Tracer-Test Planning Using The Efficient Hydrologic Tracer-Test Design (EHTD) Program (2005)

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 difficult because of a lack of prior knowledge of the basic hydraulic and geometric parameters desired and the appropriate tracer mass to release. A new efficient 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.

Application of the predicted tracer mass with the hydraulic and geometric parameters in the ADE allows for an approximation of initial sample-collection time and subsequent sample-collection frequency where a maximum of 65 samples were determined to be necessary for describing the predicted tracer-breakthrough curve (BTC). Inclusion of tracer retardation and decay cause a net increase in tracer-mass estimates so that the preset average tracer concentration will be maintained, with a consequent steepening of the BTC, but retardation also causes BTC spreading and a delay in tracer arrival.

This program is an outgrowth of field projects in which the initial design of tracer tests relied too much on guesswork. This program removes much of the guesswork in tracer test design.


This project has three objectives. The first is to develop a method that simply and efficiently calculates the appropriate quantity of some tracer material to release into ground-water systems such that successful tracer recoveries are likely, but that concentrations are not excessive. Second, is the determination of when to initiate sample collection such that first arrival is detected. Third, after initial sample-collection time has been determined it is necessary that an appropriate sample-collection frequency be established to ensure proper breakthrough curve definition.This effort is intended to facilitate the assessment of solute-transport processes in ground water for the Office of Solid Waste and Emergency Response and the Office of Water.


U.S. EPA. Tracer-Test Planning Using The Efficient Hydrologic Tracer-Test Design (EHTD) Program (2005). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-03/034B, 2003.

Additional Information contains the executable and example data files for the program Ehtd.exe. It also contains two additional files, Rgb.txt and Grfont.dat, which must remain in the same directory as Ehtd.exe for the program to produce proper graphics. contains the source for Ehtd.exe. After downloading these files use the free program WinZip to extract the file (available from