A scientific critique of EPA's guidance on sufficient, credible data and use support criteria as used in Montana

Conservation groups have brought numerous lawsuits against the EPA and stat e agencies because only a small fraction of impaired U.S. streams have had TMDLs (total maximum daily loads) developed as required under the Clean Wat er Act. In 1997, the Montana Legislature directed the Montana Department of Environmental Quality to remove streams from the impaired list unless ther e was sufficient, credible evidence of impairment. Using EPA guidance, MTDE Q has developed a protocol for evaluating whether there is sufficient, cred ible evidence to determine use support, and, if so, whether uses are being supported (see http://www.deq.mt.gov/ppa/tmdldata.htm). A number of streams have been delisted either because there was insufficient evidence to deter mine whether uses were supported, or because the criteria for use support a ppeared to be satisfied. Some of these delistings will be examined to evalu ate the clarity and consistency of the sufficient, credible data.