CT ECO Basic Data Guide

Stormwater Impaired Waters 2016

Connecticut 303(d) Impaired Waters 2010

Description and Purpose

The stormwater impaired waters layer is based on the 2016 Connecticut Integrated Water Quality Report (IWQR). All waters (rivers, lakes, estuaries) that were listed as impaired (EPA Category 5) in Table 3-4 of the report and all waters that were listed as having an adopted TMDL in place in Table 3-5 were identified.  Both lists were then compared to the Impaired Waters guidance in Appendix D of the 2017 General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems Reissuance with Modifications.

Waters with adopted TMDLs in the 2016 IWQR for the pollutants of concern listed in Appendix D (phosphorus, nitrogen, bacteria, mercury) of the General Permit were then identified and added to the Stormwater Impaired Waters layer.

Waters without a TMDL in the 2016 IWQR were evaluated for causes that matched the causes listed in Appendix D for each pollutant.  In addition, any water without a TMDL that mentioned stormwater as a potential cause was identified. These waters were then added to the Stormwater Impaired Waters layer. Waters in Table 3-4 of the IWQR that indicated any of the causes listed for Phosphorus or Nitrogen were listed as impaired for Phosphorus and Nitrogen per DEEP decision.

The resulting list of stormwater impaired waterbodies were then matched up with the Connecticut 303(d) Impaired Waters 2016 (rivers, lakes and esturaries) waterbody features using the waterbody id. Information including stormwater pollutant of concern, cause, impaired designated use and TMDL can be identified by clicking on the layer(s) in the MS4 viewer or with the identify tool in a desktop application.

Connecticut 303(d) Impaired Waters 2010 is a subset of Connecticut 305(b) Assessed Waters 2010. If one of the designated uses is categorized as not Fully Supporting the assessed waterbody is considered impaired. Additional information about Integrated Water Quality reporting is available at the CT DEEP website.

Using this information in the CT ECO Map Viewers

This information is available in the MS4 Map Viewer and on the Connecticut MS4 Guide website.

Dataset Information

  • Status - No plans to update
  • Date of Data - Based on information collected and compiled prior to 2016
  • Map Scale and Accuracy - The information meets horizontal National Map Accuracy Standards for 1:24,000-scale mapping (1 inch = 2,000 feet).

Additional Documentation


GIS Data Download

  • Connecticut 305(b) Assessed Waterbodies data is downloadable from DEEP GIS Data.
  • Connect GIS and AutoCAD software to this information online using the Water Resource Management CT ECO Map Service.