Hydrological tracer testing is the most reliable diagnostic technique available for establishing flow trajectories and hydrologic connections and for determining basic hydraulic and geometric parameters necessary for establishing operative solute-transport processes. Tracer-test design can be diffcult because of a lack of prior knowledge of the basic hydraulic and geometric parameters desired and the appropriate tracer mass to release. A new effcient hydrologic tracer-test design (EHTD) methodology has been developed that combines basic measured field parameters (e.g., discharge, distance, cross-sectional area) in functional relationships that describe solute-transport processes related to flow velocity and time of travel. The new method applies these initial estimates for time of travel and velocity to a hypothetical continuously stirred tank reactor as an analog for the hydrologic flow system to develop initial estimates for tracer concentration and axial dispersion, based on a preset average tracer concentration. Root determination of the one-dimensional advection-dispersion equation (ADE) using the preset average tracer concentration then provides a theoretical basis for an estimate of necessary tracer mass. Determining the necessary tracer mass, the initial sample-collection time, and the subsequent sample-collection frequency for a proposed tracer test are the three most diffcult aspects to estimate prior to conducting the test. To facilitate tracer-mass estimation, 33 mass-estimation equations have been developed over the past century. The 33 equations are reviewed here; 32 of them were evaluated using previously published tracer-test design examination parameters. The purpose of this paper is to answer three basic questions common at the start of any hydrologic tracer test: (1) How much tracer mass should be released; (2) When should sampling start; and (3) At what frequency should samples be collected. In this paper an e.cient hydrologic tracer test design (EHTD) methodology for estimating tracer mass based on solute transport theory is developed. Use of the methodology developed here leads to a better understanding of the probable transport processes operating in the system prior to conducting the tracer test. Improved understanding of the transport processes then leads to better estimates of tracer mass to be released. In addition, initial sample collection times and sample collection frequencies are calculated using solute transport theory.

"April 2003." "EPA/600/R-03/034." Includes bibliographical references (p. 166-175).