Division of Soil and Water Conservation

Pollutants in Delaware waters are often chemicals, such as nitrogen and phosphorus from fertilizer runoff and wastewater, but TMDLs could also be set for other pollutants such as bacteria, sediments, or even heat – anything that can injure a waterway's natural health. Pollutants can come from specific point sources or from nonpoint sources. Point sources are discrete sources of pollution, and include facilities that have a National Pollution Discharge Elimination System (NPDES) Permit, such as municipal and industrial wastewater treatment plants. 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. 

 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!