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The 2017 Municipal Separate Storm Sewer System (MS4) General Permit regulation includes several mapping requirements. New and existing statewide data layers are compiled here to assist municipalities and institutions in complying with the permit requirements.

CT DEEP has funded the acquisition of a new statewide impervious layer (based on 2012 imagery) that may be useful in calculating directly connected impervious area and tracking disconnects of impervious cover. UConn CLEAR has used this data to create both an impervious cover by basin and an impervious cover by town layer. The 1 foot resolution data contains three classes (buildings, roads and other impervious).

UConn CLEAR has also created an impaired waters layer that highlights only stormwater related impairments.

For more information, visit the MS4 website at NEMO or email nemo@uconn.edu.

CT MS4 Viewer

The CT MS4 Viewer includes data layers that are helpful in registering for and complying with the 2017 CT MS4 General Permit.

2012 Impervious Surface

Statewide raster (1 foot) and vector data of impervious surface (roads, buildings, and other).


NEMO is the Nonpoint Education for Municipal Officials Program, a part of the UConn Center for Land Use Education and Research (CLEAR).

Map Services

for advanced users
On the Map and Image Services page, look for
Built Environment.

Layer Information

Data Guide Metadata Download Map Services (click on Built Environment)
CT 2012 Impervious Surface
(more info & download)
- Impervious: Impervious_2012*
Impervious: Impervious_2012_StatePlane*,
Impervious: Impervious_2012_simplfied_vector_StatePlane
CT 2020 Stormwater Impaired Waters
(Rivers, Lakes, Estuaries)

MS4_layers: CT2020_Impaired_Rivers
MS4_layers: CT2020_Impaired_Lakes
MS4_layers: CT2020_Impaired_Estuary
CT 2018 Stormwater Impaired Waters
(Rivers, Lakes, Estuaries)

MS4_layers: CT2018_Impaired_Rivers
MS4_layers: CT2018_Impaired_Lakes
MS4_layers: CT2018_Impaired_Estuary
CT 2016 Stormwater Impaired Waters
(Rivers, Lakes, Estuaries)

MS4_layers: CT2016_Impaired_Rivers_V2
MS4_layers: CT2016_Impaired_Lakes_V2
MS4_layers: CT2016_Impaired_Estuary_V2
CT DEEP Basins with 2012 Impervious Stats - MS4_layers: Impervious Cover by Watershed Basin
CT DEEP Basins (clipped to town boundaries) with 2012 Impervious Stats - MS4_layers: Impervious Cover by Watershed Basin (Clipped)
CT Towns with 2012 Impervious Stats - - - MS4_layers: Impervious Cover by Town
CT MS4 Urbanized Area - - - MS4_layers: Urbanized Area
CT MS4 Towns - - - MS4_layers: MS4 Towns

Impervious Surfaces Classes

1 Buildings Permanent structures larger than 800 square feet.
I. Buildings and structures and greenhouses >800 square feet.
II. Excludes temporary structures such as mobile storage units.
III. Include mobile homes, structures under construction.
IV. All buildings completed or under construction, contained in the imagery will be captured. Buildings will be delineated to the maximum degree possible from the imagery.
2 Roads Any vehicular cart way including, but not limited to alleyways, paved roadways, bridges and tunnels and private roads within commercial, industrial, institutional, and residential complexes.
I. Road to edge of pavement including gravel shoulder.
II. Gravel roads.
III. All transportation routes that are hard paved to loose gravel.
IV. Driveways are excluded from this class.
3 Other Impervious Driveways, parking lots, and impervious features that are not vehicular cart ways such as sidewalks.
I. All paved or heavily compacted areas not included in roads class.
II. Bare soil is generally not considered impervious even when it is in a driveway situation.
III. Included are parking lots, sidewalks, driveways, patios, swimming pools (in-ground and above-ground), pool decks, park walkways, concrete pads.
IV. Excluded are grass, water, forest when not covering impervious, wetlands, bare soil (even when compacted), railways, baseball fields, running tracks and green roofs.