Wet Weather System Overview

Ever wonder what happens after you flush? The City of Springfield has a sanitary sewer system, consisting of pipes and treatment facilities to transport and treat wastewater. Wastewater is the used water that goes down toilets, sinks, and drains. Parts of the City are served by a separate sanitary sewer system and a separate stormwater system. In these separated systems, one set of pipes carries wastewater and a separate set of pipes carries stormwater.

When the City was first built, it was common practice to build sewers to transport both wastewater and stormwater in the same pipe. This type of arrangement is called a combined sewer system.

The figure below shows the three types of sewer systems:


Separate Sanitary Sewer System

The separate sanitary sewer system, as displayed by the light green pipes in the Urban Wet Weather Flows diagram, collects the wastewater from individual homes and businesses and transports it through a series of pipes to the wastewater treatment plant. At the plant, wastewater is treated and released into a stream or river called the receiving water.

Stormwater System

The City also has a system of culverts, drains, and pipes to carry stormwater to streams and rivers. Stormwater is rainwater and snowmelt that runs off rooftops, streets, and parking lots. The separated storm sewer system (as shown by the light blue set of pipes in the diagram) collects the rainwater and snowmelt from street catchbasins and roof drains and carries it directly to the receiving waters.

Combined Sewer System

The combined sewer system (as shown by the dark blue set of pipes in the diagram) collects wastewater and stormwater in the same pipe system. The combined wastewater and stormwater is carried to the treatment plant for treatment before being discharged to the receiving waters. During heavier storms, some combined wastewater and stormwater is diverted to the receiving waters. This is called a combined sewer overflow or CSO.

Every year, millions of gallons of raw sewage – mixed with stormwater – overflow from our sewers into Buck Creek, Mill Run, Mill Creek and Mad River. This is not an accident or oversight, but the result of a sewer system designed to meet the needs of an earlier generation, not our modern society. Overflows were considered at the time they were designed and built as a best engineering practice, which was long before current environmental regulations.

Click here for a list of CSO locations in Springfield.

Initial Solutions

The U.S. EPA has mandated that the City start new practices and projects to manage its stormwater runoff and to capture, treat, or remove all of the CSO’s. Currently it is expected that the City will be required to meet this mandate over a series of improvements to be built in multiple phases.

Phase 1 started in 2012 and included plant upgrades and the building of a “high rate treatment (HRT) facility”. A high rate treatment facility is essentially a mini treatment plant that is capable of providing primary treatment at a much higher flow rate. This will allow polluted stormwater and wastewater that currently overflow to the Mad River to be diverted to receive primary treatment.

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