Subsurface liquid transport

Palmer, C.D. and Johnson, R.L., Physical processes controlling the transport of nonaqueous phase liquids in the subsurface, in Transport and Fate of Contaminants in the Subsurface, EPA 625/4-89/019, U.S. EPA, Washington, 1989. 

Reversible and irreversible retention of contaminants on the subsurface solid phase is a major process in determining pollutant concentrations and controlling their redistribution from the land surface to groundwater. After being retained in the solid, contaminants may be released into the subsurface liquid phase, displaced as water-immiscible liquids, or transported into the subsurface gaseous phase or from the near surface into the atmosphere. The form and the rate of release are governed by the properties of both contaminant and solid phase, as well as by the subsurface environmental conditions. We consider here contaminants adsorbed on the solid phase. 

Ingersoll and Pankine, 2010 [169] studied the subsurface heat transport on Enceladus. Whether liquid water exists on Enceladus depends on the efficiency of subsurface heat transfer (see Fig. 4.18). Melting within 40 m of the surface occurs for... 

UNDERGROUND CONDITIONS AND FACTORS AFFECTING TRANSPORT OF LIQUIDS IN THE SUBSURFACE... 

The two flux equations of importance to subsurface transport are Darcy s law for the advective flow of water and other liquids and Fick s law for the diffusive flow of molecules and gases. These laws are independently discussed below. 

The behavior of nonaqueous phase liquids (NAPLs) as they enter the partially saturated subsurface from a land surface source follows two well-defined scenarios in one case, the physical properties of the NAPL remain unchanged, while in the second case, NAPL properties are altered during transport. In the case of dense NAPLs, the contaminant plume reaches the aquifer and is subject to longterm, continuous, slow local redistribution due to groundwater flushing-dissolution processes. These plumes become contamination source zones that evolve over time, often with major negative impacts on groundwater quality. 

After reaching the subsurface, contaminants are partitioned among the solid, liquid, and gaseous phases. A fraction of the contaminated gaseous phase is transported into the atmosphere, while the remaining part may be adsorbed on the subsurface solid phase or dissolved into the subsurface water. Contaminants dissolved in the subsurface aqueous phase or retained on the subsurface solid phase are subjected, over the course of time, to chemical, biochemical, and surface-induced degradation, which also lead to formation of metabolites. 

Electrokinetics has been used to mobilize metals and dissolved contaminants to in situ treatment or recovery zones. Electrokinetic transport uses these mechanisms to move bacteria through the subsurface to the contaminated media. The technology can be used to treat organic contaminants that adsorb to aquifer soils including halogenated hydrocarbons and non-aqueous-phase liquids (NAPLs). 

Electric fields use in soil restoration has been focused on contaminant extraction by their transport under electroosmosis and ionic migration. Contaminant extraction by electric fields is a successful technique for removal of ionic or mobile contaminants in the subsurface. However, this technique might not be effective in treatment of soils contaminated with immobile and/or trapped organics, such as dense non aqueous phase liquids (DNAPLs). For such organics, it is possible to use electric fields to stimulate in situ biodegradation under either aerobic or anaerobic conditions. It is necessary to evaluate the impact of dc electric fields on the biogeochemical interactions prior to application of the technique. It is not clear yet how dc electric fields will impact microbial adhesion and transport in the subsurface. Further, the effect of dc fields on the activity of microorganisms in a soil matrix is not yet well understood. 

Abstract The objective of this chapter is to present some recent developments on nonaque-ous phase liquid (NAPL) pool dissolution in water saturated subsurface formations. Closed form analytical solutions for transient contaminant transport resulting from the dissolution of a single component NAPL pool in three-dimensional, homogeneous porous media are presented for various shapes of source geometries. The effect of aquifer anisotropy and heterogeneity as well as the presence of dissolved humic substances on mass transfer from a NAPL pool is discussed. Furthermore, correlations,based on numerical simulations as well as available experimental data, describing the rate of interface mass transfer from single component NAPL pools in saturated subsurface formations are presented. 

Chrysikopoulos CV,Lee KY (1998) Contaminant transport resulting from multicomponent phase liquid pool dissolution in three-dimensional subsurface formations. J Contam Hydrol 31 1-21... 

Chrysikopoulos CV (1995) Three-dimensional analytical models of contaminant transport from nonaqueous phase liquid pool dissolution in saturated subsurface formations. Water Resour Res 31 1137-1145... 

Transport in unsaturated porous media is sufficiently complex when only two fluid phases, air and water, are present flow becomes even more complicated when a third fluid phase, such as an immiscible organic fluid, is involved. This third fluid phase (NAPL) arises when liquid hydrocarbon fuels or solvents are spilled accidentally on the ground surface or when they leak from underground storage tanks. The resulting subsurface flow problem then involves three fluids, air, water, and NAPL, each having different interfacial tensions with each other, different viscosities, and different capillary interactions with the soil. The adequate description of three-phase flow is still a topic of active research, but a few qualitative generalizations can be drawn. 

The transport of surfactant molecules from the liquid layer adjacent to the interface (subsurface) is simply determined by molecular movements (in the absence of forced liquid flow). At equilibrium - that is, when F = F the flux of adsorption is equal to the flux of desorption. Clearly, when F < F, the flux of adsorption predominates, whereas when F > F, the flux of desorption predominates [17]. 

Fountain, J.C. (1992) Field tests of surfactant flooding -mobility control of dense nonaqueous-phase liquids. In D.A. Sabatini and R.C. Knox (eds), Transport and Remediation of Subsurface Contaminants, ACS Symposium Series 491. American Chemical Society, Washington, DC, pp. 182-191. 

The liquid and gas bubbles underneath the propellant surface are treated together and referred to as the subsurface two-phase region. The physiochemical processes in this region are extremely complicated, involving an array of intricacies such as thermal decomposition, evaporation, bubble formation, gas-phase reactions in bubbles, interfacial transport of mass and... 

In the simplest theories any liquid movement is neglected. The main feature of these theories is the description of the adsorption/desorption exchange as a two-stage process transport of surfactant by diffusion in the bulk and exchange of molecules between the adsorption layer and the sublayer (or subsurface) adjacent to it, yielding two independent equations. The two unknown functions, surface and sublayer concentrations, can be determined from these equations. 

Transport in the solution bulk is controlled by diffusion of adsorbing molecules if any liquid flow is absent. The transfer of molecules from the liquid layer adjacent to the interface, the so-called subsurface, to the interface itself is assumed to happen without transport. This process is determined by molecular movements, such as rotations or flip-flops. As pointed out in Chapter 2 adsorption of surface active molecules at an interface is a dynamic process. In equilibrium the two fluxes, the adsorption and desorption fluxes, are in balance. If the actual surface concentration is smaller than the equilibrium one, T < F, the adsorption flux to the interface predominates, if F > F , the actual amount adsorbed at the interface is higher than the equilibrium value F , and the desorption flux prevails. 

Migration forms of the same element differ primarily in their attitude to natural solvents. Polar compoxmds well dissolve in water, nonpolar - better in nonpolar solvents, volatile and gas - in the subsurface gas. Preferences of the migration forms towards different subsurface transporters may be evaluated by their distribution in various media imder identical thermodynamic conditions. Let us assume that in close to normal, for instance in the aeration zone, component i has to distribute between sweet-water, underground gas at a pressure 1 bar and nonpolar hydrophobic liquid, which have equal volumes, i.e., in equation (2.336) = 5 = 1. 

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