Pollution transport studies using an in-situ fibre optic photometric sensor

In order to study the migration of contaminants in soils, we are currently using an in situ fibre optic sensor to track the movement of a dye tracer. Details of the sensor is discussed and the results presented of one-dimensional transport experiments using a water soluble dye and a copper salt. Water was forced to percolate downwards in a bed of fine sand, with the hydraulic gradient kept constant during any given experiment. A pulse of contaminant was released on the soil surface, and its concentration was subsequently measured using sensors buried at two depths. This permitted the pollution plume to be tracked. It was found that the width was independent of hydraulic gradient, as predicted by the theory of mechanical dispersion for seepage flows with a high Peclet number.