A multi-isotope (δD, δ18O, 87Sr/86Sr, and δ11B) approach for identifying saltwater intrusion and resolving groundwater evolution along the Western Caprock Escarpment of the Southern High Plains, New Mexico

Geologic influences on source-water mixing along a paleochannel in the Southern High Plains aquifer, New Mexico

“…Results of these analyses were examined along with local and regional water levels and lithologic and geophysical data collected during installation of the wells. Source waters have not been previously identified for the study site, but major source waters have been identified for the Southern High Plains and the region in previous studies (Nativ 1992;McMahon et al 2004;Scanlon et al 2005;McMahon et al 2006;McMahon and Bhlke 2007;Langman and Ellis 2009). From these previous studies, it can be assumed that recharge consists mostly of infiltration and percolation at playa lakes or other concentrated surface flow areas (natural surface recharge), infiltration and percolation under agricultural land, and cross-formational flow from the underlying Dockum aquifer(s); although, these sources have proven to be spatially and temporally variable.…”

“…Water levels at a study site 25 km to the west of this current study location indicate a potentiometric surface in the upper Dockum aquifer greater than in the Southern High Plains aquifer (Langman et al 2004). Langman and Ellis (2009) found a thin (\2 m), confined aquifer in the upper Dockum within 25-50 m of the base of the Southern High Plains aquifer at three locations at the same study site about 25 km west. Nativ (1992) estimated differences in the permeability of the contact between the Ogallala and Dockum and found mostly impermeable contacts in southeastern Roosevelt County south of the study site (no estimates for the study site).…”

“…There has been very limited local scale work that closely examined geologic influences that may induce changes in hydrochemical facies in the Southern High Plains aquifer from changes in source-water mixing. Langman and Ellis (2009) did identify cross-formational flow at a local scale that was attributed to available flowpaths between a Dockum aquifer and the Southern High Plains aquifer because of likely fracturing of Dockum shales from land subsidence. Groundwater at the Langman and Ellis (2009) study site also was influenced by agricultural recharge in selected areas.…”

“…Langman et al (2004Langman et al ( , 2006 indicated variable hydrochemical facies across short distances (less than a kilometer) within the Portales Valley of the Southern High Plains, and Falk (2005) suggested a change in source-water mixing across similarly short distances in the same area with results of these studies indicating influences from agricultural recharge and cross-formational flow. Langman and Ellis (2009) identified upwelling saltwater that originated in Permian-bedded salts, crossed upward into an upper Dockum aquifer then into the Southern High Plains aquifer thereby altering groundwater composition that was subsequently influenced by agricultural recharge near this study's site. These previous studies indicated localized mixing patterns between natural recharge, cross-formational flow, and agricultural recharge that were previously suggested as contributing factors to changes in hydrochemical facies across the Southern High Plains (Nativ 1992;Dutton 1995;Scanlon and Goldsmith 1997;Scanlon et al 2005;McMahon and Böhlke 2007;.…”

“…To evaluate these changes to an aquifer, the source waters that compose the aquifer must be identified and spatially discriminated to determine the possible source-water fractions and their effect on groundwater composition. Agricultural recharge and cross-formational flow between aquifers' in the Dockum Group and the Ogallala Formation's Southern High Plains aquifer are partially responsible for the regional variability of hydrochemical facies in the Southern High Plains aquifer (Nativ 1992;Dutton 1995;Scanlon et al 2005;Langman and Ellis 2009). An unconformity separates the Dockum and Ogallala in the western Southern High Plains.…”