On Monday, Mountain Water attorney Stephen Brown said company officials became worried after reading recent warnings from University of Montana scientists who claim much more toxic sediment than expected was released after Milltown Dam's breaching last March.
In particular, Mountain Water officials fear Missoula's sole-source aquifer also might be hit harder than predicted. And they want reassurance that EPA's modeling and monitoring systems are still accurate.
EPA Milltown project manager Russ Forba received Mountain Water's concerns Monday. He said a public meeting on Oct. 14 should provide most of the answers, and they should be both favorable and reassuring. He also maintained that competing methods of measuring sediment have created confusion.
“As the project moves along, we'll look to see any need for additional information, and we'll take the requests seriously,” Forba said. “At this point in time, I don't feel it's necessary.”
Mountain Water's letter to Forba raised several concerns. The first was a claim that more than 600,000 cubic yards of contaminated sediment had been scoured out of Milltown Reservoir so far in 2008 - when the EPA predicted about 406,000 cubic yards would come out over a four-year period.
“In light of EPA's failure to accurately predict the sediment scouring rate, MWC submits that the river protection mechanisms need to be reanalyzed to ensure that no further events like this happen again,” Brown wrote. “Unpredicted actual releases require that the monitoring and modeling program also be redone.”
The 600,000-cubic-yard figure comes from research by the University of Montana Center for Riverine Science and Stream Renaturalization, according to its director, geology professor Johnnie Moore. It's based on published U.S. Geological Survey tests of river water above and below the Milltown Dam site, and uses weekly sediment samples to mathematically estimate how much gunk has come out of the old reservoir bed.
In addition, Moore said the UM figure includes sediment from “bed-load analysis.” That's the undissolved stuff that gets pushed along the bottom of the river, which typically winds up in sandbars. Moore said the big new sandbars at Sha-Ron fishing access, by the Reserve Street Bridge and along Kelly Island are examples of bed-load deposits.
The EPA, however, disputes UM's findings.
“We disagree with that number,” Forba said. The EPA also uses USGS river data, but it has access to daily samples rather than weekly checks. Those numbers are still being crunched, and will be released at the Oct. 14 meeting. But Forba predicted they would be “considerably less” than 600,000 cubic yards.
Mountain Water also asked about new river sediment piling up in Missoula irrigation ditches, possible changes to an underground plume of arsenic-contaminated water near Milltown, and the potential for either too much toxic material or not enough water getting into Missoula's drinking water aquifer.
“It would be both ironic and unfortunate if EPA's actions to protect the environment somehow compromised the viability of the very water supply that EPA recognized must be protected,” Brown wrote.
Forba replied that those concerns were ungrounded. EPA staff members have been working with Missoula's irrigation district on the ditch sediment, and samples have shown concentrations of 13 milligrams of arsenic per kilo. By comparison, EPA's residential contamination threshold - how much arsenic can be present in someone's backyard without danger - is 150 milligrams per kilo.
EPA will be helping clean some sand out of the ditches this fall, Forba said. But while that sand may block water flows, it generally doesn't contain toxic chemicals. Milltown's underground arsenic plume has also shown decreases in arsenic since the dam was removed.
As for the potential changes in water flow into the Missoula aquifer, Forba said there was no indication that was happening. Brown acknowledged that Mountain Water does not have any new data about aquifer flows, but was worried about the possibility of sediment shifts hurting its ability to supply drinking water.
Mountain Water did ask for repayment of $7,410.63 it spent to fix two Milltown-area wells affected by the dam removal. Forba said that invoice is being reviewed.
In any case, Brown said the Sept. 25 letter to the EPA was not a threat of lawsuit or other action.
“We're at a point where the construction is going to start slowing down for the season,” he said. “If there's a time to look at things over the course of the winter, we'd like the EPA to take a look at that before construction starts up again.”
Clean talk
U.S. Environmental Protection Agency staff will be on the bluff overlooking the Milltown Dam cleanup to offer a visual tour of the project and answer questions from the public on Tuesday, Oct. 14 from 4-5:30 p.m. Then they'll hold a public meeting from 6:30-8:30 p.m. in the Bonner School gym to provide an update on project activities, report on recent water-quality and sediment studies, and to discuss community questions and concerns.
Reporter Rob Chaney can be reached at 523-5382 or at rchaney@missoulian.com.
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