Abstract:

Spring breakthrough curves provide a convenient and effective way to investigate migration and fate of contaminants
in karst aquifers. During a dry season, contaminants sequestered inside limestone are released through the wall into conduits, mix
with conduit water, and are then transported to the downstream springs. Thus breakthrough curves acquired at the springs may
be inverted to obtain the fluxes of solutes across the conduit wall as sequestered contaminants are released. Using the analytical
solution based upon an advection-dilution model, we invert for the wall solute fluxes from 40 breakthrough curves measured in
the laboratory. The basic shape of the fluxes is similar to that of the breakthrough curves. The inhomogeneity of water flux across
the wall is evident on the breakthrough curves, and appears as very strong oscillations on the wall solute fluxes. Therefore, it is
concluded that wall solute flux has higher resolution to the inhomogeneity of water flux across the wall than spring breakthrough
curve does. The wall solute fluxes are an intermediate quantity connecting spring breakthrough curves with earlier distribution of
contaminants in limestone. This study provides a new approach to investigate the release of contaminants across the conduit wall.

Key words: karst, sequestration, breakthrough curve, advection, release