Mercury Dispersion Modeling and Purge Ventilation Stack Height Determination for Tank 42H

The Savannah River National Laboratory (SRNL) Atmospheric Technologies Group performed atmospheric dispersion modeling and analysis of mercury emissions from the H-Tank Farm - Tank 42 ventilation system exhaust to evaluate potential worker exposures to mercury vapor. This analysis was used to establish a minimum stack height at which ambient mercury concentration would not exceed any worker exposure limit. The American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) was used as the dispersion modeling tool for this analysis. Results indicate that the default 10-foot stack results in ground level concentrations that significantly exceed exposure standards for the mercury discharge scenarios evaluated. For a discharge of 25 mg/m³, a 50-foot stack was necessary to raise the exhaust plume centerline from Tank 42H to a height that prevents mercury exposure problems for elevated receptors on buildings near the tank. If the discharge concentration is decreased to 10 mg/m³, the minimum stack height required to comply with exposure limits is of 40 feet.