What is Combined Sewer Overflow (CSO)?
Some communities collect both rainwater runoff and sanitary wastewater in the same sewer. these are called “Combined Sewers”. Sometimes when it rains, sewers do not have enough capacity to carry all the rainwater and wastewater and the treatment plant is not large enough to treat the total combined flow. In these situations, the combined wastewater overflows into the nearest body of water – streams or rivers, creating a combined sewer overflow. Why are there CSO’s? Much of the DELCORA sewer system, particularly in the city of Chester, was built in the early 1930’s Back then sewage was disposed simply by allowing it to be directly discharged into streams and rivers. These sewer lines also carried storm water runoff to rivers and streams. Concern for water quality and public health led to the construction of the DELCORA system in the 1970’s . The old river/stream discharge systems were left in place to act as relief valves to prevent sewage from backing up into peoples homes during storm
