GROUNDWATER AGE IN BASALT AQUIFERS OF THE COLUMBIA PLATEAU, OREGON, WASHINGTON, AND IDAHO
In 2016 a systematic sampling of 60 wells completed in CRB aquifers was undertaken by the U.S. Geological Survey National Water-Quality Assessment (NAWQA) project to better understand the distribution of groundwater age and quality across the CP. Multiple age tracers were collected to identify components of mixed-age water and dissolved noble gas samples were collected to constrain recharge conditions. Preliminary carbon-14 and tritium results indicate the widespread presence of premodern water (>70 years old) -- about 20% of the wells had results consistent with predominately pre-modern water, whereas fewer than 10% of had results consistent with predominantly modern recharge. Most contained varying mixtures of pre-modern and modern water. Age-tracer and water quality results will be incorporated into ongoing efforts by NAWQA to improve understanding of groundwater processes at a National scale and to improve management decisions at the local and regional level across the CP.