Award Date

5-1996

Degree Type

Thesis

Degree Name

Master of Science in Geoscience

Department

Geoscience

First Committee Member

David K. Kreamer, Chair

Second Committee Member

Jean S. Cline

Third Committee Member

Kevin H. Johannesson

Graduate Faculty Representative

Vernon F. Hodge

Number of Pages

111

Abstract

In the eastern Grand Canyon, secondary porosity created by north trending faults, folds, and breccia pipes, facilitates groundwater flow through the South Rim carbonate aquifer. Springs associated with the South Rim Aquifer have low 3H concentrations, [Ca2+]/[Mg2+] rations close to unity, and variable uranium concentrations. For a geochemical comparison, springs are subcategorized on the basis of geology and discharge. Type I springs are associated with high-angle normal faults and have high discharge rates. These springs discharge Ca2+ - Mg2+, HCO3- waters, have 3H concentrations <2 TR, and 234U/238U activity ratios >3 AR, which suggest long groundwater residence times. Type II and IV springs are located on canyon mesas and have low discharge rates. These springs are predominantly Ca2+ - Mg2+, SO42- waters, have tritium ratios between 1 and 6 TR, and 234U/238U activity ratios between 1 and 2 AR. Higher 3H and 238U concentrations and low 234U/238U activity ratios in the latter waters may be due to shorter groundwater residence time. Based on 3H concentration, the occurrence of dedolomitization, and the resultant uranium isotope fractionation in groundwater, the minimum residence time of water discharging from the South Rim Aquifer is indicated to be > 40 years.

Keywords

Arizona – Grand Canyon; Aquifers; Groundwater flow; Groundwater recharge; Springs

Disciplines

Geochemistry | Hydrology

Language

English

Comments

Signatures have been redacted for privacy and security measures.


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