Abstract

As the demand for water increases across the southwestern United States, the region's utilization of and dependence on water stored in groundwater aquifers has risen in kind. The Coconino Aquifer (C-aquifer) underlies much of the southwestern Colorado Plateau and is a primary source of groundwater in northeastern Arizona. One of the largest commercial users of water from the C-aquifer in Apache County, Arizona, is Springerville Generating Station, a coal-fired power plant owned and operated by Tucson Electric Power. The area surrounding the power plant, located between the cities of Springerville and St. Johns, Arizona (the Springerville-St. Johns area), is geologically complex: it contains the Cedar Mesa anticline, an underlying CO2 reservoir, extensive travertine deposits, and several faults, including the Coyote Wash fault. The Coyote Wash fault and Cedar Mesa anticline play a significant role in the relationships between the St. Johns CO2 gas field, groundwater flow, and the travertine deposits. Yet, the interaction between the structures and the effect they have on groundwater flow is poorly constrained. By mapping the subsurface geology utilizing borehole records and by creating a groundwater model of the area, this study determined that the Cedar Mesa anticline acts as a partial horizontal barrier to groundwater flow, whereas the Coyote Wash fault does not act as such a barrier. Particle tracking for the model indicates that despite the reduced water volume in the aquifer after decades of groundwater extraction, flow still occurs across the hinge of the Cedar Mesa anticline, accelerated by active pumping wells located west of the anticline axis. The model indicates that prior to the activation of the pumping wells, outflow from the C-aquifer would have occurred with greater frequency to Lyman Lake and along the extent of the Little Colorado River located downstream from the lake. The study also identified a zone of high hydraulic conductivity located between the Cedar Mesa anticline and the Coyote Wash fault that continues west of the Coyote Wash fault and may align with the Buttes anticline. This model of groundwater flow conditions improves the understanding of the complex subsurface geology and groundwater flow dynamics in the area.

Degree

College and Department

Physical and Mathematical Sciences; Geological Sciences

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