Abstract

An integrated electromagnetic (EM) and seismic geophysical study was performed to evaluate non-invasive approaches to estimate depth to shallow groundwater in arid environments with elevated soil salinity where the installation of piezometers would be impractical or prohibited. Both methods were tested in two study areas (semi-arid and arid respectively), one in Palmyra, Utah, USA near the shore of Utah Lake where groundwater is shallow and unconfined in relatively homogeneous lacustrine sediments. The other area is Carson Slough, Nevada, USA near Ash Meadows National Wildlife Refuge in Amargosa Valley. The area is underlain by valley fill, with generally variable shallow depths to water in an ephemeral braided stream environment. The methods used include frequency domain electromagnetic induction allowing for multiple antenna-receiver spacings. High resolution compressional P-wave seismic profiles using a short (0.305 m) geophone spacing for common depth-point reflection stacking and first arrival modeling were also acquired. Both methods were deployed over several profiles where shallow piezometer control was present. The semi-arid Palmyra site with its simpler geohydrology serves as an independent calibration to be compared to the Carson Slough Site. EM results at both sites show that water surfaces correspond with a drop in conductivity. This is due to elevated concentrations of evaporative salts in the vadose zone immediately above the water table. EM and seismic profiles at the Palmyra site were readily correlated to depth to groundwater in monitoring wells demonstrating that the method is ideal under laterally homogeneous conditions. Interpreting the EM and seismic profiles at Carson Slough was challenging due to the laterally and vertically variable soil types, segmented perched water surfaces, and strong salinity variations. The high-resolution images and models provided by the seismic profiles confirm the simple soil and hydrological structure at the Palmyra site as well as the laterally complex structure at Carson Slough. The EM and seismic results indicate that an integrated geophysical approach is necessary for an area like Carson Slough, where continued leaching of salts combined with braided stream deposition has created a geophysically complex soil and groundwater system.

Degree

MS

College and Department

Physical and Mathematical Sciences; Geological Sciences

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2009-12-11

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd3343

Keywords

EM, electromagnetic induction, seismic, shallow seismic, geophysics, hydrogeology, geohydrology

Language

English

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