Calibration of groundwater recharge and hydraulic conductivity for the aquifer system beneath the city of Milan (Italy)

A quasi three-dimensional model has been developed to simulate the behaviour of the aquifer system, which is the source of drinking water for the city of Milan (Italy), and extends over an area of about 400 km2. Non continuous semipermeable layers locally separate permeable levels in a multi-layered system, consisting of one phreatic and three confined aquifers. The numerical model is a conservative finite difference scheme, with a grid spacing of 500 m. Model calibration requires determination of the hydraulic conductivities of the aquifers and the aquitards, and of the parameters describing the source/sink terms. Water extraction rates from public and private wells are known, whereas estimates of recharge due to rain infiltration and losses from buried pipes, rivers and artificial channels are uncertain. Here we improve the identification of the hydraulic conductivities and perform a sensitivity analysis on some coefficients used to quantify the aquifer recharge.