SHASTA LAKE    (AP) — A U.S. Bureau of Reclamation crew has begun testing the strength of Shasta Dam’s concrete as part of preparation work to raise its height by more than 18 feet (5.5 meters).

The crew is drilling holes on top and on both sides of the dam in Shasta County to determine if the 602-foot (183-meter) structure can withstand the additional height, the Record Searchlight reported Friday.

Don Bader, the bureau’s area manager, said the crew will drill about 70 holes in the dam and also drill into the bedroom beneath over the next few weeks.

The bureau has been studying the idea of raising the height of structure since the 1980s but has faced opposition from the state of California because it would further inundate the McCloud River, which is protected under state law.

The Winnemem Wintu Tribe has also opposed raising the height of the dam because the higher lake level would destroy sacred ceremonial sites.

After decades of public meetings and planning sessions, Congress earlier this year set aside about $20 million for pre-construction work and design.

Putting a new cap on the dam is only about 20 percent of the $1.4 billion cost of raising the dam, Bader said.

The bureau plans to award a contract to raise the dam in December 2019 and work will start shortly after, he said.

“Things sort of changed when they allocated the $20 million. That put things in high gear,” said Howard Jones, who owns Sugarloaf Cottages Resort in Lakehead.

Because the shoreline of the lake will also rise, numerous bridges, roads, campgrounds and resorts along the lake will also need to be moved to higher ground.

The new height will also allow the bureau to store an additional 630,000 acre-feet of water in Shasta Lake. The dam currently holds about 4.5 million acre-feet.

Bader said Secretary of the Interior Ryan Zinke has said that he wants to see more recreation on the lake as part of the dam raise.

“Our secretary has made it abundantly clear he wants to enhance recreational opportunities on the lake,” he said.