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Water: Stormwater

Discharge Mapping Tool

The new Discharge Mapping Tool is designed to help you to determine the receiving waters to which you discharge, and to determine whether the waterbodies to which you discharge are considered "impaired" under Section 303(d) of the Clean Water Act.  The Discharge Mapping Tool uses the National Hydrologic Dataset Plus (NHDPlus) catchment datalayer and NHD waters indexed with Section 303(d) listing and TMDL information for analyzing whether a project is located with the catchment of an impaired water, and therefore discharges to that impaired water.

This tool will assist you in filling out the required receiving waters information on your Notice of Intent (NOI) for the EPA Construction General Permit (CGP) or the Multi-Sector General Permit (MSGP).  This tool can also be useful for determining general receiving waters information for other purposes.

To use the Discharge Mapping Tool, follow the steps listed below.

Step 1:  Enter the location of the site/facility.  In the box below, enter in the address or latitude/longitude of your site/facility and then click "Go".

Step 2:  Draw your site/facility or discharge point locations on the map.  On the map that appears, zoom in to your site/facility location. Using the “Draw Fixed Polygon” or the “Draw Freehand Polygon” button at the top of the map, draw an outline of your site/facility. Or, if you know your site/facility's exact discharge point(s) (i.e., outfalls), draw the point(s) using the “Draw Point” button where your site/facility will discharge.

Step 3:  Click "Execute Query" at the bottom of the map to determine your discharge information. Once you click "Execute Query", the mapping tool will provide an output table that includes information about the surface waters to which you discharge, including any surface waters to which you discharge that are impaired and the pollutants for which they are impaired, and any surface waters to which you discharge that have a TMDL and the pollutants for which there is a TMDL.

Note: If multiple points or polygons are selected, all of them will be processed upon clicking "Execute Query". To delete a point or polygon, select the point or polygon and then click "Delete Shape". Alternatively, to remove all points and polygons, click on "Clear All Points/Polygons". To save the map, click on "Save Map for Later". This will create a unique link that can be bookmarked or shared with others that contains all the points and polygons that were defined. Upon navigating to that link, the defined points and polygons will be automatically populated on the map.


The discharge mapping tool requires JavaScript to function. For assistance in obtaining data, email cgp@epa.gov.


For more information about the Discharge Mapping Tool, refer to this guidance document. For questions or comments about this tool, email cgp@epa.gov.

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