Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

Hydraulic ConductivityHydraulic Conductivity

Hydraulic conductivity is not an exclusive Hydraulic conductivity is not an exclusive property of the soil matrix alone. It also property of the soil matrix alone. It also depends upon the fluid under consideration.depends upon the fluid under consideration.Hydraulic conductivity depends upon water Hydraulic conductivity depends upon water content (total porosity), pore size content (total porosity), pore size distribution and distribution and tortuositytortuosity..Fluid properties that affect hydraulic Fluid properties that affect hydraulic conductivity are density and viscosity.conductivity are density and viscosity.One can calculate intrinsic permeability of One can calculate intrinsic permeability of the soil from hydraulic conductivity.the soil from hydraulic conductivity.

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

Soil PermeabilitySoil Permeability

Hydraulic conductivity (cm/s) = Intrinsic Hydraulic conductivity (cm/s) = Intrinsic permeability (cmpermeability (cm22) x fluidity (cm) x fluidity (cm--11 secsec--11))Fluidity=Fluidity=ρρgg//ηη where where ρρ is density (g cmis density (g cm--33) of ) of the fluid, g is acceleration due to gravity the fluid, g is acceleration due to gravity (dyne sec/cm(dyne sec/cm22), ), ηη is viscosity (cm/secis viscosity (cm/sec22).).

k= k= KKηη//ρρggk=intrinsic soil permeability (cmk=intrinsic soil permeability (cm22), K=soil ), K=soil hydraulic conductivity.hydraulic conductivity.

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

Soil PermeabilitySoil Permeability

Intrinsic Intrinsic permeabilitpermeability of the y of the soil is soil is same same irrespectivirrespective of fluid.e of fluid.

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

Two Phase FlowTwo Phase Flow

There is always two phase flow in soil. There is always two phase flow in soil. When water moves into the soil, air is When water moves into the soil, air is moving out of the soil. moving out of the soil. Water is Water is wettablewettable fluid and thus has a fluid and thus has a tendency to hug the soil particle. As a tendency to hug the soil particle. As a result, the water is always found in nooks result, the water is always found in nooks and crannies. Air on the other hand is and crannies. Air on the other hand is between water layers in the center of a between water layers in the center of a porepore..

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

Two or Multi Phase FlowTwo or Multi Phase Flow

Another example is organic contaminants Another example is organic contaminants which are not completely soluble such as oil which are not completely soluble such as oil or gasoline with water.or gasoline with water.If there is a spill of these chemicals then If there is a spill of these chemicals then these chemicals are between the water these chemicals are between the water layerslayers--in the middle of the pore.in the middle of the pore.If it is unsaturated flow then there is also a If it is unsaturated flow then there is also a presence of air. In other words, three presence of air. In other words, three phases are moving. phases are moving.

Stephens, D. 1996. Vadose Zone Hydrology, Stephens, D. 1996. Vadose Zone Hydrology, Lewis Pub.Lewis Pub.

Example of Three Phase Example of Three Phase SystemSystem

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

NonNon--Aqueous Phase Aqueous Phase LiquidsLiquids--NAPLsNAPLs

Previous discussion of flow has dealt with Previous discussion of flow has dealt with soluble contaminants.soluble contaminants.Another group of contaminants are those Another group of contaminants are those which are not miscible in water. They are which are not miscible in water. They are called noncalled non--aqueous phase liquids (aqueous phase liquids (NAPLsNAPLs).).They are characterize by their low solubility They are characterize by their low solubility in water. They are nonin water. They are non--polar compounds polar compounds and remain as a separate liquid phase.and remain as a separate liquid phase.

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

NonNon--Aqueous Phase Aqueous Phase LiquidsLiquids--NAPLsNAPLs

Depending upon the density of the liquid, Depending upon the density of the liquid, they are subdivided into two groups.they are subdivided into two groups.i. Density lower than water (light) i. Density lower than water (light) ––

LNAPLsLNAPLs: gasoline, : gasoline, diseldisel, kerosene. , kerosene. Leaking under ground gasoline tanks (LUST)Leaking under ground gasoline tanks (LUST)ii. Density greater than water (dense)ii. Density greater than water (dense)--DNAPLsDNAPLs: : tertachloroethylenetertachloroethylene (TCE), carbon (TCE), carbon tetrachloride (CTET). These are chlorinated tetrachloride (CTET). These are chlorinated solvents. Dry cleaning fluids.solvents. Dry cleaning fluids.

Fetter 2001 AppliedHydrogeology Prentice HallFetter 2001 AppliedHydrogeology Prentice Hall

Factors to consider in Factors to consider in LNAPLLNAPL’’ss SpillSpill

Fetter 2001Applied Hydrogeology Prentice HallFetter 2001Applied Hydrogeology Prentice Hall

Factors to consider in Factors to consider in DNAPLDNAPL’’ss spillspill

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

Movement of Movement of NAPLsNAPLs

In soil, In soil, DNAPLsDNAPLs and and LNAPLsLNAPLs behave quite behave quite similarly as long as they do not reach the similarly as long as they do not reach the zone of saturation.zone of saturation.Once they reach the water table then Once they reach the water table then buoyancy effects hold and the movement of buoyancy effects hold and the movement of the free product differs.the free product differs.LNAPLsLNAPLs travel in the direction of the slope of travel in the direction of the slope of the top of water table.the top of water table.DNAPLsDNAPLs travel in the slope of the lower travel in the slope of the lower boundary of the aquifer.boundary of the aquifer.

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

Migration of Migration of NAPLsNAPLs

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

Movement of Movement of NAPLsNAPLs

DarcysDarcys’’ law applies to bulk transport of all law applies to bulk transport of all fluids as long as viscosity is well defined.fluids as long as viscosity is well defined.

q= q= --KKΔΔH/LH/LK=K=kkηη//ρρgg or k=or k=KKρρg/g/ηη

k=Intrinsic Permeability; k=Intrinsic Permeability; ρρ is density, g is is density, g is gravity, gravity, ηη is dynamic viscosity (g cmis dynamic viscosity (g cm--11 tt--11); ); ηη//ρρ is called kinematic viscosity (is called kinematic viscosity (ν)ν), cm, cm22 tt--11

q= q= --k(k(νν/g)/g)ΔΔH/LH/L

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

Fate of Fate of NAPLsNAPLs

An important question in spill of An important question in spill of NAPLsNAPLs is what is is what is the residual saturation of the the the residual saturation of the the NAPLsNAPLs..Residual refers to presence of Residual refers to presence of NAPLsNAPLs in blobs that in blobs that are isolated and their movement is not controlled are isolated and their movement is not controlled by the local gradient in the fluid potential. by the local gradient in the fluid potential. Soil particles are covered with water and thus Soil particles are covered with water and thus NAPLsNAPLs form small droplets in the unsaturated zone.form small droplets in the unsaturated zone.According to Cary et al. (1989) about 5% of the According to Cary et al. (1989) about 5% of the volume that experience NAPL transport remains volume that experience NAPL transport remains filled with residual product.filled with residual product.

Selker et al., 1999, Vadose Zone Processes, Selker et al., 1999, Vadose Zone Processes, Lewis PublishersLewis Publishers

Example of CalculationsExample of Calculations

A 10,000 L of NAPL spilled 10 m above A 10,000 L of NAPL spilled 10 m above the unconfined aquifer. The spill the unconfined aquifer. The spill occurred over a 4 x 4 m area. occurred over a 4 x 4 m area. Calculate how much of the spill made Calculate how much of the spill made it to the water table.it to the water table.The residual volume of The residual volume of NAPLsNAPLs=(10x4x4)x 5%=8m=(10x4x4)x 5%=8m33=8,000 L=8,000 LAmount that may have reached water Amount that may have reached water table =10,000table =10,000--8,000=2000L8,000=2000L