Map of Maryland Stormwater System Coverage


Maryland Stormwater System Shapefile  (download)

Source: Maryland Department of the Environment


  • This polygon shapefile represents MDE’s estimate of total property area (i.e., storm sewer ownership) covered under NPDES regulated (permitted) stormwater entities statewide. The file does not represent land-cover within the polygons, rather it represents storm sewer ownership. Only urban pollutant loads are regulated under NPDES stormwater permits, so only the loads from these areas are included in the WLA. Therefore, there could be forested areas associated within an MS4 permit polygon, which are associated with the LA for a TMDL, rather than the WLA. The regulated stormwater permits/entities in this polygon file relate to WLAs in the applicable query via the MS4/regulated stormwater entity name, permit type, or possibly NPDES permit number.


Please direct questions or comments concerning Maryland's TMDL Program to at (410) 537-3818.​​