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New Boise Project Seen As Innovative Way To Improve Water Quality

Adam Cotterell
Boise State Public Radio
On maps the Dixie Drain is also labeled the Dixie Slough.

In the middle of working farms between the towns of Notus and Parma, the city of Boise owns a 49 acre field. In March the city plans to start construction there on a unique project to reduce phosphorus in the Boise and Snake Rivers. It's generally referred to as the Dixie Drain Project.

The site for the upcoming project is close enough to the Boise River that you can see the trees along its banks a little to the north.  In the other direction there’s a bluff that disappears into the horizon. But the key feature is the water that runs through the site and empties into the river.

That water is the Dixie Drain. It appears to be something between a large creek and a small river but it’s not a natural landscape feature. The drain was dug in the early 20th century to take excess water from farmer’s fields to the Boise River.

Phosphorus pollution is a serious problem in rivers around the country, including in Idaho’s Snake River. Phosphorus isn’t toxic though -- plants need it to grow. And that’s the problem: Too much phosphorus makes aquatic plants grow like crazy, sucking oxygen from the water. And a lack of oxygen kills fish.

Agricultural fertilizers and manure are the biggest sources of phosphorus pollution, but cities also contribute.

Credit Adam Cotterell / Boise State Public Radio
Boise State Public Radio
Engineers have done some testing of the phosphorus removal process at the city's Dixie Drain site, though on a much smaller scale than will eventually be done there.

By some estimates 40 percent of the phosphorus the Boise River discharges into the Snake River, comes from this drain. The Dixie Drain Project will pump the water out of drain, then remove the phosphorus and pump the water back in.

The city doesn’t have to build this processing plant. In fact, Boise Public Works Director Neal Oldemeyer says that in 2012 the Environmental Protection Agency (EPA) told Boise to do something else: cut way back on the amount of phosphorus coming out of its sewage treatment plants.

“We’re being asked to reduce that by 98 percent,” Oldemyer says. “You can treat for phosphorus in a pretty economical way, down to levels of about a 93 or 94 percent reduction.”

That last 4 or 5 percent is not so easy. Oldemeyer says by buying new equipment and increasing energy use, it would cost millions of dollars a year to get that last little bit of phosphorus out. Engineers figured it would be a little cheaper overall just to build a new facility to remove phosphorus somewhere else.

In the past Boise’s two sewage treatment plants removed the solid waste from the water. That’s where most of the phosphorus is; our digested food. The plants treated the remaining water to get rid of all the things that could directly hurt people but did not try to get dissolved phosphorus out of the water.

Credit Adam Cotterell / Boise State Public Radio
Boise State Public Radio
This pond at west Boise's sewage treatment plant is one of several stops waste water makes before being discharged into the Boise River.

But Boise Public Works leaders have known for years they would eventually have to start removing that dissolved phosphorous at their two sewage treatment plants. Idaho’s Department of Environmental Quality had made plans to deal with the deteriorating health of the Snake River near Hells Canyon. Those plans include the Boise River and would involve EPA regulations.

Knowing the EPA regulations were coming, Boise started laying the groundwork for the Dixie Drain Project in 2009 and 2010.

The city went to the EPA with a proposal. Neal Oldemeyer says they asked the EPA to let them reduce their output by 94 instead of 98 percent, in exchange for doing something better.

“Every pound that we do not remove at our treatment facility, we go downstream and remove a pound and a half." Oldemeyer says.

Credit screen grab / google.com/maps
Here's a birds-eye view of the Dixie Drain. The site where Boise plans to build its phosphorus removal facility is the the tan colored spot in the middle where the north/south road bends to go east/west.

Jim Werntz, head of the EPA in Idaho, says at first his agency was skeptical. But Werntz says it didn’t take long for them to get excited about the project. That’s because the plan essentially jumps over the regulations to address the root problem more effectively than the regulations would. That problem is the health of the Boise and Snake Rivers. 

“We understood that the river wasn’t going to get cleaned up only by dealing with the pipes that come from the city treatment plants and industries and others, without also dealing with those agricultural drains,” Werntz says.

The EPA does not have authority to regulate farmers like it does cities. The Dixie Drain Project appealed to the federal agency, in part because it gets a city on board to help deal with agricultural pollution.

Boise City Engineer John Tensen says placing the new facility near the end of the drain is far more efficient than reducing outputs in Boise. He says between Boise and Middleton two thirds of the Boise River’s water gets diverted for agriculture. He says most of that comes back to the river full of farm phosphorus.

“If we just strictly did what EPA required us to do, we’ll get 7 percent of the way to what EPA says needs to be done at the Boise confluence with the Snake River,” Tensen says. “If we do the Dixie Drain Project we’ll get 30 percent of the way.”

Jim Werntz calls Dixie Drain the most innovative project he’s seen in a long time. The idea behind it, known as pollution offset, was around for years before Boise picked it up. And though there are other innovative phosphorus cleanup projects around the country, Werntz says no one had actually done anything quite like this.

Werntz says that’s because it’s immensely complicated; they weren’t even sure it would be legal. After more than five years of work, the city just cleared the last hurdle in February when the towns of Greenleaf and Middleton gave their blessings.

Justin Hayes is another big fan of this new plant. Hayes is from the Idaho Conservation League, and says Boise is the only city in Idaho that could have taken it on.

“They have the scientific and engineering capabilities on staff,” Hayes says. “They have the legal ability on staff to negotiate with the EPA. But now others will be able to follow in their steps a lot easier. And I think that’s why we’ll see other cities proposing these, because someone else has shown them how to do it.”

EPA’s Jim Werntz says the Dixie Drain Project could inspire many proposals like it in Idaho and around the country. That is, if the city of Boise is right and building this facility is cheaper than upgrading its sewage treatment plants. Werntz says that has not yet been proven and represents a risk the city is taking.

Boise Public Works officials say they’ve already been asked to give presentations in other places with phosphorus problems including the Chesapeake Bay and Mississippi Delta.

The facility is scheduled to begin operation in the summer of 2016.

Find Adam Cotterell on Twitter @cotterelladam

Copyright 2015 Boise State Public Radio