Publication Date

2012

Document Type

Thesis

Committee Members

Chris Barton (Committee Member), David Dominic (Committee Member), Robert Ritzi (Committee Chair)

Degree Name

Master of Science (MS)

Abstract

Subsurface heat flow was simulated to study the effect of hyporheic exchange on groundwater intake temperatures of open-loop geothermal wells in glacigenic-outwash aquifers in the North American midcontinent. The model represents an aquifer kilometers wide, on the order of 100m thick, and directly connected to a perennial river. The aquifer has bimodal hydraulic conductivity with a geometric mean on the order of 100m/day, an effective thermal conductivity of 2.33W/mK, and specific heats on the order of 106J/(m^3 K) for water and 103J/kgK for solids. The aquifer is initially set to a temperature of 12.85 °C and the river is fixed to 26.85 °C. Results show that the ambient zone of hyporheic thermal influence spans the entire depth of the aquifer and extends laterally for approximately a half a kilometer from the river. Temperatures within this zone decrease, as a linear approximation, at about 1 °C per 50 m distance from the river. Aquifer heterogeneity strongly influences the extent of and the temperatures within the hyporheic zone. A well pumping at 500 m^3/day had intake temperatures as much as 2 °C greater than ambient levels and, depending on location, slightly extended the range of the river's thermal influence. However, this increase of intake temperature was not instantaneous, drifting upward on the order of 1 °C per century before achieving thermal equilibrium. A realistic distribution of 25 wells pumping at variable rates extended the range of thermal influence to a kilometer, produced intake temperatures as much as 16 °C greater than ambient levels, and increased spatial variability in aquifer temperatures.

Page Count

47

Department or Program

Department of Earth and Environmental Sciences

Year Degree Awarded

2012

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