Aquifer Tests, Chapter 7, Hydrogeologic studies and groundwater monitoring in Snake Valley and adjacent hydrographic areas, west-central Utah and east-central Nevada, USA

Hydraulic-property estimates derived from long-term aquifer tests of the basin-fill and carbonate-rock aquifers in Snake Valley were sparse prior to our work. We conducted aquifer tests at sites 11 and 3 to characterize the hydraulic properties of the upper and lower carbonate-rock aquifer, respectively, at these locations. Both tests were conducted at the maximum possible discharge rate as constrained by pump capacity, water level, and well diameter, and involved continuous monitoring of multiple observation wells using pressure transducers supplemented by manual measurements. The tests were designed to determine the hydraulic conductivity and storativity of the carbonate-rock aquifer and, for site 11, the hydraulic conductivity of the lower part of the basin-fill aquifer and the hydraulic connection between the basin-fill and upper carbonate-rock aquifers. To determine hydraulic properties (hydraulic conductivity and storativity), aquifer-test analyses use analytical solutions, numerical solutions, and/or a combination of the two (Walton, 2007). Analytical methods in aquifer-test analysis refer to matching theoretical curves to plotted groundwater level drawdown and recovery data, also known also known as curve matching. Numerical techniques generally refer to solutions obtained by numerical groundwater-flow modeling software that uses iterative processing and user-defined parameters. We used analytical and combination methods to analyze aquifer-test data from site 11, and analytical solutions to analyze aquifer-test data from site 3. Our attempt at a numerical model at site 11 was unsuccessful. This chapter describes the geologic setting of each aquifer test site, our methods of data collection and analysis, and the estimates of hydraulic properties that we derived from our aquifer-tests data analysis. We also compare our results to those of others.