Martin Kidston

(Missoula Current) With the market for poplar not what it used to be, city officials this week added details to their plans to remove the trees at Missoula's wastewater facility and replace them with another crop.

Logan McInnis, the city's deputy director of Public Works and Mobility, said the plans are still in the works and they could coincide with a small University of Montana study on potential uses for poplar chips.

But as it stands, there are few other uses for the product and it's costing the city around $100,000 a year to maintain the poplar farm's irrigation system.

“The best answer for our poplar facility is to cut them down and grow another crop, and the best solution going forward is to grow alfalfa,” McInnis said. “It can consume an equivalent amount of effluent and nutrients as we applied to the poplars. That was always the number one goal. And the alfalfa plants themselves sequester a significant amount of carbon in the soil.”

The city in 2012 sought a solution to the growing amount of nitrogen and phosphorous the wastewater facility was releasing into the Clark Fork River. As a solution, they secured a long-term lease from the Clouse family and planted around 70,000 poplar trees.

Over the past decade, the city has diverted around 1 million gallons of effluent a day from the plant, which represents 15% of the plant's flow during the summer months. The trees absorb the product and, as a result, divert a large amount of phosphorous and nitrogen from the river.

“The primary goal of the poplar farm was to reduce loading of nitrogen and phosphorus of the Clark Fork River,” McInnis said. “Our goal at the time and still today was to demonstrate the feasibility of land application with hope to expand in the future.”

When the poplar farm was established, the Boardman Mill in Oregon was fully operating. The city planned to log its poplar trees after 12 to 15 years and ship them to the mill to be processed into a product Missoula could sell. The revenue would have helped offset the poplar farm's operating costs.

“The challenge now is that years ago the Boardman Mill closed. The market they had built evaporated. The mill is gone and their groves and groves of poplar trees were all cut down. We were caught up in the middle of that. At this point, we can find no viable market for the trees.”

The Clark Fork River below Missoula.
The Clark Fork River below Missoula.

McInnis said the city convened a team of experts last year to explore its options. They worked with UM to locate sawmills but found that transporting wood to the East Coast was financially unfeasible. They also talked with Roseburg Forest Products of Missoula, which runs a chipping mill, put that didn't pan out.

Other options were also explored including biochar, but the process is to too slow for poplar logs. McInnis said poplars aren't suited as wood pellets due to their high ash content. Nor is there any local interest for using the product for biomass energy.

“The moisture content in poplars is extremely high. We wanted them to take up a lot of wastewater, which they did,” he said. “But their extremely large growth rings make them hard to mill.”

McInnis added that some small specialty providers may use a handful of logs for products like RV flooring. They'll also cut one acre for a study on how fast poplar chips degrade.

Of the 70,000 trees planted, only 36,000 remain. Some have been thinned and some have died of disease, he said.

“Hybrid poplars put all their energy into growing and very little into defending themselves from the various things that want to kill them. We are starting to see the trees die off.”

City officials said the trees have done their job in diverting nutrients from the river and once they're gone the city will look for another crop capable of absorbing effluent.

State standards around discharging treated wastewater into Montana's rivers are likely to tighten as well and without a crop to divert effluent, the city could face “tens of millions of dollars” in costs to upgrade the wastewater facility.

“It's an expense to have whatever we end up having, whether it's poplars or alfalfa, but it's something we need to do to reduce the amount of nutrients that get discharged,” said Missoula City Council member Mirtha Becerra. “I appreciate the experience of the group of people who are providing advice to our staff to help make decisions.”