HR: 16:30h
AN: H24C-03    [Abstracts]
TI: Pumping Test Analyses Based on Gravity Measurements
AU: * Ferre, T P
EM: ty@hwr.arizona.edu
AF: University of Arizona, 1133 E. North Campus Drive, Tucson, AZ 85721-0011 United States
AU: Cordova, J
EM: jtc@hwr.arizona.edu
AF: University of Arizona, 1133 E. North Campus Drive, Tucson, AZ 85721-0011 United States
AU: Hill, M C
EM: mchill@usgs.gov
AF: United States Geological Survey, 3215 Marine St., Boulder, CO 80303 United States
AB: Pumping tests often suffer from a limited number of observation locations. Installation of monitoring wells is commonly too expensive to allow for addition of monitoring points for pumping tests. In contrast, gravity stations can be installed inexpensively, allowing for addition of multiple monitoring locations specifically for use during a pumping test. However, given the difference between the point scale support volume of monitoring wells and the distributed sensitivity of a gravimeter, it is not clear that gravimeters can provide useful data for constraining a pumping test. Specifically, there are two limitations facing the use of gravimeters for monitoring pumping tests. First, the absolute accuracy of gravity measurements, compared with the measurement of water levels, may limit the accuracy of inversions. Second, because most pumping test analyses are designed to use point measurements of hydraulic head, it is tempting to attempt to convert gravimeter readings to local hydraulic head without consideration of the spatial sensitivity of a gravimeter, adding a systematic error. As part of an effort to improve interpretation of geophysical methods for hydrologic applications, we examine the optimal use of gravity measurements made during a pumping test for estimating aquifer properties. We demonstrate that even if measurement imprecision is not considered and if the distributed sensitivity of gravimeters is considered correctly (i.e. using a coupled hydrologic-gravimeter model), measurements made with gravimeters during a pumping test may be as capable as monitoring wells for constraining the inversion of aquifer properties. However, the measurement precision associated with current field gravimeters leads to larger errors in property estimation based on a given number of gravimeter measurements than based on measurements made with the same number of monitoring wells. Ongoing work is aimed at assessing the optimal mix of monitoring well and gravimeter measurements in a cost-benefit framework.
DE: 0920 Gravity methods (1219)
DE: 1805 Computational hydrology
DE: 1829 Groundwater hydrology
DE: 1835 Hydrogeophysics
DE: 1848 Monitoring networks
SC: Hydrology [H]
MN: Fall Meeting 2005