Residual Designation in the Charles River Watershed, Mystic River Watershed and Neponset River Watersheds

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Record of Updates on Residual Designation Authority Activities in the Charles, Mystic, and Neponset River Watersheds

Petitions to Designate Certain Properties in the Charles River Watershed, Mystic River Watershed and Neponset River Watershed

On May 9, 2019, the Conservation Law Foundation (CLF) and the Charles River watershed Association (CRWA) submitted to the Regional Administrator of EPA Region 1 a "Petition for a Determination that Certain Commercial, Industrial, Institutional, and Multi-Family Residential Property Dischargers Contribute to Water Quality Standards Violations in the Charles River watershed, Massachusetts, and that NPDES Permitting of Such Properties is Required." On August 24, 2020, CLF followed this submission with two additional petitions requesting the same residual designations for two other watersheds in Massachusetts: the Mystic River watershed and the Neponset River watershed. The three petitions call for "a determination pursuant to 40 C.F.R. § 122.26(f)(2) that discharges of stormwater that are not currently subject to direct permitting by EPA from privately owned commercial, industrial, institutional, and multi-family residential real properties of one acre or greater" in the Charles River, Mystic River, and Neponset River watersheds "contribute to violations of water quality standards" in the Charles River and Boston Harbor, of which the Mystic River watershed is a sub-basin, and (3) the Neponset River, "and require permits under the National Pollutant Discharge Elimination System ('NPDES')." The petitions can be found here:

EPA's RDA Designation for the Charles River, Mystic River and Neponset River Watersheds

On September 14, 2022, EPA exercised its residual designation authority in response to the water quality impacts caused by stormwater discharges in all three watersheds as well as responding to the petitions received for the three watersheds. EPA's action will supplement a watershed-wide approach that already includes significant decades-long investments by municipalities to comply with their Municipal Separate Storm Sewer (MS4) permits; wastewater treatment plant upgrades in the region, including the creation of the new Deer Island treatment plant; the near-elimination of combined sewer overflows (CSOs); and intensive efforts to find and eliminate illicit discharges of sewage into stormwater systems. Cities and towns in these three watersheds have made significant efforts to reduce phosphorus in municipal stormwater and are subject to permits that will require them to do much more in coming years. A significant portion of the phosphorus load also comes directly from privately-owned or unregulated sources, and residual designation could provide a mechanism to reduce the load from these sources, complementing the work municipalities are doing on municipal property under their MS4 permits.

More information is below:

Notice of Preliminary Designation of Certain Stormwater Discharges in the Commonwealth of Massachusetts and Notice of Availability of Draft Permit Under the National Pollutant Discharge Elimination System of the Clean Water Act

THE PUBLIC COMMENT PERIOD FOR BOTH OF THESE PROPOSED ACTIONS IS CLOSED AS OF 11:59 PM MARCH 17, 2025.

The Environmental Protection Agency ("EPA") provided notice of two proposed actions.

The first action is the Preliminary Designation of certain stormwater discharges from commercial, industrial, and institutional properties with one acre or more of impervious surface in the Charles, Neponset, and Mystic River watersheds in Massachusetts for regulation under the Clean Water Act's ("CWA") National Pollutant Discharge Elimination System ("NPDES") permitting program.

EPA Region 1 is concurrently providing notice of availability of a draft NPDES General Permit for Private Commercial Industrial, and Institutional Stormwater Discharges in the Charles, Mystic, and Neponset River Watersheds in Massachusetts ("Draft CII GP").

More information about the Preliminary Designation and Draft Permit.

Resources

What is RDA? Video Series

English

Spanish

Parcel-Level Interactive Map

Residual Designation Authority (RDA) Parcel-Level Interactive Mapping Tool

Information Fact Sheets and Translations

Municipal-Specific Fact Sheets

Parcel-Level Watershed Analyses Reports

Frequently Asked Questions

Stakeholder Outreach for the Charles River, Mystic River and Neponset River Watersheds

Throughout 2024, EPA hosted several informational sessions with a range of stakeholders to provide some background on the residual designation permit development process and to highlight the necessary reductions in phosphorus and other pollutants for the Charles, Mystic and Neponset River watersheds. Those stakeholder sessions included:

EPA also conducted stakeholder meetings that focused on a set of specific questions about permit implementation challenges. These questions and a summary report of the comments from the focus groups is below:

Stakeholder Outreach Prior to 2024

More information

For additional information contact: R1.RDA@epa.gov

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Last updated on March 18, 2025