A GIS-Based Fit for the Purpose Assessment of Brackish Groundwater Formations as an Alternative to Freshwater Aquifers

Abstract

A fit for purpose (FFP) framework has been developed to evaluate the suitability of brackish water resources for various competing uses. The suitability or the extent of unsuitability for an intended use is quantified using an overall compatibility index (OCI). The approach is illustrated by applying it to evaluate the feasibility of the Dockum Hydrostratigraphic Unit (Dockum-HSU) as a water supply alternative in the Southern High Plains (SHP) region of Texas. The groundwater in Dockum-HSU is most compatible for hydraulic fracturing uses. While the water does not meet drinking water standards, it can be treated with existing desalination technologies over most of the study area, except perhaps near major population centers. The groundwater from Dockum-HSU is most compatible for cotton production, but not where it is currently grown. It can be a useful supplement to facilitate a smoother transition of corn to sorghum cropping shifts happening in parts of the SHP. Total Dissolved Solids (TDS), Sodium Absorption Ratio (SAR), sodium, sulfate, and radionuclides are major limiting constituents. Dockum-HSU can help reduce the freshwater footprint of the Ogallala Aquifer in the SHP by supporting non-agricultural uses. Greater regional collaboration and more holistic water management practices are however necessary to optimize brackish groundwater use.

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

“…Though there are few studies outside of the Ogallala region [15,16] where groundwater blending of multiple groundwater sources are considered, many studies have examined groundwater quality using many approaches to gain greater general understanding and evaluate suitability. Examples include the use of geochemical data with GIS and spatial analysis [17][18][19][20][21], water quality indices and use thresholds [19,[22][23][24][25][26][27][28], classical hydrochemistry visualization and interpretation [23,[25][26][27][29][30][31][32], multivariate techniques [19,23,25,27,33], geochemical modeling [18,33], and integration of decision-support systems (DSS) [20,21].…”

“…One of the saline aquifer sources is in Dockum group sediments. [16] Regional data analysis and decision support study Use of the entire Dockum aquifer water quality record for suitability. Use of the Dockum to illustrate making decisions concerning brackish groundwater generally.…”

“…Their study was on the aquifer fringe, and yet TDS varying more than 500 mg/L over short distances were not unheard of. Karim et al [16] interpolated many water quality parameters over all of the Dockum in Texas and found an estimate of TDS by aerial coverage of 12.5% for TDS > 10,000 mg/L. Differences between their TDS water fractions and those of Bradley and Kalaswad can likely be explained by one estimate based on aerial coverage and the other based on total water volume.…”

“…The study of Karim et al [16] examined the recent water quality history of the entire Dockum region within Texas, both inside and outside of the 5000 mg/L downdip region [34,42] using a Fit-For Purpose (FFP) framework. They interpolated all known water quality data onto a spatial grid over the Texas lateral extent of the Dockum.…”

Quality Assessments of Shallow Groundwaters for Drinking and Irrigation Purposes: Insights from a Case Study (Jinta Basin, Heihe Drainage Area, Northwest China)

“…The WQI index was selected in the current study to evaluate the drinking water quality of the groundwater samples according to standards of the World Health Organization (WHO, 2004). Firstly, weights (wi) were assigned to ten selected parameters in the relative importance of pH > TDS > Ca Table 1) [14,15]. The WQI was then calculated according to Equations (1)- (4).…”