A threat to water table
Geologist says Nevada project could harm western Utah level
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.
"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.
Baker, Nev., could experience serious changes. "It shows that after 10 or so years of pumping in the carbonate aquifer (deeper aquifer) the water levels would decline by over 200 feet, and about 150 feet in the basin-fill aquifer."
Another important effect is on biology. When springs go dry or have reduced flow, it could further endanger species of concern such as the least chub, spotted frog, snails and the Lake Bonneville cutthroat trout.
If these already-scarce animals are likely to be impacted, he said, "all kinds of extra federal regulation might come in."
To better understand the situation, the Utah Geological Survey is soon to begin constructing a series of groundwater monitoring wells in a project costing $2 million to $3 million in state money, Hurlow said. Some may be as deep as test wells drilled by SNWA, 1,700 feet. Eight wells paralleling the border are to be drilled soon.
E-mail: bau@desnews.com
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