Nevada State Engineer Tracy Taylor issued a 56-page decision this week authorizing the Southern Nevada Water Authority (SNWA) to take up to 40,000 acre-feet of water annually from Spring Valley, located west of Great Basin National Park, for a 10-year period. An acre-foot is typically the amount of water a family of four consumes in a year.

If it is determined there are minimal or no impacts from such a withdrawal, the state will authorize the withdrawal of an additional 20,000 acre-feet annually, bringing the total yearly take to 60,000 acre-feet. The SNWA's permit application requested a withdrawal of 91,000 acre-feet annually.

Utah water officials say they don't expect the decision, outwardly anyway, to affect negotiations between the states over how groundwater in neighboring Snake Valley, located east of Spring Valley along the state line, will be shared. Such an agreement is necessary before the SNWA can pursue groundwater in Snake Valley - the next phase of its pipeline project.

"I haven't had an opportunity to study it in detail, but just reviewing it briefly, it appears to be a very sound decision," Utah State Engineer Jerry Olds said Tuesday. "The Nevada state engineer has tried to administer the resource based on the safe yield that he knows is there."

Nevada engineer Taylor has determined that the perennial safe yield in Spring Valley - the amount of water that can be taken without significantly depleting the valley's groundwater table - is 80,000 acre-feet per year.

"It's a conservative decision but a reasonable one that allows us to move forward with the project," said SNWA General Manager Pat Mulroy in a statement.

But ranchers and conservationists have argued that any significant groundwater withdrawal from Spring Valley will not only have an impact on that area, but Snake Valley as well because of the way water flows between connecting aquifers.

"We can probably expect some impacts to springs with native species, even with the 40,000 acre-feet," said Don Duff, president of the Great Basin chapter of Trout Unlimited. "We'll be keeping close tabs on Spring Valley, as well as the south end of Snake Valley because the connectivity is there."

The connectivity issue has been even heightened in recent weeks following a preview of an upcoming U.S. Geological Survey study that shows more water flowing from Spring Valley to Snake Valley than previously thought. It has become a factor in the Utah-Nevada negotiations.

"It changes things some, but not dramatically," said Olds, the Utah engineer. "A lot of the water [the USGS] shows coming over is basically used up by higher evapotranspiration rates in Snake Valley."

jbaird@sltrib.com