Groundwater pumping can increase arsenic levels in San Joaquin Valley irrigation and drinking water; recovery possible if withdrawals stop

  • Satellite-derived measurements of ground sinking could predict arsenic concentrations in groundwater and serve as an early warning system to prevent dangerous levels of arsenic contamination in aquifers with certain characteristics worldwide.
  • Researchers found signs that aquifers contaminated as a result of overpumping can recover if withdrawals stop.

June 5, 2018 Stanford University Read full ScienceDaily article here

Pumping an aquifer to the last drop squeezes out more than water. A new study finds it can also unlock dangerous arsenic from buried clays — and reveals how sinking land can provide an early warning and measure of contamination.

Now research published in the journal Nature Communications suggests that as pumping makes the ground sink, it also unleashes an invisible threat to human health and food production: It allows arsenic to move into groundwater aquifers that supply drinking water for 1 million people and irrigation for crops in some of the nation’s richest farmland…

…Importantly, the group found signs that aquifers contaminated as a result of overpumping can recover if withdrawals stop. Areas that showed slower sinking compared to 15 years earlier also had lower arsenic levels….

…When water pumping slows enough to put the brakes on subsidence — and relieve the squeeze on trapped arsenic — clean water soaking in from streams, rain and natural runoff at the surface can gradually flush the system clean.

However, study co-author Rosemary Knight, a professor of geophysics and affiliated faculty at the Woods Institute, warns against banking too much on a predictable recovery from overpumping. “How long it takes to recover is going to be highly variable and dependent upon so many factors,” she said….

Ryan Smith, Rosemary Knight, Scott Fendorf. Overpumping leads to California groundwater arsenic threat. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-04475-3