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ITERATIVE APPLICATION OF THE EPA'S STRESSOR IDENTIFICATION GUIDANCE DISCOVERS AN ILLICIT DISCHARGE AND RESIDUAL DAM-ASSOCIATED IMPAIRMENT
Citation:
Cormier, S M., S B. Norton, G Suter, B Subramanian, C. Bellucci, AND G. Hoffman. ITERATIVE APPLICATION OF THE EPA'S STRESSOR IDENTIFICATION GUIDANCE DISCOVERS AN ILLICIT DISCHARGE AND RESIDUAL DAM-ASSOCIATED IMPAIRMENT. Presented at Society of Environmental Toxicology & Chemistry, Portland, OR, November 14-18, 2004.
Impact/Purpose:
The purpose of this research project is to provide methods, tools and guidance to Regions, States and Tribes to support the TMDL program. This research will investigate new measurement methods and models to link stressors to biological responses and will use existing data and knowledge to develop strategies to determine the causes of biological impairment in rivers and streams. Research will be performed across multiple spatial scales, site, subwatershed, watershed, basin, ecoregion and regional/state.
Description:
EPA guidance for identifying causes of biological impairments is becoming more commonly applied by states to analyze evidence, logically determine causes, and document the process. One example is an investigation of biological impairment in the Willimantic River in Connecticut that occurred upstream from an NPDES regulated source. Initial analysis of six possible candidate causes indicated that none of the causes were sufficient to result in the level of effects at the site. Additional data, collected to identify the spatial extent of the impairment, revealed an episodic, illicit discharge of industrial wastewater. Biological condition improved following rerouting of the discharge to the waste treatment facility, providing a form of experimental evidence supporting a toxic cause of the biological impairment. Although improved, the biological diversity at the site remained at levels that precluded attainment of state biocriteria. The biological impairment was re-examined based on similarities of the site and four additional impaired sites and dissimilarities with four reference sites in the same waterhsed. All five impaired sites were located below old mill dams where water temperatures were elevated to levels reported to cause biological effects. The impoundments may also reduce summertime base flow and alter food resources towards more fine filterable particles. Hence, reservoirs may be reducing diversity at the impaired sites by more than one mechanism.