RAC staff found modeling error; November Air Quality Control Commission hearing for SIP rulemaking still on track

Regional Air Quality Council planning staff told the board that a technical error was identified in modeling inputs used to evaluate control strategies and that staff have paused public presentations tied to the modeling while contractors correct the processing differences with EPA‑provided meteorological/model ready data.

Kira, RAC planning staff, said the issue relates to how EPA’s 36‑ and 12‑kilometer domain data were processed for mobile‑source model inputs. She said RAC staff do not believe the error affects Colorado’s emissions inventory that underlies the SIP the board endorsed in June, and that the commission’s November rulemaking hearing remains scheduled. ‘‘We do not believe it impacts the SIP you all considered a few months back and endorsed for consideration by the Air Quality Control Commission,’’ Kira said.

Why it matters: the SIT (State Implementation Plan) and related modeling support rulemaking at the Air Quality Control Commission. Staff said they will work with the contractor to correct the modeling, reissue updated results and reconvene workshops before releasing final strategy modeling results to avoid public confusion from multiple conflicting model outputs.

Staff described the QA process that found the discrepancy and said the contractor is correcting the work at no additional cost to RAC. Staff emphasized the importance of accurate modeling inputs and noted that if further impacts are found, there are procedural opportunities (for example prehearing statements) to incorporate updates before the commission hears rulemaking in November.

Ending: Staff said they expect to reconvene a conference to present corrected modeling in a few months and that the November AQCC hearing remains the important near‑term milestone for the SIP rulemaking calendar.