JACKSON, Amador County (CBS/AP) — State officials are warning that a 99-year-old dam in Northern California is at risk of collapsing if a big rainstorm comes through.

The concrete Eastwood Multiple Arch Dam in Jackson was built in 1916 and holds back large quantities of arsenic-contaminated tailings left over from gold mining.

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In June, the U.S. Army Corps of Engineers found that the dam was structurally unsound.

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California Department of Toxic Substance Control officials say they recently began a $1 million emergency repair operation that is expected to be completed this month.

The Eastwood Multiple Arch Dam in Jackscon, Calif. (Photo courtesy of Bill Lavallie/Amador Ledger Dispatch)

The Eastwood Multiple Arch Dam in Jackscon, Calif. (Photo courtesy of Bill Lavallie/Amador Ledger Dispatch)

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The city of Jackson says the National Weather Service will issue a warning if rainfall amounts reach certain levels that could exacerbate the dam’s structural problems.

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