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2007 Ground Water Summit |
Monday, April 30, 2007
4:30 p.m. - 7:30 p.m.
Tuesday, May 1, 2007
9:30 a.m. - 1:30 p.m.
Tuesday, May 1, 2007
4:30 p.m. - 7:30 p.m.
Time-Domain Electromagnetic Soundings to Characterize Water Quality in a Freshwater/Saline-Water Transition Zone, Estancia Valley, New Mexico, USA—A Reconnaissance Study
During July 2005, The U.S. Geological Survey, in cooperation with the New Mexico Bureau of Geology and Mineral Resources, conducted a reconnaissance study in an area of about 525 square kilometers in the Estancia Valley in central New Mexico to characterize water quality using time-domain electromagnetic (TDEM) surface geophysical soundings. Seven TDEM soundings were collected along an east-southeasterly profile about 19.3-kilometer long in which apparent electrical resistivity was measured to depths of about 80 meters. The study area is composed of deformed Paleozoic and Mesozoic rocks overlain by Cenozoic (Quaternary) sediment. Paleozoic and Mesozoic-age strata generally dip eastward and Quaternary sediment overlies progressively younger strata from west to east. Subsurface geologic units contain water of varying quality, from fresh to slightly saline. Faults and fractures characterize the subsurface. A Geonics Protem 47 system using a 60-meter by 60-meter square loop transmitter antenna was used to collect the TDEM soundings. For each sounding, voltage data were averaged and evaluated statistically using a computer program called NTEMAVG v. 3.04. The principle finding of this study is the potential relation between faulting and the occurrence of freshwater and slightly saline water, based on the configuration of resistivity along the TDEM profile.