Division of Soil and Water Conservation

Total Maximum Daily Loads (TMDLs)

When monitoring reveals that waterways do not meet Delaware's water quality standards, they are reported on a list of impaired waterways (303(d) List). For each impaired waterway, the Federal Clean Water Act (CWA) requires states to develop Total Maximum Daily Loads (TMDLs) for the pollutants of concern. A TMDL sets a limit on the amount of pollution that can be discharged into a waterbody such that water quality standards can still be met. A non-scientific definition for TMDL could be "pollution limit." 

Nonpoint source pollution travels over and through the ground from many diffuse sources, including human activities on agriculture and developed lands like septic systems and runoff from lawns, farms, parking lots, and golf courses.

TMDLs consist of three parts: a wasteload allocation (WLA) for point sources, a load allocation (LA) for nonpoint sources, and a margin of safety (MOS): TMDL = WLA + LA + MOS

Delaware has been establishing TMDLs for our State's impaired waters since 1998.  Monitoring and other types of data are used to develop models that can predict how water quality will change under a variety of pollutant loading scenarios. These models help us determine TMDL levels that will achieve water quality standards. The table below lists all of the TMDLs that have been established in Delaware and provides links to technical analysis documents and the resulting regulations. Maps summarizing reductions in nonpoint source nitrogen, phosphorus, and bacteria required by TMDLs in order to achieve water quality goals are also shown below. 

PROPOSED ACTIONS

Proposed Amendment of the Murderkill River Watershed TMDL

The Department of Natural Resources and Environmental Control (DNREC), Watershed Assessment and Management Section, will conduct a Public Hearing regarding proposed amendments to the Waste Load Allocation (WLA) of the 2005 Murderkill River Total Maximum Daily Loads (TMDLs) Regulation on Tuesday, April 29, 2014 at 5:00 pm, in the DNREC Auditorium, 89 Kings Highway, Dover, Delaware.

If you cannot attend the hearing, you are encouraged to submit written comments. All written comments must be received by May 16, 2014.  Please send written comments to:

Hassan Mirsajadi
DNREC/Division of Watershed Stewardship
Watershed Assessment and Management Section
820 Silver Lake Boulevard – Suite 220
Dover, DE 19904-2464
Phone: (302) 739-9939
Facsimile: (302) 739-6140
Email: (Hassan.Mirsajadi@state.de.us)

You are encouraged to submit comments electronically.

• Draft Amendment of the 2005 Murderkill TMDL Regulation
• Proposed Amendment of the 2005 Murderkill River Watershed TMDL -Technical Report
• Proposed Site-specific Nutrient and DO Criteria for Tidal Murderkill River
• Murderkill River Watershed Modeling Report
• Appendices for Murderkill River Watershed Report

Maps:  The maps below show the amount of reduction needed from nonpoint sources across the state to achieve TMDLs for nitrogen, phosphorus, and bacteria.

Click on the maps to view a larger image.

Setting pollution limits is just the first step toward improving water quality.  Once the pollutant limits are established, efforts must be taken to reduce the pollutant loads from point and nonpoint sources. The Watershed Assessment Section works with Tributary Action Teams to identify voluntary and regulatory actions for each impaired region of the state. Collectively, these actions are called pollution control strategies (PCS) and they are designed to achieve TMDLs and water quality standards. In addition, other types of watershed plans and strategies have also been developed across the state.

 Related links:

• Whole Basin Management Plan and Timeline and TMDL Development Process Schedule.
• The Federal Environmental Protection Agency TMDL Web page
• EPA Region 3 TMDL Web page.

Learn more about Delaware's Watersheds!