Situated in the mid-Atlantic region of the U.S., southeastern Pennsylvania experiences strong seasonality. During winter months, road salting is used to keep roads, sidewalks, and parking lots safe for travelers and pedestrians. The accumulation of salt and the associated changes in water chemistry affect groundwater and surface water used for drinking water supply.

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The “freshwater salinization syndrome” (FSS), which pertains to increases in concentrations of major ions and metals in fresh waters, has been attributed to long-term application of road salt. FSS in six southeastern Pennsylvania streams was characterized by flow-normalized ion concentrations from 1999 through 2019.

The results highlight the roles of impervious surfaces (including paved areas, buildings, etc.) and treated wastewater discharges in FSS in suburban and exurban watersheds in southeastern Pennsylvania. Observed salinity and corrosivity increases potentially increase risks to human health and drinking-water infrastructure. Key findings include:

• Increasing specific conductance from 1999-2019 in all six study streams, as evidence of salinization of surface waters;
• Increasing flow-normalized concentrations of calcium, magnesium, sodium, and chloride from 1999-2019 in all six study streams, as evidence of the FSS;
• Positive associations between chloride, magnesium, and calcium with impervious surface cover;
• Positive associations between sodium and impervious surface and treated wastewater discharge;
• Increasing corrosivity indexes (i.e., Chloride to Sulfate Mass Ratio (CSMR) and Larson ratio (LR)) from 1999-2019 in all six study streams – Corrosivity indexes of surface water presently exceed thresholds of concern for the corrosion of lead, iron, steel, and copper pipes; and
• Elevated sodium concentrations that exceed the U.S. Environmental Protection Agency’s recommended threshold of 20 milligrams per liter for those following a low sodium diet – Some individual samples of surface water exceed the threshold by a factor of 10.

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