8. Mapping the three-dimensional distribution of hydrogeologic properties in carbonate-rock aquifers of the Great Basin

The eastern two-thirds of the Great Basin is underlain by Middle Cambrian through Permian carbonate rocks that form one of the larger regional aquifer systems in the country. Largely undeveloped, this aquifer system has the potential of holding hundreds of millions of acre-feet of water in storage within eastern Nevada and western Utah. Ever-increasing water demands from population growth in the southwestern United States are adding pressure to develop this untapped resource. Withdrawal of water from bedrock aquifers could limit water availability for current users and affect ecological habitats such as springs and riparian communities reliant on natural discharge from the aquifer system.

A number of published USGS studies, including the USGS RASA program, conceptualized the Paleozoic carbonate rocks as single, thick bedrock aquifer that is typically represented in ground-water flow models as an equivalent porous medium. Yet, it has been demonstrated that the effective permeability of carbonate-rock aquifers is created by fracturing and subsequent karstification resulting in significant aquifer heterogeneity. In general, stratigraphic and structural controls on permeability have not been considered. Characterization of the permeability distribution is essential for estimating flow paths and travel times, determining the degree of hydraulic connectivity among water-bearing zones, and identifying areas vulnerable to ground-water depletion.

This same carbonate sequence hosts major Carlin-type sediment-hosted gold deposits and are the primary deep aquifer system controlling the circulation of metallogenic fluids and the migration of petroleum in the Great Basin. Understanding of the stratigraphic and structural controls on the permeability of carbonate-rock aquifers thus bears on the understanding of Carlin-type ore deposit formation and also bears on the migration and entrapment of petroleum.

Integration of existing with new geologic and hydrologic data provides an unprecedented opportunity to characterize the porosity and permeability architecture of one of the nation’s largest undeveloped water resources. Conducting geologic mapping of stratigraphic and structural features, ranging from local to regional in scale, will lead to a better understanding of the three-dimensional distribution of enhanced permeability zones, the permeability types controlling ground-water flow, and degree of aquifer heterogeneity and anisotropy. Outcrop-scale observation of stratigraphy, fracture network and fault zone architecture need to be upscaled through links to stratigraphic facies changes and regional structural domain to develop basin-wide and regional-scale understanding of permeability structure in these units.

Opportunities exist to link geologic characteristics of the carbonate-rock aquifer to hydrologic responses. Central to this research opportunity is the ability to correlate geologic observations with available carbonate aquifer hydraulic data compiled from aquifer tests, drill-stem test from oil and gas exploration wells, and interpreted from the geometry of drawdown cones around active mines. An important contribution of this research will come through interdisciplinary work and collaboration with USGS advisors and with State and local agencies conducting hydrologic testing, computer modeling, and other activities. This research is expected to result in maps and interpretive reports showing the three-dimensional distribution of hydrogeologic properties in carbonate-rock aquifers. Such maps will help define the distribution of aquifer permeability and storage capacity and improve our understanding of the effects of aquifer heterogeneity on flow fields to protect ground-water resources and support sustainability in the face of ever increasing water demands.

Proposed Duty Station: Denver, CO

Areas of Ph.D.: Geology, hydrology

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Hydrologist, Hydrologist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): Donald Sweetkind, (303) 236-1828, dsweetkind@usgs.gov; Poul Emsbo, (303) 236-1113, pemsbo@usgs.gov; David Prudic, (775) 887-7611, dprudic@usgs.gov; Lari Knochenmus, (775)887-7613, lari@usgs.gov

Human Resources Office contact: Kathleen Scheich, (303) 236-9581, kscheich@usgs.gov

Summary of Opportunities