Increasing Salinization of our Drinking Water

According to the Izaak Walton League of America in Virginia: “The data collected by Virginia Save Our Streams volunteers shows, without a doubt, that urbanization and development have had a significant impact on the water quality of streams in Virginia. Impervious surfaces like roads and roofs drive tremendous amounts of polluted runoff into gutters, storm drains, streams, and rivers. This water runs untreated into critical sources of drinking water like the Potomac River and reservoirs. Although this water will be treated before it enters people’s homes, some chemical pollutants are difficult to remove.”

One of those pollutants is chloride from sodium chloride. Analyses from three different studies at multiple locations have found increasing freshwater salinization in Northern Virginia. Chloride salts dissolve easily in water. High concentrations can impede the ability of freshwater animals (including humans) and plants to control their water and salt content (osmoregulation) and certainly affects taste. Concentrations in the Potomac River have risen almost 10 fold since 1940. The rise is especially noticeable since 2000 in winter months, where average concentrations have increased to 37.8 mg/L in the 2010s.

from ICPRB the increasing blue and green show the increasing Cl concentrations

Road salting during snow and ice storms is now considered the largest source of chlorides to the Potomac and its tributaries in the Washington, D.C. region (e.g., Porter et al. 2020). Concentrations are also rising in the other three seasons. According to the Interstate Commission on the Potomac River Basin (ICPRB) this may indicate that groundwater is holding chlorides deposited during winter and slowly releasing them to the river as baseflow during drier months. Evaporation from the river surface during warm weather could also concentrate chloride in the water.

Salts are very effective at deicing roads; however, after application, the salts are washed off into local waterways or seep through soils into groundwater systems with negative impacts on water quality and the environment. Salts pollute drinking water sources and are very costly to remove. The only available technology to remove salt from the source water is reverse osmosis which is extremely costly and requires a significant amount of energy to run.   

Weathering of rocks and sediment, natural sources of chloride in rivers, contribute to the problem but high concentrations  come from winter road salting, fertilizer runoff, water softeners and oil and gas production. Due to their corrosive nature, salts also increase the costs of maintenance, repair, and replacement of infrastructure like roads, sidewalks, driveways, bridges, and pipes which are subject to stress cracking. Improved management and use of salts during winter weather events can maintain public safety and hopefully minimize the negative impacts of salty runoff. However, adding more paved surfaces to treat increases the challenge. Despite VDOT efforts to brine the roads, the salt level in the Occoquan Reservoir continues to rise. 

The ICPRB has been working with the Virginia Department of Environmental Quality (VDEQ) and the Northern Virginia Regional Commission to decrease salt levels in area streams, hoping to prevent the need to invest billions of dollars in desalination equipment in the region’s water treatment plants. The plan is to implement a voluntary management of the use of salts for roadways and walkways through the implementation of the Salt Management Strategy just published by the ICPRB and VDEQ. The central purpose of the Salt Management Strategy is to try and reverse the trend of increasing salt levels and reduce the amount of salt in area waters to ensure protection of aquatic life and drinking water while continuing to maintain public safety and accessibility during the winter.