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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."
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. Watershed numbers (in parentheses) and organization of the Table is in accordance with Map 1 below. In addition, Maps 2, 3, and 4 at the bottom of the page are provided to show reductions in nonpoint source nitrogen, phosphorus, and bacteria loads as required by the TMDLs in order to achieve water quality goals.

Map 1 |
Find Your Watershed Address
To find out which watershed a particular address falls in, use the "Find Your Watershed Address Tool" below.

Step 1. Type in your address.
Step 2. Once the map zooms to your address, click the map with your left mouse button. A dialog box will appear showing what is selected. Determine what your watershed address is.
Step 3. Use the + and – tools to zoom out to get a better look at what your watershed looks like. You can also click on the legend to understand data features that are represented on this map. Want to change the Basemap? Click the dropdown arrow next to Basemap.
Step 4. Through ArcGIS Online you can turn data off and on as well as add additional data to your map and share it with others. Click link below the map to view your map within ArcGIS Online.
Click here to view within ArcGIS Online |
Piedmont Drainage |
Naamans Creek (1) |
DNREC |
2005 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Shellpot Creek (2) |
DNREC |
2005 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Brandywine Creek (3), Red Clay Creek (4), White Clay Creek (5), and Christina River (6) |
EPA |
Revised 2006
2006
Revised 2006 |
High-Flow Nutrients
High-Flow Bacteria
Low-Flow Nutrients |
Red Clay Creek (4) |
DNREC |
1999, Amended 2009 |
Zinc |
Zinc |
White Clay Creek (5) |
DNREC |
1999 |
Zinc |
Zinc |
Delaware Bay Drainage |
Army Creek (8) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Red Lion Creek (9) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Dragon Run Creek (10) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
C&D Canal East and Lums Pond (11) |
DNREC |
2012 |
Nutrients |
Nutrients
|
Appoquinimink River (12) |
EPA
DNREC |
2003
2006 |
Nutrients
Bacteria |
Bacteria |
Blackbird Creek (13) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Smyrna River (15) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Leipsic River (16) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Little Creek (17) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
St. Jones River (18) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Murderkill River (19) |
DNREC
DNREC |
2014 Amended
2006 |
Nutrients
Bacteria
|
Nutrients
Bacteria |
Mispillion River (20) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Cedar Creek (21) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Broadkill River (22) |
DNREC |
2006 |
Nutrients and Bacteria |
Nutrients and Bacteria |
Chesapeake Bay Drainage |
Chester River (28), Choptank River (29), Marshyhope Creek (30), Nanticoke River (31), Gum Branch (32), Gravelly Branch (33), Deep Creek (34), Broad Creek (35), and Pocomoke River (37) |
DNREC |
2006 |
Bacteria |
Bacteria |
Chester River (28) |
DNREC |
2005 |
Nutrients |
Nutrients |
Choptank River (29) |
DNREC |
2005 |
Nutrients |
Nutrients |
Marshyhope Creek (30) |
DNREC |
2005 |
Nutrients |
Nutrients |
Nanticoke River (31), Gum Branch (32), Gravelly Branch (33), Deep Creek (34), and Broad Creek (35) |
DNREC |
1998
2000 |
Nutrients in the mainstem of the Nanticoke River and Broad Creek
Nutrients in the tributaries and ponds of the Nanticoke River and Broad Creek |
Nutrients |
Pocomoke River (37) |
DNREC |
2005 |
Nutrients |
Nutrients |
Inland Bays/Atlantic Ocean Drainage |
Lewes-Rehoboth Canal (38), Rehoboth Bay (39), Indian River (40), Iron Branch (41), Indian River Bay (42), Buntings Branch 43), Assawoman Bay (44), and Little Assawoman Bay (45) |
DNREC |
2006 |
Bacteria |
Bacteria |
Lewes-Rehoboth Canal (38), Rehoboth Bay (39), Indian River (40), Iron Branch (41), and Indian River Bay (42) |
DNREC |
1998 |
Nutrients |
Nutrients |
Little Assawoman Bay (45) |
DNREC |
2005 |
Nutrients |
Nutrients |
Indian River (40) |
EPA |
2004 |
Temperature |
Buntings Branch (43) |
DNREC |
2004 |
Nutrients |
|
Delaware Estuary |
Zones 2-5 |
EPA |
2003 |
PCBs |
Zone 6 |
EPA |
2006 |
PCBs |
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:
Learn more about Delaware's Watersheds!