Rapid City Tests Biochar to Fix Compost

The city is piloting biochar to neutralize herbicide contamination that has affected its compost for about four to five years.

Updated on Nov. 5, 2026 in Agriculture

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Should your city invest public money in turning wood waste into biochar?

Rapid City is running a pilot project to test whether biochar can neutralize herbicide contamination in its compost, which the city sells for a penny a pound. The city continues to advise against using its compost in gardens or on broadleaf plants while the test proceeds.

Why it matters

The pilot aims to restore a product the city already sells while also addressing wood debris left after the December windstorm. Diverting bulky wood material could help preserve landfill capacity and delay construction of additional disposal cells.

The compost is sold for $0.01 per pound and has been affected by herbicide contamination for four to five years, while Dakota BioChar's demonstration operation produces about 1,600 tons of biochar from roughly 8,000 tons of feedstock annually. Whether biochar will neutralize the contamination remains unproven, with initial pilot results hoped for around spring.

The players

Dakota BioChar

A biochar producer that uses pyrolysis and has delivered material for Rapid City's compost pilot while proposing a landfill-based processing operation.

The details

The city plans to mix biochar into a test row of compost and compare plant growth with compost lacking added biochar. Dakota BioChar, which uses pyrolysis to produce biochar after grinding wood, has delivered material for the pilot and has taken some of the city's wood waste.

The Dec. 17-18, 2025, windstorm increased the city's wood debris problem.
Reporting described a proposed memorandum of understanding framework in September.
Hannon hopes to have an initial indication of pilot results around spring.

Market Landscape

Biochar, produced through pyrolysis, is being tested here as a way to bind herbicide residues in compost while also giving municipalities a use for wood waste. The approach positions private biochar producers as partners in managing both landfill capacity and soil-amendment supply in the region.

Residents who buy the city's compost for a penny a pound should avoid using it in gardens or on broadleaf plants until the pilot shows results. Homeowners dealing with storm-downed wood may see the city's debris handling change if the biochar program expands.

The takeaway

Until results are in, treat Rapid City compost with caution for plants sensitive to herbicides. Watch for spring updates on whether biochar can neutralize the contamination.