Approaches to TMDL planning and implementation and policy tools for implementation to achieve water quality standards.

Abstract

Abstract This review is based primarily on information gathered in the TMDL Knowledgebase Clearinghouse developed by the Center for Total Maximum Daily Load (TMDL) and Watershed Studies at Virginia Tech. The TMDL programme has received renewed attention since the US Environmental Protection Agency (EPA) published revised guidelines in 1991. Under the TMDL programme, pollutant-specific TMDLs are developed for impaired waters. A TMDL specifies the pollutant load reductions needed to achieve water quality standards. The magnitude and distribution of the load reductions among pollution sources can have implications for watershed stakeholders. Implementing the TMDL load reductions is the responsibility of the individual US states. Adaptive implementation occurs when limited corrective actions designed to improve water quality are implemented using available information and data; and as information and data availability improve implementation adjustments are made, i.e. 'learn while doing'. While several policy tools are available to ensure that corrective actions are implemented, economic incentives are most often used, particularly for non-point source pollution sources. Typically, successful TMDL implementation depends on careful planning and stakeholder engagement. However, meaningful stakeholder engagement requires that stakeholders be empowered to make decisions about outcomes relevant to their goals, which may be problematic given the narrow way the TMDL process is currently enacted. Planning using watershed-scale models to assess plausible load reduction scenarios is most likely to produce credible TMDL pollutant load estimates. Models should be coupled with adaptive implementation so that pollutant load estimates can be revised as better information becomes available. TMDL implementation plans should consider both barriers to and opportunities for implementation.