Modeling Trihalomethane Increases Associated with Source Water Bromide Contributed by Coal-Fired Power Plants in the Monongahela River Basin.

Abstract

Increases in source water bromide concentrations are challenging for drinking water utilities since bromide contributes to the formation of disinfection byproducts (DBPs) that have negative human-health effects. The present work evaluates the role of coal-fired power plant wet flue gas desulfurization (FGD)-associated bromide loads on in-stream bromide concentrations in the Monongahela River Basin in the water year (WY) 1998 (during a nationwide study) and over a five-year period from WYs 2013 through 2017. Under mean flow conditions in the lower Monongahela River for the WYs of interest, the median-estimated wet FGD bromide discharges are modeled to represent a significant fraction (27-57%) of observed bromide concentrations with the range representing the change in load conditions across WYs. Seasonal effects are predicted due to changes in the dilution capacity of the river with elevated concentrations under lower flows in the third and fourth quarters (July through December). The effect of these bromide concentration contributions, which range from 6.8 to 23 μg/L under median load estimates and median flow conditions, on trihalomethane (THM) formation and associated risk were assessed. A simple model was applied to demonstrate an analytical approach for evaluating the power plant total THM (TTHM) and risk contributions. Utilizing this model, the power plant TTHM contribution was estimated to range from 7.6 to 27 μg/L with a median risk contribution of 0.0014.