Application of two new fluorescent dyes and fluorescent particles in a horizontal and vertical fracture

Two experiments were conducted at the Lindau Test Site (southern Black Forest, Germany) to investigate solute and colloid transport processes in fractured rock. The tracers were injected into a radial-convergent flow field (monopol-test). Two newly developed fluorescent dyes and colloid tracers (D1, D2, C1) were used (Einsiedl et al., 1999a,b). The tracer breakthrough curves were observed in pumping wells located at a distance of 6.2 m and 10.2 m. The tracer experiments were evaluated using the Single Fissure Dispersion Model (Maloszewski and Zuber, 1985), which considers the convective-dispersive flow in the fracture (mobile water) and diffusion of tracer into the porous matrix (stagnant water). The results of earlier experiments performed at the Lindau Test Site have demonstrated that one of the newly developed fluorescent dyes (D1) has a conservative behaviour and can be used as a reference (ideal) tracer. The second tracer (D2) was found to be subject to sorption processes. This result was contrary to those of earlier experiments performed under similar conditions at the Grimsel Test Site (Switzerland) where the tracer (D2) was transported conservatively (Einsiedl et al., 1999a). The reason for the sorption of the D2-tracer was the lower pH-value of water in fractures at the Lindau Test Site. To examine the matrix diffusion process a multi-tracer experiment was performed in which the fluorescent dye (D1) and a colloid tracer (C1) were injected. The colloids, ranging in size of about 5 μm, were detected with a fluorimeter. The experiment with the colloid tracer (C1) showed that the developed colloidal particles migrated at a velocity greater than the average flow velocity in the capillary tube, and that the tailing effect can not be explained only by tracer diffusion into the matrix.