Multiple Risks of Saltwater Intrusion to Drinking Water Supplies

Increased pumping of coastal aquifers and sea-level rise driven by climate change are expected to increase saltwater intrusion and subsequent contamination of fresh groundwater. The primary constituents of saltwater are sodium and chloride, which are typically regulated as secondary drinking water standards. Severe saltwater intrusion can increase the total dissolved solids of fresh groundwater such that reverse osmosis (RO) is needed to produce potable water. Retrofitting an existing water plant with RO can be a daunting challenge, especially for small systems. An overlooked aspect of saltwater intrusion is the co-transport of bromide with chloride. Although bromide is present in seawater at a much lower concentration than chloride, the increased bromide in groundwater can form bromine-containing disinfection byproducts (DBPs). Recent toxicological studies have shown that incorporation of bromide into DBPs makes these chemicals much more toxic. However, the risk of saltwater intrusion on the formation of more toxic DBPs has not been previously investigated. This presentation will highlight a recent case of severe saltwater intrusion at a coastal water system in Florida, and also discuss the likely effects of saltwater intrusion on DBP formation and toxicity.