TY - RPRT TI - Estimates of tracer-based piston-flow ages of groundwater from selected sites: National Water-Quality Assessment Program, 2006-2010 AU - Stephanie D. Shapiro AU - Niel Plummer AU - Eurybiades Busenberg AU - Peggy K. Widman AU - Gerolamo C. Casile AU - Julian E. Wayland AU - Donna L. Runkle PY - 2012 DO - 10.3133/sir20125141 UR - https://pubs.usgs.gov/publication/sir20125141 ID - sir20125141 ER -