Print this pageABSTRACT: The Use of Electromagnetic Methods to Locate Potential Sources of Highly Saline Water Entering the Canadian River Valley
Lake Meredith, located 50 km northeast of Amarillo, supplies water to 500,000 residents of the Texas panhandle. Over the last decade, the chloride concentration in the reservoir has risen from 200 to 400 ppm, with the result that Lake Meredith water must be diluted with Ogallala Aquifer water to meet secondary standards. Past studies have shown that the Canadian River carries saline water into the reservoir, where dissolved solids are further concentrated by evaporation. The source of the salinity is natural dissolution of Permian evaporite beds underlying eastern New Mexico and the Texas panhandle. Circulating ground water has dissolved evaporite minerals and carried ions to the surface where they are discharged into the Canadian River and its alluvium.
Electromagnetic methods were used to locate highly conductive areas within the Canadian River alluvium. Surveys were completed along river reaches between Ute Reservoir (Logan, New Mexico) and the Texas-New Mexico border, where surface-water-quality surveys indicate the greatest inflows of saline water. Frequency-domain equipment (Geonics(tm) EM34-3) was used to measure lateral conductivity variations along about 20 km of the river and tributaries; time-domain equipment (Geonics(tm) Protem 47-S) was used to determine conductivity variations with depth at selected sites.
Lateral surveys revealed that apparent conductivities in the upper 10-30 m of alluvium within the Canadian River valley vary from a few to nearly 300 millisiemens/m. Several high-conductivity areas were detected near Logan and 35 km downstream in the "Dunes" area; many of these high-conductivity areas are located where secondary drainages enter the main Canadian River valley. Vertical electromagnetic soundings indicated that conductivity increases downward at most sites. These observations are consistent with a hypothesis that saline water from depth flows into Canadian River alluvium through bedrock fractures.
AAPG Search and Discovery Article #90991©1993 AAPG Mid-Continent Section Meeting, Amarillo, Texas, October 10-12, 1993.