Fig. 7. Results of the NaCl advection experiment for the seepage configuration (upstream level at 20 cm, downstream at 10 cm). (a) Upstream reservoir conductivity, exponentially decreasing due to advection of salt to the sand and dilution with fluid from the recharge reservoir; (b) electric potential differences between the z = 5 cm electrodes and the reference (see Fig. 3). All electric potential differences decrease as soon as salt is added and return to positive values after the salt front passes the electrode. (c, d) same as (b) for lines z = 8 and z = 11 cm.