|
Interpretation of dye tracing data is not the same as interpreting the results of chemical analyses. Background levels of dye are often present above the quantitation limits of
the fluorescent dyes used for tracing. One of the reasons for these background levels is due to the commercial use of the various dyes used for tracing. Non-toxic fluorescent dyes are rare. For this reason, the dyes used for tracing can often be found
in products ranging from food coloring to toilet bowl cleaners. Another reason for these background levels is the extremely low detection limits of fluorescent dyes. Virtually any tracer will have background levels if one can measure at very low
concentrations. Figure 1 is a histogram of dye levels from an actual dye trace where background dye was present. This particular dye was not even used for the trace, nor had any other dye trace been performed in this area in the past. Background
levels often fluctuate more in karst aquifers and to this end, Crawford Hydrology Laboratory developed a standard protocol used to determine what is background, what is positive, and what is negative (non-detect). This protocol is based upon the results of
over 900 dye tracer investigations Dr. Crawford and Crawford Hydrology Laboratory, formerly Crawford and Associates, has performed over the last 20 years. It has been used for dye tracer studies at numerous State and EPA Superfund sites as well as at Industrial Sites.
|
|
