Division of Water Resources
William R. Snodgrass Tennessee Tower
312 Rosa L. Parks Avenue, 11th Floor
Nashville, Tennessee 37243
Questions? Ask TDEC
Section 303(d) of the Clean Water Act establishes the Total Maximum Daily Load (TMDL) program.
A TMDL is a study that:
Some of the actions that might be taken are:
Re-allocation of limits on the sources of pollutants documented as impacting streams. It might be necessary to lower the amount of pollutants being discharged under NPDES permits or to require the installation of other control measures, if necessary, to ensure that water quality standards will be met.
For sources the Division does not have regulatory authority over, such as ordinary agricultural or forestry activities, provide information and technical assistance to other state and federal agencies that work directly with these groups to install appropriate Best Management Practices.
TMDLs can also be described by the following equation:
TMDL = sum of nonpoint sources + sum of point sources + margin of safety
The Division of Water Resources has structured monitoring and permitting activities on a rotating watershed basis. In keeping with this approach, Tennessee is developing TMDLs on a watershed basis, with each watershed examined at the appropriate time in the five-year watershed cycle.
Announcements of the availability of proposed TMDLs on public notice:
The following is a list of proposed TMDLs that have completed public notice and have been submitted to EPA for final approval.
Tennessee’s TMDL Program is a part of Water Resources’ Watershed Management Section. The development of TMDLs follows the schedule established as part of the 1998 agreement between EPA and TDEC, which is based upon the 1998 303(d) List.
Load Allocation (LA): The portion of a receiving water's loading capacity that is attributed either to one of its existing or future nonpoint sources of pollution or to natural background (40 CFR 130.2(g))
Loading Capacity (LC): The greatest amount of loading that a water can receive without violating water quality standards (40 CFR 130.2(f))
Margin of Safety (MOS): The "MOS" accounts for uncertainty in the loading calculation. The MOS may not be the same for different waterbodies due to differences in the availability and strength of data used in the calculations.
Nonpoint Source: A nonpoint source is essentially any source of pollutant(s) that is not a point source. Examples are sheet flow from pastures and runoff from paved areas.
Point Source: A point source is simply described as a discrete discharge of pollutants as through a pipe or similar conveyance (e.g., a ditch). A technical definition exists in federal regulation at 40 CFR 122.2.
Total Maximum Daily Load: The sum of the individual wasteload allocations for point sources and load allocations for nonpoint sources and natural background (40 CFR 130.2(I))
TMDL "budget": The allocations are simply the amounts of pollutants that can be discharged from each category. The TMDL does not specify how the dischargers must attain their particular load allocation. In other words, the TMDL will not set best management practices for a discharger or otherwise tell the discharger how to meet their goal, it merely sets their goal.
Water quality-limited segments: Those water segments that do not or are not expected to meet applicable water quality standards even after the application of technology.
Wasteload allocation (WLA): The portion of a receiving water's loading capacity that is allocated to one of its existing or future point sources of pollution. WLAs constitute the type of water quality-based effluent limitation. (40 CFR 130.2(h))