HR: 0830h
AN: H31B-0449    [PDF]
TI: Azimuthal Resistivity Analysis Using a Capacitively-Coupled Resistivity Meter for the Determination of Hydrologic Parameters
AU: * Mayer, C A
EM: cm25@buffalo.edu
AF: University at Buffalo, Geology Department, Buffalo, NY 14260 United States
AU: Baker, G S
EM: gbaker@geology.buffalo.edu
AF: University at Buffalo, Geology Department, Buffalo, NY 14260 United States
AB: The contamination of groundwater has become a major concern during the last century. Methods are currently being developed to calculate hydrologic parameters for groundwater models. Azimuthal electrical resistivity (AER) has been used to calculate hydraulic transmissivity and effective porosity. Traditionally, a galvanically-coupled resistivity meter (GCRM) has been used to collect AER data. Using a GCRM for an AER survey requires large amounts of time to set the array. As an alternative for large study areas that require vast amounts of resistivity measurements, a capacitively-coupled resistivity meter (CCRM) may be used. Since the dipole cables connected to the transmitter and receiver are capacitively-coupled with the ground, there is no need for metal electrodes; thus the time needed to collect data is greatly reduced. The CCRM makes it feasible to collect a large amount of data in a relatively short period of time (e.g., 144 azimuthal readings per hour). The CCRM array is initially set with a 2.5 m distance between the transmitter and the receiver (x-distance); the spread of dipole cables on either sides of the transmitter and receiver (a-spacing) is 5 m. The x-distance and a-spacing remain constant while readings are taken at 10-degree increments until the array has been rotated 360-degrees. The x-distance in the array is then expanded by 2.5 m, and the above procedure is repeated. The maximum x-distance used is 20 m, which means that at any given azimuth 8 readings will have been taken with varying x-distances. Varying x-distances at each azimuth allow for the calculation of "true" resistivity through an inversion process. The array is then moved to a different location (station) at the same site and the aforementioned procedure is repeated. During this study AER surveys were completed at four sites in Western New York. Sites were chosen based on three criteria: 1) their proximity to outcrop containing fractures, 2) lack of elevation change, and 3) lack of obstructions (eg. trees, buildings, etc.). Readings were taken at three or four stations at each site. The inverted "true" resistivity values at each station were then normalized and averaged with all the other stations at the site. Therefore, variations in the hydraulic transmissivity by depth can be analyzed and any small-scale lateral heterogeneities removed from the final results. The theoretical basis for this approach and field data from these four sites will be presented.
UR: http://www.geophysics.buffalo.edu
DE: 1800 HYDROLOGY
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting