Expect new debate in the coming weeks and months about the future of the Hetch Hetchy Reservoir and the submerged valley below its waters, after today’s release of a state report that concludes draining the reservoir could cost as much as $10 billion.

A new study from the state’s Department of Water Resources pegs the cost of restoring the valley once admired by John Muir at somewhere between almost $3 billion and $9.8 billion. You can read the report here.

That’s a pretty wide range of costs. The report concludes that most of the cost would be to create replacement system for all of that water; and much of that cost is attributed in the report to creating new surface storage of water– as much as 450,000 acre feet of water. By the way, an acre foot is about 326,000 gallons of water.

The actual removal of O’Shaughnessy Dam, according to the report, would probably cost no more than about $900 million.

Reaction to the report was swift from both supporters and opponents of Hetch Hetchy restoration, a valley flooded some 73 years ago as a place to store drinking water for San Francisco.

Some say the study shows that the idea isn’t really so far fetched. “There is no longer a question of whether restoring Hetch Hetchy is possible,” said Assemblymember Lois Wolk (D-Davis), chair of the Assembly Water, Parks, & Wildlife Committee. Wolk says everyone should keep an open mind, and that more study needs to be done.

But even some prominent San Franciscans are against the restoration, most notably U.S. Sen. Dianne Feinstein (D-SF). In a written statement this morning, Feinstein also alluded to the power generated through the Hetch Hetchy hydroelectric system, saying that the restoration “would be far too expensive and leave the state vulnerable to both drought and blackout.” And some in the business community are suggesting that the high cost of the project confirms it’s time to move on. “This idea has now officially been studied to death,” said Jim Wunderman of The Bay Area Council.