The Environmental Protection Agency has established a new plan to reduce mercury pollution in the Willamette Basin but it may be hard to achieve.

This comes after the EPA rejected the Oregon Department of Environmental Quality’s Total Maximum Daily Load or TMDL plan last month. The agency said the DEQ’s plan would not sufficiently reduce mercury pollution in certain tributaries of the Willamette and it did not comply with Clean Water Act and federal regulations.

The TMDL plan limits the amount of mercury pollution that can be present in all 12 sub-basins of the Willamette Basin.

The EPA’s new plan incorporates much of DEQ’s plan, with the most significant changes being revisions to several load and waste load allocations.

David Croxton is a watershed manager with the EPA who worked on developing the plan. He said the biggest contributor to mercury pollution is atmospheric deposition.

“One thing to understand about mercury contamination is that 96% is from atmospheric deposition and the amount of mercury that’s coming directly from these kind of point source problems like industrial facilities or wastewater treatment plants, that’s 1%,” said Croxton. “Then there’s 3% that’s made from controlled stormwater.”

Croxton said atmospheric deposition has been increasing over time, but there are a number of international efforts working to reduce the global transmission of mercury.

But the plan sets a high bar that the agencies may not be able to reach.

“They’re assuming that there will be this greater reduction in mercury in the atmosphere that then leads to less mercury going into the river from that cause. We already had a pretty high number,” said DEQ’s Harry Esteve.

The agency kept DEQ’s recommended 88% mercury reduction in seven sub-basins but increased to 97% reduction in five sub-basins.

Esteve said the DEQ’s plan was already a challenge to fully implement.

“By increasing some of the percentages, the EPA’s plan would present an even greater challenge,” Esteve said.

EPA senior public information officer Mark MacIntyre said the agency will continue to work with the DEQ in developing ways to reduce water toxicity.

“We recognized that the state of Oregon has done just an incredibly heavy lift on creating a TMDL,” MacIntyre said. “… no matter where they are written, [they] take a lot of energy and a lot of time.”

The EPA’s Willamette Basin Mercury TMDL will be open for public comment through Feb. 4.