Groundwater pumping to remediate groundwater pollution
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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.

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Groundwater pumping to remediate groundwater pollution

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Groundwater pumping to remediate groundwater pollution

Groundwater pumping to remediate groundwater pollution

March 5, 2002


Groundwater pumping to remediate groundwater pollution

TOC

  • 1) Squares

  • 2) FieldTrip: McClellan

  • 3) Finite Element Modeling


First squares

First: Squares

  • Oxford Dictionary says

  • “a geometric figure with four equal sites and four right angles”


Squares

Squares

  • Units within a flow net are curvilinear figures…

  • In certain cases, squares will be formed

    • Constant head boundary…


Flownet

Flownet


Flownet1

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

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

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


Second mcclellan airbase

Second: McClellan Airbase


Piping system

Piping system


Groundwater extraction wells

Groundwater extraction wells


Waste water treatment plant

Waste water treatment plant


How to determine the spacing of wells

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

Confined Aquifer

  • Well discharge under steady state can be determined using


Unconfined aquifer

Unconfined Aquifer

  • Well discharge under steady state can be determined using


Unconfined aquifer1

Unconfined Aquifer

  • Well discharge under steady state WITH surface recharge can be determined using


What is optimal well design

What is optimal well design ?

  • In homogeneous soil:


In heterogeneous situation

In heterogeneous situation:

  • Wells have flow rate between 1 and 100 gpm

  • Some wells are in clay, others in sand


Finite difference method

Finite Difference method

  • Change the derivative into a finite difference D


Approach to numerical solutions

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 solutions1

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 solutions2

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

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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