title: Water hardness and sodium trends in Texas aquifers.
abstract: Median hardness and sodium levels in groundwater were calculated for 244 Texas counties from measurements at 7728 water wells. The data were mapped and analyzed with a geographic information system (GIS). County median hardness levels varied widely, from 4-2304 mg L-1. More than 60% of the counties had hardness medians above 180 mg L-1. County medium sodium concentrations ranged from 6-1170 mg L-1, with more than 90% of those values exceeding 20 mg L-1. There was a significant positive correlation between hardness and sodium concentrations in six of Texas' nine major aquifers. A significant negative correlation between hardness and sodium was observed in two aquifers. Several factors control hardness and sodium variations in Texas aquifers including rock/sediment composition, groundwater chemical evolution, and seepage from nearby formations. Probable human controls include agricultural return flow and pumping-induced saltwater intrusion.
authors: Department of Geography, University of North Texas, Denton, USA. hudak@unt.edu
authors: P F
authors: PF
authors: Hudak
mesh_terms: D000383:Agriculture; D000538:Aluminum Silicates; D002118:Calcium / Q000032:analysis; D000077215:Clay; D005618:Fresh Water / Q000737:chemistry*; D019015:Geologic Sediments; D012623:Seawater / Q000032:analysis / Q000737:chemistry; D012822:Silicon Dioxide; D012964:Sodium / Q000032:analysis*; D013781:Texas; D014881:Water Supply / Q000032:analysis*
chemical_list: D000538:Aluminum Silicates; D012822:Silicon Dioxide; D012964:Sodium; D002118:Calcium; D000077215:Clay