Collaborative Res: Assessing Aquifer Properties from Stress and Strain Distributions in Leaky-Confined Aquifers using Insar, GPS and Three-Dimensional Deformation and Flow Modeling

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

0106474 Burbey Aquifer tests typically involve collecting time-drawdown data in the vicinity of a pumping well for the purpose of producing plots for estimating the storage coefficient and transmissivity of the aquifer or aquifer system. Recent advances in GPS technology and INSAR (interferometric synthetic aperture radar) satellite imagery, allow for detailed and precise calculation of land surface displacements. Stationary GPS monitoring during an active pumping test in conjunction with INSAR interferograms for the same region will allow for time-compaction (and time-horizontal strain) data to be collected in conjunction with the hydrograph data providing a far more diagnostic test for estimating storage coefiricient of confined aquifers. Furthermore, in leaky aquifer systems in which the confining unit is the primary compressible unit, the time-compaction data can provide the necessary information to accurately calculate the speciric storage and vertical hydraulic conductivity of the confining unit, parameters that are typically difficult to evaluate. A new analytical solution has been developed to derive the storage coefficient from time-subsidence data and numerical simulation results applied to this semi-log (conrined) and semi-log (leaky) methodology indicates that extremely accurate estimates for storage of the aquifer and storage and vertical hydraulic conductivity of the confining unit can be made. GPS and INSAR surveys will also provide detailed information on horizontal deformation occurring at the land surface and can corroborate results from hypothetical modeling of three-dimensional deformation and flow, which indicate that more than 50 percent of pumped water is released from storage associated with horizontal strain in confined aquifers. These results may have tremendous implications with regard to measuring subsidence, the quantity of leakage that can actually be expected through confining units, and the interpretation of long-term aquifer tests. Furthermore, the strain configuration through the confining unit will be much different in the presence of three-dimensional strain, which will affect the potential compaction and leakage through the confining unit over time. The potential contribution of water from horizontal strain may require us to rethink the current definition of storage coefficient where such strains have been neglected.