TMDLs: Paring Back Impairments


Currently, some U.S. rivers, streams, and lakes are so loaded down with pollutants they're almost like watery graves. Instead of teeming with a rich diversity of aquatic flora and fauna, these water bodies are barely capable of sustaining life. The reason is contamination from a variety of sources. When the Cuyahoga River in Cleveland caught on fire on June 23, 1969, it became an ironic symbol of how our society's relentless pollution of our water bodies had turned nature on its head.

In 1987, in an effort to improve the health of U.S. water bodies, Congress amended the Clean Water Act to include Section 303, which established the new measurement called the total maximum daily load (TMDL), a calculation of the maximum amount of a pollutant that a water body can receive and still meet water-quality standards, and an allocation of that amount to the pollutants' sources. Under Section 303, water quality standards are set by states, territories, and Native American tribes. They identify the uses for each water body, for example, drinking water supply, contact recreation (swimming), and aquatic life support (fishing), and the scientific criteria to support that use.

Water bodies that do not meet the state water-quality standards are listed as "impaired" under Section 303 (d). The listing then triggers development of a TMDL specifically designed to remove the contaminated river, stream, or lake from the impaired waters list. The process requires identification of chemical and biological pollutants, allocation of pollution discharges among the dischargers (which typically include industrial manufacturers, agricultural operations, and municipal wastewater treatment plants), and frequent monitoring to ensure the daily budget for pollutant discharges is not being exceeded. Dischargers' releases of contaminants are regulated under their individual National Pollutant Discharge Elimination System (NPDES) permits.

Although most discharges of pollutants from factories and cities have been controlled through NPDES permits for years, water quality problems still remain. Some of these problems are associated with runoff from rain and snow melt. The stormwater runoff picks up soil and pollutants from city streets, construction sites, loading docks and other areas at industrial facilities, suburban lawns, and rural farm fields and then deposits the contaminants in nearby water bodies. Even air pollutants from cars, power plants, and other combustion sources harm our water bodies when pollutants fall back to earth or are carried to the ground by precipitation.

EPA's TMDL data released in January show an increase in the number of impaired water bodies in the United States. EPA notes that roughly 34,000 impaired water bodies are listed by 50 states, territories, and tribes with about 59,000 impairments from multiple pollutants. Metals rank at the top of the list of impairments, followed by pathogens, nutrients, sediment/siltation, and organic enrichment/low dissolved oxygen. EPA has approved only slightly more than 18,000 TMDLs.

Some critics think that mercury pollution plays a disproportionately large role in impairing our water bodies. Linda Eichmiller, the deputy director of the Association of State and Interstate Water Pollution Control Agencies, recently pointed out that the vast majority of water impairments from metals are due to mercury deposition from air. Mercury is typically produced as a byproduct of the combustion of coal at coal-fired power plants and dispersed through air emissions from the plants.

"Mercury TMDLs require the assistance of state and federal air programs, but that coordination has been lacking," Eichmiller said. "If you take mercury away from the list of impairments, the remaining major causes are nutrients and pathogens."

EPA has been working to find ways to better implement the TMDL process. Early this year, it released the first phase of an online system that helps investigators in states, territories, and tribal areas determine the most likely causes of aquatic impairments and recommend appropriate remedial, regulatory, or restorative actions. The Causal Analysis/Diagnostic Decision Information System (CADDIS) is an online system that builds upon EPA's Stressor Identification Guidance, which was published in December 2000. The guidance provides a formal process to identify stressors causing biological impairments in aquatic ecosystems -- such as fish kills -- and provides a structure for organizing the scientific evidence to reach a particular conclusion, according to the agency.

Hopefully, new tools like CADDIS will lead to improved implementation of the TMDL program and allow stakeholders to work together on the important goal of restoring the health of our nation's waterways.


This editorial originally appeared in the October 2006 issue of Environmental Protection, Vol. 17, No. 8

This article originally appeared in the 10/01/2006 issue of Environmental Protection.

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