Total maximum daily loads
- By Kyle S. Swinney
- Nov 01, 1999
Water quality management has reached a crossroads in the United States. Despite significant progress in the fight for clean water and water-dependent resources over the last 25 years, in 1996 35 percent of rivers and streams, 39 percent of lakes, 38 percent of estuaries and 13 percent of ocean shoreline waters were still not meeting their designated uses. This equates to approximately 20,000 waterbodies across the country that are threatened or impaired.
Stormwater, which acts as a major conveyance of pollutants from urban, agricultural and forest settings to surrounding waterbodies, is a leading cause of these continuing impairments. This polluted runoff, known as nonpoint source pollution, is very difficult to control because of its diffuse nature, and because regulatory mechanisms for controlling it are widely distributed among a variety of federal, state and local agencies.
The water quality management community has focused significant effort over the last five years on improving its ability to manage nonpoint sources of pollution, including assessing watershed impacts associated with various nonpoint sources, developing and transferring effective monitoring techniques, and evaluating best management practices for controlling nonpoint sources.
Among the most far-reaching and controversial of these efforts is the U.S. Environmental Protection Agency's (EPA) emphasis on a tool known as total maximum daily loads (TMDLs). Depending upon who you ask, TMDLs represent a comprehensive and valuable water quality planning tool, a technical challenge, a regulatory burden, a legal battle, a workload conundrum or all of the above. At a minimum, the processes and issues involved in the development of TMDLs are at the leading edge of water quality management in this country.
What is a TMDL?
Simply stated, TMDLs represent an estimate of the capacity of a specific waterbody to assimilate pollution and still achieve designated uses. The designated uses of a waterbody are identified for protection by states through their water quality standards. Typical designated uses include public drinking water supplies; recreational waters; uses supporting agriculture (e.g., irrigation, consumption by livestock, etc.); uses supporting industry (e.g., cooling water, process water supplies); protection and propagation of fish, shellfish and wildlife; and navigational uses. The ability of a waterbody to maintain these uses is affected by a variety of natural and human-induced factors, including the introduction of pollutants. Therefore, the ultimate goal of a TMDL is to restrict these human-induced factors to levels that protect desired waterbody uses.
The process for developing a TMDL involves a number of technically rigorous requirements. First, the nature of the waterbody impairment must be understood, including identifying the desired water quality objective and the pollutant, or combination of pollutants, that is causing the impairment. Second, the maximum load of the pollutant that can be allowed while still achieving the water quality objective must be determined. Third, this total maximum allowable pollutant load must be allocated to the various point sources and nonpoint sources that discharge the pollutant to the waterbody.
The process of determining the maximum allowable pollutant load and allocating that load to the appropriate point and nonpoint sources typically involves a variety of watershed-scale models. This process must also make appropriate allowances for factors such as seasonal variations and future growth in the watershed, along with a margin of safety to account for any uncertainty in the models that are used.
Finally, appropriate regulatory control measures (e.g., discharge permits) and voluntary management practices (e.g., fertilizer management plans) must be implemented by the point and nonpoint sources to achieve their allocated loads. This final step provides an opportunity to better coordinate the universe of water quality management practices, with a focus on the problems that create the highest risk. When properly applied, a TMDL can be a significant tool that contributes to the attainment of water quality goals.
The Clean Water Act and TMDL regulations
The concept of TMDLs is rooted in Section 303(d) of the Clean Water Act (CWA), which requires states to identify waterbodies that do not meet designated uses and establish TMDLs to restore them. EPA requires the states to submit their lists of impaired or threatened waterbodies (known as 303(d) lists) for review every two years, identifying those waterbodies that will receive priority attention for TMDL development. The CWA also requires EPA to complete these actions if the states fail to do so.
Section 303(d) and the development of TMDLs went virtually unnoticed throughout the 1970s and most of the 1980s. That all changed, however, in 1986, due to a series of nearly 30 lawsuits brought by a number of environmental advocacy groups. The plaintiffs in these groups alleged that EPA had failed both to carry out its responsibilities to oversee states' activities under Section 303(d), and to step in when states had failed to carry out the program.
One of the more prominent of these lawsuits, filed by the Sierra Club against EPA and the state of Georgia (939 Federal Supplement 865 (N.D. Ga. 1996)), was resolved in 1997 through a consent decree that sets out a schedule for establishing TMDLs in each of Georgia's watershed basins. The consent decree also requires EPA to establish TMDLs if Georgia fails to do so, review Georgia's continuing planning process and conduct a biennial review of Georgia's TMDL program.
Similar results stemming from other litigation around the country have greatly increased the visibility of the TMDL/303(d) program, along with EPA's and state water quality agencies' associated workloads. EPA Region 4 estimates that between 10,000 and 12,000 TMDLs will need to be developed in its states alone (Kentucky, Tennessee, North Carolina, South Carolina, Georgia, Alabama, Mississippi and Florida) over the next 10 years.
This legal pressure has led EPA to place a much higher priority on the TMDL program, to better meet the responsibilities associated with it. In 1996, EPA convened a TMDL advisory committee, under the auspices of the National Advisory Council for Environmental Policy, to "develop advice on new policy and regulatory directions for the program regarding its role in watershed protection, the identification of impaired waters, the pace of TMDL development, the science and tools needed to support the program, and the roles and responsibilities of States, Tribes and EPA in implementing the program."
Among its recommendations, the committee concluded that restoring impaired waters identified through the 303(d) listing process must become a high priority in the United States; that TMDL implementation, not just TMDL development, is the key to success; and that governments' capacity to carry out the responsibilities associated with TMDLs must be significantly strengthened.
Partly as a result of the recommendations made by the TMDL advisory committee, on August 23, 1999, EPA proposed revised regulations for Section 303(d) and the TMDL program to "provide States, Territories and authorized Tribes with the necessary information to identify impaired waters and to establish TMDLs to restore water quality." The proposed revisions to the TMDL regulations provide a more detailed explanation of the program, including what constitutes an acceptable list of impaired or threatened waterbodies under Section 303(d); requirements concerning schedules for TMDL development; and clarification of what must be included in a TMDL, including a new requirement for a plan that describes how the TMDL will be implemented.
Not surprisingly, EPA's proposed revisions to the TMDL regulations have been greeted by a high level of anxiety from a variety of directions. Several states have expressed concern that establishing TMDLs as the primary mechanism for managing water quality exceeds EPA's authority to regulate nonpoint sources under the CWA. In particular, some states assert that Congress intended for nonpoint sources to be managed by the states, not by EPA through the proposed regulatory requirement for TMDL implementation plans.
These concerns have been echoed by the agriculture industry. The National Cattlemen's Association, the National Pork Producers Council, and the American Crop Protection Association have all gone on record stating that "There is no indication in CWA section 303(d) that TMDLs have any application to nonpoint sources."
Ironically, EPA's proposed revisions to the TMDL regulations have also drawn fire from the point source community, which is concerned that an unfair burden for cleaning up the nation's waterbodies could be placed on them relative to nonpoint sources. This concern is based on the fact that point sources represent a "path of least resistance" compared to nonpoint sources, in terms of available regulatory mechanisms for improving water quality. With increased workloads and limited resources at federal and state government levels, organizations like the Association of Metropolitan Sewerage Agencies fear that TMDL implementation will focus on "low-hanging fruit", such as increased limits for wastewater treatment plants, rather than difficult-to-control nonpoint sources.
Despite the legal and technical controversies associated with the revised regulations, many water quality management professionals welcome the attention EPA has brought to the issue of nonpoint source pollution through the TMDL process. There is little argument that the most pressing need in the fight for clean water is implementation of a balanced approach that targets the pollution problems of individual rivers, streams, lakes and estuaries. The TMDL concept offers such an approach. We can only hope that this conclusion is not lost during future debates over its implementation.
What are nonpoint sources of pollution?
Technically speaking, nonpoint sources include any sources of water pollution that do not meet the legal definition of point sources found in Section 502(14) of the Clean Water Act. Practically speaking, the term nonpoint source pollution is generally defined as pollution of the nation's waterbodies by contaminated rainfall or snowmelt moving over and through the ground. As this runoff moves, it picks up and carries away pollutants associated with human activities and deposits them in lakes, rivers, wetlands, coastal waters and ground waters.
Common categories of nonpoint sources include agricultural practices (e.g., over-application of fertilizers, pesticides and large amounts of manure from animal feeding operations), forestry practices (e.g., erosion and sedimentation associated with road construction), stormwater runoff from urbanized areas, recreational boating and marinas, and direct deposition of pollutants onto waterbodies from the atmosphere (i.e., air pollution). On a national level, agricultural nonpoint sources have been blamed for 70 percent of impaired rivers and streams and 49 percent of impaired lake acres.
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This article originally appeared in the November, 1999 issue of Environmental Protection magazine, Vol. 10, Number 11, pp. 28-31.
This article originally appeared in the 11/01/1999 issue of Environmental Protection.