Groundwater pumping to remediate groundwater pollution

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# Groundwater pumping to remediate groundwater pollution - PowerPoint PPT Presentation

Groundwater pumping to remediate groundwater pollution. March 5, 2002. TOC . 1) Squares 2) FieldTrip: McClellan 3) Finite Element Modeling. First: Squares. Oxford Dictionary says “a geometric figure with four equal sites and four right angles”. Squares.

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### Groundwater pumping to remediate groundwater pollution

March 5, 2002

TOC
• 1) Squares
• 2) FieldTrip: McClellan
• 3) Finite Element Modeling
First: Squares
• Oxford Dictionary says
• “a geometric figure with four equal sites and four right angles”
Squares
• Units within a flow net are curvilinear figures…
• In certain cases, squares will be formed
Flownet
• No flow crosses the boundary of a flowline !
• If interval between equipotential lines and interval between flowlines is constant, then volume of water within each curvilinear unit is the same…
Flow nets (rules)
• Flowlines are perpendicular to equipotential lines
• One way to assume that Q’s are equal is to construct the flownet with curvilinear squares
• Streamlines are perpendicular to constant head boundaries
• Equipotential lines are perpendicular to no-flow boundaries
Flow nets (rules 2)
• In heterogeneous soil, the tangent law is satisfied at the boundary
• If flow net is drawn such that squares exist in one part of the formation, squares also exist in areas with the same K

a1

K1

K2

a2

How to determine the spacing of wells?
• Determine feasible flow rates
• Determine range of influence
• Determine required decrease of water table
• Calculate well spacings
Confined Aquifer
• Well discharge under steady state can be determined using
Unconfined Aquifer
• Well discharge under steady state can be determined using
Unconfined Aquifer
• Well discharge under steady state WITH surface recharge can be determined using
What is optimal well design ?
• In homogeneous soil:
In heterogeneous situation:
• Wells have flow rate between 1 and 100 gpm
• Some wells are in clay, others in sand
Finite Difference method
• Change the derivative into a finite difference D
Approach to numerical solutions
• 1) Subdivide the flow region into finite blocks or subregions (discretization) such that different K values can be assigned to each block and the differentials can be converted to finite differences
Approach to numerical solutions
• 2) Write the flow equation in algebraic form (using finite difference or finite elements) for each node or block
Approach to numerical solutions
• 3) Use “numerical methods” to solve the resulting ‘n’ equations in ‘n’ unknowns for h subject to boundary and initial conditions
1-D example
• Boundaries: h left = 10, h right = 3
• Initial conditions h = 0
• K is homogeneous = 3
• Delta x = 2