MT HB587

Revises the definition of "material damage" to the hydrologic balance outside a mine permit area, requiring a "quantifiable adverse impact" that "precludes an existing or reasonably foreseeable use" of surface or ground water rather than the previous standard of any degradation affecting water quality standards or water rights

Clarifies that when federal or state hydrologic information is unavailable for permit applications, the Department of Environmental Quality must make determinations using hydrologic and geologic information collected by the applicant

Applies retroactively to pending judicial review actions and other challenges to mining permits, amendments, or licenses that have not yet been decided

Includes contingent voidness provision: any portion disapproved by the U.S. Secretary of the Interior under federal mining regulations (30 CFR 732) becomes void

Takes effect immediately upon passage and approval