The potential for odor from the Coffin Butte Landfill expansion was a focal point of technical testimony at the Oct. 22 Benton County hearing. Staff and independent reviewers examined the applicant’s odor dispersion modeling, proposed mitigation and conditions to make odor enforcement actionable for the county.

County staff described the approach taken by Mall Foster and other consultants to evaluate the applicant’s odor model and translate subjective smell reports into an engineering threshold. Staff said the applicant’s model predicts ‘‘a noticeable odor below 4, above 1 at the property boundary’’ on a typical day and recommended conditions that include daily odor survey points, regular boundary patrols and an independent third‑party odor verification program. The staff report proposed that an independent verification measurement at or above a 4 d/Dt (dilution to threshold) trigger require immediate mitigation steps and that the county require third‑party verification for the first 48 months of commercial operation, continuing beyond that if disagreements persist.

Staff planning and consultants emphasized that state agencies regulate air quality and that DEQ permits must be obtained prior to ground disturbance; county authority is limited to addressing land‑use criteria and to attaching enforceable conditions to the conditional use permit.

Republic Services’ representatives and their odor experts described site‑specific dispersion modeling based on on‑site meteorological data; the applicant said the model follows best practices and that company consultants and the county’s third‑party reviewers found the modeling to be consistent with accepted methods. As Brian Roop, Republic’s area vice president, said during the presentation, the company had revised the proposal and submitted additional studies on odor as the application evolved.

Opponents pressed two technical concerns: that the meteorological dataset used for modeling was old (staff and consultants said the modeling used a one‑year on‑site dataset from Nov. 2004–Oct. 2005 pre‑approved by DEQ), and that weather conditions such as inversions or stagnant air can produce stronger odors than the model predicts. Neighbors also argued that monitoring results and mitigation actions must be publicly reported and independently verified.

Staff and the applicant proposed several enforceable operational conditions tied to odor management: daily cover limits and methods, restricted working face size, required third‑party evaluation of odor claims, a publicly reported monitoring program and a mechanism for the county to take action if independent verification indicates exceedances. The staff report and the applicant differ on who will perform which monitoring tasks: the applicant expects to conduct daily on‑site surveys and to fund specialized third‑party reviews; staff recommended the county receive funding (proposed $80,000/year) to retain independent monitoring and enforcement support.

"Odor was a very, very difficult impact to really get your head around as a planner," a county planner said. "We asked MFA to evaluate the applicant's odor model…on a typical day, you would have a noticeable odor below 4, above 1 at the property boundary, and that is something that we determine is not rising to a level of serious interference under the proposed model and with conditions." Republic’s representatives said they will fund third‑party reviews and daily operational surveys and that they had revised operations to reduce potential odor sources.

The board pressed staff and the applicant to clarify the trigger values, the mitigation steps that would follow a verified exceedance, and how monitoring results would be shared with the public; staff said they would incorporate clarifications into the record. No final determination was made; the board continued the hearing to Nov. 4 for deliberation.