The Clean Water Act and Total Maximum Daily Loads in New Mexico: Frequently Asked Questions

Technical Report 39
Rhonda Skaggs and Maryfrances Decker
College of Agricultural, Consumer and Environmental Sciences, New Mexico State University

Authors: Respectively, Professor and former graduate research assistant, Department of Agricultural Economics and Agricultural Business, New Mexico State University (Print Friendly PDF)


The objective of this publication is to answer basic questions about water quality regulations in New Mexico. In recent years, there has been increased water quality regulatory and research activity in the state, particularly as related to the requirements of the federal Clean Water Act. This publication addresses water quality issues in New Mexico and provides additional sources of information. It is the result of a project funded by the New Mexico Environment Department-Surface Water Quality Bureau and the U.S. Environmental Protection Agency through a Clean Water Act Section 319 Grant. New Mexico State University's Agricultural Experiment Station also supported the work.

What is the Clean Water Act?

The 1972 Water Pollution Control Act (33 U.S.C. §§ 1251 et seq.), commonly called the Clean Water Act (CWA), is the primary federal law responsible for limiting pollution in U.S. waters. The law includes provisions for standards and financial assistance to address water pollution of all types with the objective of improving water quality in impaired areas (USEPA, 2002a). The Clean Water Act evolved through a series of legislative actions in response to declining water quality and increasing environmental awareness from the 1940s to the 1970s. The Clean Water Act, administered by the U.S. Environmental Protection Agency (USEPA), applies to lakes, rivers, aquifer and coastal areas.

The Clean Water Act has roots in the 1948 Water Pollution Control Act. This act offered technical assistance and federal funds to state and local governments for water quality protection efforts. This was the first attempt by the federal government to directly influence water quality throughout the United States. Another significant piece of legislation was the 1965 Water Quality Act, which sought to establish water quality standards for interstate navigable waters.

The 1972 Water Pollution Control Act was amended in 1977, 1981 and 1987. The 1977 amendment passed responsibility for some federal programs onto the states and made controls on toxic pollutants more stringent (USEPA, 2002b). The 1981 statute reduced the amount of funding from the federal government for wastewater treatment infrastructure (USEPA, 2002a). The 1987 amendments created a source of low-interest loans to states for water quality initiatives. States can loan this money tolocalgovernments at lowinterest rates(USEPA, 2002a).The 1987 legislation focused on stricter regulation of toxic chemicals and on water pollution from diffuse, nonpoint sources and required states to devise programs to deal with nonpoint-source pollution.

What Does the Clean Water Act Do?

A permit system is the principal mechanism used by the Clean Water Act to reach its objective of reducing and eventually eliminating water pollution. Anyone engaged in point-source polluting activities is required to obtain a permit from the U.S. Environmental Protection Agency. The permit contains detailed limitations on the amount and type of pollutants that may be discharged. It also details the manner in which those pollutants will be discharged (Olexa, 1991). This permitting system is called the National Pollutant Discharge Elimination System (NPDES).

The Clean Water Act also required states to establish total maximum daily loads (TMDLs) for pollutants in their waters. States were directed to develop best available technology standards for each industry. In addition, the act required an upgrade of municipal wastewater facilities from primary to secondary treatment, created a national pretreatment program and authorized grants for municipal wastewater treatment infrastructure (USEPA, 2002a).

What is the Status of the Nation's Waters?

The 1998 National Water Quality Inventory Report to Congress indicated that of the 23 percent of the nation's rivers that were assessed, 35 percent were considered polluted and 10 percent were threatened. In 1998, 32 percent of estuary waters had been assessed and 44 percent were polluted, while 10 percent were threatened. Also at that time, 42 percent of the nation's lakes, ponds and reservoirs had been evaluated, with 45 percent found to be polluted and 9 percent threatened (USEPA, 2000). Siltation, bacteria and nutrients were the leading pollutants of rivers and stream. Lakes, ponds and reservoirs were contaminated primarily by nutrients, metals and siltation. Estuaries were damaged and threatened by bacteria, organic enrichment and metals (USEPA, 2000). Organic enrichment creates water quality problems because contamination by organic compounds, such as fertilizer, manure or untreated sewage, can lead to excessive algae growth.

How is Point-Source Pollution Different From Nonpoint-Source Pollution?

Point-source pollution occurs at identifiable discharge points, such as at a factory. Nonpoint-source pollution is pollution that cannot be traced to the end of an outlet, such as runoff from forest logging, sheet flows from pastures or movement of soil and fertilizer from cropped lands into waterways. Nonpoint-source pollution is much more difficult to deal with than point-source pollution for several reasons. The exact source is impossible to establish. For example, excess sedimentation, or turbidity, is one of the most common pollutants in New Mexico. This pollution can be attributed to many sources, such as shifts in vegetative communities, wildlife grazing and livestock grazing. It also is difficult to quantify amounts of nonpoint-source pollution. Using the turbidity example, it is difficult to ascertain how much sediment is natural and how much has been added by a polluter. Furthermore, an individual field's or pasture's contribution to nonpoint-source pollution may be small, but the total amount of runoff from all fields or pastures can be extremely large. Because of these issues and others, there is great debate about how to manage, regulate or even quantify nonpoint-source pollution.

What is a Total Maximum Daily Load (TMDL)?

Individual states are required by Section 303(d) of the Clean Water Act to identify water bodies that do not meet water quality standards. Such a water body is referred to as a water quality limited segment, or WQLS. Once the state identifies water quality limited segments, it is required to develop TMDLs according to a priority ranking (NMED, 1998). TMDLs set the maximum amount of pollution from all sources that a water body can receive without violating water quality standards (Copeland, 1997). In practice, a TMDL is a planning document that establishes a budget for types of water contaminants by source. A TMDL also develops water quality management strategies.

Federal regulations dictate that once the allowable level of pollutants is determined, some slack must be left in the budget for a margin of safety (MOS), which accounts for uncertainties in calculations of safe pollutant levels. The MOS takes into account the availability and strength of data and may vary from stream to stream. Nonpoint pollution sources are grouped into a load allocation (LA), and point pollution sources are grouped into a waste load allocation (WLA). Total maximum daily loads are described by the following equation:

TMDL = sum of nonpoint pollution sources (LA) + sum of point pollution sources (WLA) + margin of safety (MOS).

Who is Responsible for Total Maximum Daily Loads?

Under the federal Clean Water Act, states have the first right to establish TMDLs. The New Mexico Water Quality Control Commission (NMWQCC) has the authority to set water quality standards and create TMDLs in the state. The commission includes representatives from the Environment Department, the State Engineer/ Interstate Stream Commission, Oil Conservation Division, Game and Fish Department, the State Park and Recreation Division, the Soil and Water Conservation Commission, the Bureau of Mines and Minerals, and the Department of Agriculture. Three members at large are appointed by the governor to represent the public. In practice, the Environment Department does most of the research and submits TMDL proposals to the commission for approval (NMED, 1998). Establishment of the commission was authorized by the New Mexico Water Quality Act (Chapter 74, Article 6 NMSA) in 1978.

In addition to involvement by the NMWQCC, the U.S. Environmental Protection Agency and the New Mexico Environment Department, any citizen can participate in developing the TMDLs. Both federal and state statutes require the opportunity for public participation (NMED, 1998).

What Happens Once a Total Maximum Daily Load is Developed?

TMDL implementation is different for point-source and nonpoint-source pollutants. For point sources, National Pollutant Discharge Elimination System (NPDES) permits are issued by the U.S. Environmental Protection Agency. The National Pollutant Discharge Elimination System permits are based on the limits established in a TMDL for the pollutants of concern. The Point Source Regulation Section of the New Mexico Environment Department's Surface Water Quality Bureau is responsible for administering the state's NPDES program.

Nonpoint-source polluted water bodies are not regulated by the federal Clean Water Act. There is no federal or New Mexico discharge permitting process for nonpoint-source pollution. Abatement of nonpointsource pollution in New Mexico employs a voluntary approach that involves best management practices (BMPs) that should be used to meet TMDL standards in a polluted water body. In New Mexico, BMP guidelines are available from the Environment Department's Surface Water Quality Bureau.

What is the Status of Total Maximum Daily Loads in New Mexico?

Under the federal Clean Water Act, states are required to develop TMDLs for pollutants that cause nonattainment of state water quality standards. If a state does not establish TMDLs for impaired waters, then the federal Environmental Protection Agency is required to develop the TMDLs in lieu of the state.

There was very limited TMDL development in New Mexico until the late 1990s. In June 1996, environmental groups brought suit against the U.S. Environmental Protection Agency to force TMDL development and implementation. As a result of the case, Forest Guardians and Southwest Environmental Center v. Browner (Civ. No. 96-0826 LH), the plaintiffs and the U.S. Environmental Protection Agency signed a consent decree that defined a 10-year schedule for establishing TMDLs for 61 specified water bodies that weren't meeting water quality standards. These water quality limited segments are on what is called the state's §303(d) list of waters in need of TMDLs.

According to the consent decree, if the state does not create the TMDLs within the established time frame, then the U.S. Environmental Protection Agency will be responsible for their development. There also was a companion settlement agreement that directs that the remaining water quality limited segments on the 1996 §303(d) list will have TMDLs developed within 20 years. Again, according to the settlement, the state has the right to develop them. But if it fails to do so, then the
U.S. Environmental Protection Agency is responsible for their development.

The §303(d) list is named for the Clean Water Act section that requires each state to identify surface waters within its boundaries that are not meeting or not expected to meet water quality standards (NMED, 2000).

TMDL development and implementation has been underway in New Mexico since 1998. A list of water quality limited segments having or needing TMDLs is available online. Completed TMDLs in the state also are available online, as are TMDL delistings for the state. Several creeks and watered areas have been removed from New Mexico's §303(d) list, because investigation by the Surface Water Quality Bureau indicated that TMDLs were not required. For example, some watered areas originally designated as fisheries (thus subject to fishery water quality standards) were placed on the original §303(d) list. However, it was determined later that these watered areas were not fisheries (due to the existence of extended dry periods) and, thus, not subject to fishery water quality standards. Further evaluation of water conditions in these areas led to their removal from the §303(d) list.

What are the Designated Uses of Watered Areas in New Mexico?

The NMWQC issues New Mexico interstate and intrastate water quality standards. These standards specify designated uses for the waters, which include warm-water and cold-water fisheries, livestock watering, wildlife habitat, fish culture, irrigation water storage, irrigation, primary and secondary contact, domestic water supply, and municipal and industrial water supply. Primary contact includes recreational uses, such as swimming and water skiing, in which a human has prolonged and intimate contact with water. Secondary contact refers to recreational uses, such as fishing, wading, and boating. A water body is considered impaired or polluted if the existing water quality is not sufficiently high to support the designated use.

In designating uses for a water body, states and tribes examine the suitability of a water body for the uses based on its physical, chemical and biological characteristics (USEPA, 2001a). Other factors that must be taken into account include a water body's geographic setting, scenic qualities, as well as the socioeconomic and cultural characteristics of the surrounding area (USEPA, 2001a).

What is the Impact of the Clean Water Act and Total Maximum Daily Loads on Agriculture?

In past years, the National Pollutant Discharge Elimination System primarily focused on point-source pollution and had a significant impact on wastewater treatment facilities, factories and other industries that had pollutants coming out of pipes. All sources of nonpoint pollution currently are unregulated. However, with nonpoint-source pollution being recognized and targeted in the TMDL process, agriculture has become a focus of clean water regulations. Most agricultural activities that can negatively impact water quality currently are not regulated through any permitting process.

Compliance with TMDLs for nonpoint-source pollution is voluntary. Landowners and land management agencies are encouraged to use best management practices to improve water quality and meet TMDL contaminant limits. Technical assistance also is available through the state and federal governments to help public and private landowners meet TMDL objectives. Cost sharing programs are available to private landowners through a variety of sources, including the U.S. Department of Agriculture's Water Quality Incentive Program (WQIP).

Does the Clean Water Act Define Any Agricultural Operations as Point Sources of Pollution?

Concentrated animal feeding operations (CAFOs) are defined by the Clean Water Act to be potential point sources of pollution. Thus, they are required to have National Pollutant Discharge Elimination System permits. A concentrated animal feeding operation has either 1,000 or more animal units (AU) or 300 to 1,000 animal units with the wastes discharged through man-made conveyance or directly into U.S. waters (USEPA, 2001b).

What is the Quality of Surface Water in New Mexico?

Surface water quality varies throughout the state. Generally, water at higher elevations is of excellent quality, while water in the lower elevations is of lower quality (NMWQCC, 2000). Again, water bodies or watered areas are considered impaired if water quality is reduced to a point where designated or attainable uses are not possible. In New Mexico, 2 percent of the sources of stream impairment are point sources. Natural causes contribute another 2 percent of the pollution, and 4 percent comes from unidentified sources. By far the largest source of stream impairment comes from nonpoint sources, fully 92 percent of the total (NMWQCC, 2000). Agriculture and recreation are the predominant sources of water quality impairment in New Mexico's lakes (NMWQCC, 2000).

Agriculture and rangeland together contribute 26 percent of the nonpoint-source pollution in New Mexico streams. Recreation is responsible for 8 percent, while hydromodification (e.g., channelization, channel modification, dams, stream bank alterations) contributes 43 percent. Two percent of New Mexico's nonpoint-source pollution is attributed to forestry, while construction is responsible for 1 percent. Resource extraction contributes 5 percent of nonpoint pollution, while other sources make up the remaining 15 percent (NMWQCC, 1998).

What Water Quality Standards are Relevant to Total Maximum Daily Loads in New Mexico?

Water quality standards in New Mexico include general standards, use designation for specific water bodies and the subsequent standards related to use (NMWQCC, 1998). Contaminants affecting designated uses in New Mexico include stream bottom deposits, temperature, turbidity, fecal coliform, phosphorus, ammonia and aluminum. New Mexico interstate and intrastate standards for these and other contaminants are available from the NMWQCC and the Internet.

What are the Sources of the Water Contaminants?

Stream bottom deposits are particulate matter resulting from weathering and erosion. The erosion that results in stream bottom deposits can be caused by numerous factors, ranging from natural causes (wind, sheet wash, gully erosion and drought) to man-made causes (excavation, road construction, improper grazing practices and recreation). Sediments are transferred to waterways via runoff. Following high flow events (strong rains or flooding), the sediment settles in the stream bottoms as the water flow decreases. When deposits accumulate in streams, the available habitat for fish species and macroinvertebrates is reduced. Macroinvertebrates make up a large category of animals that do not have backbones and can be seen with the naked eye, including worms, snails, spiders, insects and crayfish.

New Mexico water quality standards have established 68°F as the maximum temperature for cold-water fisheries. The maximum temperature for warm-water fisheries is set at 90°F. New Mexico water quality standards do not allow the introduction of heat into fishery waters by anything other than natural causes. Three factors can affect stream water temperatures: heat added by a point source or by the sun; the amount of shade along a stream resulting from vegetation or landforms; and stream characteristics, including temperature of tributaries, geothermal effects, width and depth of a stream. Reduced riparian vegetation, including species like willow and alder, leads to reduced shade and increased temperatures. Wider, more shallow streams resulting from stream bank destabilization also are subject to increased warming by the sun. Improper grazing practices along stream banks or in riparian areas often are blamed for increased temperatures in streambeds throughout New Mexico.

According to New Mexico water quality standards, any turbidity created by humans cannot reduce light transmission to the point that common, desirable aquatic life is inhibited. Nonnatural turbidity also should not be obviously visible to the naked eye. Turbidity is assessed by measuring total suspended sediment concentrations. Increased total suspended sediment concentrations, which result from the same causes as described for stream bank deposits, usually are related to natural and man-made erosion and increased sediment loads. Increased turbidity (and later sediment movement to stream bottoms) reduces the habitat for macroinvertebrates and fish. The reduced light penetration in turbid waters also decreases the ability of fish to capture prey and reduces total fish production.

Fecal coliform bacteria are present naturally in the guts of warm-blooded animals. Fecal coliform can be found in New Mexico waters, resulting from human waste contamination or the waste of wild or domesticated warm-blooded animals. The presence of coliform bacteria often indicates the presence of other pathogens that can pose human health hazards. Diseases caused by waterborne pathogens include ear infections, dysentery, typhoid, gastroenteritis and hepatitis. During rainy periods, storm water can pick up and move the feces of mammals and birds from parks, areas where livestock are produced and areas inhabited by wild game. Septic tanks, outhouses and inadequately treated sewage also can be sources of the bacteria.

Total phosphorus levels in natural waters usually are low because phosphorus tends to be absorbed by soil particles or algae and other aquatic plants. Depending on soil characteristics in a watershed, soil erosion can be a significant contributor to high total phosphorus levels in streams. Animal wastes, including wildlife and domestic livestock, also can contribute to high total phosphorus levels in streams when the feces are washed into watercourses. High phosphorus concentrations can result in high levels of algae growth, which can impair fish habitat and reduce fish production.

In some forms, ammonia can be toxic to fish. Ammonia is excreted by fish, birds and mammals. It also results from decomposing organic materials, including plants, manure and dead animals. Ammonia can be released from wastewater treatment plants (a point source) or washed into streams from lands grazed by wildlife and domestic livestock. Home septic systems also can discharge ammonia.

Aluminum often is present in New Mexico waters at levels exceeding state standards. High levels of aluminum often are linked to increased turbidity, especially when aluminum is naturally present in soils and rocks. Weathering of soils and rock leads to the release of aluminum that ends up in streams and lakes. Rangeland grazing, mining, forestry activities, recreation and road maintenance are all activities that can increase erosion and lead to increased aluminum levels in streams. High levels of aluminum are toxic to fish and macroinvertebrates.

What Does a Typical Total Maximum Daily Load Look Like?

There is no typical TMDL, since it is a planning document specific to a geographic location. The sources of water impairment and other factors vary greatly between the areas for which TMDLs have been developed. In most New Mexico watershed areas, several TMDLs (or contaminant budgets) are required to address the various sources of water quality impairment. A closer examination of one New Mexico TMDL area is helpful for understanding TMDLs throughout the state. The final version of the complete TMDL for an area of the Canadian River Basin in northeastern New Mexico is presented here as an illustration. A preliminary copy was released by the New Mexico Environment Department in June 1999. After a public comment and input period, the final version was released in August 1999 (NMED, 1999).

The Cimarron River Basin is a 1,032-square-mile subbasin of the Canadian River Basin. The TMDL area covers 225 square miles and all or portions of Cieneguilla Creek, Six-Mile Creek, Moreno Creek, and North Ponil Creek. Almost 90 percent of the land in this watershed area is privately owned, 9 percent is U.S. Forest Service land, and 2 percent is owned by the State of New Mexico.

As a result of surface water quality monitoring in the area, it was determined that water quality standards for turbidity, total phosphorus and stream bottom deposits were not being met. There were no water quality impairments in the area as a result of point-source pollution, but water quality was reduced as a result of nonpointsource pollution. Suspected reasons for the water quality impairment were:

  • Improper installation and maintenance of culverts on Cieneguilla Creek, leading to stream bank destabilization.
  • Recreation, development of resort areas, erosion from ski slopes, parking areas, road construction and maintenance, and land development in the Cieneguilla Creek area.
  • Stream bank destabilization in the Six-Mile Creek area as a result of removing riparian vegetation and extensive rangeland grazing.
  • Stream bank destabilization in the Moreno Creek area.
  • A U.S. Forest Service fishing pond in the North Ponil Creek was removed in 1996. The stream was not restored to its natural condition, and stream bank destabilization had occurred.

Based on extensive monitoring and sampling, the TMDLs listed below were established by the New Mexico Environment Department's Surface Water Quality Bureau. These are the amounts of pollutants that may be discharged into the affected streams without exceeding water quality standards.

TMDLs for turbidity (measured as total suspended solids):

Moreno Creek
WLA (0) + LA (3,160) + MOS (1,054) = 4,214 lbs/day

Six-Mile Creek
WLA (0) + LA (1,144) + MOS (381) = 1,525 lbs/day

Cieneguilla Creek
WLA (0) + LA (4,750) + MOS (1,584) = 6,334 lbs/day

North Ponil Creek
WLA (0) + LA (1,258) + MOS (420) = 1,678 lbs/day

TMDLs for stream bottom deposits:

Cieneguilla Creek
WLA (0) + LA (15) + MOS (5) = 20 percent fines

North Ponil Creek
WLA (0) + LA (15) + MOS (5) = 20 percent fines

TMDL for total phosphorus:

North Ponil Creek
WLA (0) + LA (4) + MOS (1.4) = 5.4 lbs/day.


LA = load allocation for nonpoint-source pollution

WLA = waste load allocation for point-source pollution

MOS = margin of safety

Plans to implement these TMDLs focus on a combination of best management practices to control sediment. Reducing sediment in the streams also is expected to reduce total phosphorus levels in North Ponil Creek. Best management practices listed in the TMDL document included riparian restoration and rehabilitation of the former fishing pond area. Good range management was to be encouraged along the river reaches. The Surface Water Quality Bureau planned to work with private landowners, the U.S. Forest Service and local and state highway departments to encourage best management practices. Culvert repair and maintenance, erosion control, stream bank stabilization, and improved road maintenance are listed in the final TMDL document as practices that will be promoted by the Surface Water Quality Bureau. Federal funding, made available through provisions of the Clean Water Act, was obtained to increase vegetative cover of ski slopes on Angel Fire Resort property.

How Many Total Maximum Daily Loads Have Been Established in New Mexico?

The number of TMDLs in New Mexico is changing continually. New TMDLs are being drafted regularly, draft TMDLs are moving into final versions, and some water quality limited segments have been delisted. Delistings have occurred as a result of monitoring and evaluating the areas, which showed that water quality standards were not being violated or that current designated uses were inappropriate.

How Can the Public Participate in the Total Maximum Daily Load Process?

Public participation in the TMDL development process is required by the Clean Water Act. Public comment periods, usually 30 days in length, are held after draft documents are released by the Surface Water Quality Bureau. Public comments are taken into account when the final versions are prepared. Public input is essential for TMDLs to accurately reflect conditions in affected areas and watersheds throughout the state. Announcements of the public comment period go out from the Surface Water Quality Bureau to newspapers, radio stations, and through the NMWQCC. For the Cimarron River Basin TMDL described above, public criticism pointed out that the draft document was too complex, the maps were confusing and monitoring methodologies were inadequately described. The final version was revised in response to some of the comments. Meetings of the NMWQCC in which final TMDLs are considered and approved are open to the public. The meetings are held regularly in Santa Fe, but they also are held in other parts of the state where TMDL issues are being considered by the NMWQCC.

What Does it Cost to Develop A Total Maximum Daily Load in New Mexico?

A recent study examined the costs of New Mexico's TMDLs developed by November 2000, including those still in draft stages at the time (Decker, 2001). Variable costs were evaluated; no administrative or overhead costs were considered. Labor, monitoring and public participation costs were derived from information supplied by the New Mexico Environment Department and the New Mexico Department of Health's Chemistry Bureau. The average cost of developing a complete TMDL for a single water quality limited segment in New Mexico was estimated to be $30,500. The cost reflects only development and does not include any expenses associated with TMDL implementation. This is a minimum estimate, because it only includes variable costs directly associated with TMDL development. The estimate does not include personnel costs incurred by New Mexico Environment Department employees who develop the TMDLs.

Where Can I Learn More About Total Maximum Daily Loads in New Mexico?

Much information about the Clean Water Act, TMDLs and water quality in general in New Mexico is available from the New Mexico State Environment Department. The New Mexico Surface Water Quality Bureau has extensive information available at its Web site. Information about the topics discussed in this report also is available from other online sources, including the U.S. Environmental Protection Agency. NMSU's Cooperative Extension Service staff can help you locate information about these topics.


Decker, Maryfrances. 2001. The Cost and Descriptions of Developing Total Maximum Daily Loads in New Mexico as Directed by the Clean Water Act. Unpublished M.S. thesis, Department of Agricultural Economics and Agricultural Business, New Mexico State University.

New Mexico Environment Department (NMED). 1998. Questions and Answers about TMDLs. World Wide Web site: Accessed: February 5, 2002.

New Mexico Environment Department (NMED). 1999. TMDL for Turbidity, Stream Bottom Deposits and Total Phosphorus in the Cimarron River. Available online: Accessed February 5, 2002.

New Mexico Environment Department (NMED). 2000. Questions and Answers on TMDLs. Available online: Accessed. April 3, 2002.

United States Environmental Protection Agency (USEPA). 2000. Water Quality Conditions in the United States: A Profile from the 1998 National Water Quality Inventory Report to Congress. Available online: . Accessed: February 5, 2002.

Relevant Web Sites

The New Mexico Environment Department's Surface Water Quality Bureau Web site is at

The United States Environmental Protection Agency Web site is at:

Information about Total Maximum Daily Loads in New Mexico can be found at:

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June 2002