In the San Joaquin Valley, California, arsenic contamination affects over 10% of wells drilled in the San Joaquin Valley. Arsenic levels as low as 10 parts per billion have been linked to increased risk of cancer and numerous other health problems. Some have hypothesized that arsenic contamination is linked to groundwater pumping, but this had never been explored or quantified in California.

We processed subsidence data from satellites (interferometric synthetic aperture radar, or InSAR), which are a proxy for groundwater pumping. We then ran a machine learning model to explore the relationship between groundwater pumping (inferred by subsidence), geochemical conditions, and arsenic concentrations.

Our findings indicate that groundwater pumping is a significant factor in arsenic concentrations. This suggests that continued unsustainable pumping of groundwater in the San Joaquin Valley could raise arsenic levels throughout the Valley. However, our results also indicate that reductions in pumping are likely to improve water quality.