University of Rhode Island scientists assess saltwater intrusion into water wells

November 5, 2020


The University of Rhode Island reports many water wells at homes along the Rhode Island coastline are being contaminated by an intrusion of saltwater, and, as sea levels rise and storm surge increases as a result of the changing climate, many more wells are likely to be at risk.

This prompted a team of URI researchers to conduct a series of geophysical tests to determine the extent of the problem.

“Saltwater cannot be used for crop irrigation, it can’t be consumed by people, so this is a serious problem for people in communities that depend on freshwater groundwater,” said Soni Pradhanang, associate professor in the URI Department of Geosciences and the leader of the project. “We know there are many wells in close proximity to the coast that have saline water, and many others are vulnerable. Our goal is to document how far inland the saltwater may travel and how long it stays saline.”

Saltwater can find its way into well water in several ways, according to Pradhanang. For instance, It can flow into the well from above after running along the surface of the land or it could be pushed into the aquifer from below. Sometimes it recedes on its own at the conclusion of a storm, while other times it remains a permanent problem.

Since saltwater is denser than freshwater, it typically settles beneath the freshwater. The scientists are using ground-penetrating radar and electrical resistivity tests — using equipment loaned from the U.S. Geological Survey and U.S. Department of Agriculture — to map the depth of the saltwater/freshwater interface.

The URI researchers planned to drill two deep wells in November to study the geology of the area and the chemistry of the groundwater to verify the data collected in their geophysical tests.

The first tests were conducted in Summer 2019, and a second series was completed this fall after being delayed by the pandemic. Final tests will be conducted next spring when groundwater levels should be at their peak.

“The groundwater level was at its lowest point in 10 years this summer because of the drought,” graduate student Jeeban Panthi said. “That will be a good comparison against what we expect will be high levels in April and May.”

Panthi has collected well water samples from nearly two dozen residences for analysis.

Another URI graduate student, Mamoon Ismail, is developing a model to simulate saltwater intrusion into drinking water wells based on the changing pattern of precipitation and the potential for extreme storms. They hope to be able to predict how far inland saltwater will intrude following a Category 1 hurricane compared to a Category 2 storm, for instance.

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