Snake Valley Groundwater Monitoring-Well Project
In early 2007 the Utah State Legislature requested the UGS to establish a long-term (50+ years) ground-water monitoring network in Snake Valley (western Millard County) and adjacent areas, in response to planned ground-water development in east-central Nevada.
Objectives included (1) determining baseline water-level and chemical trends as a basis for evaluating possible future changes in local and regional groundwater flow systems, (2) establishing ground-water monitoring wells near the planned pumping wells to assess their potential impacts on groundwater in Utah, (3) establishing monitoring of discharge from selected springs, (4) conducting aquifer tests to measure the capacity of the aquifers to transmit and store groundwater, and (5) evaluating regional flow patterns in the deep carbonate aquifer from Snake Valley to Fish Springs National Wildlife Refuge, based on water levels, isotope and tracer geochemistry, and geologic framework.
The network includes wells and spring gages in Snake Valley, and wells in Tule Valley and Fish Springs Flat. We installed new monitoring wells at 27 sites, including one to four boreholes per site and one to five piezometers per borehole. Sixty-six of the new piezometers are equipped with pressure transducers that measure water levels hourly. We also placed transducers in ten pre-existing wells. Eleven surface-flow gages are in place at six springs, and sixty shallow (~3 feet) piezometers are installed in wetlands in the outflow areas of springs.
Our Web-based data server provides access to water-level data, lithologic and geophysical logs, and well-construction information for the new UGS wells; water-level data from pre-existing wells equipped with UGS pressure transducers; surface-flow data from UGS gages; and water-level data from shallow piezometers in Snake Valley wetlands.
New well sites are in a variety of hydrologic settings, including (1) the basin-fill aquifer in agricultural areas using ground-water wells for irrigation, (2) the basin-fill aquifer far from agricultural areas, (3) the carbonate aquifer near agricultural areas, (4) the carbonate aquifer along the hypothetical ground-water flow path from Snake Valley to Fish Springs, and (5) spring systems that host sensitive aquatic species and consist of multiple upwelling points and therefore cannot be gaged.
Nested piezometers are screened at different depths to evaluate vertical hydraulic gradients. Where possible, both the basin-fill and carbonate aquifers are screened at the same site to evaluate their hydraulic connectivity. The new well data table summarizes well construction and water levels.
The UGS conducted two aquifer tests during March 2009. At site 11, a 12-inch-diameter well was pumped at 1200 gpm for 17 days while changes in water levels in four nearby and five distant (up to about 3 miles away) wells were monitored. The water was pumped from the carbonate aquifer (Pennsylvanian Ely Limestone) while water-level changes were recorded in carbonate and basin-fill monitor wells. At site 3, the carbonate aquifer (Devonian Guilmette Formation and Simonson Dolomite) was pumped at 180 gpm for 12 days while three nearby wells in the carbonate aquifer were monitored. Analysis of both tests is in progress.
We installed flow gages at large-discharge springs that could be impacted by future ground-water development. These springs have relatively large water rights on record and/or their outflow areas provide habitat for sensitive aquatic species. In all, 11 gages are in place at 6 sites and the real-time data are streamed to Department of Natural Resources via radio telemetry.
UGS assisted with installation of 60 shallow piezometers in five spring-outflow areas as part of a U.S. Environmental Protection Agency-funded project to establish baseline physical habitat conditions of wetlands in Snake Valley. This work, installation of nested piezometers, and surface gaging were done in coordination with the Utah Division of Wildlife Resources, which monitors the populations of sensitive aquatic species in the spring pools and wetlands.