Subsurface migration factors

Migration of free-phase NAPLs in the subsurface is governed by numerous properties including density, viscosity, surface tension, interfacial tension, immisci-bility, capillary pressure, wettability, saturation, residual saturation, relative permeability, solubility, and volatilization. The two most important factors that control their flow behavior are density and viscosity. 

The limiting factors for successful soil mixing treatment include the presence of boulders and subsurface utilities such as underground wires or piping. Depth to the water table may adversely impact the vapor extraction components effectiveness because vapor phase off-gas systems cannot process liquid streams. The vendor claims that depth to the water table may also influence lateral migration of processing gases. 

The time required for diffusion to occur can sometimes be restrictive. Indeed the time required not only often exceeds the age of the hydrocarbon accumulation but also quite often exceeds the age of the host rock. If this were the dominant process for migration, then the appearance of soil-gas anomalies in the near subsurface would indicate only very shallow accumulations. If a non-steady state exists, where the hydrocarbon signal observed represents only 0.001 times the steady-state signal, then diffusion times could be reduced by a factor of 25 compared to that of the steady-state model. Table 5-V... 

The extent of water saturation in the subsurface is a critical factor affecting the transport and retention of nanomaterials in soil. Completely saturated soil has a water samration = 1, and unsaturated soil contains some fraction of gas phase with water samration < 1. As nanomaterials migrate in the subsurface they may encounter varying saturation conditions. Transport and retention of nanomaterials in saturated soil will be discussed first. 

It has been found that the fate and transport of colloids and colloid-associated contaminants in saturated porous media are controlled by a combination of several basic factors including (1) the presence of colloidal particles in the subsurface environment (2) their release, dispersion stability, migration, and straining/plugging at pore constrictions and (3) association of contaminants with colloidal particles/solid matrix (Sen and Khilar, 2006,2009 Sen et al., 2002,2004,2005). Similar observations by several investigators have been compiled by Sen and Khilar (2009). 

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