Two approaches of physical non-equilibrium transport were followed, i) Single Porosity Flow and Non-Equilibrium Transport (SFNET) simulation (first type of non-equilibrium), and ii) Double Porosity Flow and Non-Equilibrium Transport Simulation (DFNET) (second) type of non-equilibrium ). Comparison of equilibrium and two non-equilibrium transport models (SR-HOSFET, SR-HOSFNET, and SR-HODFNET) with sorption reaction.
L IST OF F IGURES
L IST OF T ABLES
L IST OF SYMBOLS
C Concentration of dissolved pollutants M L-3 Cm Concentration of dissolved pollutants in mobile water ML-3 Cim Concentration of dissolved pollutants in stationary. T-1 λ2 First-order hydrolysis rate constant for sorbed species T-1 λb First-order biodegradation rate constant T-1 αl, αt Longitudinal, transverse L dispersivity.
L IST OF A BBREVIATIONS
IE-HOSFNET - Ion Exchange in Homogeneous Medium with Single Porosity Flow, Non-Equilibrium Transport Model. IE-HODFNET - Ion exchange in homogeneous medium with double porosity flow, non-equilibrium transport model.
C HAPTER 1
I NTRODUCTION
- Acid Mine Drainage (AMD)
- Physical non-equilibrium
- Introduction to FEMWATER
- Need for modification in FEMWATER model
- Organization of the thesis
- Chapter 2 presents the literature review on AMD, mobile immobile flow, physical non- equilibrium transport and reactive transport models followed by overall summary
- presents the analysis and selection of parameters for the numerical simulation run and explains the parameters used in the simulation, also describes the results from the
- Chapter 5 presents the application of and validation of the FEMWATER model, with non- equilibrium transport property, on hypothetical mine water movement situation, effects of non-
- Chapter 6 presents the summary and conclusions from the whole research work and model limitations. The scope for further research in is also presented in the final chapter
Incorporating non-equilibrium mass transfer for fluid flow as well as solute transport can address some of the heterogeneous situations of the field. To analyze the effects of non-equilibrium mass transfer of fluids and solutes on the transport of conservative and reactive AMD contaminants in the subsurface medium.
C HAPTER 2
L ITERATURE R EVIEW
Acid Mine Drainage
- Literature Review on AMD
- Studies on the effects of mine water around the world
They studied the feasibility of the above technique and found increased pH level of acidic water. Of this microbiological factor (iron oxidizing bacteria) plays a vital role (Rawat et al. 1982, Bernardes de souza and Mansur 2011) in the generation of AMD.
Mass transport and non-equilibrium
- Non-equilibrium types
- Physical non-equilibrium
- Chemical non-equilibrium
- Literature Review on physical non-equilibrium
In much of the literature, the physical non-equilibrium process is attributed solely to the mass transport of solutes. Non-equilibrium transport studies may be applicable for field-scale remediation purposes (Pang et al. 1999).
Numerical models
- Literature review on application of numerical models to AMD problem
- AMD and numerical models
- Evolution of FEMWATER
- Application of FEMWATER to the field study
Very few studies have been conducted to simulate the effects of mobile/immobile water on the transport of pollutants in mine drainage (Bibby, 1981 and Selim et al. 1987). HP1 1D simulation of flow water, heat and reactive transport of multiple solutes in variable saturated media. FRAC3DVS 1D/2D/3D simulation of water flow and solute transport in variably saturated porous fractured media.
HYDROGEOCEM 1D coupled simulation of water flow, chemical reactions and reactive solute transport in variable saturated porous media zone. HYDROGEOCHEM2 2D coupled simulation of water flow, chemical reactions and reactive solute transport in variable saturated porous media zone.
Summary
GMS-FEMWATER has been applied to study the herbicide transport to the water bodies and it has been demonstrated as an effective tool to evaluate the fate of non-point source pollution. It is modified using Latin Hypercube Sampling (LHS) and comes with an Argus ONE GUI and named as FEMWATER- LHS. Model was validated with two benchmark problems (Hardyanto and Merkel used GMS-FEMWATER to analyze seawater intrusion into the aquifer.
When the deep groundwater is set up or developed, it is important to do the preliminary investigation due to the pollution or intrusion of sea water into the aquifer. If the trapped contaminants in the immobile regions are subject to reactions such as oxidation and precipitation, they can be more effective in the remediation process.
C HAPTER 3
M ODIFICATION AND U PDATION OF FEMWATER MODEL AND ITS VALIDATION
Finite Element Method (FEM)
In the finite element method, the problem domain under consideration is divided into a series of smaller areas (or) finite elements. Instead of providing continuous solutions as with the exact solutions, the FEM concept is intended to determine solutions at predefined locations. The procedures for the finite element method are given as follows. i) Discretization of the computational domain into a number of elements. ii) Selecting the element type and their interpolation functions. iii).
Collecting element equations to form a system of equations. v) Applying boundary conditions and solving equations for nodal solutions.
Element type and shape function
That is, if there are 10 nodes in the vertical direction and 15 nodes in the horizontal direction, the numbering sequence must be in the vertical direction to reduce the bandwidth of the matrix.
Pressure head based Richards equation
- Mixed form Richards equation
- Numerical modelling using Galerkin Finite Element Method
- Numerical approximation and solution technique in 3DFEMWATER
- Governing equation
- Numerical approximation and solution technique in 3DLEWASTE
- Inclusion of ion exchange reaction into FEMWATER Model
Substituting the current time step and the current iteration value of the immobile water content into the above equation yields 3.39. Where 'n' is the slope of the graph of log c versus log C and K is the intercept of the x-axis. Rj is the accumulation rate of the jth substance as a result of the aqueous complexation.
Rj is the rate of accumulation of the jth substance due to ion exchange reaction. Rj is the rate of accumulation of the jth substance due to acid base reaction,.
Summary
Modification and updating of the Femwater model and its validation. 5) Upon completion of the second step, the new species concentration is used as initial conditions in the physical step to solve the solute transport equations for time t+2Δt. The chemical reaction equation system must be included in the FEMWATER model and the MINTEQ program is selected for the chemical reactions. For now, only physical multispecies transport has been added, so this study has not included any simulations of reactive multispecies transport.
C HAPTER 4
P ARAMETER ANALYSIS AND SELECTION
- Flow parameters
- Residual (θ r ) and saturated (θ s ) moisture content, [-]
- Saturated hydraulic conductivity (K s ), [L/T]
- Permeability (k), [L 2 ]
- Relative permeability (or Hydraulic conductivity) (k r ) [-]
- Pressure head (h), [L]
- Moisture content capacity (F(θ)), [L -1 ]
- Distribution coefficient (K d ), [L 3 /M]
- Bulk density (ρ b ), [M/ L 3 ]
- Molecular diffusion coefficient (D m ), [L 2 /T]
- Tortuosity (τ), [-]
- Dual porosity parameters
- Mobile (θ m ) and immobile water (θ im ) content, [-]
- Fraction of site available for sorption (f), [-]
- Ion-exchange parameters
- Cation exchange capacity (Q ct ), [meq/g]
- Total solution concentration (C tot ), [eq/L 3 ]
- Equilibrium ion exchange coefficient (K ex ), [-]
- Problem description and parameter analysis .1 Description of two dimensional domain
- Effect of Van Genuchten parameter, α
- Dual porosity / mobile-immobile flow parameters
- Effect of ratio of mobile water to total water content
- Effect of mass transfer rate
- Effect of spatial discretization
- Effect of time discretization
The extended application of the model to the AMD cases will be elaborated in chapter 5. In general, vertical hydraulic conductivity is smaller than horizontal hydraulic conductivity for most of the soils. Molecular diffusion is less significant compared to mechanical dispersion in the process of dispersion of dissolved substances in most of the underground systems.
Defines the total concentration of the solution, including the sorbed and replaced solutes, available in the solution. The effects on the output results of the numerical model depend on the input values/parameters.
C HAPTER 5
RESULTS AND DISCUSSIONS
Two dimensional transport of AMD using modified FEMWATER
In this study, the focus is on the transport character of ferrous ions with non-equilibrium conditions and reaction. Most non-equilibrium transport models obtain the value of water content from flow simulation using Darcian conditions and then decompose this water content into mobile and immobile regions, for the simulation of pollutant transport. In those types of simulations, the distributed values of the mobile and immobile water contents have no influence on the hydraulic head used in flow simulations.
This is the Darcian mechanism only estimates total water content by solving flow equations based on head and/or water content. Therefore, this research work includes mass transfers of water as well as pollutants between the mobile and stationary regions in the subsurface zone to increase the accuracy of the model prediction.
Field condition and problem domain selection
- Flow boundary conditions
- Transport boundary conditions
Infiltration or evapotranspiration can be represented in the boundary part by specified flux (Cauchy) boundary condition. The flux boundary condition is used when infiltration rates in the underground media are known. It represents a combined Dirichlet/specified flux boundary condition to simulate boundaries with known pressure head or flux velocities.
The definite flux limit (Cauchy) represents the limit where infiltration can be quantified. It represents 1) infiltration of leachate migration from landfills, mine tailings or surface impoundments, 2) field application of pesticides, fertilizers and 3) dilution of existing pollutants by rainfall or irrigation. Equal to the flow boundary condition, it represents 1) infiltration of leachate migration from landfills, mine tailings, or surface impoundments, 2) field application of pesticides, fertilizers, and 3) dilution of existing pollutants by precipitation or irrigation.
Domain description
- Assumptions
- Simulation in homogeneous medium
- Single porosity flow and equilibrium transport (HOSFET)
- Single porosity flow and non-equilibrium transport (HOSFNET)
- Comparison of simulations of non-equilibrium transport models (HOSFNET vs
- Reactive transport and non-equilibrium mass transfer effects on contaminant transport
- Single porosity flow and equilibrium transport (advective dispersive model) with sorption reaction (SR-HOSFET)
- Single porosity flow and non-equilibrium transport with sorption reaction (SR- HOSFNET)
- Dual porosity flow and non-equilibrium transport with sorption reaction (SR- HODFNET)
- Comparison of equilibrium and two non-equilibrium transport models (SR- HOSFET, SR-HOSFNET, and SR-HODFNET) with sorption reaction
- Single porosity flow and equilibrium transport with ion exchange reaction (IE- HOSFET)
- Single porosity flow and non-equilibrium transport with ion exchange reaction (IE-HOSFNET)
- Dual porosity flow and non-equilibrium transport with ion exchange reaction (IE- HODFNET)
- Comparison of equilibrium and non-equilibrium transport with ion-exchange reaction
- Simulation in heterogeneous medium
- Single porosity flow and equilibrium transport (HESFET)
- Comparison of two non-equilibrium models
- Comparison of non-equilibrium conservative transport in homogeneous and heterogeneous medium
- Comparison of equilibrium and non-equilibrium model simulation with sorption reaction for heterogeneous domain
- Comparison of non-equilibrium transport with sorption reaction in homogeneous and heterogeneous medium
- Single porosity flow and equilibrium transport with ion exchange reaction (IE- HESFET)
- Single porosity flow and non-equilibrium transport with ion exchange reaction (IE- HESFNET)
- Dual porosity flow and non-equilibrium transport with ion exchange reaction (IE- HEDFNET)
- Comparison of equilibrium and non-equilibrium transport with ion-exchange reaction
- Comparison of non-equilibrium transport with ion-exchange reaction in homogeneous and heterogeneous medium
- Effects of mass transfer rate coefficient
Fig.5.9 Simulation of concentration distribution with single porosity flow and non-equilibrium transport model with sorption reaction at (a) 600th day (b) 1200th day (c) 1825th day ( - - - concentration in mobile water, concentration ___ in stationary water). Fig. 5.10 Simulation of concentration distribution from dual porosity flow and non-equilibrium transport model with sorption reaction at (a) 600th day (b) 1200th day (c) 1825th day ( - - - concentration in mobile water, - . Concentration ___ in stationary water). Fig.5.13 Simulation of concentration distribution with single porosity flow and non-equilibrium transport model with ion exchange reaction at (a) 600th day (b) 1200th day (c) 1825th day ( - - - concentration in mobile water, concentration ___ in still water).
Fig.5.14 Simulation of concentration distribution from dual porosity flow and non-equilibrium transport model with ion exchange reaction at (a) 600th day (b) 1200th day (c) 1825th day (- - - concentration in mobile water, concentration ___ in still water). Fig.5.15 Comparison of the concentration of iron ions in the moving water in the vertical segment (x=20 m) on the 1200th day from the simulation of the equilibrium and non-equilibrium transport model with ion exchange reaction. This section presents the model of non-equilibrium transport of the first type with ion exchange reaction in heterogeneous medium.
Fig.5.24 Simulation of concentration distribution in heterogeneous medium with single porosity flow and non-equilibrium transport model with ion exchange reaction at (a) 600th day (b) 1200th day (c) 1825th day (- - - . concentration in mobile water, Concentration ___ in stationary water).
C HAPTER 6
Conclusions from the simulation run
Difference in contaminant (iron ion) distribution pattern is observed between the conventional equilibrium and physical non-equilibrium models. Mainly the progress of solute front in the direction of water flow is observed for non-equilibrium simulation results with respect to equilibrium simulation result. Difference in contaminant distribution pattern is also observed between first and second type non-equilibrium models.
Due to the addition of time-dependent water mass transfer between mobile and immobile zones in the flow model in the second type of non-equilibrium models,. It is observed that at the initial time (600th day) less concentration contour (0.001 mol/l) more spread in the saturated zone, under non-equilibrium condition with conservative and reaction transport.
Limitations and future scope
At later time (1825th day), distribution of less concentration contours and 0.003 mol/l) decreased under non-equilibrium condition due to mass transfer from mobile region to immobile region. Second type non-equilibrium model simulates natural mass transfer process unlike the first type model, which could not properly capture the velocity details of mobile-immobile flow. This is evident in the mass transfer nature and arrival time of solute front at downdrafts.
Little difference is observed in the contaminant diffusion pattern of the homogeneous and heterogeneous domain simulations, especially in the still water region. Compared to absorption, the ion exchange reaction is less affected by the non-equilibrium process and in the conservative case transport is greatly affected by the non-equilibrium process and increases the accuracy of the prediction.
Appendix - A
Appendix – B
R EFERENCES
The effects of acid mine drainage (AMD) on the internal and external environment in the open-pit coal mining operations. Acid mine drainage and heavy metal contamination in arid area metal sulphide mine groundwater (BS mine, Western Australia). Community perceptions of the health risks of acid mine drainage: the struggle for environmental justice of communities near mining fields.
Reactive transport modeling of acid mine drainage within discretely fractured porous media: plume development from a surface source zone. The interaction of acid mine drainage and a carbonate terrace: evidence from the Obey River, north-central Tennessee.
