The rulings follow extensive hearings last year, during which everyone from the ranch-owning LDS Church to Salt Lake County and the Confederated Tribes of the Goshute Reservation requested a denial. Many fear that the interconnected valley aquifers will plunge because, according to some hydrological studies, the pipeline would take more than mountain snows can replenish.
Davis said there is no proof of that, and he noted that development would have to occur in stages with monitoring to ensure other users, wildlife and plant communities are not harmed.
"It's nothing more than speculation," he said of the opponents' fears.
King approved 61,000 acre-feet from Spring Valley alone, though only 38,000 may be developed in an initial eight-year phase. The rest would depend on confirmation that other interests are not harmed.
"The state engineer worked very hard to provide in these four rulings an unprecedented level of insight into the analysis used to reach his decisions in each of the valleys," Nevada Conservation and Natural Resources Department Director Leo Drozdoff said in a written statement accompanying the rulings' release.
But the Great Basin Water Network, an alliance of environmental, municipal and agricultural interests, said the rulings clearly snubbed the scientific input.
"It's an indefensible decision that's not based on science that's probably based on politics and development pressures," said Rob Mrowka, an ecologist with the Center for Biological Diversity and a Great Basin Water Network board member.
Either the water network or his own organization likely will sue both in state and federal courts to block the water rights, he said.
Nevada law limits pumping to sustainable yields, he said, creating one opening for a state lawsuit.
The U.S. Bureau of Land Management's anticipated approval of a pipeline route across federal lands later this year sets up a potential federal court challenge.
At stake is spring water for the relatively rare Bonneville cutthroat trout, shrub cover for the potentially endangered sage grouse, even food for elk, Mrowka said. And if plant roots are left dry, he said, the BLM's analysis indicates pumping from these valleys and Snake Valley could send 35,000 tons of new dust swirling toward the Wasatch Front. Some of that dust would include radionuclides from old nuclear weapons tests, he warned.
"Salt Lake City is going to be a downwind community once again," he said.
Salt Lake County Mayor Peter Corroon said the rulings trouble him, though the greater threat is from Snake Valley pumping.
"If groundwater pumping is allowed," he said, "it will be years before the effects will be known. If they are harmful, it will be too late to turn back the clock."
A study last year estimated the pipeline could cost $15.5 billion, potentially adding $31 to the average Las Vegas monthly water bill of $36. Opponents said that may be unaffordable, especially with Thursday's ruling granting less water to fill it than SNWA had requested. But Davis said the utility can handle the cost, and rates would remain competitive with other Western cities.
Mike Gorrell contributed to this report.