Background
Effective water management requires that the hydraulic recharge/discharge relations that manifest at springs (and other outlets contributing to river flows) be understood well enough to assess impacts of changes in recharge and/or groundwater withdrawals. Innovative hydrochemical applications are considered one of the few approaches which can lead to understanding complex recharge/discharge relations. Geochemical frameworks, which comprise geochemical characteristics (i.e., isotopes, major ions, trace elements, physiochemical parameters), can be employed as a powerful tool to elucidate spatiotemporal variability in spring discharge, evolution along flow paths (e.g., water-host rock interactions), and sources of recharge that manifest as discharge in springs. Developing a geochemical framework is a promising approach because it can highlight subtle differences in flow regimes and flow paths that are not as easily discernable through other methodologies, such as dye tracer tests and potentiometric surface mapping.
The San Solomon Springs System in west Texas provides an ideal location to develop and test a geochemical framework that includes expanded isotopic considerations. Previous studies established that multiple source areas contribute to spring discharge in the San Solomon Springs system. At this time, however, neither the identification of which particular isotopes would comprise an effective suite in a geochemical framework nor sufficient isotopic data to perform such analyses are available for complex spring systems in west Texas or other semi-arid areas in general. A previous Targeted IR&D project (15-R8981) established a statistical approach to identify multiple source areas to this multi-outlet spring system. Further development of this promising multi-component statistical approach will allow enhanced characterization of complex multi-outlet spring recharge-discharge relations.
Approach
A geochemical framework has been developed to better understand recharge-discharge relations manifested as spring discharge. Comprehensive hydrochemical datasets (in addition to extensive mining of existing data) provide the baseline for a multicomponent approach: (1) multivariate statistical analyses to evaluate hydraulic relationships using physiochemical parameters, major ion and trace element concentrations, and isotopes; (2) evaluation of spatiotemporal variability in hydrochemistry; and (3) geochemical modeling to identify evolution along flow paths between points of recharge and discharge.
Accomplishments
The project team assembled a comprehensive geochemical database from public databases and previous project work in the study area.
Two field campaigns were conducted in September 2020 and March 2021 to collect robust geochemical data from springs and wells in the study area. These data have and will be incorporated in the geochemical database and subsequent geochemical framework.
The project team targeted and subsequently sampled wells in data sparse regions in the study area to better constrain sources of recharge to the springs.
The project team used baseline geochemical analyses to identify source rocks of groundwater recharge and differentiate between modern and submodern recharge to San Solomon Springs.
The project team used multivariate statistical analyses to effectively segregate geochemical data by source area.
The project team expanded and refined the geochemical framework by developing workflows to interpret geochemical data.
The project team developed a conceptual model of groundwater flow paths to San Solomon Springs to implement in equilibrium and reaction-path models.