BASIN HYDROCHEMISTRY AND RELATED FLOW SYSTEMS: INTEGRATED DATA ANALYTIC METHODS

Interbasin and intrabasin recharge sources, and surface water – groundwater interactions were examined using hydrochemistry. Applying mutually supportive methods in sequence to the hydrochemical data, greater insights were gained of the potential significance of interbasin and intrabasin recharge to lower Virgin River Basin’s water budget, and of the interactions among the floodplain aquifer, the Muddy Creek Formation aquifer, and the Virgin River.

The hydrochemical data were analyzed by sequentially applying mutually supportive methods. Robust hydrochemical facies better than chance alone were defined using cluster analysis, Discriminant Function Analysis, and measures of association (Cohen’s Kappa and Kramer’s V). Hydrochemical evolution end members were identified using the Schoeller diagram and discriminant functions plot. Flowpaths were conceptualized based on GIS displayed geographic coherence of the characteristic facies and the available information on geology and hydrology. In this study the PHREEQC inverse modeling code was used beyond the contemporary application for identifying processes of hydrochemical evolution to give insights into significance of the potential recharge sources to the lower Virgin River Basin. Mineral phases and constraints selected were based on compositional plots, saturation indices calculations, and the available geologic information. Modeling indicates that at least 80% of the groundwater in the lower Virgin River Basin is derived from interbasin flow. In addition, the floodplain aquifer (cluster 3) interacts highly with the Virgin River, but both are unlikely to be hydraulically connected to the Muddy Creek Formation aquifer.