Sedgwick County is currently allowed to discharge stormwater to waters of the United States through its Municipal Separate Storm Sewer System (MS4 - inlets and pipes, as well as open ditches, which discharge to waters of the U.S. and are owned and maintained by Sedgwick County). This is possible due to our Kansas Water Pollution Control General MS4 Permit and Authorization to Discharge under the National Pollutant Discharge Elimination System (NPDES).
Essentially, the NPDES is a permit program managed by the Environmental Protection Agency.