ON EVALUATING THE REGIONAL GROUNDWATER FLOW SYSTEM IN SOUTHERN NEVADA WITH AN INTEGRATED HYDROGEOCHEMICAL APPROACH

Integrating groundwater flow and geochemistry can help identify groundwater sources, provide quantitative estimates of groundwater recharge, and improve predictions of contaminant fate and transport in groundwater systems. Understanding groundwater flow paths in and around the Nevada Test Site (NTS) and Yucca Mountain (YM) region is important due to the possible migration of contaminated groundwater from the NTS and YM to the neighboring communities. More than 100 samples from well installations, as well as spring water discharge, have been collected from the NTS and YM region for trace element and major solute analyses. Principal Component Analysis (PCA) and Cluster Analysis, were used to analyze the large amounts of geochemical data and statistical analyses on the major solute data and have resulted in three different groupings of groundwater chemical compositions consistent within the region: volcanic water, carbonate water and mixing of both volcanic and carbonate waters. Subsequently, a two-dimensional groundwater flow and transport model is implemented along a northeast-to-southwest groundwater flow path. The simulation captures the general spatiotemporal distribution of hydraulic head and various chemical species. The sources of water and evolution of chemical processes along the groundwater flow path can then be quantitatively identified. The results will improve our understanding of the natural rock-water interactive geochemical processes and also provide valuable information for risk assessment and management for waste storage sites.