SWAPE was retained to conduct air dispersion modeling to estimate historical impacts to hundreds of residents living near one of the largest corn wet milling facilities in the United States.  The Facility manufactured alcohols, maltodextrins, starches and other co-products for the animal nutrition industry.  The manufacturing processes at this plant generated a variety of air pollutants that were emitted into the surrounding community for decades. The primary air pollutants included Criteria Air Pollutants (CAPs), including sulfur dioxide (SO2), particulate matter (PM), and volatile organic compounds (VOCs).  The facility also emitted a variety of toxic and odorous chemicals such as acetaldehyde.

For this project, SWAPE conducted air dispersion modeling using AERMOD, the U.S. EPA’s preferred regulatory dispersion model. AERMOD is a computer-based air dispersion modeling system designed for short-range (up to 50 kilometers) dispersion of air pollutant emissions from stationary industrial sources. Inputs to the model included meteorological and terrain data, as well a detailed inventory of source term emission factors for the Facility’s stacks and fugitive sources.  Source terms for Facility’s numerous sources of air pollutants were developed by an independent expert based on engineering analysis and extensive documentation of the processes and emissions sources at the plant. 

SWAPE’s air dispersion modeling included SO2, VOCS, PM10, PM2.5, acetaldehyde, and hydrogen chloride.  The results of the modeling were presented by SWAPE in an expert report, used as the basis for defining a class area boundary for delineation of class members with residential properties in the surrounding community that were similarly impacted by historical emissions from the Facility.  To explain the formula for calculating damages for each Class Member, SWAPE integrated a geodatabase of property information for individual residential parcels with air modeling results in a geographic information system (GIS) and developed a customized Java-based software tool to process hourly estimated ambient air concentrations for hundreds of properties over a damages period of many years.

Ultimately, the Plaintiffs prevailed following Court approval of a $51.5 million Class Action Settlement for nuisance damages from smoke, odor and haze emitted from the Facility [1]. Individual Class Member damages were based on the exposure model developed by SWAPE in collaboration with Plaintiffs’ legal team.  This successful case was one of few air pollution class actions that has involved the computation of damages for residents based on retrospective analysis of historical air pollution.

[1] Miner, Barnhill & Galland Secures Landmark $51.5 Million Class Action Settlement Against Grain Processing Corporation.  Businesswire.com. February 6, 2019.