Missouri regulations: Stormwater

Stormwater is a major source of water pollution and therefore is regulated under the federal Clean Water Act. As rainfall or snow melt runs off buildings, sidewalks, cleared land and other hard surfaces it collects and deposits pollutants from the land and air into nearby bodies of water. “Pollutant” is a broadly-defined term that includes various chemicals or chemical compounds that can harm human health, wildlife, fish or aquatic life. It also includes total suspended solids (TSS), biochemical oxygen demand (BOD), phosphorus oil and grease.

Common stormwater pollutants from business practices include lubricants and fuels from vehicle maintenance, pesticides from grounds keeping activities, unprotected storage of materials that dissolve in water, detergents from vehicle washing and liquids from leaking aboveground storage tanks. Also regulated are sediments from construction sites of more than one acre of land.

In Missouri, the Department of Natural Resources (MDNR) regulates runoff that leaves a particular site as “stormwater discharge.” Discharges from a particular site are known as point source, while runoff from streets and residential areas is sometimes referred to collectively as non-point source pollution.

Missouri stormwater permits may be general or site-specific:

  • General permits are written for specific industrial types on behalf of a group of industries. Organizations interested in submitting a petition request for development of a general permit should contact the department for what information is needed. After the general permit is prepared, it is up to the individual facility operator to apply for a permit.
  • Site specific permits are written for businesses that store toxic materials or large amounts of potential contaminants on site that are exposed to rainfall. Site specific permits are also issued to businesses that require close monitoring or types of businesses of which there are only a few of its kind in the state. An individual facility can make application directly to the department.

Certain exemptions are written into the regulations. For example, agricultural discharges, sites that disturb less than one acre, linear, strip or ribbon construction that is routine or less than two feet in width, or landfills that have been closed under conditions approved by the department. Stormwater discharges to combined sewer systems are also exempt. Contact the MDNR or consult regulations for specific exemptions.

Who should apply for a permit?

  • Is the business undertaking a project that will require more than one acre of excavation or earth moving?
  • Will the business use storage, process or transport areas exposed to precipitation?
  • Is the business undertaking a project that involves dredging, filling or construction near a waterway or wetland?

A “yes” answer to any of these questions may indicate that the business is required to obtain a permit from the MDNR. Contact the Water Protection Program – Water Pollution Control Branch or your MDNR Regional Office.


For more information on stormwater permit requirements, see MDNR’s Environmental Permits and How to Obtain Them.