Piston-flow age dates were interpreted from measured concentrations of environmental tracers from 812 National Water-Quality Assessment (NAWQA) Program groundwater sites from 27 Study Units across the United States. The tracers of interest include chlorof
Shapiro, Stephanie D.,Plummer, L. Niel,Busenberg, Eurybiades ebusenbe@usgs.gov,et al. Estimates of tracer-based piston-flow ages of groundwater from selected sites: National Water-Quality Assessment Program, 2006-2010. 2012-01-01.