Introduction to Groundwater

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Designing of a groundwater pumping field (s) in
the vicinity of landfill sites By 1- Sulaiman
AL-Mulaifi 980711413 2- Ahmed
AL-Harrasi 199905029 3- Mohammed
AL-Awadi 199905040 4- Ahmed AL-Waeel
200001489 Advisor Prof. Mohsen Sherif
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Importance of Groundwater Resources in UAE

• One of the critical problems that hinder the
  development in UAE is the lack of renewable water
  resources.
• Rainfall events are random and infrequent in UAE,
  average annual rainfall is around 110 mm/year.
• The groundwater resources constitute about 70 of
  the total water production in the country, and
  mainly used for agriculture development.
• Alternatives
• Conservation in water use.
• water pricing.
• Reuse of treated wastewater.
• Minimizing losses.
• Surface water harvesting
• Improving the potentiality of aquifers.
• Protection of the available groundwater resources
  from any possible contamination hazards.

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Project Summary
Phase One

• Groundwater flow and transport of pollutants in
  groundwater systems will be studied and simulated
  numerically.
• A comprehensive review and understanding of the
  theoretical background including
• Hydrogeological parameters and coefficients
• Governing equations of groundwater flow and
  pollutant transport in porous media
• Initial and boundary conditions.
• Concepts of numerical models.
• The USGS groundwater and solute transport model,
  SUTRA will be studied
• and applied.

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Project Summary

• Phase two
• Different hydrogeological settings and boundary
  conditions will be considered.
• Groundwater pollution from landfill sites will be
  simulated in the vertical and horizontal domains.
• Groundwater pumping field(s) will be located in
  the vicinity of a landfill site and the pollution
  will be simulated under different pumping rates.
• The maximum pumping rate that would not allow any
  pollutants to migrate into the protection zone of
  the pumping field(s) will be identified.

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Objectives of the Project

• Study the groundwater flow and transport of
  contaminants in groundwater systems
• Employ a numerical model to analyze the
  groundwater flow and solute transport under
  different hydrogeological settings.
• Present the equi-potential, equi-concentration
  lines and velocity vectors
• Design of the well field(s), near a landfill
  including rates and locations of pumping.

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HYDROLOGIC CYCLE

• Never-ending circulation.
• Constant movement.
• Sun heating is the key factor.

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Aquifers System

• Groundwater, Unsaturated zone, Saturated zone.
• 1- Unconfined Aquifers
• The water table is subjected to atmospheric
  pressure
• Is directly recharged by rainfall
• Also called water table aquifer
• 2- Confined Aquifers
• Bounded by impermeable layers (from top and
  bottom)
• Pressure is not atmospheric
• 3- Artesian Aquifers
• Are confined aquifers but under high pressure.
• Water will rise above the ground surface without
  pumping
• 4- Leaky Aquifers
• One of the upper or lower confining layers is
  semi-permeable
• 5- Perched Aquifers

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Porosity

• The porosity or pore space is the amount of air
  space or void space between soil particles.

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Specific Yield

• Specific yield is the ratio of volume of water
• that drains from a saturated rock due to
• gravity to the total volume of rock.
• A sample with smaller grain sizes will have a
• lower specific yield because of the Surface
  Tension.
• The specific storage of an aquifer can be defined
  as the volume of water that a unit volume of the
  aquifer under a unit decline in the average head
  releases from storage due to
• expansion of water and compression of the
  aquifer.

Specific Storage (Ss)
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Storage coefficient (Sc)

• It's the volume of water that a permeable unit
  will absorb or loss from storage per unit surface
  area per unit change in head.
• Sc B Ss (Confined aquifer)
• Sc Sy h Ss (Unconfined aquifer)

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Hydraulic conductivity (K)

• Its a function of properties of both porous
  media and the water passing through it which
  represent the specific rate (L / T ) of water
  passing through the porous media.
• K k (? g/µ)
• k (permeability) a function of porous media
  only which present the actual
• permeability of that media, ? density of
  fluid, g the acceleration of gravity
• and µ dynamic viscosity of fluid

Transmissivity
Its amount of water that can be transmitted
horizontally through a unit width by the full
saturated thickness. T K B
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Transport Processes in Groundwater

• Advection, Mechanical Dispersion, and Diffusion

• Advection

• Advection depends on the velocity of the water in
  the porous media and its always in the flow
  direction.

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2. Mechanical Dispersion

• The Mechanical Dispersion depends on the shape of
  the soil particles and the distance between them.

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3. Diffusion

• Diffusion is a chemical process. It depends on
  the pollutant it self and the characteristic of
  groundwater.
• It does not depend on the velocity of the fluid.
• Any pollutant tends to move from areas of high
  concentrations to areas of lower concentrations.

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Governing Equations
1- Darcy Equation
Can also be written as
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• 2- Fluid Continuity Equation
• For Steady State

3- Hydrodynamic Dispersion Equation
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Initial conditions

• Assumed values for the unknowns (H, C).
• Initiate the simulation.
• No effect in the final solution.
• Could be based on field observations.

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Boundary Conditions

• Three types of conditions
• 1st type Specific head.
• 2nd type Specific flux.
• 3rd type Mixed boundary.

Ground surface
Water table
Hinge point
Piezometric head
Mixed water
Seaside
Aquitard
Land Side
Floating point
Aquifer
Freshwater
Seawater
qn 0
Bottom boundary Impermeable

• The state of equilibrium

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Modeling steps

• 1- Calibration
• The simulated values are compared with field
  measurements.
• - Input data are altered within range until
  simulated and observed values
• are fitted within a chosen tolerance.
• - Proper calibration will allow for good
  validation .
• - Model calibration is time consuming as it
  requires a number of simulation runs.

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• Calibration for an observation wells.
• For about five years.
• Difference between the observed and calculated
  heads should be within certain accuracy

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• 2- Validation
• The comparison of the model with a new
  (independent) data set not used in model
  calibration.
• - One time fit of calculated and measured values
  does not guarantee accuracy.
• - Should be conducted for a number of
  observation wells.

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• Validation for observation wells.
• For about eleven years.
• Difference between the observed and calculated
  heads should be within certain accuracy.

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A comparison between the observed and calculated
water levels at a specified time.
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• 3-Predection
• The outcome of a numerical model must be reviewed
  critically.
• After calibration and validation, the model can
  be used for assessment of future scenarios.
• Extrapolation the future scenarios is more
  accurate if it is based on a long-term series of
  observed events in the past.

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Sutra Model

• Applicable to
• Saturated and (or) unsaturated flow in porous
  medium.
• Constant or variable-density fluid flow.
• Solute or energy transport (2D,3D finite element
  codes)
• GUI is a preprocessor and postprocessor
  graphical-user interfaces for preparing SUTRA
  input data and viewing model output for use
  within Argus Open Numerical Environments (Argus
  ONE).

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Argus ONE Description

• Imports data from different sources. 
• Graphically defines the problem domain, boundary
  conditions and other excitations to the
  groundwater system like pumping or recharge. 
• Automatically creates finite-element meshes and
  finite-difference grids.

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Argus ONE Description

• Interpret the data to the developed meshes and
  grids 
• Mathematically manipulate the data 
• Organize information using GIS and other
  databases 
• Visualize your model's input and results

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Study Domain and Parameters (Basic Run)
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Discritization of Domain and Layers
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Resulted Equipotential lines and Velocity Vectors
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Resulted Equi-concentration Lines
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Run 2 Reducing the pumping rate
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Resulted Equipotential lines and Velocity Vectors
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Resulted Equi-concentration Lines
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Run 3 Specified Flux Boundary
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Resulted Equipotential lines and Velocity Vectors
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Resulted Equi-concentration Lines
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Run 4 non-isotrpic system
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Resulted Equipotential lines and Velocity Vectors
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Resulted Equi-concentration Lines
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Conclusion

• Groundwater resources constitute an important
  element in the water budget and cornerstone for
  the agriculture in the UAE
• Groundwater resources might be polluted
  contaminated from different sources including,
  among other, landfill sites
• Many factors affect the transport of pollutants
  in groundwater systems
• -Hydrogeological parameters.
• -Isotropy and homogeneity.
• -Pumping and recharge.
• -Location of the pollution source.
• -Boundary conditions.

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• Conclusion
• Groundwater models should be calibrated using
  real data sets and verified against another
  independent data sets in order to ensure that
  they are representative of the hydrogeological
  system under consideration.
• SUTRA has been used to simulate the groundwater
  flow and pollutant transport under different
  conditions.

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Future work

• Based on the availability of data, a landfill
  site will be selected. The possible contamination
  from the selected landfill will be simulated
  using SUTRA-Argus model under the unsteady state
  conditions.
• The optimum location of the well field and
  pumping rates will be identify.

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• Thanks for Listening