Air Emission Risk Assessment Sensitivity Analysis for a Coal-Fired Power Plant

Abstract

The Electric Power Research Institute’s Air Emissions Risk Assessment Model (AERAM), which assesses the risk of toxic air emissions from coal-fired power plants, was used to study the excess cancer risk due to inhalation of airborne emissions from the Mt. Tom Power Plant in Holyoke, Massachusetts, and the key sensitivities of the risk assessment process were investigated as a guide for future analyses. With arsenic used as the pollutant, source-term descriptions, air-dispersion parameters, population exposure parameters, and dose-response models were varied to assess the effect on the risk result. It was found that eliminating pollutant enrichment on fly-ash particles reduced the risk by 50%. Changing from complete ground reflection to no reflection in the air-dispersion model reduced the risk by 57%; changing the settling velocity had no effect on the risk. Using the urban mode 2 stability pattern increased the risk by 124%, while using different stability array data changed the risk by about ±30%. The effect of using age-specific breathing rates in the exposure module was small (an 11% decrease in the risk), as was the impact of considering only respirable particles (a 4% decrease). The largest variation in the risk was observed when the Environmental Protection Agency’s unit risk factor was replaced with one of four different low-dose extrapolation models utilized with three dose-response data sets; variations of up to 10 orders of magnitude were found. These results show that careful selection of dose-response data and low-dose extrapolation models should be a fundamental concern in risk assessment.