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Introduction to Groundwater

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Rainfall events are random and infrequent in UAE, average annual ... Isotropy and homogeneity. -Pumping and recharge. -Location of the pollution source. ... – PowerPoint PPT presentation

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Title: Introduction to Groundwater


1
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
2
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.

3
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.

4
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.

5
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.

6
HYDROLOGIC CYCLE
  • Never-ending circulation.
  • Constant movement.
  • Sun heating is the key factor.

7
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

8
Porosity
  • The porosity or pore space is the amount of air
    space or void space between soil particles.

9
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)
10
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)

11
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
12
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.

13
2. Mechanical Dispersion
  • The Mechanical Dispersion depends on the shape of
    the soil particles and the distance between them.

14
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.

15
Governing Equations
1- Darcy Equation
Can also be written as
16
  • 2- Fluid Continuity Equation
  • For Steady State

3- Hydrodynamic Dispersion Equation
17
Initial conditions
  • Assumed values for the unknowns (H, C).
  • Initiate the simulation.
  • No effect in the final solution.
  • Could be based on field observations.

18
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

19
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.

20
  • Calibration for an observation wells.
  • For about five years.
  • Difference between the observed and calculated
    heads should be within certain accuracy

21
  • 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.

22
  • Validation for observation wells.
  • For about eleven years.
  • Difference between the observed and calculated
    heads should be within certain accuracy.

23
A comparison between the observed and calculated
water levels at a specified time.
24
  • 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.

25
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).

26
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.

27
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

28
Study Domain and Parameters (Basic Run)
29
Discritization of Domain and Layers
30
Resulted Equipotential lines and Velocity Vectors
31
Resulted Equi-concentration Lines
32
Run 2 Reducing the pumping rate
33
Resulted Equipotential lines and Velocity Vectors
34
Resulted Equi-concentration Lines
35
Run 3 Specified Flux Boundary
36
Resulted Equipotential lines and Velocity Vectors
37
Resulted Equi-concentration Lines
38
Run 4 non-isotrpic system
39
Resulted Equipotential lines and Velocity Vectors
40
Resulted Equi-concentration Lines
41
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.

42
  • 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.

43
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.

44
  • Thanks for Listening
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