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TMDL Information


What is a TMDL?


A TMDL or Total Maximum Daily Load is the calculation of the maximum amount of a pollutant that a waterbody can receive and still meet Vermont Water Quality Standards. In a broader sense, a TMDL is a plan that identifies the pollutant reductions a waterbody needs to meet Vermont's Water Quality Standards and develops a means to implement those reductions. TMDLs can be calculated for correcting water pollution from specific point source discharges or throughout a watershed and balance the location and amount of needed pollution reductions.


When are TMDLs developed?


Under Section 303(d) of the Federal Clean Water Act, all states are required to develop lists of impaired waters. The list includes impaired lakes, ponds, rivers and streams that do not meet Water Quality Standards. For Vermont, impairment is substantiated by chemical, physical or biological data collected through monitoring and these waters are noted on the state's List of Waters. The Federal Clean Water Act requires TMDLs to be developed for waters on the list, the list provides a schedule indicative of TMDL completion priority.

Since 2001, several TMDLs have been developed by DEC, with subsequent approval from the New England regional office of EPA, affecting several waters.  Approved TMDLs concern the following waters:

              * Winooski River - Cabot - pathogens

              * Black River - Ludlow - phosphorus

              * Tributary #1, Ball Mountain Brook - Stratton - sediment

              * Styles Brook - Stratton - sediment

              * Lake Champlain (9 segments) - phosphorus

              * 37 ponds - various locations - low pH

              * Potash Brook - South Burlington - stormwater

              * Bartlett Brook - South Burlington- stormwater

              * Centennial Brook - South Burlington & Burlington - stormwater

              * Englsby Brook - Burlington - stormwater

              * Morehouse Brook - Winooski & Colchester - stormwater

              * Northeast region - Vermont, 5 other New England states & New York state - mercury (note: concerns 31 Vermont waters)

              * Allen Brook - Williston & Colchester - stormwater

              * Indian Brook - Essex & Colchester - stormwater

              * Munroe Brook - Shelburne - stormwater

              * Sunderland Brook - Colchester - stormwater

Persons interested in reading any of these finalized and EPA-approved documents noted above are encouraged to contact the Vermont TMDL Coordinator (click on "contacts" and refer to individual in Planning Section).  Approved TMDLs noted above concerning stormwater can be seen by visiting the "Stormwater" web page.


What is the TMDL process?


TMDLs are unique to each waterbody. The general process by which they are developed can be summarized as follows:

  • Problem Identification: the pollutant for which the TMDL is developed must be identified. Examples might include sediment that impacts habitat for aquatic organisms, nutrients that cause excessive algal growth, or bacteria that creates an unsafe environment for swimming.
  • Identification of Target Values: this element establishes water quality goals for the TMDL. Target values may be stated explicitly in the Water Quality Standards or they may need to be interpreted.
  • Source Assessment: all significant sources of the pollutant in question must be identified in the watershed. This often requires additional water quality monitoring.
  • Linkage Between Targets and Sources: this element of the process establishes how much pollutant loading can occur while still meeting the Water Quality Standards. This step can vary in complexity from simple calculations to development of complex watershed models.
  • Allocations: once the maximum pollutant loading is established, the needed reductions must be divided among the various sources. This is done for both point sources and nonpoint sources.
  • Public Participation: stakeholder involvement is critical for the successful outcome of any TMDL. Draft TMDLs are released for public comment prior to their c(pdf 3.4 MB)ompletion.
  • EPA Approval: EPA approval is needed for all TMDLs as required by the Federal Clean Water Act. The New England regional office of EPA, located in Boston, Massachusetts is responsible for TMDL approval.
  • Followup Monitoring: additional monitoring may be needed to ensure the TMDL, once implemented, is effective in restoring the waters.

Vermont Statewide Total Maximum Daily Load (TMDL) for Bacteria-Impaired Waters.

TMDL Appendices

Additional Resources


VT DEC Watershed Management Division 1 National Life Drive, Main 2  Montpelier, VT  05620-3522  Tele: 802-828-1535   Fax: 802-828-1544


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