Although it held its own throughout much of the 1998 legislative session, Idaho Conservation League officials believe they suffered their major setback within weeks of the opening gavel.
League issues director Scott Brown says he believes the measure exempting the mines from state groundwater quality standards in certain circumstances has the potential for environmental damage.
The Division of Environmental Quality rule will not consider naturally occurring substances as pollutants when found in groundwater around active mines as long as the miners have used best management practices in extracting the ore.
Environmentalists urged lawmakers to reject the rule, arguing that contamination can migrate from mining sites in groundwater that is all but impossible to purify again.
But Idaho Mining Association Director Jack Lyman led the campaign in support of the proposal, maintaining it would not threaten public health or the environment.
He said state regulators could still hold mining companies responsible if contamination away from mines reached unacceptably high concentrations of mining-related pollutants and force them to cease operations.