Why were our sewers built to overflow?

When our sewers were first constructed in the 1850's, they represented a major advancement in community planning and public health. These combined sewers, which carried both sewage and stormwater in the same pipes, emptied directly into our rivers and streams to help reduce the incidence of disease and flooding in our neighborhoods. At that time, this was the latest technology, but by the early to mid 1900’s the construction of combined sewers was phased out in favor of separate sewers. Separate sewers use different pipes to handle sanitary waste and stormwater and are not as easily overwhelmed by heavy storms as combined sewers. Yet despite this change in sewer design, both types of sewer systems continue to have difficulty managing large amounts of rainwater in short periods of time and are thus prone to sewer overflows.

Even though sewer overflows are serious environmental threats, the amount of sewage discharged into our waterways has decreased drastically over the years. As noted previously, early sewer systems drained directly into local rivers and streams, which meant that all of our waste was sent untreated into the environment until the mid-1900’s. By the 1950's and 60’s, communities throughout the United States, including St. Louis, constructed wastewater treatment plants to disinfect or clean our sewage before returning it to the environment.

Now, our treatment plants clean the majority of our wastewater, but sewer overflows still remain during moderate to heavy rain storms. In the combined sewer system, increased commercial, residential and industrial development has caused a loss of green space, comprised of trees, bushes, grass and other natural elements that naturally absorb water. Roads and buildings are constructed of asphalt and concrete and these impervious surfaces do not absorb rainwater during storms.

In the separate sewer system, overflows remain because our wastewater or sanitary sewers are not designed to handle stormwater. However, stormwater often enters sanitary sewer pipes through weakened joints that connect sections of pipe and that have deteriorated over time. It also enters through cracks in the sewer pipe that develop with standard usage and age. Additionally, rainwater comes into this system when people illegally connect their downspouts and stormwater drains to nearby sanitary sewers. As with combined sewers, too much rainwater flows into the sanitary sewer system and when this happens, it overwhelms and discharges into our waterways to keep from flooding our neighborhoods and basements with sewage.