"Substantial impact" would occur in western Utah if a Nevada groundwater proposal goes ahead, says Hugh Hurlow, a geologist with the Utah Geological Survey. In some places the water table could drop enough to damage ranching and the environment.

Hurlow, an expert in geologic framework studies of hydrologic basins, spoke Monday at a luncheon of the Utah Geological Association, held at UGS offices, 1584 W. North Temple.

The project is sponsored by the Southern Nevada Water Authority. SNWA wants to to pump out 200,000 acre-feet of groundwater yearly and pipe it to the Las Vegas vicinity. In some cases, the pumping would be done only five miles from the Utah border.

The project would tap water from Spring Valley, Nev., and Snake Valley, which straddles the state boundary.

The authority had requested 90,000 acre-feet from Spring Valley. In April, Hurlow noted, the Nevada state engineer said the authority could withdraw 40,000 acre-feet per year from Spring Valley for 10 years. If monitoring shows no serious problems after that period, an additional 20,000 acre-feet per year would be taken.

SNWA also applied for permission to take 50,680 acre-feet yearly from Snake Valley; this application is pending.

Hurlow said a recent study by the U.S. Geological Survey shows that the underground aquifers are connected with water generally flowing from Spring Valley in Nevada into Snake Valley in both states, and then toward western Utah towns like Garrison, Millard County, and Callao, Juab County. It also flows toward wildlife areas like Fish Springs, Juab County.

"What kind of impact would these proposed wells have on the aquifers in Utah?" he asked. "And the answer right now is, we really don't know. We have only the broadest estimates."

In that vein, he said, a 1995 USGS study simulated the effect of pumping groundwater as SNWA would like to do. While admittedly not detailed and limited in geological modeling, the study shows a "significant depression" in the water table in Utah.

In some places the water table would drop 50 feet, in some others 100 feet. "The 50-foot contours extend well into Utah. And for those areas, that is a significant amount of draw-down of their aquifers."

Groundwater may drop below the root zone of some plants, he said. But it's hard to tell exactly how much impact there would be, at this stage in the studies.

A 100-foot drop would extend well over the border and envelop "this area of agriculture south of Garrison," he said.

The 50-foot contour, where the water table would drop that much, "extends over into this area in Utah," he said, pointing to a map.