Maryland Department of the Environment (for pda/handhelds)

TMDL

Total Maximum Daily Loads (TMDLs) are a requirement, found in §303(d), of the federal Clean Water Act (CWA) that became law in 1972.   

The CWA requires that Maryland: 

1. Establish Water Quality Standards (WQS) for its waters. 
2. Monitor the conditions of its waters. 
3. List waterbodies that do not meet WQSs with technology-based controls alone (303(d) list).
4. Set priority rankings for the waterbodies listed. 
5. Establish TMDLs that meet WQS for each listed waterbody. 
6. Solicit public comment.
7. Submit 303(d) list and TMDLs to EPA for approval.
8. Incorporate TMDLs into the State's Continuing Planning Process.  

What is a TMDL? 

• A TMDL (Total Maximum Daily Load) establishes the maximum amount of an impairing substance or stressor that a waterbody can assimilate and still meet WQSs and allocates that load among pollution contributors.
• TMDLs are a tool for implementing State water quality standards.  They are based on the relationship between pollution sources and in-stream water quality conditions. 
• A TMDL addresses a single pollutant or stressor for each waterbody.   
  

  

Which waterbodies require TMDLs? 

Waterbodies require TMDLs when the following pollution control requirements are not stringent enough to meet applicable WQSs:   

• Technology-based effluent limitations required by the CWA; 
• More stringent effluent limitations required by either State or local authority; and 
• Other pollution control requirements (e.g., best management practices) required by local, State, or Federal authority are not stringent enough to implement any water quality standard applicable to such waters. 

In Category 5 of Maryland's Integrated Report of Surface Water Quality (Integrated Report) is the current list of waterbodies that may require TMDLs. The 2008 Integrated Report was approved by EPA September 8, 2008.  For more information about the 2008 Integrated Report, please click here. 

The current list identifies 134 impaired watersheds. Various combinations of waterbodies and pollutants result in over 393 potential TMDLs statewide.   

How are TMDLs calculated? 

A TMDL is the sum of the allowed pollutant loads for point sources, non-point sources, projected growth and a margin of safety. 

TMDL = Point Sources + Nonpoint Sources + Projected Growth + Margin of Safety   

Load allocations are determined through the review of monitoring data and watershed modeling. The tools used depends upon the complexity of the problem.   

Key Components of TMDL Documentation 

• Describe Impairment 
• Identify Cause of Impairment 
• Set Quantitative Goal or Endpoint 
• Identify Pollutant Sources 
• Describe Methodology 
• Determine Allowable Load and Allocation 
• Determine Margin of Safety 
• Public Involvement 
• Provide Reasonable Assurance of Implementability   

  

Public Education and Participation in the TMDL Process   

• The document called "Maryland's TMDL Development Program and Local Government Participation" was created with the help of stakeholders to provide an outreach policy followed by the Department with local governments.
• Once work on a specific TMDL begins, local governments, identified interested parties, and appropriate dischargers in that watershed will be consulted during key stages of development.
• Introductory TMDL briefings may be provided upon request.  A second round of more in-depth briefings will be provided to those who request more detail.
• The public is invited to become involved in the listing process.
• After a draft TMDL has been developed, a formal public notice and comment period will be provided prior to the TMDL's submission to EPA.
• When a TMDL is approved, stakeholders will participate in determining how the TMDL should be implemented to reach allowable loading levels.   

  

Implementing TMDLs 

• After a TMDL has been approved, State and local water quality management plans should be updated and control measures implemented.
• NPDES Permit limits based on TMDLs, known as water quality-based limits, must be issued for point sources.
• Non-point source controls may be established by implementing Best Management Practices (BMPs) through voluntary or mandatory programs for enforcement, technical assistance, financial assistance, education, training, technology transfer, and demonstration projects.
• When allowing for non-point source controls, implementation plans should provide: 
  • A reasonable assurance that the controls will be implemented and maintained, or 
  • An effective monitoring program to demonstrate that nonpoint source reductions are taking place.  

• See also our TMDL Implementation page. 

  

Evaluating TMDL Implementation 

• Monitor pollutant loadings. 
• Track implementation and effectiveness of controls. 
• Assess water quality trends in the waterbody. 
• Reevaluate TMDL for attainment of water quality standards.

  

Current Status of Maryland's TMDL Program 

•  Maryland is a partner state for the Chesapeake Bay TMDL under development by EPA Region 3.  A new website dedicated to EPA Region 3's Bay TMDL has been created.  The website will serve as an important source of information about the nation's largest collective TMDL. It is a work in progress that will continually be updated, improved and expanded.  Click here to visit this site (you will be leaving MDE's website).
• Maryland Department of the Environment has begun bacteria monitoring to support the development of bacteria TMDLs.  For more information, click here.
• The 2008 Final Integrated Report of Surface Water Quality [303(d) List] has been approved by EPA and is now available.  For more information, click here.

  Contact Info

Please direct questions or comments concerning Maryland's TMDL Program to Melissa Chatham at (410) 537-3937.

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