52 years worth of subsidence in California's San Joaquin Valley. And there's been another four decades of subsidence since this image.
Now the water-strapped Central Valley has another scourge - arsenic.
The article discusses the perils and tribulations of the people of the Central Valley in their pursuit of clean, consumable freshwater. What is not mentioned is what the arsenic is doing to the crops they're growing and selling.
Towns across the Central Valley region of California have had tap water arsenic levels above the federal limit for almost two decades, levels that research suggests can raise the risk of a variety of cancers and lower IQ in children. During the same period, locals and scientists have noticed another odd phenomenon: the valley is sinking, at rates as fast as 25cm a year. Now it seems that the two problems are connected.
...Over the past century, groundwater levels in some places have fallen as much as 200 meters during drought conditions, according to the United States Geological Survey. The subsequent changes in water pressure alter underground architectures, leading to a sometimes-surreal slumping of land by as much as 10 meters.
...The same subsurface change in pressure can suck arsenic out of layers of clay and into groundwater, like a sponge being squeezed, said Dr Scott Fendorf, a professor of earth science at Stanford University and a co-author of a new study on the subject. “When we’re overdrafting the aquifer, the two things happen simultaneously.”