Circling the Dixie Drain

A new solution to the Boise River's phosphorous problem

by and

Near the confluence of the Snake and Boise rivers, the water runs dark brown, loaded with sediment and spiked with phosphorous. But after being sifted through a new treatment facility south of Notus, it courses almost clear past an observation deck where Idaho state and local leaders gathered Aug. 24 to christen the so-called Dixie Drain.

"What's happening here is on the leading edge of environmental science," said Idaho Department of Environmental Quality Director John Tippets.

The Dixie Drain is Treasure Valley cities' answer to EPA guidelines that limit the Boise River's phosphorous load.

The problem is severe. Untreated, the Boise River contains approximately 4,000 micrograms of phosphorus per liter—far higher than EPA limits, which say the river should contain no more than 70 micrograms of phosphorus per liter between the months of May and September.

Members of the press got their first look at how the Dixie Drain diverts the brackish water into the facility, deliberately slowing the stream's flow and allowing it to deposit silt and other solids into the drain's collection area. That's where polyaluminum chloride is added to the mix, turning phosphorous into a flotsam that can be removed from the surface of the water before the Boise River returns to its normal course. Every year, the process is expected to remove up to 10 tons of phosphorous and 8,000 tons of silt.

"It's not so hard to do something that makes things better," said Boise Mayor Dave Bieter.

The Dixie Drain is the first phosphorous offset project of its kind in the United States.

"The EPA gave us flexibility to come up with an alternative," said U.S. Rep. Mike Simpson. "That's what we expect the government to do."

"The flexibility has generated something I believe could be a national model," said U.S. Sen. Mike Crapo.

"This is a treasure for Idaho ... and projects like this will bring [the Boise River] back," said EPA Region 10 Administrator Dennis McLerran.

The facility is also poised to save money. EPA penalties for phosphorous-laden water are high and add up quickly. Boise Public Works Director Neal Oldemeyer stood before the Boise City Council and members of the Ada County Commission in 2011 and told them in order to stay ahead of the curve, long-range improvements to the West Boise Wastewater Treatment Facility and Lander Street Wastewater Plant would have to be made, with projected costs running to as much as $92 million and $36 million, respectively.

By contrast, the Dixie Drain's price tage was $21 million.

By building the drain on the Boise River between Notus and Parma, Boise can capture huge amounts of sediment and phosphorous that would otherwise be inaccessible to treatment facilities in the eastern end of the Treasure Valley.

According to Public Works engineer John Tensen, it removes 1.5 pounds of phosphorous from the river for every pound of phosphorous untreated at Boise's water treatment plants.

"On a pound-for-pound basis, there's just no comparison," he said.