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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. Importance of Groundwater Resources in UAE.
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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
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.
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.
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.
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.
HYDROLOGIC CYCLE • Never-ending circulation. • Constant movement. • Sun heating is the key factor.
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 Water is collected above a layer of Clay of limited extension Provides limited amount of groundwater
Porosity • The porosity or pore space is the amount of air space or void space between soil particles.
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)
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)
Hydraulic conductivity (K) It’s 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 (ρ g/µ) k (permeability) a function of porous media only which present the actual permeability of that media, ρ 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
Transport Processes in Groundwater • Advection Advection, Mechanical Dispersion, and Diffusion • Advection depends on the velocity of the water in the porous media and its always in the flow direction.
2. Mechanical Dispersion • The Mechanical Dispersion depends on the shape of the soil particles and the distance between them.
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.
Governing Equations 1- Darcy Equation Can also be written as
2- Fluid Continuity Equation For Steady State: 3- Hydrodynamic Dispersion Equation
Initial conditions • Assumed values for the unknowns (H, C). • Initiate the simulation. • No effect in the final solution. • Could be based on field observations.
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 Land Side Aquitard Floating point Aquifer Freshwater Seawater qn = 0 Bottom boundary Impermeable • The state of equilibrium
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.
Calibration for an observation wells. • For about five years. • Difference between the observed and calculated heads should be within certain accuracy
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.
Validation for observation wells. • For about eleven years. • Difference between the observed and calculated heads should be within certain accuracy.
A comparison between the observed and calculated water levels at a specified time.
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.
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).
ArgusONEDescription • 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.
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
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.
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.
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.
