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Groundwater pumping to remediate groundwater pollution

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

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  1. Groundwater pumping to remediate groundwater pollution March 5, 2002

  2. TOC • 1) Squares • 2) FieldTrip: McClellan • 3) Finite Element Modeling

  3. First: Squares • Oxford Dictionary says • “a geometric figure with four equal sites and four right angles”

  4. Squares • Units within a flow net are curvilinear figures… • In certain cases, squares will be formed • Constant head boundary…

  5. Flownet

  6. 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…

  7. 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

  8. 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

  9. Second: McClellan Airbase

  10. Piping system

  11. Groundwater extraction wells

  12. Waste water treatment plant

  13. How to determine the spacing of wells? • Determine feasible flow rates • Determine range of influence • Determine required decrease of water table • Calculate well spacings

  14. Confined Aquifer • Well discharge under steady state can be determined using

  15. Unconfined Aquifer • Well discharge under steady state can be determined using

  16. Unconfined Aquifer • Well discharge under steady state WITH surface recharge can be determined using

  17. What is optimal well design ? • In homogeneous soil:

  18. In heterogeneous situation: • Wells have flow rate between 1 and 100 gpm • Some wells are in clay, others in sand

  19. Finite Difference method • Change the derivative into a finite difference D

  20. 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

  21. Approach to numerical solutions • 2) Write the flow equation in algebraic form (using finite difference or finite elements) for each node or block

  22. 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

  23. 1-D example • Boundaries: h left = 10, h right = 3 • Initial conditions h = 0 • K is homogeneous = 3 • Delta x = 2

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