Excessive Concentration Demonstration Study at Chesapeake's West Point Mill, 1992 Environmental Conference Proceedings

Dispersion modeling performed for Chesapeake’s West Point, Virginia mill has shown that three existing power boilers stacks are the major contributors to modeled exceedances of the NAAQS for SO2 . The high predicted concentrations are due to the combined effects of short stacks (each power boiler stack is less than 65 m) and building downwash. As a means of eliminating the modeled exceedances, Chesapeake is considering raising the power boiler stacks up to 88 meters. Dispersion modeling demonstrates compliance with the ambient standards at this stack height. GEP formula height for these stacks is about 122 meters.

Before stack height increases could be adopted as a viable control strategy, excessive concentrations due to building downwash effects had to be demonstrated. The EPA stack height regulations (40 CFR 51.118) require that sources seeking credit for increases in existing stack height up to Good Engineering Practice (GEP) formula height demonstrate by fluid modeling that downwash created by nearby structures results in an "excessive concentration" in the vicinity of the source. A fluid modeling (wind tunnel) study was conducted to demonstrate excessive concentrations due to the three power boiler stacks. This paper discusses the study performed by Chesapeake to obtain dispersion credit for the proposed stack height increases and presents a review of the applicable stack height regulations.