Cost – performance curves
A tool to evaluate alternative remedial options
before and
during projects
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©2006 Ben Keet 1
Background Drs Ben Keet
Free University of Amsterdam : Physics & Hydrogeology
Work experience
•
•
•


5 years Ass. Lect. Physics & Groundwater Models
5 years Shell International : UK, Algeria, Gabon, London
19 years Geo & Hydro: New Zealand, Australia, US, Europe, NZ
Proj. manager 2500 site assessments, 1500 remediations
Design & manage : 400 in situ & biological remediations
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CP curves: Conditions of use
• Good understanding of uncertainties involved
• Thorough knowledge of effects of remedial
techniques to be evaluated
• Cost estimates need to be complete
• Accurate and relevant monitoring data
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Uncertainties
keep in mind:
What we know is not much
What we know we don’t know is limited
But what don’t we know we don’t know ?
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Groups of Uncertainties
1.
2.
3.
4.
5.
Initial conditions
Effect of chosen remedial technique(s)
Quality of implementation
Technical uncertainties
Contractual uncertainties
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Initial conditions
 Heterogeneity :
 Soil
 Contaminants
 Time
 Contaminant movement
 Retardation (actual)
 Leaching (TCLP)
 (Re-) mobilisation
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Effect of chosen remedial
technique(s)
• - Breakdown speed (half-life time)
• - The natural or enhanced breakdown potential
• - Leaching / migration potential (current, during and after
remedial action)
• - Lowest possible attainable concentration by mixing or
bioremediation
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Quality of implementation

Focus on results


Use soil heterogeneity
Monitoring aimed at




System check
Process control
Effect monitoring
So not only Verification
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Technical uncertainties
Just a few:
• Presence of sulphides – acid soils
• Change of redox – mobilisation (As)
• NA of VOCl’s formation of VC (gas)
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Contractual uncertainties




Definition of goals vs.
definitions of the deliverables
Final sampling methodology
Allowable residual risk /
contaminants
Ownership intellectual property
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Cost – performance curves
Case - midpoint evaluation
- oil spill ½ under glass house
- Emergency response :
-
-
Dig trench
Pump fluid to oil/water separator
After 21 months evaluate alternatives
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4 scenarios:
0 = no added activity
I, II, III = addition of several in situ techniques
Evolution of contaminant mass removal
kg
oil
re
mo
ved
3500
98 %
94 %
89 %
Scenario I
Scenario II
Scenario III
70 %
Scenario 0
3000
2500
2000
1500
1000
500
0
0
365
730
1095
May 1998
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1460
1825
days after spill
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Set out cost vs. kg contaminant removed
cost curves
300000
Scenario I
$
250000
Scenario II
200000
scenario 0
150000
100000
Conclusion:
50000
00
500
100
0
150
0
200
0
May 1998
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250
0
300
0
350
0
Simplest system will
eventually remove same
oil mass at lowest costs
kg oil removed
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Now evaluate S/kg in time
Evolution of remedial efficiency
Remedial efficiency
as $/kg oli removed
500
Scenario I
Scenario II
400
Scenario III
300
200
Scenario 0
133
100
Scenario 00
Immediate total excavation
0
0
365
730
1095
May 1998
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1460
1825
days after spill
lek
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Conclusions this Case
With the added knowledge of hint sight:
In this case
1. Full excavation immediately after spill gives
highest cost efficiency
2. Note added cost to shut down operations
3. Plus cost for demolition / rebuilding glass house
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Conclusion CP curves
1. Allows technique independent comparison
2. Easy to explain to lay person
However:
1. Requires thorough insight in techniques
2. Requires firm costing of alternatives
3. Requires identification of residual uncertainties
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Questions - Discussion
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