Soil and groundwater contamination due to release and transport of DNAPLs, represents a diffuse environmental problem, due to their large use in industrial processes. The characterization of sources is a fundamental step to identify the most appropriate strategy for remediation, because the size of the accumulations and their morphology strongly influence, together with the hydrogeological conditions, the processes of mass transfer. For this purpose laboratory experiments have been carried out with different values of water flow velocity to study both the processes of DNAPLs migration and the dissolution process under controlled conditions in a homogeneous porous medium. Those experiments allow to assess the influence of groundwater flow on DNAPL migration and dissolution and architecture of the sources (shape and dimensions) on source reduction processes. Hydrofluoroether has been used as DNAPL and glass beads have been utilized as porous medium. An image analysis procedure has been used to determine saturation distribution of DNAPL source and evaluate the mass reduction. This analysis coupled with the measure of dissolved concentration returns important information about the influence of initial conditions (DNAPL mass and shape) and boundary conditions (hydraulic gradient) on the mass reduction and DNAPL dissolution processes The experimental results show that the hydraulic gradient promotes the infiltration process, increasing the infiltration rate. It hampers DNAPL spread and fingering bringing to a reduction of residual DNAPL and it also promotes the DNAPL redistribution, and it reduces the amount remaining at residual saturation. Furthermore the hydraulic gradient promotes downward and down-gradient migration. DNAPL migration in the direction of water flow, can be considered important due to significant errors in the location of sources in the case of high gradients and high aquifer thicknesses, and for high water flow velocities, such as those which can be expected during pumping actions in water supply or in remediation activities. The mass transfer, in the case of high water flow speed, is flow controlled. It means that the mass is transported away from source area. In the case of natural water flow conditions, instead, the mass transfer is meanly governed from the rate of dissolution that occurs within the source in condition of no water flow. In the case of water flow velocity representative of natural aquifers, the water circulation, being small, does not significantly influence the process of mass transfer, which is controlled by the sources morphology. Anyway the DNAPL can be considered as a sort of low hydraulic conductivity zone with the possibility to have changes in the fluid-dynamic field at the local scale. These aspects should be considered in all these approach of remediation based on source treatments or which consider an increase in water circulation (i.e. pump & treat).

Laboratory investigation on DNAPLs distribution and source reduction processes in saturated porous media / Luciano, Antonella; PETRANGELI PAPINI, Marco; Viotti, Paolo. - ELETTRONICO. - (2010). (Intervento presentato al convegno CONSOIL tenutosi a Salisburgo nel 22-24 Settembre 2010).

Laboratory investigation on DNAPLs distribution and source reduction processes in saturated porous media.

LUCIANO, Antonella;PETRANGELI PAPINI, Marco;VIOTTI, Paolo
2010

Abstract

Soil and groundwater contamination due to release and transport of DNAPLs, represents a diffuse environmental problem, due to their large use in industrial processes. The characterization of sources is a fundamental step to identify the most appropriate strategy for remediation, because the size of the accumulations and their morphology strongly influence, together with the hydrogeological conditions, the processes of mass transfer. For this purpose laboratory experiments have been carried out with different values of water flow velocity to study both the processes of DNAPLs migration and the dissolution process under controlled conditions in a homogeneous porous medium. Those experiments allow to assess the influence of groundwater flow on DNAPL migration and dissolution and architecture of the sources (shape and dimensions) on source reduction processes. Hydrofluoroether has been used as DNAPL and glass beads have been utilized as porous medium. An image analysis procedure has been used to determine saturation distribution of DNAPL source and evaluate the mass reduction. This analysis coupled with the measure of dissolved concentration returns important information about the influence of initial conditions (DNAPL mass and shape) and boundary conditions (hydraulic gradient) on the mass reduction and DNAPL dissolution processes The experimental results show that the hydraulic gradient promotes the infiltration process, increasing the infiltration rate. It hampers DNAPL spread and fingering bringing to a reduction of residual DNAPL and it also promotes the DNAPL redistribution, and it reduces the amount remaining at residual saturation. Furthermore the hydraulic gradient promotes downward and down-gradient migration. DNAPL migration in the direction of water flow, can be considered important due to significant errors in the location of sources in the case of high gradients and high aquifer thicknesses, and for high water flow velocities, such as those which can be expected during pumping actions in water supply or in remediation activities. The mass transfer, in the case of high water flow speed, is flow controlled. It means that the mass is transported away from source area. In the case of natural water flow conditions, instead, the mass transfer is meanly governed from the rate of dissolution that occurs within the source in condition of no water flow. In the case of water flow velocity representative of natural aquifers, the water circulation, being small, does not significantly influence the process of mass transfer, which is controlled by the sources morphology. Anyway the DNAPL can be considered as a sort of low hydraulic conductivity zone with the possibility to have changes in the fluid-dynamic field at the local scale. These aspects should be considered in all these approach of remediation based on source treatments or which consider an increase in water circulation (i.e. pump & treat).
2010
CONSOIL
04 Pubblicazione in atti di convegno::04b Atto di convegno in volume
Laboratory investigation on DNAPLs distribution and source reduction processes in saturated porous media / Luciano, Antonella; PETRANGELI PAPINI, Marco; Viotti, Paolo. - ELETTRONICO. - (2010). (Intervento presentato al convegno CONSOIL tenutosi a Salisburgo nel 22-24 Settembre 2010).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/412296
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