Comparative Water Qualities and Blending in the Ogallala and Dockum Aquifers in Texas

Abstract

Within the US Southern High Plains, it is known that the Ogallala Aquifer (OA) has been over pumped since large-scale agriculture began making use of the water in the 1950s. One option to address the decline is to find new water sources. The last 10–15 years have seen an increase in drilling large capacity, deeper wells in the co-located Dockum Aquifer in the Texas Panhandle. This lower aquifer is separated from the OA by low hydraulic conductivity sediment and is thus generally considered independent from the OA. We examined the suitability of the Dockum to supplement OA water by comparing recent water chemistries where the aquifers coexist. We also examined historical information on well yield, well development, and water quality. We found that water quality is equivalent to the Ogallala in some places but in others it is saltier, softer, and more sodic. Use of PCA and hydrochemical facies revealed that even in this small area Dockum water quality is highly variable. We used USGS-PHREEQC to model water blending at ratios of 0–>100% Ogallala. We show that there is irrigation water quality risk no matter the blend, that risks differ according to location, and that the most frequent risks are salinity, sodicity, and nitrate. We conclude that growers can manage these risks if they use blending to choose the risks they feel most apt to mitigate.