1. A plot of relative concentration versus time, where relative concentration is defined as C/Co with C as the concentration at a point in the ground-water flow domain, and Co as the source concentration . 2. A plot of tracer concentration, C, versus time, t, for a ground-water tracing study in karst conduit for the purpose of quantitatively determining how much tracer mass was recovered, mean time of travel, mean tracer flow velocity, and related hydraulic flow and geometric parameters. Synonyms: recovery curve; tracerbreakthrough curve; tracer-recovery curve.