RAPID CITY, S.D. (KOTA) -Rapid City is testing whether a product made from wood waste can help address herbicide contamination in its compost, but residents should not treat the pilot as a green light to use the compost in their gardens.
The city is working with Dakota BioChar to evaluate whether adding biochar can make the compost more suitable for plants. Results are not yet available, and the city continues to advise against using its compost in gardens or on broadleaf plants.
“We have a compost that is contaminated with herbicides, so what we’re doing is we’re running a pilot project to try and neutralize our compost,” said Ria Hannon, the city’s solid waste education and outreach coordinator.
Hannon said the herbicide problem has affected the operation for about four to five years. The city sells compost for a penny a pound, but the contamination limits where residents should use it.
A plant comparison planned
Hannon said Dakota BioChar has delivered material for the pilot. The city plans to mix it into a test row of compost and compare how plants grow in that material with how they grow in compost without added biochar.
The comparison could include tomatoes and basil grown in small pots in her office window.
Hannon hopes to have an initial indication of the results around spring. The project is a test of a possible use for biochar, rather than a completed solution or a citywide rollout.
Turning wood into biochar
Dakota BioChar has already taken some of the city’s wood waste, Hannon said.
The company uses pyrolysis, a process that heats wood with very little oxygen, to produce biochar. Brad Walton, the company’s controller, described grinding the wood before feeding it into reactors.
Justin McNeal, Dakota BioChar’s CEO and founder, said producing the material efficiently has presented challenges.
“We’re having technology issues on figuring out the best way to efficiently make this, this product,” McNeal said.
McNeal described the company’s demonstration operation at Baker Timber Products in Rockerville as processing roughly 8,000 tons of feedstock annually and producing about 1,600 tons of biochar. He outlined a proposed landfill operation that would process about 20,000 tons annually and produce roughly 4,000 tons of biochar.
Those figures describe the company’s existing operation and proposed expansion, not results from the city’s compost pilot.
Why the city is exploring wood diversion
The Dec. 17-18, 2025, windstorm increased the city’s wood debris problem. KOTA previously reported gusts of 91 mph in east Rapid City and 94 mph at Rapid City Regional Airport during the storm.
Public Works Director Mike Theis previously said diverting bulky material could preserve landfill capacity and delay expensive construction of additional disposal cells, helping limit future pressure on resident rates.
September reporting described a proposed memorandum of understanding as a framework for exploring projects. It would not itself commit money, staff or equipment; projects needing resources would require separate agreements and approval.
For gardeners, the immediate guidance remains unchanged: Hannon says the city’s compost is not recommended for gardens or broadleaf plants while the pilot’s results remain unknown.
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