Fig. 5. Photograph of weathered bedrock trench exposure showing the wetting front of the tracer suspension and the distribution of the strongly adsorbing blue dye that was added to tag preferential flow pathways. The overlying soil horizons (combined thickness of 7 cm) were removed and the tracer was applied on the exposed soil–weathered bedrock interface. The wire grid used for sampling is in place against the face of the trench. Vertical scale is approximate.