Sources of groundwater based on Helium analyses in and near the freshwater/saline-water transition zone of the San Antonio segment of the Edwards Aquifer, South-Central Texas, 2002-03

• DOI: 10.3133/sir20105030
• Publication Date: 2018-08-15T18:47:28Z
• Authors: Andrew G. Hunt; Rebecca B. Lambert; Lynne Fahlquist
• Keywords: Saline water

This report evaluates dissolved noble gas data, specifically helium-3 and helium-4, collected by the U.S. Geological Survey, in cooperation with San Antonio Water System, during 2002-03. Helium analyses are used to provide insight into sources of groundwater freshwater/saline-water transition zone segment Edwards aquifer. Sixty-nine samples were from 19 monitoring wells (categorized as fresh, transitional, or saline on basis solids concentration fluid-profile logging boreholes) arranged five transects, one exception, across interface (the 1,000-milligrams-per-liter threshold) The helium-4 dominant isotope atmospheric terrigenic helium) ranged 63 microcubic centimeters per kilogram at standard temperature (20 degrees Celsius) pressure (1 atmosphere) a well East Uvalde transect 160,587 Kyle transect. Helium-4 concentrations 10 generally increase western transects eastern transects. Increasing southwest northeast zone, indicating increasing residence time northeast, is consistent longstanding conceptualization aquifer which water recharges southwest, flows northeasterly (including although more slowly than fresh-water zone), discharges major springs northeast. Excess was greater 1,000 percent for 60 69 samples, that helium largely present most excess comes other atmosphere. data this cannot be identify near terms specific geologic (stratigraphic) units hydrogeologic (aquifers confining units). However, indicate source helium, thus dissolved, mostly origin rather atmospheric. Whether originated either rocks outside depth adjacent Trinity uncertain; but had enter because unit immediately beneath laterally Thus support hypothesis sufficient hydraulic connection between aquifers allow movement