Assessing the TMDL Approach to Water Quality Management (2001) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-11
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Today, pollutants such as nutrients and sediment, which are often associated with nonpoint sources and were not considered criteria pollutants in the Clean Water Act, are jeopardizing water quality, as are habitat destruction, changes in flow regimes, and introduction of exotic species. This array of challenges has shifted the focus of water quality management from effluent-based to ambient-based water quality standards.
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assess the scientific basis of the TMDL program, including: · the information required to identify sources of pollutant loadings and their respective contributions to water quality impairment, the information required to allocate reductions in pollutant Toadings among sources, whether such information is available for use by the states and whether such information, if available, is reliable, and · if such information is not available or is not reliable, what methodologies should be used to obtain such information. Of concern to the nation's lawmakers was the paucity of data and information available to the states to comply with program requirements and meet water quality standards.
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However, the success of the nation's premier water quality program should not be measured by the number of TMDL plans completed and approved, nor by the number of NPDES permits issued or cost share dollars spent. Success is achieved when the condition of a waterbody supports its designated use.
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The states and EPA should move forward with decision-making and implementation of the TMDL program in the face of this uncertainty while making substantial efforts to reduce uncertainty. Securing designated uses is limited not only by a focus on administrative rather than water quality outcomes in the TMDL process, but also by unreasonable expectations for predictive certainty among regulators, affected sources, and stakeholders.
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TMDL plans should employ adaptive implementation. As shown in Figure ES-2, adaptive implementation is a cyclical process in which TMDL plans are periodically assessed for their achievement of water quality standards including designated uses.
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. TMDL Planning ..
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\ yes Back to initial list of all waters for continuing assessment in the rotating basin process FIGURE ES-2 Adaptive implementation flowchart. USE OF SCIENCE IN THE TMDL PROGRAM 7 This report suggests changes in the data used and analytical methods employed that wall support the revisions to the TMDL process recommended above.
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In general, biological criteria are more closely related to the designated uses of waterbodies than are physical or chemical measurements. However, guiding management actions to achieve water quality goals based on biological criteria also depends on appropriate modeling efforts.
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For biological parameters, they might focus on improvement of sampling designs, more careful identification of the components of biology used as indicators, and analytical procedures that explore biological data as well as integrate biological information with other relevant data. TMDL Development The scientific basis of the latter half of the TMDL process revolves around a wide variety of models of varying complexity that are used to relate waterbody conditions to different land uses and other factors.
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Prediction uncertainty must be estimated in a rigorous way, models must be selected and rejected on the basis of a prediction error criterion, and guidance/software needs to be developed to support uncertainty analysis. The TMDL program currently accounts for the uncertainty embedded in the modeling exercise by applying a margin of safety (MOS)
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FINAL THOUGHTS Through the adoption and use of the preliminary list/action list approach, adequate monitoring and assessment approaches, sound selection of appropriate models, and adaptive implementation described in this report, the TMDL program will be capable of utilizing the best available scientific information. It is worth noting that the success of these approaches is directly related to the provision of adequate personnel and financial resources for data collection, management, and interpretation and for the development of sufficiently detailed and stratified water quality standards.
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