QUANTIFYING FOUR DECADES OF CHLORIDE AND SODIUM INPUTS TO THE BALTIMORE CITY DRINKING WATER RESERVOIRS

As a result of road de-icing agents, the salinization of surface waters has substantially amplified across the mid-Atlantic and northeast United States over the past several decades. And in 2011, the USGS reported two key emerging water-quality concerns: (1) elevated and increasing chloride and sodium in reservoirs and streams, and (2) elevated concentrations of disinfection byproducts (DBPs). In the Baltimore region, three drinking water reservoirs – Liberty, Loch Raven, and Prettyboy – serve 1.8 million people, and while chloride and sodium concentrations of nearly all Maryland streams are generally understood to be increasing, several things remain unclear regarding the tributaries of these reservoirs. Specific seasonal, annual, and decadal scale trends in fluxes and loads of chloride, which carry implications for DBP formation, are unknown. Additionally, trends in the corrosivity of these tributaries are also unknown. This study will collect data by conducting periodic and selected event sampling, placing in-situ specific conductivity sensors, and use nearly four decades of historical data provided by the Baltimore City Department of Public Works and Maryland Department of Environment. To assess chloride flux and load, a weighted regression on time, discharge, and season will be used, and trends in corrosivity indices will be assessed as well. Preliminary findings show sodium and chloride concentrations increasing over the past three to four decades, and data is expected to show fluxes and loads increasing annually due to a legacy effect. It is also expected to find that the waters have become more corrosive over time. The conclusions of this study will have implications vital to understanding the impacts of road de-icing agents on stream chemistry, Baltimore City drinking water reservoirs, and disinfection processes.