Identification of geochemical facies through major ion data and additional parameters from shallow groundwater utilizing a comparison of geomathematics and traditional methods in Las Vegas Valley, Nevada

There has been little exploration to identify geochemical facies in shallow groundwater in the Las Vegas Valley in Clark County, Nevada. Identification of hydrochemical facies in Las Vegas Valley is important for assessing the extent and nature of a potential groundwater resource. The identification of facies could be complicated by the possibility that secondary recharge constitutes a hydrochemical facies of its own. To identify geochemical facies, groundwater samples for major ions, stable isotopes and some municipal tracers were collected from 35 wells in an established network of monitor wells. Wells were purged with a bailer or 12V pump and EC, pH, and Temperature were collected in the field. Collected samples were submitted to SNWS laboratory for analysis. Total dissolved solids ranged from 997 to 9121 mg/l with a standard deviation of 1981. PCA was run with a Statistica and the resulting in 90% of the variance associated with the first five components. The results were then kriged with Surfer and projected as a raster grid in ArcMap. A successful attempt was made to identify facies utilizing PCA and a comparison of the results to traditional trilinear diagram methods supported the findings. Identified facies ranged from a Mg-Ca-SO4-HCO3 water in the northwest to a Na-Mg-SO 4-Cl water in the southeast. Facies occur roughly perpendicular to the general direction of flow in the basin. An attempt to identify secondary recharge as a distinct facies was unsuccessful. This was either due to a uniform impact throughout the shallow groundwater system, or the impact of secondary recharge is less significant and more localized.