Total Maximum Daily Loads:

TMDLs are required to be established for all 'impaired' water bodies that do not meet water quality standards after implementation of pollution controls. EPA is required to do this if states fail to do so.

TMDLs have been required for years, but a spate of recent lawsuits over federal versus state issues and the exact process for implementing TMDLs have slowed the TMDL process and tied many up in court. No doubt the dozens of court settlements will influence future TMDL policy, including for NPS impacts.

Under the law, states are required to identify waters that are and will remain polluted after the application of technology standards, identify pollutants causing the impairment to the water bodies, prioritize those waters, and establish TMDLs to meet state water quality standards. An individual TMDL is developed to address each pollutant, quantifying the pollution problem and identifying the contributors. The plans also map out a strategy for restoring the stream to state standards and for using monitoring and assessment programs.

Since EPA is ultimately responsible for what the states do or don't do on this, EPA has been sued repeatedly for lax attention to listing of impaired waters and development and implementation of TMDLs.

In general, a TMDL is a quantitative assessment of water quality problems, contributing sources, and pollution reductions needed to restore water quality standards for impaired waters.

To calculate a TMDL, the State determines how much of the total loading of a given pollutant is due to NPS discharges to the affected water body, considering natural background levels, future increases and providing an adequate margin of safety. Any remaining unallocated portion is divided among the point source dischargers.

These point source 'waste load allocations' are then incorporated into enforceable effluent limits (NPDES permits) for the point source dischargers.

TMDL PANEL RECOMMENDATIONS

Faced with a growing number of lawsuits over its handling of TMDL policy, EPA convened a Federal Advisory Committee in late 1996 to evaluate the overall TMDL issue and recommend policy changes. Recently the panel published its final report. EPA has promised to seriously consider the report as it revises TMDL rules and guidance this year and next.

Although the panel was unable to reach consensus on many of the most contentious issues, several conclusions will likely affect agricultural policy: (a) all sources of pollution (point and NPS) must share responsibility for restoring impaired waters; (b) governments' capacity to carry out the TMDL program must be strengthened significantly; (c) if high quality data are not available for TMDL development, states should use "evaluated" information, such as adjacent land uses, applications for NPDES permits and predictive modeling; (d) "threatened" waters should be protected in advance of "impaired" status by placement of constraints on source activities; (e) waters listed by states as "impaired" should not be de-listed until TMDLs are developed, fully implemented, and water quality standards are achieved; (f) states should fully implement and EPA enforce the restriction of new or expanded discharges (and NPDES permits) that would add impairment; and (g) states should develop "stabilization" plans to reduce or limit further impairment until TMDLs can be developed and put in place. The report is available from NCGA.

Currently nonpoint source dischargers are not required to participate in the waste load allocation unless specific States have enacted legislation for watershed management which incorporates mandatory NPS load allocations. TMDL policy will soon be revised by EPA, and will play a key part of the upcoming national focus on watershed planning.

Last reviewed May 29, 2001