Tora recently partnered with a grain and corn handling facility in the Pacific Northwest to support the development of a new construction project requiring an air quality construction permit. As part of the application, Tora led a sophisticated air dispersion modeling effort to evaluate the project’s potential ambient air impacts. The process began with a Significant Impact Level (SIL) analysis for all criteria pollutants, followed by a National Ambient Air Quality Standards (NAAQS) analysis.

Preliminary modeling results highlighted challenges related to particulate concentrations at the facility’s ambient air boundary. A key factor was the presence of a public rail line intersecting the southern portion of the site, located less than 100 feet from a dense cluster of emission sources.

To address this complication, Tora conducted a detailed review of seasonal operating patterns for each emission source. We then developed two distinct models:

• Rail line–only model — assessed potential impacts on a human receptor moving along the track
• Full-property model — evaluated impacts across the entire facility-owned area

For the rail line–only model, Tora applied adjusted emission rates based on the maximum time a person might reasonably be present on the track while a train passed. While Amtrak data showed that trains crossed in front of the facility for no more than two minutes, Tora applied a conservative 30-minute duration when calculating emissions to ensure maximum public safety.

This two-model approach enabled the facility to demonstrate compliance with both SILs and NAAQS for all relevant criteria pollutants.

Tora’s innovative strategy not only secured regulatory approval but also set a precedent for how technical modeling can adapt to real-world infrastructure constraints.

Have a complex modeling challenge? Let Tora guide you through it.