CARSON CITY, Nev. — A hearing scheduled to last into late fall began Monday on the Southern Nevada Water Authority's plans to pump billions of gallons of water from remote valleys along the Nevada-Utah line to quench Las Vegas' thirst.

In opening statements before the state engineer, critics of the proposal said the water authority's own data and modeling used to justify the 300-mile, $3.5 billion pipeline are flawed. They say tapping 126,000 acre-feet of groundwater would result in economic and environmental catastrophe for those in and around Spring, Cave Valley, Delamar and Dry Lake valleys.

An acre-foot is the amount of water it takes to cover 1 acre 1 foot deep.

"Under their data, every single spring in Spring Valley will go dry," said Paul Hejmanowski, a Las Vegas lawyer representing The Church of Jesus Christ of Latter-day Saints, which owns the sprawling Cleveland Ranch in Nevada's White Pine County.

Other opponents include Great Basin Water Network, several Indian tribes and various rural counties in Nevada and Utah.

Pat Mulroy, general manager of the water authority, testified that the agency is only seeking water rights for unappropriated, annual recharge.

Southern Nevada, the state's population hub, is home to 2 million people and attracts 40 million visitors annually.

Most of the region's water comes from the overtapped Colorado River, a source shared by seven western states and Mexico.

"There are no easy solutions left on the Colorado River," Mulroy said.

The water authority will have three weeks to present its case to Jason King, the state engineer. Opponents will be given the same amount of time to offer counter-testimony and expert opinions, and public comment will be heard Oct. 7.

A ruling could come early next year.

The agency was granted the permits it seeks once before, but last year, the Nevada Supreme Court sent the matter back for a new round of hearings. The court ruled the state engineer failed to act on the water authority's applications in a timely manner, and that people who were not part of the original case but have a stake in the outcome should be allowed to participate in the proceedings.

If the authority secures approval of all the rights it is seeking, the pipeline could end up carrying as much as 65 billion gallons of water from the north to the south on an annual basis. Daily flows would total up to 178 million gallons under that scenario — enough to cover an area the size of nearly 500 football fields with a new foot of water each day.

Hejmanowski said his clients don't object to southern Nevada wanting to develop available, unappropriated water, but they have concerns about the effects the pumping would have on existing water rights holders.

"We are not here to argue against progress or water for Las Vegas," he said, but added, "good intentions are no substitute for good science."

He said the LDS Church is opposed to 12 of the 19 permits SNWA has applied for in Spring Valley. Of the 12, four were denied previously.

Lawyers for Millard and Juab counties in Utah also oppose what critics call a "water grab," fearing that pumping from Spring Valley could alter groundwater flows in Utah's nearby Snake Valley.

Paul Taggert, a lawyer representing the water authority, said over the past 10 years, Lake Mead's water level plunged 140 feet because of drought, and the river-supplied water came within 6 feet of a shortage declaration that would trigger tough measures to curtail use.

He said opponents were "blinded by "personal prejudices" against SNWA and "fundamentally opposed to moving water from where it is to where the people need it."

But Simeon Herskovits, with Great Basin Water Network, said the agency's estimate of perennial recharge is "grossly exaggerated" and its projections on the effects of groundwater drawn down "greatly skewed."

He said pumping the water would cause economic and environmental harm by eliminating plant communities and take a toll on wildlife.

"We believe the state engineer will not be able to legally grant the applications," he said.