HR: 0800h
AN: H41F-0479    [Abstracts]
TI: Advantages and Pitfalls of Time-lapse Ground Penetrating Radar in Characterizing Hydraulic Properties
AU: * May, C
EM: may1cl@cmich.edu
AU: Kinnicutt, P G
EM: kinni1p@cmich.edu
AB: The use of 4-D (time-lapse) ground penetrating radar (GPR) applies a method that enables the principle investigator to look at changing hydraulic properties over time. 4-D GPR is a survey that acquires temporal 3-D GPR profiles without changing the location of the survey grid. Assuming that the earth material does not change, changes in the temporal GPR profiles should be a result from groundwater movement [Birken and Versteeg]. Brewster and Annan carefully collected data on the Canadian Forces Base Borden using 200 MHz GPR to observe a controlled release of DNAPL [Brewster and Annan]. GPR proved itself as a fast, cost-effective method of investigating glacial outwash aquifers and is very applicable to this study, which is also located in glacial terrain [Taylor and Baker]. This study, located Lumberjack's Park 15 miles southwest of Mt. Pleasant and about 15 miles west of Alma, MI, collected 4-D GPR data over the course of one month using GSSIs' SIR-3000 and a 200 MHz monostatic antenna. GPR works by sending electromagnetic waves (EM) from a transmitting antenna into the subsurface. The 4-D GPR surveys, acquired over a 60' x 30' invariant grid, were located along side the Pine River, allowing the river to be used as a marker for the water table. There are numerous pitfalls that occur in a study using time-lapse GPR. One of these pitfalls is the need to account for changes in the dielectric constants, due to changes in soil moisture content, making processing of the temporal files time consuming. Inaccurate navigation in this study resulted in different size GPR files, complicating the creation of a 3-D model using a subtraction program that subtracts files of the same size. GPR proved to be a valuable tool for showing the differences in the ground water over of this study. Differences in the temporal GPR profiles suggested variations in hydraulic properties, resulting in the ability to estimate the hydraulic properties. Two boreholes were drilled, using a power soil auger, for ground-truthing purposes to measure water table depth. Slug tests used in these boreholes measured the water table at about 5.75ft. The ground-truthing aided in the interpretation of the GPR data and identified the approximate location of the water table. The results of this study showed time-lapse GPR to be a potentially useful and inexpensive tool for estimating hydraulic properties.
DE: 1829 Groundwater hydrology
DE: 1835 Hydrogeophysics
SC: Hydrology [H]
MN: Fall Meeting 2005