A permit model that stands up at inquiry

An air quality assessment for a permit turns an emissions inventory, a stack layout and five years of meteorological data into a map of concentrations. The regulator reads the map. An objector, if there is one, reads the inputs, and a small error in one of them, such as a stack height, a building outline or a wind sector, can change what the map shows.

The consultancy’s model files had grown by project and by consultant. Checking one meant opening it, and checking that the checker had opened the right one meant a second person.

GraphAtlas AERMOD reads the inputs as data and runs the dispersion procedure on the kernel, so that the same inputs give the same map on any machine. Each run ends in a receipt that names the inputs, and the web interface lets the user change one of them and see the effect at once.

When the meteorological data for a region was reissued, the firm reran 214 permit scenarios overnight and compared the receipts of the old and the new run, which showed it which of the 214 had moved and by how much.

Quality assurance of the models takes 60% less time, because it is a comparison of receipts and a review of what differs. At a public inquiry in the spring the objector’s expert asked for the height of a stack to be changed. The firm changed it and ran the model in the room, and the inspector took the result into the record.