Research from the U.S. Geological Survey (USGS) shows a worrying increase in groundwater salinity across the United States, linked to road salting and irrigation. This poses a threat to aquatic life, infrastructure and human health through elements such as radium. For more than three decades, U.S. Geological Survey (USGS) scientists have been tracking groundwater quality in wells across the United States. Their work focuses on detecting potentially harmful chemicals or substances that could negatively impact ecosystems or human health.
In total, the crew measured up to 500 chemical compounds, including major ions, metals, pesticides, volatile organic compounds, fertilizers and radionuclides.
In these compositions, there is a significant increase in the content of Na and Cl ions and dissolved solids, all of which are related to salinity. Details and trends found in this multi-decadal study were recently presented at the Geological Society of America's "GSAConnects2023" conference.
This research, now part of the National Water Quality Network, is a continuation of work begun in 1992 as part of the National Water Quality Assessment Project. "The initial goal was to assess water quality conditions across the country, including groundwater, surface water and ecological health," said U.S. Geological Survey hydrologist Bruce Lindsey. "Over time, they focused on certain components that may have long-term harmful effects."
The researchers sampled wells in three different network types: residential, urban and agricultural areas. Domestic wells or private wells not regulated by the Environmental Protection Agency or local municipalities represent intermediate depth aquifers and drinking water. Wells in urban and agricultural areas are shallower, usually about 30 to 50 feet deep. "The purpose of [sampling] these wells is to understand conditions and trends at the shallowest water levels," Lindsay explains. These shallow wells are "sentinels for possible changes deeper in the aquifer," so to speak.
The team identified 82 water networks, each with 20 to 30 wells, and identified 28 ingredients of concern that needed to be tracked. The water is sampled every 10 years to track changes in chemical concentrations. These compositions and sampling results can be seen on the U.S. Geological Survey's interactive groundwater map, which shows changes over a decade.
Increased salinity and its effects
"If we look at 28 ingredients across all 82 networks, dissolved solids, chloride and sodium are statistically increasing more frequently than other ingredients on our list," Lindsay said. "If you look at the map, you can see the pattern right away. Especially in peri-urban areas where the weather is colder and there is a lot of road salt. We got data on road salting and found a correlation between increases in chloride, sodium and dissolved solids and the rate of road salting."
But levels of Cl, Na, and dissolved solids also increased in another area: the arid regions of the United States, especially the Southwest. Soil salinity in these areas is already high, but irrigation compounds the problem.
"When you irrigate agriculture in arid areas, there's a lot of evaporation," Lindsay explains. "So if the irrigation water has relatively low salinity, but a large portion of it is evaporated, [salinity levels] can become very high."
environmental and health impacts
Rising levels of Na, Cl and dissolved solids can lead to a variety of problems, the first being environmental ones. Many streams are fed from groundwater, and higher concentrations of chlorine in the water can disrupt the natural balance of aquatic life habits. "[Rising levels] could take 20, 30 or 40 years to develop... which means that if there are changes in the management of salinity sources, it could also take that long to recover," Lindsay said.
Dissolved salt ions can also cause problems for infrastructure. Corrosivity also becomes a problem as groundwater salinity increases. Corrosive groundwater, if left untreated, can dissolve lead and other metals in pipes and other components in your home's plumbing.
Finally, Lindsay and his colleagues also identified a unique problem related to rising salinity, with implications for human health. In a sandy aquifer in southern New Jersey, they found that low-pH water mixed with high-salinity groundwater created more salt.