Multilevel characterization of vertical hydraulic gradient, permeability, temperature and salinity in shallow coastal aquifers with low pressure packers.

In this study we tested the ability of straddle low pressure packers to characterize simultaneously vertical hydraulic gradients, permeability, temperature and salinity in order to quantify the magnitude and direction of groundwater fluxes and understand salinization processes in coastal aquifers. The straddle packers are employed to isolate a window of 0.2 m within fully penetrating piezometers. The system is set at the desired depth within the piezometer and a constant rate pumping test is performed. A Levelogger is positioned between the packers to monitor head, temperature and electrical conductivity, from which the equivalent freshwater head and intrinsic permeability values can be derived. Two piezometers located in a coastal aquifer of Ferrara Province (Italy) have been characterized using this technique. In addition core samples from the same piezometers have been analysed for grain size, porosity and organic matter. The laboratory data are used to compare the results obtained using the packers system with intrinsic permeability calculated by pedotransfer formulas. The comparison of the two techniques shows a general agreement along each piezometer profile, although discrepancies of more than 1 order of magnitude occur in peaty layers. The multilevel equivalent freshwater heads highlight a steep vertical gradient created by the drainage system. This seepage is contrasted by lenses of silt and clay that prevent the complete salinization of the shallow aquifer.