An integrated flow and transport modeling approach for a contaminated fractured limestone aquifer: the area of ex Gasometer in Bari (Italy)

The present study concerns the dismissed industrial area of ex Gasometer, located in the city centre of Bari (Italy), where the aquifer is constituted mainly by extremely fractured limestone formations and is heavily contaminated by petroliferous substances, due both to the past industrial activity and to the subsequent removal of the installation and the tanks. In the area different campaigns of investigations have been carried out, together with pilot tests of Pump &Treat and air sparging. In previous studies carried out on the area, the analysis of the possibilities of remediation of the aquifer has considered flow and solute transport in an equivalent porous medium, and the anisotropy of the fractured formation was synthesized in a coefficient of hydraulic conductivity obtained by a geostatistical study. The distribution of hydraulic heads coming from the flow simulation turned out to be adherent to reality but the velocity fields obtained proved to be considerably lower, affecting predominantly the propagation of the contaminants. This paper has taken into account the uncertainty connected to the pronounced spatial heterogeneity due principally to the fractured and karstified nature of the soil, to the complexity of the state of contamination due to accidental episodes happened in the area, and to the dishomogeneity of the results obtained from campaigns of investigations carried out with different procedures. A system based on the fuzzy logic has been implemented, composed by different blocks of inference interacting among themselves that, on the basis of a process of inverse modeling, has permitted to characterize the source of contamination, to calibrate and/or estimate the flow, transport and biodegradation parameters. For the automated tuning of the fuzzy system the algorithm of Simulated Annealing has been implemented. A more effective simulation has been obtained in the present study through the application of the approach of Dual Domain Mass transfer, able to describe the solute transport in a fractured medium. The three dimensional transport model realized on the basis of the computer code Seam3D considers also the presence of possible sources of contamination by NAPL and simulates direct degradation processes. This model has allowed to study the dynamic behavior of the aquifer and has permitted to realize that it is necessary to remove the NAPL source of contamination in the soil, still active, before carrying out any interventions of remediation of the aquifer.