Esben Auken

We present the results from a more than a year long time-domain induced polarization (TDIP) monitoring setup from the Pillemark landfill in the Danish island of Samsø. The setup consisted of a 100 m profile installed permanently in a 30 cm deep trench, placed orthogonal to the regional groundwater flow direction, and positioned between a landfill and a nearby waterwork, which is the sole waterwork on the island. Full-waveform IP data, sampled at 3750 Hz, were collected daily, and temperatures were measured in a borehole nearby at 7 different depths. Measurements, signal processing and data handling was done by a computer installed in the field, without human interaction required. In general the IP signal quality was really high, with almost four decades in time usable for spectral inversion. However, the IP signal quality decreased in extended periods without rainfall, also clearly visible in the increased contact resistances measured. Full-decay IP data were inverted in time-lapse for selected dates, in terms of a re-parameterization of the Cole-Cole model which includes temperature effects. The time-lapse inversions show changes in soil water content in the upper 5-8 m, but also a possible deeper plume having seasonal variations.