Improving the detection of fluorescent tracer dyes in groundwater investigations

Groundwater tracing with fluorescent tracer dyes is a valuable tool in many remediation projects. Three of four common dyes can be used concurrently, effectively separated, and their concentrations quantified if modern laboratory instruments and appropriate protocols are used. Unfortunately, investigators often overestimate the amount of introduced dye likely to be detected, use too little dye because of these estimates and concern that colored water might be detectable off‐site, and place sampling reliance solely on grab samples of water. The common result is flawed studies that identify only some of the points to which the dyed water flows. Results are quantitatively compared for monitoring sites during periods where both water samples and granular activated carbon samplers (referred to as carbon samplers) were used. The results demonstrate that carbon samplers are superior to water samples for detecting the presence of the fluorescent tracer dyes evaluated. A technically sound and cost‐effective strategy is to place primary sampling reliance on carbon samplers for detecting the presence of the dyes and secondary reliance on grab samples of water for determining dye concentrations when they are greater than the detection limits.