States are required to develop total maximum daily load (TMDL) pollutant levels for waterways that are not adequately meeting federal Clean Water Act water quality standards.
What is a Total Maximum Daily Load (TMDL)?
TMDLs are a requirement of Section 303(d) of the Clean Water Act (CWA). According to the CWA, each state must develop TMDLs for all the waters identified on their Section 303(d) list of impaired waters. A TMDL is a calculation of the maximum amount of a pollutant that a waterbody can receive while still meeting water quality standards. An overview of TMDLs is provided on EPA’s website.
Simply, a TMDL is a plan to achieve water quality standards for impaired waterbodies.
In general, states are responsible for developing TMDLs and submitting them to EPA for approval. Even if third parties assist in the development of the TMDL or its supporting analysis, such TMDLs must still be submitted to EPA by the states.
Under the CWA, the EPA reviews and either approves or disapproves the TMDL. If EPA disapproves a state TMDL, EPA must develop a replacement TMDL.
The TMDL Program coordinates with several other DEQ programs including the Monitoring, Assessment, Permitting, and Nonpoint Source Programs to accomplish water quality restoration goals in Wyoming. TMDLs are one step in the “water quality restoration pipeline”.
The process begins when a waterbody is placed on the 303(d) list due to an exceedance of one or more water quality standards. Once an impaired water is placed on the 303(d) list, water quality restoration planning begins.
The TMDL is the planning step in the process where sources of pollution to streams, rivers, and lakes within Wyoming are identified and it is determined by how much pollution those waters can sustain and still fully support beneficial uses.
TMDLs are not self-implementing. Rather, TMDLs are implemented through existing regulatory and non-regulatory drivers. Point sources of pollution are addressed through the Wyoming Pollution Discharge and Elimination System (WYPDES) permit program. Federal regulations require that discharge permit limits be consistent with the assumptions and requirements of any available wasteload allocation in approved TMDLs (40 CFR 122.44(d)(1)(vii)(B)). Non-point sources load reduction actions are implemented through a wide variety of programs at the state, local and federal level. These programs may be regulatory, non-regulatory or incentive-based (e.g., a cost-share program). Wyoming works closely with conservation districts and watershed stakeholders through voluntary actions, often with support from Wyoming’s Nonpoint Source Program using Clean Water Act Section 319 and 205(j) grant funds for projects aimed at reducing the nonpoint source pollution.
Follow-up monitoring to examine water quality trends over time, and BMP effectiveness monitoring to evaluate the efficacy of implemented best management practices, are important components of the process. Achieving the ultimate goal of meeting the applicable water quality standards often takes many years and follow-up monitoring data can both facilitate and inform adaptive management actions, and track progress over time. Much of the follow-up monitoring in Wyoming is conducted by watershed stakeholders with technical support provided by WDEQ.