Combined Sewer Overflow

Combined sewer (CS) systems are integrated underground sewerage systems that carry both domestic and industrial sewage and periodic stormwater flows. Most of these systems were built in the 19th and early 20th centuries, when population densities were lower and extreme weather events less frequent. In American cities, where such infrastructure was often financed through public bond issues, the relative cheapness of building CS systems also worked to favor their proliferation. Most U.S. and European jurisdictions now prohibit the construction of new CS systems, and various strategies are being implemented to make them fit for use in the 21st century. Climate change, the inexorable aging of the underground infrastructure, and continued urban expansion are likely to negatively affect CS systems, increasing the frequency and intensity of ...