Nearly one-fifth of the raw groundwater used for public drinking water systems in California contains excessive levels of potentially toxic contaminants, according to a decade-long U.S. Geological Survey study that provides one of the first comprehensive looks at the health of California’s public water supply and groundwater.

One of the surprises in the study of 11,000 public supply wells statewide is the extent to which high levels of arsenic, uranium and other naturally occurring but worrisome trace elements is present, authors of the study said. MORE