MS4 Map


  • View the map legend
  •  View additional data layers
  •  Change the basemap
  •  Add data
  •  Additional functions, including printing, sharing, drawing, and measuring
  •  View data table
  • Click here for a larger version of this map
  • Most layers can be downloaded from the MS4 section of CT ECO.

We compiled existing and new data layers in the MS4 map viewer to help municipalities meet several MS4 permit requirements. You can use this map to:

1. Find the impaired waters in your area.

The impaired waters that count for the MS4 General permit are a subset of the full impaired waters list that DEEP produces and submits to the EPA every two years. The impaired waters layers in this map only include the impaired waterbodies relevant to the MS4 permit.

About the impaired waters data on this map:

  • It's divided into three layers: 2016 CT Stormwater Impaired Estuaries, 2016 CT Stormwater Impaired Lakes and 2016 CT Stormwater Impaired Rivers.
  • Areas that discharge to the red waterbodies are part of your priority areas (more on priority areas below).
  • The requirement to sample outfalls to impaired waters (permit page 41) applies to both red and purple waterbodies.

2. See how much impervious cover is in your town and your watersheds.

The Statewide Impervious Cover (2012) data is new! It's a statewide 1 foot resolution impervious cover dataset and it separates IC into buildings, roads, and other impervious. You can download the data at CT ECO.

We created two layers from this dataset to help with MS4 compliance.

  • IC by DEEP Basin: Click on a basin in your town and a pop-up window will display impervious cover data for that basin. This can help with determining priority areas (more on priority areas below).
  • IC by Town: Helps with estimating your baseline DCIA (see Mapping under the Implementation section for more guidance).

3. Get a quick sense of where your priority areas are.

Use the Urbanized area layer + Red Stormwater Impaired waterbodies + IC by DEEP Basin to estimate your priority area.