Laboratory device to investigate the heterogeneity’s influence on the effective hydraulic conductivity

Groundwater flow and contaminant transport are strongly influenced by the aquifer’s heterogeneity (Chao et al., 2000; Fernàndez-Garcia et al., 2004). Generally, the flow (and transport) variables, such as the effective conductivity K_eff, can be modelled as random space functions (RSFs) and determined by means of a self-consistent approximation (Severino, 2018). In particular, we aim at estimating the effective conductivity K_eff of a highly heterogeneous aquifer made of 12 different porous materials, whose K-values were experimentally measured.

A heterogeneous phreatic aquifer was built in the GMI Laboratory of the Department of Civil Engineering of the University of Calabria, inside a metal box (2 m x 2 m x 1 m). The thickness (0.35 m) of the aquifer was built by overlapping 7 different layers of 0.05 m, each consisting of 361 cells (19 x 19), with dimensions equal to 0.1 m x 0.1 m x 0.05 m. For each layer, each cell was filled with one of the 12 porous materials previously characterized in the lab, making the choice randomly. A central (pumping) well and 37 piezometers were located at different distances from the first according to a radial configuration.

A pumping test was carried out by a constant flow rate of 70 L/hour. The hydraulic head data, evaluated by using the Neuman method and verified in compliance with the boundary conditions, allowed an effective hydraulic conductivity value K_eff to be obtained.

Afterwards, this value was compared with K values measured in laboratory by permeameter for each of the 12 porous media used to build the heterogeneous aquifer considered here and with the main statistical parameters related to them. We found the K_eff value in a very good agreement with the expression obtained by the self-consistent approximation (Severino, 2018).

 

References

Chao C.-H., Rajaram H. and Illangasekare T. H. (2000). Intermediatescale experiments and numerical simulations of transport under radial flow in a two-dimensional heterogeneous porous medium, Water Resour. Res., 36(10), 2869– 2884.

Fernàndez-Garcia D., Illangasekare T. H. and Rajaram H. (2004). Conservative and sorptive forced-gradient and uniform flow tracer tests in a three-dimensional laboratory test aquifer. Water Resour. Res., Vol. 40, W10103, doi:10.1029/2004WR003112.

Severino G., 2018. Effective conductivity in steady well-type flows through porous formations. Stochastic Environmental Research and Risk Assessment, Vol. 5, https://doi.org/10.1007/s00477-018-1639-5.