Aquatic Life Use Support (ALUS) - Integration of Different Data Types in Making an ALUS Determination

The following guidelines apply to ALUS determinations for wadeable streams and rivers when biological, habitat, chemical, and/or toxicity data types are available.

Determination of ALUS Using More Than One Data Type

ALUS Attainment
A. Fully Supporting:	No impairment indicated by all data types
B. Fully Supporting but Threatened:	No impairment indicated by all data types; one or more categories indicate an apparent decline in ecological quality over time or potential water quality problems requiring additional data or verification, or  Other information suggests a threatened determination
ALUS Non-attainment
C. *Partially Supporting:	Impairment indicated by one or more data types and no impairment indicated by others.
D. *Not Supporting:	Impairment indicated by all data types
* A determination of partially supporting or not supporting could be made based on the nature and rigor of the data and site-specific conditions in the results of the data types. If bioassessment (usually Level 3 or 4) indicates impairment, then a determination of not supporting should be made. See case studies.

These guidelines strongly emphasize the use of biological data for the assessment of ALUS specific to wadeable streams and rivers. However, the basic principles are applicable to other waterbody types. This guidance has undergone external peer-review and has been revised to address the principle peer-review recommendations to improve the guidance. In addition, peer review recommendations were made to expand the guidance to (1) develop a confidence icon for the overall assessment and (2) develop guidelines that consider the results from biological, chemical and physical assessments in relation to their role as response, stressor or exposure indicators. The peer review specifically recommended that EPA develop a weighting algorithm for biological results (as response indicator) in relation to results from physical/chemical, habitat, and toxicological assessments (as stressor/exposure indicators). These latter recommendations will be evaluated for future guidelines. EPA considers the current guidelines, particularly consideration of level of information, as providing the initial basis for addressing these additional peer review recommendations.

Case Studies

EPA recommends consideration of the level of information of the different data types in evaluating degree of impairment (partial support vs. nonsupport). Case studies demonstrate how ALUS determinations could be made based on types of data, level of information, and site specific information and conditions, and are not intended to cover all possible situations but to highlight commonly encountered scenarios. These case studies are based on actual State examples that represent a State's decision process in making an ALUS determination, and are presented in a uniform manner for illustration. Different states use different ordinal scales for assessment.

Generally, assessments based on data with high levels of information should be weighted more heavily than those based on data with low levels of information, and biological data should be weighted more heavily than other data types. In particular, it is recommended that the results of biological assessments, especially those with high levels of information, be the basis for the overall ALUS determination if the data indicate impairment. This is because the biological data provide a direct measure of the status of the aquatic biota and detect the cumulative impact of multiple stressors on the aquatic community, including new or previously undetected stressors. This approach is consistent with EPA's Policy on Independent Application while incorporating a weight of evidence approach in determining the degree of impairment (partial or nonsupport). The Policy does not allow for a determination of full support when there are differences in assessment results when at least one assessment indicates impairment. For example, it is possible to arrive at an overall assessment of partial support where biological data indicate full support and other data types indicate some level of impairment.