Maryland Department of Natural Resources

Road-deicing Salt Contamination in Maryland Piedmont Groundwater

Project Details


The use of deicing salts has been shown to have significant impacts on surface and groundwater, resulting in degradation of aquatic life and threatening drinking water sources. Chloride has been increasing in Maryland streams for several decades, including those feeding into Liberty Reservoir (a water source for Baltimore City). In the central Maryland Piedmont, unconfined aquifers are the primary water source for people on private water wells, and these aquifers are very susceptible to surface-based contamination. High-chloride water can damage plumbing fixtures, appliances, and pipes. Since chloride is unreactive, it does not degrade in the environment. Additionally, the impacts of these salts on the mobilization of trace elements, heavy metals, and adsorbed contaminants in Maryland groundwater have not been adequately evaluated. The objectives of this project are to: (1) Map the spatial distribution of chloride in groundwater throughout the Piedmont region of Maryland; (2) Evaluate the temporal variation of chloride concentrations in groundwater, and; (3) Determine potential associations between elevated chloride and other chemical constituents (trace metals, radionuclides, etc.). These results will document how road salt practices have impacted water supply aquifers. This work will also provide a foundation for developing guidance for private well owners regarding testing for sodium and chloride and other possible contaminants related to road salt.

Chloride in Piedmont groundwater
Groundwater chloride data were collected from various sources including the U.S. Geological Survey, Maryland Department of the Environment, National Uranium Research Evaluation, and Counties in the Piedmont. Chloride concentrations were grouped by sample collection date (by decade) where the mean of all data in each group was calculated. Over time chloride concentrations in groundwater have increased exponentially over time, likely due to long term-application of road-deicing salt. The U.S. Environmental Protection Agency Secondary Maximum Contaminant Level (SMCL) is noted on the graph as the red line.