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Water: Total Maximum Daily Loads (303d)

Fact Sheet

Memorandum on Listing Waters Impaired
by Atmospheric Mercury Under
Clean Water Act Section 303(d):
Voluntary Subcategory 5m

March 8, 2007


We are using Clean Water Act tools to encourage comprehensive state and regional mercury control programs, particularly for watersheds impaired by mercury from the air.  Specifically, EPA is issuing a memorandum describing a voluntary approach for listing waters impaired by mercury mainly from atmospheric sources under Clean Water Act Section 303(d).  The memorandum provides information to states, territories, and authorized tribes, and supplements EPA’s clarification memo on 2008 state Integrated Reports. The voluntary approach acknowledges the challenges involved in addressing waters impaired due to atmospheric mercury deposition; uses the Clean Water Act Section 303(d) listing process to encourage and recognize states that are taking early action to address their mercury sources; and is designed to achieve environmental results sooner.  Under this approach, we are encouraging states to put a priority on multi-pronged mercury control strategies.   

EPA, the states, and other stakeholders have been working to determine how best to address waters impaired by mercury, particularly where the primary source of the mercury is atmospheric deposition.  To date, over 8,500 water bodies in 43 states and Puerto Rico are listed under Section 303(d) of the Clean Water Act as impaired due to mercury.  State water programs have tools for addressing mercury discharges from water sources under the Clean Water Act, but they need to work closely with their air, waste, and toxics programs to address other sources of mercury.  U.S. mercury deposition results from domestic man-made sources and global sources, including natural, re-emitted, and man-made.  EPA has estimated that, on average, over three-quarters (83 percent) of the mercury deposited in the U.S. originates from international sources, with the remaining 17 percent coming from U.S. and Canadian sources.  The mix of long-distance and local sources makes it difficult in some waterbodies to achieve water quality standards for mercury.  A number of states have developed or are in the process of developing Total Maximum Daily Loads (TMDLs), and there are currently approved mercury TMDLs for over 300 waterbodies in 20 states and the District of Columbia.  In addition, a number of states are moving ahead to address mercury sources within their control through comprehensive mercury reduction programs.

Highlights of Subcategory 5m Approach

  • Using the voluntary approach, where a state has in place a comprehensive mercury reduction program, the state may separate their waters impaired by mercury primarily from atmospheric sources in a specific subcategory (“5m”) of their impaired waters lists.  States using this approach may also defer development of TMDLs for these waters beyond the currently recommended schedules for TMDLs.
  • The memorandum identifies the recommended components of the voluntary approach, such as:  having a comprehensive mercury reduction program in place; demonstrating initially that a state has begun to make progress in reducing the mercury loadings over which it has control; identifying those water bodies in the state impaired by atmospheric mercury deposition and the potential emission sources contributing to that deposition; implementing appropriate regulatory and non-regulatory controls; and describing reduction goals and targets, implementation schedules, monitoring, and public reporting.
  • Multi-state efforts are encouraged where possible to identify regional goals and targets.
  • A state would include a description of the elements of its comprehensive mercury program and regularly reporting of progress in conjunction with the existing biennial section 303(d) listing process.  Reporting through the 303(d) listing will provide public visibility and accountability regarding a state’s mercury reduction efforts.
  • Nothing in the approach is meant to imply that EPA believes it is inappropriate for states to put mercury TMDLs in their schedules sooner rather than later.  Nor would use of the "5m" approach remove the obligation to develop TMDLs for mercury-impaired waters if such mercury reduction programs do not result in attainment of water quality standards. 
  • There are a number of potential advantages to pursuing a “5m” approach, including the potential to focus more resources earlier on implementation of pollutant controls.
  • EPA will continue to assist all states in their efforts to attain water quality standards and will work with states to provide additional information on approaches to developing mercury TMDLs in the coming months.

For further information, or a copy of the memorandum, please contact Ruth Chemerys at (202) 566-1216 or John Goodin at (202) 566-1373.

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