The small, white city of Boise fleet vehicle was way outside its usual jurisdiction--winding through Canyon County country roads near the confluence of the Boise and Snake rivers, passing by the communities of Notus and Parma. The truck slowed as it rattled over a cattle gate and entered a landscape of fields and wetlands maintained by ranchers for duck hunting. Nearby was a volcano-shaped mound draped with a black, waterproof covering, and a grove of trees and shrubs pointing to the Boise River.
"When the project's completed this won't look very different from the land around it," said Steve Burgos, senior manager with Boise's Environmental Division.
"The project" is the Dixie Drain, a $12 million water treatment facility that will be built and run by the city of Boise and designed for a single purpose: to drastically reduce phosphorous levels in the Boise River before it reaches the Snake River. As Burgos said, it's a non-scenery-chewing solution to the inelegant problem of excess nutrients leaching from drain pipes, fertilized lawns, farmland and erosion into the Snake River watershed. Originally proposed in 2009 and expected to go online by spring 2016, the Dixie Drain also represents long negotiations between the city of Boise, the Environmental Protection Agency and other parties who use or regulate the Boise River. Though the drain will treat phosphorus entering the river from across the Treasure Valley, the bill for the drain and other EPA compliance projects projects is being footed by Boise sewer district users with a 5 percent rate increase.
"It was a long process of working things out between the Idaho Department of Environmental Quality, the Environmental Protection Agency and the city of Boise. There was a lot of care taken to ensure we didn't violate any regulations in the process. There hasn't been a lot of this done, so it was quite difficult, but in the end we came out with a pretty good scenario," said EPA Water Quality Coordinator Bill Stewart.
Phosphorus is a major problem for Idaho waterways; it's a primary factor in the growth of algae, and while most algae is harmless to humans, some varieties can pose a risk to people, livestock and, if left unchecked, river and lake ecosystems. While the Boise River may look clean and fresh near Boise, the Snake River has characteristics that make it more susceptible to algae blooms fueled, in part, by nutrients fed into it by the Boise River.
"The reason you notice it more on the Snake: It's a slower-moving body of water. It behaves like a lake, and you have species of blue-green algae that can hit the lake," Stewart said.
With no treatment at all, the Boise River contains about 4,000 micrograms of phosphorus per liter, and Boise's current water treatment facilities remove more than 90 percent of that phosphorous, bringing the level down to 350 micrograms of phosphorus per liter. But according to the EPA, it should contain about 70 micrograms per liter between the months of May and September. The Dixie Drain is expected to help bring the Boise River closer to compliance with EPA standards by removing about 140 pounds of phosphorus per day. According to Burgos, removing these last traces of phosphorus can be difficult and expensive.
"It's definitely a case of the law of diminishing returns," he said.
Near the future site of the Dixie Drain, reeds, trees and shrub thickets line the Boise River's banks. The water is saturated with silt and the air thick with mosquitoes, which breed near slow-moving water and wetlands.
That's where Boise is expected to build a raisable diversion dam redirecting water out of the river's main channel and into the Dixie Drain facility, where it will undergo a three-part treatment process. From the diversion dam, the water will slow to a standstill in a pond, allowing sediment (including phosphorus) to settle at the bottom. After being drained from the sedimentation pond, the water will be treated chemically, likely with an aluminum compound that bonds to phosphorus, though the city is considering other chemical treatment options as well. Finally, the water will be allowed to flow slowly through a maze, where remaining sediments can be removed before the water is reintroduced to the Boise River.
Near cities, phosphorus enters waterways through so-called point sources like drain pipes exiting water treatment facilities, which hold EPA National Pollutant Discharge Elimination System permits. These facilities extract phosphorus that enters wastewater from grassy lawns, toilets, soaps, stormwater and thousands of other sources.
In Meridian, wastewater is treated in a number of different ways before reaching its drain at Five Mile Creek. Though Idaho's second-largest city is currently in compliance with its NPDES permit, it is beginning the process of renewing that permit, and several cities, including Meridian, were initially in talks with the EPA and Boise to share responsibility for the project, and though they're not any longer, Meridian Environmental Programs Manager Mollie Mangarich said the Dixie Drain is a symbol of innovation that will help other communities along the Boise River achieve EPA compliance.
"While we are going to have to capitalize to the tune of many millions of dollars to meet EPA standards, we appreciate innovative solutions," she said. "There are a lot of things we can do to reduce phosphorus in the Boise River."
But phosphorus also enters waterways from agricultural and ranching sources like cow manure and fertilizers, called non-point sources. Because of the Boise River's proximity to both point and non-point sources of phosphorus, its presence--and effect--is cumulative. It also makes it difficult to assign responsibility for the Boise River's phosphoric glut.
"There isn't a big villain you can point your finger at and say, 'This is the problem.' If you fertilize your lawn you're contributing to the issue," said Stewart. "In order to address this problem, it's going to take an effort from virtually everyone."