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Willamette Basin Mercury 2019

Title: Revised Willamette Basin Mercury
Water Quality Limited Parameters: Mercury
Pollutants: Methylmercury and Total Mercury
Status: EPA Issued Final TMDL on Feb. 4, 2021

Project summary

On Nov. 22, 2019, DEQ issued the Final Revised Willamette Basin Mercury Total Maximum Daily Load that was submitted to the U.S. Environmental Protection Agency for action. EPA disapproved DEQ's TMDL on Dec. 30, 2019 and issued their final TMDL on Feb. 4, 2021 following a public comment period. EPA notified DEQ that, “EPA has established this TMDL and is hereby providing it to the State for implementation."  EPA's TMDL states that reasonable assurance for their TMDL relies on DEQ's Water Quality Management Plan. The plan was issued on Nov. 22, 2019 as part of the DEQ TMDL. The total mercury allocations specified in EPA's TMDL are effective for designated management agencies and responsible persons named in DEQ's management plan. 

DEQ will be working with agencies and responsible persons to implement the water quality management plan. The plan describes a multi-faceted approach that requires implementation of management practices through development of TMDL implementation plans by multiple federal, state, and local agencies, and responsible persons across the entire Willamette Basin to reduce human-caused sources of mercury. TMDL implementation plans will contain measurable objectives, milestones and timelines, and must be approved by DEQ staff. Annual and five-year reviews ensure agencies and responsible persons are on track for making sustained progress in implementing management strategies to reduce mercury primarily through control of erosion and sediment runoff. In addition, the plan includes development of mercury minimization plans for major point source dischargers and reduction of mercury in stormwater runoff through requirements contained in stormwater permits. DEQ expects that with implementation of the water quality management plan, mercury water quality standards will be met. 

DEQ will further develop its Monitoring Strategy to Support Implementation of the Willamette Mercury Total Maximum Daily Load in collaboration with designated management agencies and other stakeholders to inform adaptive management strategies and assess progress toward attaining mercury criteria over time. In addition, DEQ developed an empirical relationship between total suspended solids and total mercury using observed data. DEQ set interim goals for reductions in total suspended solids to measure progress in the reduction of total mercury loads.

DEQ is developing workshops to help designated management agencies and responsible persons understand their implementation responsibilities to reduce mercury inputs to waterbodies as specified in the Nov. 22, 2019 Water Quality Management Plan. DEQ will announce workshop dates on the Willamette Basin webpage in the near future.

DEQ and the EPA worked together to revise the 2006 Willamette Basin Mercury TMDL to meet the fish tissue methylmercury criterion adopted in 2011. This criterion allows Oregonians to safely consume higher amounts of fish (approximately 23 8-oz fish meals a month) caught in Oregon waterways. Among those who rely on Willamette Basin fish and shellfish as a food source are tribal, immigrant and low-income communities and other historically marginalized communities.

Water quality standards are in place to protect people from high levels of mercury exposure when eating fish and shellfish. The Willamette River and many of its tributaries do not currently meet water quality standards for mercury and are included on Oregon's list of impaired waters under Clean Water Act §303(d). Mercury fish consumption advisories are in place throughout the Willamette Basin.

The TMDL identified sources of mercury and how much mercury needs to be reduced to meet water quality standards. The TMDL used linked models and significantly more data than the 2006 TMDL. The greatest source of mercury in the basin is from atmospheric deposition, which is mercury in the air falling onto the land or into the water. The mercury in air originates mainly from national and global sources rather than from sources in Oregon.

Once mercury is deposited on the landscape, the major pathways to streams are erosion of sediment-bound mercury and surface runoff. Of the many different types of land use that exist within the Willamette Basin, forestry, agriculture and urban uses comprise most of the area within the basin. Management actions on these land uses influence the amount of mercury from these sources that reach streams and rivers in the basin. Point source discharges, such as sewage treatment plants or industries, contribute significantly less mercury to streams than nonpoint sources, such as runoff from logging roads and agricultural fields.

The water quality management plan describes DEQ's plan for implementing actions to reduce mercury in fish tissue. Mercury minimization measures will be applied for both point and nonpoint source activities, with primary focus on reducing runoff and erosion from nonpoint source activities and urban stormwater. Effectiveness of these measures will be tracked, evaluated and improved, as warranted, to meet the standards.​

Following a public comment period from July 3, 2019 to Sept. 6, 2019, DEQ issued the Revised Willamette Basin Mercury TMDL on Nov. 22, 2019. The updated TMDL built upon the original TMDL modeling analysis and made substantial improvements.

On Nov. 29, 2019, EPA disapproved the TMDL after determining that the load and waste load allocations based on percent reductions would not achieve the TMDL target in all the subbasins addressed by the TMDL. Under the Clean Water Act and implementing federal regulations, EPA established a new TMDL on Dec. 30, 2019, which became effective for Clean Water Act purposes. EPA's TMDL incorporated some of Oregon's 2019 TMDL with the major changes being revisions of some of the load and wasteload allocations.

EPA accepted public comments on the Dec. 30, 2019 TMDL from Jan. 6, 2020 through Feb. 4, 2020, and revised the TMDL in response to comments received. EPA issued the final TMDL on Feb. 4, 2021.  EPA's TMDL (EPA's 2019 TMDL, as revised to address public comments received in 2020) incorporates by reference those sections of DEQ's 2019 TMDL that EPA found to be consistent with the Clean Water Act and EPA's requirements. ​

​Monitoring Strategy

DEQ will announce workshops on this website to assist DMAs and responsible persons in implementing requirements specified in the Willamette Basin Mercury WQMP.

Guidelines, Tools and Reporting

​​For requesting data, models or other information used in this TMDL, please complete a "Public Records Request".

Advisory committee meetings

Public hearing and request for comments

Fact Sheets


Willamette Basin Coordinators

For questions about EPA’s TMDL, please contact: