Identifying Ecological Impairment

Background

The objective of the Clean Water Act (CWA) is to "restore and maintain the physical, chemical, and biological integrity of the Nation's waters". To achieve this objective, Section 303(c) of the Act mandates that states adopt Water Quality Standards that include designated uses for waters, as well as narrative and numeric criteria to protect those uses. When a state determines that waters do not meet these standards or criteria, they are considered impaired. Under section 303(d) of the CWA, states must develop lists of all impaired water bodies and prioritize these waters for establishment of Total Maximum Daily Loads (TMDLs) designed to restore degraded areas. Given limited financial resources and limited data, models are needed that help predict aquatic resource impairment in support of the 303(d) process, thus providing states with an explicit rationale for targeting their follow up investigations of aquatic resources in a focused manner.

Approach

AED is employing a staged approach that starts with an accurate, though broad-scale, overall assessment of the quality of all waters, then refines that assessment through screening models to target monitoring in areas which have a high probability of impairment. AED's research to identify ecological impairment is intended to develop assessment tools to improve our understanding of the quantitative relationships among watershed characteristics associated with impairment, known stressors, and aquatic resource condition. Building upon such associations, the probability of impairment in streams and coastal waters across an entire state or region should be predictable. The tools developed to make such predictions will support the states in meeting the listing requirements of 303(d). These tools will link 305(b) reports on condition to 303(d) listing of impairment, and ultimately to the establishment of TMDLs. All of this research supports implementation of the recent Consolidated Assessment and Listing Methodology (CALM) provided by the EPA Office of Water.

Contact: Wayne Munns

Identifying Ecological Impairment

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