Study of permeability and contaminant flow in granitoid rocks using dyes


Jan Holeček, Lenka Rukavičková

Geoscience Research Reports 44, 2011 (GRR for 2010), pages 239–241

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Rock permeability has significant influence on spreading of contaminants in granitic rock environment. Even fresh granite rock contains small intergranular and intragranular spaces where the contaminants can flow. The study is involved in determination and characterisation of microstructures and diffusion velocity measurements using dyes as a contaminant analogue in ex-situ as well as in-situ granitoid environments. New method of sample preparation and observation was developed during laboratory tests. Eight different dyes and pigments were experimentally tested as contaminant analogues. 1) Cation active water soluble dyes were used to simulate chemical contamination with sorption ability. 2) Alkali reactive water soluble dyes constitute potentially non-sorbent contaminations. 3) Fine pigments (<10-4 m) and ultra fine (<10-6 m) milled pigments simulated colloid and particle contaminants of various sizes. The advantage of using dyes and pigments as a contaminant analogue is their easy optical detection and low risk oftoxicityduring in-situ experiments. Fresh granitoid borehole cores (from depth 80-100 m) from two different localities (Pozďátky at Třebíč, Potůčky-Podlesí) in the Bohemian Massif were collected for laboratory experiments. Sets of samples were immersed into dye solution. Penetration lengths were measured after determined time steps. Results show differences in diffusion speed according to rock structure and mineral composition. Pictures of flow channels were taken for subsequent optical analysis. Feldspars and micas occurred to be the main minerals allowing inter-and intragranularflow. Ultra slim borehole (0 20 mm) was drilled into the bottom of existing 76 mm borehole in the 100 m depth at two localities. These slim boreholes will be filled by non-sorbent dye to examine diffusion velocities under lithostatical pressure. The results will be compared with laboratory experiments. In-situ experiment is planned in spring 2011.