HR: 09:30h
AN: H41J-07    [Abstracts]
TI: A Multi-isotope (B, Sr, O, H) and Age-Dating (³H-³He, ¹⁴C) Study of Saline- Water Intrusion and Cross-Formational Flow in the Southern High Plains Aquifer
AU: * Langman, J B
EM: jlangman@usgs.gov
AF: U.S. Geological Survey, New Mexico Water Science Center, 5338 Montgomery Blvd, NE, Suite 400, Albuquerque, NM 87109, United States
AU: * Langman, J B
EM: jlangman@usgs.gov
AF: University of Texas at El Paso, Geological Sciences, 500 W University Ave, El Paso, TX 79968, United States
AU: Ellis, A S
EM: aellis@utep.edu
AF: University of Texas at El Paso, Geological Sciences, 500 W University Ave, El Paso, TX 79968, United States
AB: Identification of aquifer source waters can be difficult with traditional geochemical tracers such as solute concentrations because of the variability of rock-water interactions and complex recharge pathways. The growing use of traditional and non-traditional stable isotopes for identification of hydrologic processes allows the coupling of multiple stable isotopes and ion concentrations for cross-validation and better constraint of influences within an aquifer. A multi-isotope and age-dating study of ground water along the Western Caprock Escarpment of the Southern High Plains was implemented to identify saline-water intrusion and cross-formational flow in the Southern High Plains aquifer. This study coupled major ion and trace element concentrations with the stable isotopes of boron, strontium, hydrogen, and oxygen along with tritium-helium and carbon-14 age dating to identify potential source waters through differences in rock-water interactions and recharge pathways. Ground-water samples were collected from 16 wells, 13 of which were completed in the Ogallala Formation (primary formation of the Southern High Plains aquifer) and three that were completed in a minor aquifer of the underlying Dockum Group. Within the study area, a separate, local flow system originates at a topographic high and flows into a regional flow system defined by a large paleochannel. At a recharge area atop the topographic high and within the regional flow system, ground water is composed of a mixed cation-bicarbonate water, but a sodium-chloride type is present in parts of the local flow system and in ground water from the underlying aquifer in the Dockum Group. Major ion and trace element concentrations and the stable isotope composition of water (δ²H of -43.29 to -71.74 ‰ and δ¹⁸O of -5.85 to -9.95 ‰) do not indicate a simple two member mixing scenario but likely multiple sources and cross-formational flow between three formation deposits-- Permian salts, Dockum shales, and Ogallala alluvium. Boron (δ¹¹B of 6.0 to 46.0 ‰) and strontium (0.70845 to 0.70906) stable isotope results helped to constrain the influence of rock-water interactions through different mineral signatures likely associated with the three formation deposits. The combining of various ion and isotope tracers allows the discrimination of source waters and the mixing strengths of the waters within the primary aquifer. Preliminary analysis suggests dissolution of Permian salts and migration of salt-laden water through fractures in the Dockum shales to a productive sand lens in the upper Dockum Group. Mixing within the Ogallala Formation and Dockum Group is likely occurring through upward and downward leakage between the two formations. Changes in the aquifers' potentiometric surfaces and available pathways control spatial mixing that produces a greater saline water contribution to parts of the local flow system that is diluted and (or) suppressed in the regional flow system of the Southern High Plains aquifer.
DE: 1804 Catchment
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2007 Fall Meeting