Stanford geophysicist maps saltwater threat to California aquifers

Earlier this fall, a team led by Stanford geophysicist Rosemary Knight performed an ambitious experiment to determine the extent of ocean saltwater intrusion into underground freshwater in the Monterey Bay region. Freshwater is at a premium in much of California, especially along the agriculturally productive Monterey and Santa Cruz coasts. Many of the region's communities rely on groundwater to meet the freshwater needs of their residents and farmers, and the state's current unprecedented drought is only increasing that demand. But pumping freshwater out of the ground changes the fluid pressure of underground aquifers, and if an aquifer is located near the coast, the result can be an influx of saltwater. Over the course of decades, saltwater intrusion can dramatically change the salinity of an aquifer, rendering it unusable. In order to determine the seriousness of this problem in the region, researchers led by Stanford geophysicist Rosemary Knight and her former student Adam Pidlisecky, now an assistant professor of geosciences at the University of Calgary, conducted an ambitious scientific survey earlier this fall. The team used an advanced geophysical imaging technique called electrical resistivity tomography, or ERT, to map the salinity of aquifers along the entire Monterey Bay coastline to a depth of up to 1,000 feet.