What happens when Salinity Rises

In 2021, Dr. Marc Edwards the Charles Edward Via Professor of Civil and Environmental Engineering at Virginia Tech and MacArthur Fellow gave a talk at a virtual meeting of the ICPRB about some of the consequences of rising salinity in our source water. This was one half of a program about rising salinity in the Occoquan Reservoir.  In addition, research that has highlighted the corrosive effects of salt on private and public infrastructure has been published in recent years.

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. The reservoir’s current storage capacity is estimated by ICPRB to be 8.3 billion gallons. Prince William land accounts for 40% of the Occoquan watershed which contains 1,300 stream miles, Lake Jackson and Lake Manassas as well as the Occoquan Reservoir.  Water from the Occoquan Reservoir is distributed to customers in Fairfax and Prince William Counties. This water is essential, but we are not adequately protecting it from the damage of increasing development and growth in the region. The salinity in the reservoir has been rising over time and may be reaching a critical stage. 

With rising salinity comes rising chloride concentrations, after all, salt is sodium chloride which forms a solution in water with available free chloride. According to recent research, increase salinization and resulting source water contamination has widespread implications for corrosion of drinking water infrastructure, including chloride acceleration of galvanic corrosion of water infrastructure and other premature plumbing failures. Chloride can corrode and rupture hot water heaters.  Chloride potentially enhances hydrogen gas production which is explosive at higher levels, but at low levels also be food for bacteria – Harmless and smelly H2 S and far more serious Legionella.

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.  According to Dr. Edwards a chloride-to-sulfate mass ratio (CSMR) > 0.58 can trigger catastrophic galvanic corrosion of lead solder. The thresholds for the catastrophic galvanic corrosion of other metals is not yet known.

Regionally, as salt levels have risen, WSSC is seeing colored water problems related to winter deicing when chloride levels were observed to spike from 40mg/L to too mg/L. Increasing chloride levels is from rising sea levels, increased direct and indirect potable reuse of waste water, the increased amount of pavement and the salting of roads in the winter. Nearly all road salt eventually enters adjacent rivers, streams, and aquifers.  

Road salt’s impact on drinking water infrastructure in terms of lifetime, leaks, and water contamination is an emerging problem for both private well owners and municipal water suppliers These spikes have caused changes in water chemistry triggering the release of lead in solder to be released. Chloride is an aggressive ion that exacerbates corrosion, especially galvanic corrosion in hot water heaters and at pipe joining’s.

Dr. Edwards stated that every $1 of road salt applied produces $46 in public infrastructure damage. This figure excludes private plumbing damage.  Chloride levels are rising nationally in freshwater sources. We increasingly need to reuse water to meet water demand and increased pavement and road building increases the use of road salt for de-icing.  Road salt is applied to de-ice roads in the winter for highway safety, with more than 18 million metric tons applied annually and most used in northeastern and midwestern states to ensure public safety. The more paved roads we build, the more salt is used in the winter.