First Released in July 1997 Go to Latest Update

    TMDL stands for "Total Maximum Daily Load". A TMDL can be best described as a watershed or basin-wide budget for pollutant influx to a watercourse. TMDLs may also be established for a portion or segment of a watershed. A TMDL, in actuality, is a planning document. The "allowable budget" is first determined by scientific study of a stream to determine the amount of pollutants that can be assimilated without causing the stream to exceed the water quality standards set to protect the stream's designated uses (e.g.,fishery, irrigation, etc.). Once this capacity is determined, sources of the pollutants are considered.

    Both point and nonpoint sources must be included. Once all the sources are accounted for, the pollutants are then allocated or budgeted among the sources in a manner which will describe the limit (the total maximum load) that can be discharged into the river without causing the stream standard or "budget" to be exceeded. Nonpoint sources are grouped into a "load allocation" (LA) and point sources are grouped into a "wasteload allocation" (WLA). By federal regulation, the budget must also include a "margin of safety" (MOS). Thus, 100% of the budget cannot be allocated to pollutant sources. TMDLs can also be described by the following equation:
 

What is a "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.

What is a "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 forest logging.  Current estimates indicate that nonpoint sources are the cause of 93 % of the state's surface water quality problems.

What is the "margin of safety"?

    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.

What does the TMDL "budget" involve?

    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.  Trading is allowed between, or within, the load allocation and the wasteload allocation categories. The MOS cannot be "traded". The TMDL may specify more stringent effluent limitations that will later be incorporated into an NPDES permit (see next question).

If the TMDL does not tell the discharger how to manage their discharge, how is the TMDL implemented?

    The (point source) WLA is implemented through an existing regulatory program under the Federal Clean Water Act (CWA) called the National Pollutant Discharge Elimination System (NPDES) permit program (ref. CWA Section 402). These permits set effluent quality limitations and require implementation of best available technologies which may include specific best management practices already established by the United States Environmental Protection Agency (USEPA) through regulation. In New Mexico, nonpoint sources are currently not regulated through a permit program. The New Mexico Environment Department has for several years advocated and implemented a voluntary approach to nonpoint source pollution prevention. Even though New Mexico has demonstrated the effectiveness of the voluntary approach, national trends and direction from USEPA indicate a regulatory approach may be mandated by Congress in the future.

Who sets the water quality standards?

    Water quality standards are set by the NM Water Quality Control Commission (WQCC) after public participation and hearings. According to the NM 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. Standards adopted by the WQCC ultimately must be approved by the USEPA (ref. Clean Water Act Section 303). If EPA does not approve the standards adopted by the state then they may either refer them back to the state or promulgate their own standards for the state. The state's surface water quality standards are published in the New Mexico Administrative Code (20 NMAC 6.1).

Who sets the TMDL?

    The Federal Clean Water Act provides that the state has the first right to establish TMDLs. Under the New Mexico Water Quality Act, the State Legislature has empowered the New Mexico Water Quality Control Commission with the authority to create such planning documents. Normally, the bulk of the work is done by the Environment Department and submitted to the WQCC as a proposal for their consideration. However, if the state does not set TMDLs to USEPA's satisfaction, then USEPA is required to do so (ref. CWA Section 303(d)).

What agencies are represented on the WQCC?

    Environment Department; State Engineer/Interstate Stream Commission; Game & Fish Department.; Oil Conservation Division; State Park & Recreation Division; Department of Agriculture; Soil & Water Conservation Commission; and Bureau of Mines & Minerals. Additionally, three members-at-large are appointed by the Governor to represent the public.   (ref. Section 74-6-3.A NMSA 1978, 1993 Replacement pamphlet.)

Who else is involved in TMDL development?

    Both federal and state statutes require the opportunity for public participation. This participation may include any permittee (point sources), affected land owners (nonpoint sources), regulatory or management agencies, local governments, public interest groups, and concerned citizens. Watershed associations, or similar local organizations, are encouraged to foster communication, planning, and consensus among those concerned.

Has New Mexico ever set a TMDL?

    Yes. Three TMDLs have been adopted by the WQCC. They include the Twining Water & Sanitation District (the Rio Hondo) in the vicinity of the Taos Ski Valley (1981); the Red River from above the Town of Red River to below the town's wastewater treatment facility (1982); and the Rio San Jose below the City of Grants to the Pueblo of Acoma (1989). A fourth TMDL for the Rito Peñas Negras (southeast of Cuba), initiated in 1995, is now in the final stages of development. Because there are no point sources on the Rito Peñas Negras, this TMDL will be the first strictly nonpoint source TMDL in New Mexico and in EPA Region 6 (Texas, Oklahoma, Louisiana, Arkansas, & New Mexico).

Has there been litigation regarding TMDL development in New Mexico?

    Yes. Two environmental interest groups, Forest Guardians and Southwest Environmental Center, jointly filed a lawsuit against the USEPA alleging that adequate TMDLs had not been developed by the State. The State of New Mexico was NOT a litigant in this suit. USEPA 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.

Has there been litigation regarding TMDL development elsewhere in the nation?

    Yes. Similar litigation has occurred in more than 30 states nationwide.

What is the primary effect of the negotiated consent decree and settlement agreement on the future of TMDL development in New Mexico?

    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 the state fails to develop a TMDL by the appropriate deadline, the USEPA must develop the TMDL within two years.

What is the TMDL schedule for the next 10 years?

    The following timeline graph depicts anticipated TMDL development in New Mexico: