Water Quality

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 specific pollutant and a specific water body, and reflect the highest attainable condition for a specific period of time.

Willamette B​​​asin Mercury Variance

On January 24, 2020, the Environmental Quality Commission adopted rules that 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. EPA approved adopted changes to the variance authorization rule. U.S. EPA is still evaluating the mercury multiple discharger variance.​

Related docu​ments and links

EQC staff report

EPA Approval of Variance Authorization Rule

Mercury MDV Rulemaking web page 

Background Fact Sheet: Mercury in Oregon Waters 

Keep up-to-date

green envelopeStay informed about the mercury variance rulemaking by signing up here to receive email updates. DEQ will add new information about the rulemaking to this webpage as it becomes available.


Aron Borok, 503-229-5050 
Debra Sturdevant,503-229-6691 (toll-free at 800-452-4011)