pollutants such as pathogens, nitrogen, phosphorus, sediment, heavy metals, pesticides, herbicides, and synthetic organic compounds. Stormwater discharges also pose a threat to aquatic ecosystems by physically altering the receiving waterbody.
