Fluorescent dye-tracing as a cost-effective tool in applied contaminant hydrology: A case study of synchronous spectro-fluorometry in a heavily oil-contaminated aquifer

Two successful dye-tracing experiments carried out in an aquifer beneath a 5 acre inaccessible factory where thousands of liters of cutting oil and chlorinated solvents have contaminated the subsurface for decades are presented. Synchroscans of the background samples at different dilutions indicated that uranine, Na-naphtionate, and sulforhodamine B could be suitable for dye-tracing at the site. In the first test, uranine reached the drainage system in ∼12 days along what appears to be a preferential flow path. In contrast, sulforhodamine B sorbed to the aquifer matrix or possibly its fluorescence was quenched by chlorinated hydrocarbons mixed with the cutting oil near the injection zone. Uranine, and Na-naphtionate, were appropriate for use in dye tracing tests in groundwater contaminated with cutting oils. Both dye-tracing tests indicated that heterogeneities in the flow system under the industrial site, be they lenses of tight porous media in the fill or anthropogenic structures such as buried pipes and construction debris, created a far more complex flow field than was previously assumed from routine and standard hydrogeologic investigations. The locations of the pumping centers were not efficiently modifying the hydraulic head to force contamination towards them although contamination was moving towards the drain surrounding the southern end of the factory.