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Stormwater Management

MSD is two utilities in one—providing collection and treatment of wastewater generated by residential, commercial, and industrial activities, while also responsible for operation and maintenance of the separate storm sewer systems that serve approximately 90% of St. Louis County area municipalities.

Stormwater is generated when rain or snowmelt is not able to be absorbed into the ground because it falls on a hard or impervious surface, the ground is already saturated or it rains faster than the water can be absorbed. This excess water flows over the ground and then into stormwater inlets, sewers or directly to local ponds and streams. 

Unlike wastewater or combined sewers, stormwater sewers DO NOT connect to the wastewater treatment plants (WWTP). Anything that is picked up by stormwater including trash, pesticides, pet waste, etc., as it flows over yards, streets, and parking lots will make its way into nearby lakes, creeks, and rivers.

MSD owns and maintains approximately 3,000 miles of stormwater sewers and force mains, but does not own or maintain lakes and creeks. MSD is involved in helping the St. Louis region to curb water pollution by partnering with 58 municipalities (co-permittees) and St. Louis County to comply with stormwater permit requirements for the St. Louis Metropolitan Small Municipal Separate Storm Sewer System (MS4). Likewise, MSD actively works to reduce pollutants that stormwater picks up and carries into local bodies of water though the St. Louis County Phase II Stormwater Management Plan. MSD maintains public storm sewers, plans and designs improvements to stormwater infrastructure, regulates stormwater drainage and floodplain impact related to development projects, and helps coordinate regional efforts to address pollution carried in or caused by stormwater runoff.

Good water quality is important. Our goals are to balance water quality protection and Clean Water Act (CWA) compliance with economic growth and help provide a sustainable path to stormwater management for our region.