QUANTITATIVE TRACERS AS CONTAMINANT SURROGATES – AN IMPORTANT TOOL FOR PLANNING AND MANAGING SOURCE WATER PROTECTION AREAS

Water soluble fluorescent compounds have been used for more than one hundred years to delineate groundwater basin boundaries, estimate groundwater velocities, and indicate surface water/groundwater relationships in carbonates and more recently in all lithologies. Fluorescent tracing agents that have been approved by the U.S. Food and Drug Administration for use in drugs and cosmetics, offer a powerful tool for resource managers charged with protecting public water supply systems and endangered species critical habitats. Four of these dyes: uranine, eosine, pyranine, and Phloxine B have very low detection limits (<0,1 ppb), low analytical cost, and low sorption. A fifth dye, erythrosine, is available but is only weakly fluorescent and may not be quite so useful

Properly designed quantitative tracer tests, using fluorescent dyes provide the maximum information about contaminant flow paths, accurate time of travel, peak concentration, duration of passage of the tracer and estimates of hydraulic parameters. Such data yield valuable insights into management strategies to monitor and remediate contaminants. Tracers can also be used to empirically test flow path and time of travel estimates derived from other techniques of source water protection delineation such as ground-water models, arbitrary fixed radii, hydrologic boundaries, and “rule of thumb” estimates.

Quantitative tracing done with fluorescent dyes has firmly established a relationship between amount of tracer injected and peak concentration at the discharge point of concern. This relationship may also allow a reasonably accurate estimation of the concentration of contaminants from a hazardous materials release. These equations have been used with success to determine potential impacts on springs from a PCE/TCE – contaminated site in Nashville, Tennessee and from a leaking storage tank in New Braunfels, Texas. This method has also been used to successfully calculate the volume of dyes for tracing to public water supplies or critical surface water habitat.