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Uranium, arsenic, other toxins found in 20% of Calif. groundwater used for drinking

| Wednesday, July 15, 2015, 10:15 p.m.

SAN FRANCISCO — 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 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.

Public-water systems are required to bring many contaminants down to acceptable levels before supplying customers. But the findings highlight potential concerns involving the more than 250,000 private wells where water quality is the responsibility of individual homeowners, state officials said.

Several million Californians rely on public water systems in which raw supplies bear potentially toxic amounts of those trace elements, according to the first cumulative findings of the state and federal Groundwater Ambient Monitoring and Assessment program, which California established in the early 2000s.

The survey gives public-policy-makers the first sweeping look at the extent to which agricultural irrigation, industrial pollutants and other uses of groundwater are adding to problems for underground water reserves, now under heavy demand in California's drought.

Uranium, for example, is a naturally occurring element — one that can raise the risk of kidney ailments and cancer if consumed long-term at high levels.

But farm irrigation draining into underground water aquifers has contributed to uranium showing up at unsafe levels in 7 percent of public water supplies in the farm-rich San Joaquin Valley, the study found.

For California's water managers, “the challenge right now, of course, is the drought,” said John Borkovich, an official with the state Water Resources Control Board who helps oversee the groundwater monitoring program. “Being able to sustain delivery of a safe water supply is the No. 1 concern, of course. But water quality is hand in hand with water quantity.”

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