Experimental evaluation of connectivity influence on dispersivity under confined and unconfined radial convergent flow conditions
Abstract
Data di Pubblicazione:
2014
Citazione:
Experimental evaluation of connectivity influence on dispersivity under confined and unconfined radial convergent flow conditions / S. Guzzi, A. Molinari, C. Fallico, D. Pedretti. - In: GEOPHYSICAL RESEARCH ABSTRACTS. - ISSN 1029-7006. - 16:(2014). ((Intervento presentato al convegno EGU General Assembly tenutosi a Vienna nel 2014.
Abstract:
Heterogeneity and connectivity have a significant impact on the fate and transport of contaminants due to
the occurrence of formations with largest permeability than the surrounding geological materials, which can
originate preferential pathways in groundwater system. These issues are usually addressed by tracer tests and
a radial convergent (RC) flow setting is typically selected for convenience but more complicated for model
interpretation than uniform flow transport. An experimental investigation was performed using RC tracer tests in a
3D intermediate scale physical model to illustrate the role of connected features on the estimation of dispersivity
using the classical Sauty solution and the method of moments, under confined and unconfined aquifer conditions.
The physical model consists of 26 piezometers located at difference distances from a constant-discharge central
pumping well. The box is filled with gravel channels embedded in a sandy matrix and organized in different
layers. Materials have been well characterized before and after the test. For the confined configuration, a silt
layer was placed above the previous layers. Tracer tests were performed using potassium iodide solutions with
concentration of 3•10-3 M and under a constant pumping flow rate of 0.05 L/s. To mimic a pulse injection in each
piezometer we used syringes and pipes, whereas a probe allowed continuous measuring of tracer concentration.
Average velocity and longitudinal dispersion coefficient were defined from the first and second central moment of
the observed breakthrough curves for each piezometer (integrated over the outflow boundary of the domain) and
using the classical curve matching from the Sauty’s solution at different Péclet numbers. Results reveal in some
cases that estimates of hydrodynamic parameters from the Sauty solution and the method of moments seem to be
different. This is related to the different basic assumptions of the two methods applied, and especially because of
the presence of preferential flow paths which have been found to strongly control the highest values of the average
velocity at the source and affect the resulting longitudinal dispersion coefficient. This study showed additional
lights on the impact of connectivity on transport and its role to obtain effective measurements of macrodispersion
throughout the aquifer under RC transport.
Tipologia IRIS:
01 - Articolo su periodico
Elenco autori:
S. Guzzi, A. Molinari, C. Fallico, D. Pedretti
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