Many urban drainage systems convey both wastewater and stormwater. These systems are called Combined Sewers. Relief points are located within the sewer systems that discharge excess flows directly into rivers, streams and creeks during intense rainfall. These relief points are known as “Combined Sewer Overflows.”

During periods of heavy rainfall, Combined Sewer Overflows discharge floatables, sediments and gross pollutants into the environment, impairing water quality.