Monitoring Wastewater Disposal Dynamics through Infiltration Ponds by Using Time-Lapse ERT Survey

In Italy, during the last decades, the infiltration ponds are increasingly used to dispose of effluent in the subsurface, according to the current regulation DL 152/06. In Apulia Region, Southern Italy, about 30 wastewater treatment plants are connected to an infiltration ponds network where the effluent is naturally infiltrated in the unsaturated zone, exploiting its natural filtering capacities against organics, chemicals and contaminants. At the same time, this approach could be particularly efficient in treatment plants located near the coastline to face contamination phenomena such as salt-water intrusion, as well as to artificially recharge shallow aquifer. The infiltration ponds are typically subjected to cyclic saturation and desaturation conditions that can affect the hydrological properties of the filtering medium, hence itd life cycle. Therefore, for the optimal management of the infiltration ponds, a detailed monitoring of infiltration dynamics is required. In the experimental test area of Castellana Grotte, more than 2000 m3/day are alternatively infiltrated into nine infiltration ponds.In order to evaluate infiltration patterns under different hydrological conditions, a time-lapse Electrical Resistivity Tomography (ERT) has been carried out in two periods of the year, in March and July, corresponding about to the maximum and minimum rainfall periods of a hydrological year.