On a recent sunny afternoon, Missoula Wastewater Treatment Facility Superintendent Starr Sullivan walks through a poplar grove that's dotted with deer scat, mossy patches and the shadows of birds flitting above.
"This is a wildlife refuge," Sullivan quips from inside the 1.6-acre grove, located just behind the treatment facility's pungent clarifiers and bubbling bioreactors. "You see everything in here—deer, marmots, birds. I actually saw a coyote down here one time."
The poplar grove stands out, mostly because it marks a calm contrast to the nearby treatment facility, Super Walmart and other big box stores situated along North Reserve Street. But it's how these poplars are cared for that is garnering the most attention. The grove, unlike any other in the state, is watered and fertilized with liquid sewage waste, or effluent, and Missoula officials believe it can serve as a template for how to manage municipal waste in the future.
The Missoula wastewater plant sterilizes more than 8 million gallons of sewage per day. Bioreactors kill potentially damaging bacteria, including E. coli, salmonella and giardia before dehydrated solids are transported to EKO Compost, which makes use of the waste. The remaining fluid is pumped into the Clark Fork. The problem is, some natural waste byproducts, specifically nitrogen and phosphorous, remain in the effluent when it flows into the Clark Fork. Those nutrients feed algae, which consume oxygen and ultimately harm fish.
As western Montana population centers grow more dense, scientists are becoming increasingly wary of effluent's long-term effects on aquatic ecosystems. Those concerns are prompting the state Department of Environmental Quality to craft new rules that will in the future further limit how much nitrogen and phosphorous municipalities will be allowed to pump into rivers and streams.
"Some communities like Missoula will certainly face nutrient standards that are tougher," says DEQ environmental engineer Terry Campbell.
That's where the poplar grove comes in. Sullivan and city officials are hoping that effluent irrigation will offset the city's impact on the Clark Fork and, in doing so, save taxpayers the expense of making costly improvements to the treatment facility under the DEQ's new rules.
Thus far, the pilot project appears a success. Testing in and around the grove shows no significant negative effects on groundwater or soil. The poplars, meanwhile, are thriving, growing from 12-inch "whips" in 2009 to trees that now stand roughly 13 feet.
Following the project's favorable outcome, the Missoula City Council last month agreed to contract with Colorado-based Hybrid Energy Group, a private company that focuses on renewable energy development, and Watershed Consulting of Missoula to plant a new 130-acre hybrid poplar tree farm a half-mile west of the treatment facility off Mullan Road. The contract, which includes the cost of leasing the land from the Clouse family, will cost roughly $1.3 million to maintain for the next 12 years.
Sullivan estimates that once the new plantation's 70,000 trees have taken root, they will consume one million gallons of effluent per day. "The expansion has the potential to remove about 10 percent of what our discharge is to the river," he says.
The poplars will be harvested for saw logs and to be used as biomass, with some to serve as bulking material for EKO Compost. Hybrid Energy Vice President Tom Platt sees the project as groundbreaking because effluent is becoming a commodity.
"It's taking a waste product that currently is a liability in the river and a liability to the city and it's turning it into something that maybe can be an asset," he says. "This is a big water discharge the city will use for productive purposes."
Platt hopes that this type of effluent irrigation could one day completely eliminate wastewater discharge into the Clark Fork. "I don't think it's too ambitious," he says. "I've spent quite a bit of time talking to landowners along the floodplain out toward the confluence of the Bitterroot River and there's certainly some interest there."
There's a significant amount of excitement stemming from the expanded project, but there are also cautionary voices, most notably from Heath Nicolas Carey, who helped launch the poplar pilot project in 2009. Carey planted the trees and charted nutrient concentrations in the soil, making the grove the focus of his thesis while earning a master's degree in resource conservation from the University of Montana. Carey last month publicly stated additional testing is necessary to measure how, for instance, pharmaceuticals that linger in wastewater could affect agricultural land.
State and federal regulatory agencies are only now beginning to understand how excreted drugs and personal care products washed off in the shower, like sunblock, affect waterways, let alone soil. But Sullivan notes that to get a pill's worth of even the strongest pharmaceutical, such as the anticonvulsant carbamezipine, a human would have to drink roughly two million gallons of treated wastewater. Once wastewater is applied to the soil, it only degrades further. Sullivan sees it as unlikely that effluent irrigation will harm the land.
To the contrary, as Sullivan wanders the poplar grove and points to an osprey nest overhead, he expresses hope that this project will serve as a blueprint for other communities.
"I think you're going to see much more of this nationwide," Sullivan says.