Sunday, December 25, 2022

Freshwater Salinization Syndrome

Freshwater contains natural salts and minerals. However, dramatic increases in salt concentrations are occurring due to human activities including road salt application, water softening, mining and oil production, commercial and industrial processes, weathering of concrete, sea level rise, and fertilizer application. Over the last several decades, scientists have measured increases in salt concentration in several rivers around urban areas including the Potomac River and the Occoquan Reservoir. The salinity in the reservoir has been rising over time and may be reaching a critical stage. 

Many different types of salts contribute to freshwater salinization including sodium, chloride, potassium, calcium, and magnesium. Too much salt in freshwater can harm aquatic life, but there's more to the problem than that. Increased salt concentrations lead to a phenomenon called freshwater salinization syndrome (FSS). This syndrome is due to direct and indirect effects of salts that cause other pollutants in soil, groundwater, surface water, and water pipes to become more concentrated and mobile.

With rising salt levels comes rising chloride concentrations, all salts contain chloride which forms a solution in water with available free chloride. One example of these effects is that salts can increase the rate of metals reacting and  mobilizing from soils and pipes and can cause the breakdown of infrastructure. This process is called galvanic corrosion. The rising salinity is also associated in some areas with changing water chemistry. Sulfate levels are decreasing and alkalinity is rising. These are other factors that influence corrosion  in our infrastructure.  

Excess nutrients in the soil like nitrate-nitrogen can also be mobilized by high salinity, thereby exacerbating nutrient pollution, which contributes to the increasing presence of dead zones and/or harmful algal booms. Radioactive materials such as radium uranium naturally occurring in soils in Virginia can also be mobilized and become more concentrated in groundwater and surface water. Excess salts can make water undrinkable, increase the cost of treating water, and harm freshwater fish and wildlife.

The Occoquan Reservoir is an important part of our region’s drinking water supply, providing about 40% of the clean drinking water for around 2 million people. Though sodium mass loading to the reservoir is primarily from watershed runoff during wet weather and reclaimed water during dry weather, sodium concentration in the reclaimed provided by the Upper Occoquan Service Authority wastewater treatment plant water is higher than in outflow from the two watersheds at the present. However, the new Comprehensive Plane recently approved by the Board of County Supervisors will accelerated industrial, commercial and residential development in the Bull Run and Occoquan river watersheds. History has told us that development increases salinity. The massive development on currently open and forested land in Prince William will accelerate the rate of rising salinity. The solutions will not be cheap. – Desalination for the drinking water supply, new shortened life cycle for water, wastewater and distributions systems, nitrogen removal to meet the requirements of the Chesapeake Bay TMDL and so much more.

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