The Colstrip Steam Electric Station, east of Billings, MT, consists of four coal-fired generating units capable of producing a total of up to 2,094 MW of electricity. Units 1 and 2 began commercial operation in 1975 and 1976, and Units 3 and 4 started in 1984 and 1986. Units 1 and 2 each have about 307 MW of generating capacity. Units 3 and 4 each have about 740 MW of generating capacity. The units are equipped with 22 venturi type particulate control/flue gas desulfurization (FGD) systems.

AECOM Process Technologies is performing a FGD upgrade project to meet new Mercury Air Toxics Standards (MATS) and regional haze requirements. The project includes computational fluid dynamics (CFD) engineering, new gas flow distribution devices, new tray, new absorption spray piping and pumps, and a new mist eliminator system. As part of the FGD upgrade, AECOM Process Technologies is performing SO₂ testing, particulate testing and characterization of the particulate.