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A variance is a regulatory mechanism that provides a temporary alternative target for permitted discharges if a criterion is not currently attainable. The variance includes requirements that the source reduces the pollutant and makes progress toward achieving the standard. Variances are created based on a specific pollutant and a specific water body, and reflect the highest attainable condition for a specific period of time.

Variance authorization rules and the Willamette Basin mercury variance

On Jan. 24, 2020, the Environmental Quality Commission adopted rules that established a multiple discharger variance for methylmercury in the Willamette Basin. The variance proposes a temporary change in the water quality standard because the current standard is not achievable due to global sources of pollution. The EQC also approved amendments to the state variance authorization rule to ensure it is consistent with recent federal variance regulations. On April 13, 2020, U.S. Environmental Protection Agency approved adopted changes to the variance authorization rule. EPA is still evaluating the mercury multiple discharger variance.

Related documents and links


Aron Borok
Water Quality Standards Specialist

James McConaghie
Water Quality Standards Program Coordinator

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