Hydrological tracer testing is the most reliable diagnostic technique available for identifying and quantifying hydrodispersive transport processes. As such, hydrologic tracing is an essential tool that is commonly used to establish flow trajectories, to understand solute-transport processes, and to develop human health and ecological risk assessments. Unfortunately, the use of anthropogenic materials to trace the flow of water may also impart another source of risk to human health and the environment. In general, attempts are usually made to deliberately release tracer agents at concentrations far below their recognized toxic levels. Ecotoxicologically safe levels for injection concentrations of fluorescent tracer agents are generally set at levels far below that which are necessary to maintain measurable downstream concentrations. Appropriate tracer test design is important, because incorrect tracer-mass estimates may result in the release of larger tracer masses than are necessary and that exceed expected environmental concentrations (EECs). To maintain tracer concentrations at or below accepted levels, optimal tracer-test design is essential and may be achieved using the Efficient Hydrologic Tracer-Test Design methodology. By applying an optimal tracer-test design, it is more likely that downstream tracer EECs will be maintained at or below accepted concentrations while maintaining sufficiently high downstream EECs necessary for positive tracer detection.