TMDL stands for "Total Maximum Daily Load" and can be described as a watershed or basin-wide "budget" for the amount of pollutants that can be assimilated without causing the stream to exceed the state water quality standards. TMDLs also may be established for a portion of a watershed.
In actuality, a TMDL is a planning document. The "allowable budget" is determined by scientific study of a stream to ascertain the greatest loading or amount of a particular pollutant that may be introduced into a water-course or stream reach from all sources.
Three components make up the TMDL: the sum of all load allocations, that is, the pollutant loads contributed by nonpoint sources; wasteload allocations, which are those portions of the total loading set aside for contributions of the pollutant from point source discharges; and a margin of safety (MOS) to account for uncertainty.
According to Section 303 (d) of the federal Clean Water Act, TMDLs must be developed for surface waters that do not meet water quality standards.
TMDL allocations are the amounts of pollutants that can be discharged from each category. The TMDL does not specify how dischargers must attain their particular load allocation. In other words, the TMDL will not prescribe best management practices for a discharger or otherwise tell the discharger how to meet their goal; it merely sets the numerical allocation.
Trading is allowed between or within the load allocation and the wasteload allocation categories. However, the MOS cannot be "traded."
For point sources, the TMDL may require more stringent effluent limitations that will later be incorporated into an NPDES (National Pollutant Discharge Elimination Systems) permit. NPDES permits set effluent quality limitations and require implementation of best available technologies.
Nonpoint sources are not regulated through a permit program. The New Mexico Environment Department has advocated and implemented a voluntary approach to non-point source pollution prevention.
The ultimate goal is for the state's surface waters to meet water quality standards, which are set by the New Mexico Water Quality Control Commission (WQCC) after public input. According to the New Mexico Water Quality Act, any person can propose changes to the standards. Federal law requires the WQCC to review the standards at least once every three years and New Mexico currently is in a review year.
Standards adopted by the WQCC must be approved by the U.S. Environmental Protection Agency (EPA). If the EPA does not approve the standards adopted by the state, EPA may refer them back to the state or promulgate their own standards.
New Mexico's surface water quality standards are published in the NM Administrative Code (20 NMAC 6.1) and the document entitled, State of New Mexico Standards for Interstate and Intrastate Streams.
The federal Clean Water Act allows states the right to first establish TMDLs. The New Mexico legislature has empowered the WQCC to create the planning "budgets." Normally, the bulk of the work is done by the Environment Department and their plan is submitted to the WQCC for consideration. However, if the State does not promulgate TMDLs to EPA's satisfaction, EPA is required to do so.
Federal and state statutes require public participation. Participation is encouraged for permitees (point sources), affected landowners (nonpoint sources), regulatory or management agencies, local governments, public interest groups, and concerned citizens. Watershed associations or similar local organizations are encouraged to foster planning, communication and consensus among those interested.
To date, three TMDLs have been adopted by the WQCC: the Twining Water and Sanitation District (Rio Hondo) in the Taos Ski Valley area; Red River above the town of Red River to below the town's wastewater treatment facility; and the Rio San Jose below Grants to the Pueblo of Acoma.
On July 25, 1997, two environmental interest groups, Forest Guardians and Southwest Environmental Center, jointly filed a lawsuit against the EPA alleging that TMDLs had not been developed by the State. The State of New Mexico was not a litigant in this suit. EPA and plaintiffs negotiated a consent decree and settlement agreement avoiding formal litigation.
EPA and the New Mexico Environment Department have signed a Memorandum of Understanding outlining tasks the State will complete to meet the terms of the settlement. Similar litigation has occurred in more than 30 states.
A schedule for TMDL development has been established to address certain watersheds and stream segments. The consent decree schedule, which is supervised by the Court, reaches 10 years into the future. The settlement agreement reaches 20 years into the future. If New Mexico fails to promulgate a TMDL by the appropriate deadline, the EPA must develop the TMDL within two years.
For more information on TMDLs, contact the Environment Department's Surface Water Quality Bureau at http://www.nmenv.state.nm.us.
Timeline depicting TMDL Development in New Mexico
Beaver Pond on the upper Rito Penas Negras Project. Photo by David Hogge.
