Tracer-Test Planning Using the Efficient Hydrologic Tracer-Test Design (Ehtd) Program (2003)

Notice - This site contains archived material(s)

Archive disclaimer
Archived files are provided for reference purposes only. The file was current when produced, but is no longer maintained and may now be outdated. Persons with disabilities having difficulty accessing archived files may contact the NCEA Webmaster for assistance. Please use the contact us form if you need additional support.


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.


U.S. EPA. Tracer-Test Planning Using the Efficient Hydrologic Tracer-Test Design (Ehtd) Program (2003). U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-03/034, 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

This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.