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Skip Navigation LinksDNREC : Division of Watershed Stewardship : Watershed Assessment & Management : Watershed Assessment TMDLs


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

Watershed

Developed by

Year

Analysis Documents

Regulations

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


Map 2


Map 3


Map 4

 

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!

 
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