In those cases where evidence suggests more than on e conclusion, independent application applies. States should carefully consider how to codify these criteria. A. Resident biota integrate multiple impacts over time and can detect impairment from known and unknown causes. Biocriteria can be used to verify improvement in water quality in response to regulatory efforts and detect continuing degradation of waters. They provide a framework for developing improved best management practices for nonpoint source impacts.
Numeric criteria can provide effective monitoring criteria for inclusion in permits.
The process of developing biological criteria, including refined use classes, narrative criteria, and numeric criteria, must include agency managers, staff biologists, and the public th rough public hearings and comment. The key to criteria development and revision is a clear statement of measurable objectives. This program guidance document will be supplemented by the document Biological Criteria Development by States that includes case histories of State implementation of biological criteria as narratives, numerics, and some data procedures. The document will be available in October 1 990. A general Biological Criteria Technical Reference Guide wil l also be available for distribution during FY 1991.