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(003) Mercury TMDLs: A Case Study in Addressing a Cross-Media Pollutant.
Chemerys, Ruth*,1, Waite, Randy2, Atkinson, R. Dwight1, Cocca, Paul1, 1 US Environmental Protection Agency, Washington, DC, US2 US Environmental Protection Agency, Research Triangle Park, NC, US
ABSTRACT- Total Maximum Daily Loads (TMDLs) for mercury-impaired waters illustrate the regulatory challenges that EPA and state water programs face in addressing a cross-media pollutant. Under the Clean Water Act, states must identify waters not meeting water quality standards and develop TMDLs for those waters. TMDLs specify pollutant reductions needed to meet standards and allocate the load reductions among pollutant sources. Yet mercury sources may be outside the purview of state and even federal regulatory programs. Atmospheric deposition is the dominant mercury source in many waterbodies and may be from local, regional, and international sources. Similar issues pertain to TMDLs involving air deposition of other pollutants such as nitrogen, dioxin, and cadmium. The limited number of mercury TMDLs developed to date manifest these issues. In TMDLs for waterbodies in Georgia, an estimated 99% of the mercury load is from air sources, with less than 1% from water point sources. Previous analyses of air sources indicate that emissions reductions anticipated under existing requirements will not always be sufficient to achieve water quality standards. Continued coordination with the air and international programs is needed to identify expected reductions in mercury loadings to water. In waterbodies where naturally-occurring mercury or loadings from past mining activity are significant, water managers must coordinate with programs such as Superfund regarding solutions. Given the widespread mercury fish consumption advisories nationwide, EPA, states, and others are examining tools and approaches for addressing mercury impairments. In two pilot projects, EPA evaluated air modeling tools for estimating relative mercury deposition to a waterbody from different source categories (e.g., incinerators) and geographic areas (e.g., neighboring states). Another approach to mercury TMDLs is the use of screening tools that can predict mercury reductions needed to achieve water quality standards on a broad geographic scale, rather than on an individual waterbody basis. EPA and states are also examining whether approaches other than TMDLs, such as state commitments to mercury phase-out activities, may be more effective mechanisms for achieving water quality goals.
Key words: mercury, TMDLs, air, regulatory
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