Missoula County outlines special-exception review for proposed Bonner Mill AI data center; neighbors press on water, noise and heat

Missoula County planning officials told the Bonner Milltown Community Council on April 13 that a proposed AI data center at the old Bonner mill site must go through a special-exception review because part of the site lies within 500 feet of residentially zoned property. County staff said the review concentrates on how the facility would interface with nearby homes — including noise, lighting, landscaping and traffic — while some technical questions, notably water quality and water-rights issues, fall to other agencies.

“Data centers are permitted in industrial zones, but if they are within 500 feet of residential areas… they are required to go through a special exception,” Karen Hughes, a county planner, said during the meeting. She and case planner Jenny (who identified herself as the project case planner) described a two-step process: a narrow special-exception review by the Missoula County Consolidated Land Use Board that focuses on impacts to neighbors, followed by zoning-compliance and building-permit reviews that examine technical details.

Why it matters: the site abuts neighborhoods and a school, and residents pressed officials for concrete information on potential impacts — especially water use, noise from fixed equipment and the effect of large data facilities on local temperatures. Those concerns shaped much of the evening’s public comment and prompted staff to commit follow-up with water and health authorities.

What county staff said - Notification and timing: Staff said property owners within the 500-foot radius will receive mailed notice, the county will run a legal ad, post information at the site and publish materials on MissoulaCountyVoice. Staff also said they will summarize public comments for the Land Use Board. The county noted the case’s Land Use Board hearing is currently scheduled for June 3 at 6 p.m. in Sophie Moe’s room at the County Courthouse (first floor) and online; that date is subject to change. - Review focus: Jenny, the case planner, said the special-exception review will not re-litigate every technical aspect of the internal data-center operations but will examine how the use interfaces with residences (access, parking, traffic, lighting, noise, screening and vibration). Technical details such as megawatt demand and renewable-energy procurement typically appear later at the zoning-compliance stage when permit-level plans are submitted. - Renewable-energy requirement: County staff said applicants must show procurement of new renewable energy that will cover the facility’s operation at the zoning-compliance phase; how much renewable energy is required depends on the facility’s actual power use and will be verified at permit review.

Residents’ top concerns - Water: Several neighbors asked which agencies will examine water quantity and quality. County staff said Missoula Public Health and the Missoula Valley Water Quality District would review water-quality impacts, and that DEQ or DNRC could be involved if discharge or water-right issues arise. “That is the health department's job,” a county official said, adding the planning office’s regulatory purview on water quantity is limited. - Local water operator’s context: Mike, the site’s water operator, said his daily metering shows prior building operations used about 800 gallons per day for one building and that an estimated 500 gallons per megawatt (a figure cited in prior meetings) was not inherently alarming given the mill site's historical usage. “Those numbers weren’t scary to me,” he said, while urging that applicant-provided details and agency reviews remain the authoritative source. - Noise and frequency: Neighbors recalled a prior tenant whose operation produced a persistent fan whine because of equipment frequency rather than simple decibel levels. County staff said noise and vibration regulations adopted in 2022 include decibel and frequency considerations and that the county enforces fixed-source noise via complaints and zoning enforcement actions. - Heat-island effects and environmental impacts: Residents raised research suggesting large data facilities can produce localized warming; staff said they are researching mitigation (for example, planting trees) and will consider heat-island impacts where relevant to the special-exception review.

Applicant capacity and jobs Staff said the applicant’s current special-exception filing is pitched at an initial 5 megawatts; county staff noted the site infrastructure might technically support larger loads but that precise megawatt figures and associated renewable-energy commitments will be verified at later permitting stages. Staff also said data centers typically generate few ongoing operational jobs (staff cited roughly 15 long-term jobs in the application) but can create construction employment during build-out.

How residents can participate Staff urged residents to submit comments through MissoulaCountyVoice, to attend the Land Use Board hearing and to contact county staff directly. “All the comments on Missoula County voice will go to the commissioners…and will also be made available to the land use board as part of the special exception review,” a county official said.

What happens next The consolidated land-use board will hold a public hearing (currently scheduled for June 3 at 6 p.m.), receive the staff report and public testimony, and decide on the special exception by making findings against specific criteria. If the board approves the exception, the applicant will later seek zoning-compliance and building permits that require more detailed technical documentation. If the board denies the exception, the project would not proceed in its proposed form without material changes.

The council said it will invite additional agencies (public health, DEQ/DNRC, power providers) and the applicant to future meetings so neighbors can get more technical answers before the Land Use Board hearing.