HR: 14:55h
AN: H33M-06    [Abstracts]
TI: Using Transient Temperature-Depth Data to Constrain Groundwater Flow Velocities in Thermal Aquifers of Long Valley Caldera, California
AU: * Randolph, J
EM: rando035@umn.edu
AF: University of Minnesota, 310 Pillsbury Drive SE, Minnespolis, MN 55455,
AU: Saar, M O
EM: saar@umn.edu
AF: University of Minnesota, 310 Pillsbury Drive SE, Minnespolis, MN 55455,
AU: Farrar, C
EM: cdfarrar@usgs.gov
AF: U.S. Geological Survey, PO Box 1360, Carnelian Bay, CA 96140,
AU: Hurwitz, S
EM: shaulh@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS 439, Menlo Park, CA 94025,
AB: Temperature-depth profiles are a fundamental tool for studying groundwater flow in porous media and fracture zones. They have been used to measure vertical and horizontal groundwater flow velocities in zones of significant permeability, ascertain changes in mean annual surface temperature, estimate geothermal energy potential, and measure magma emplacement rates and eruption hazard. The vast majority of studies that rely on temperature- depth profiles assume steady-state temperature and groundwater flow conditions. Here, we present an analysis of temperature data from two hot water wells (maximum temperatures 100°C and 129°C) in Long Valley Caldera. Ten resistance temperature devices (RTDs) installed in each well continuously measure temperature at discrete depths, from 24m to 76m in one well and from 67m to 200m in the other. A previously developed model (S. Ge, JVGR 1998) using steady-state temperature-depth profiles in fracture zones to constrain groundwater flow velocity was employed. It assumes a characteristic linear conductive profile outside thermal fluid flow zones and a concave profile within. Here, a modified approach is applied to profiles from the two study wells, which allows for deviation from the characteristic form as well as incorporation of observed transient temperature fluctuations. These variations range from approximately 0.5°C on a daily scale to 1°C on a scale of weeks to months.
DE: 1829 Groundwater hydrology
DE: 1847 Modeling
DE: 1849 Numerical approximations and analysis
DE: 1872 Time series analysis (3270, 4277, 4475)
SC: Hydrology [H]
MN: 2007 Fall Meeting