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The application of fluorescent substances as hydrogeological tracers may provide relevant information about subsurface water dynamics. For a better in situ control in the application of tracers, it is relevant to define the chemical and physical behavior of these substances in soils and sediments through bench laboratory experiments in order to predict their behavior during the injection into the aquifer. The objective of this work was to quantify the adsorption and the retardation factor of the fluorescence tracer uranine in quaternary sediments of the upper portion of the São Paulo aquifer. The water/soil distribution coefficients for uranine were obtained by means of batch-tests assays. The experiments consisted in mixing three different soils (organic, clayey and coarse) with uranine solutions in five initial concentrations (5, 10, 50, 100 and 150 μg / L). The fluorescence measurements of the liquid phase were performed through a laboratory fluorometer. The calculated values of the distribution coefficient and retardation factor for the coarse soil were, respectively: 2,60x10-3 L/g ± 0,22x10-3 and 1,51 ± 0,13 (deionized water), and 1,80x10-3 L/g ± 0,12x10-3 and 1,35 ± 0,09 (aquifer water). For organic and clayey soils, the apparent fluorescence generated by the suspended particles in the uranine solutions overlapped the real fluorescence of the tracer, preventing the distribution coefficient and the retardation factor from being calculated. In a porous medium with a high content of organic matter and clay minerals, uranine exhibits high susceptibility to sorption phenomena. However, its use is indicated for the measurement of hydraulic properties in quartz-rich aquifers, since in this sediments the uranine presented a low retardation factor.

Determinação do fator de retardamento da uranina em sedimentos quaternários do aquífero São Paulo