Risk assessment: 3rd discussion session

Transcription

1 Risk assessment: 3rd discussion session 4th International Congress on Environmental Geotechnics Rio de Janeiro, 14/8/02 14/8/02 Waldemar Hachich 1

2 Supporting papers Hachich, W. Risk assessment: some views on current practice as evidenced by papers presented to conferences and symposia - page 1001 Gilbert, R.B. Questions for the future of risk assessment in environmental geotechnics - page 1007 Jefferis, S.A. Can we identify sustainable remediation techniques for contaminated land? - page /8/02 Waldemar Hachich 2

3 Why risk assessment? To make technically sound decisions on a case to case basis for the development of codes To decide better 14/8/02 Waldemar Hachich 3

4 What is being done? Risk assessment as an end in itself Whilst risk assessment is an important and perhaps key procedure for the management of contaminated land it is only a part of the process by which sustainable remediation can be achieved (Jefferis, 2002 on Decision Tools ) Simplifications that lack theoretical justification in probability theory, utility theory and decision analysis... there is a preponderance of simplifications being made on the probabilistic and decision-making side with little consideration to how sound they are (Gilbert, 2002) Are we making good decisions? 14/8/02 Waldemar Hachich 4

5 Components of risk Components Quantification Uncertainty Probability of undesirable event Consequences Attributes Monetary Environmental Social 14/8/02 Waldemar Hachich 5

6 Risk = uncertainty x consequence C = C* Risk = E[C] = p. C* p 1 - p C = 0 14/8/02 Waldemar Hachich 6

7 Risk = expected consequence C = C n p n C = C i Risk = E[C] = p i.c i p i Obs.: indicial notation p 1 p 2 C = C 2 C = C 1 14/8/02 Waldemar Hachich 7

8 Decision: minimize risk R[A n ] = E[C A n ] Decision criterion: choose action A j such that R[A j ] = min E[C A i ] A i R[A i ] = E[C A i ] A n A 1 R[A 1 ] = E[C A 1 ] 14/8/02 Waldemar Hachich 8

9 Probability-consequence matrix Probability Low Medium High Consequence Low Medium High /8/02 Waldemar Hachich 9

10 Logarithmic scales 10-1 P x M$ 1M$ 10M$ 100M$ C x 14/8/02 Waldemar Hachich 10

11 Quasi-quantitative matrix A ( R A ) Probability < a10-2 > 10-2 Consequence < a > /8/02 Waldemar Hachich 11

12 Quasi-quantitative matrix B ( R B ) Probability < a10-2 > 10-2 Consequence < a > /8/02 Waldemar Hachich 12

13 Risk comparison Hypothetical scenarios p C E[C] R A R B 1 0, , , , ,02 5 0, /8/02 Waldemar Hachich 13

14 Generalized consequences Consequences can be measured by different attributes C = money is just one possibility C = pollutant concentration for deciding on effectiveness or efficiency of remediation technique Utilities 14/8/02 Waldemar Hachich 14

15 Utility theory Single attribute C = utility of money C = utility of pollutant concentration for deciding on effectiveness or efficiency of remediation technique Multi-attribute C = utility of combination of monetary, environmental, social attributes (multi-attribute utility functions) 14/8/02 Waldemar Hachich 15

16 Recommendations Keep in mind that risk assessment is not an end in itself: risks are quantified to improve decisions Make sure that adopted risk scales are able to represent decision maker s preferences Do derive matrices with simplified scales for practical purposes, but remember that they should not be your starting point Do examine classical theories based on fundamental axioms Utility theory, probability theory Decision analysis 14/8/02 Waldemar Hachich 16

17 Practical examples Stiber, Pantazidou, Small Developing an expert-knowledge scoring system for evaluating reductive dechlorination at TCE sites - page 419 Scoring system; limitations Gilbert, R.B. Questions for the future of risk assessment in environmental geotechnics - page 1007 Interesting case-study of multi-criteria decision for remediation at a refinery site 14/8/02 Waldemar Hachich 17

18 Cost-effective decisions? Williams Sensitivity Analysis of a Risk Assessment Model Applied to the Rehabilitation of Open Cut Coal Mine Spoil Areas - page 383 Sensitivity analysis; robustness (?) Marques, Calijuri, Lorentz, Souza, Azevedo, Carvalho Multi-criteria analysis for the identification of potential areas for marble and granite waste at Cachoeiro do Itapemirim, ES-p.??? Choice of ordered weights and weighted weights (!?) Nakahara, Oliveira, Boscov, Boggiani Selection of MSW landfill site by means of the Analytic Hierarchy Process - p. 407 Punctuation criteria; consistency index; random index 14/8/02 Waldemar Hachich 18

19 Do maps induce good decisions? Pizani, Silva, Bettini Aquifer vulnerability assessment in Resende basin, Brazil, with the DRASTIC method - page 413 Weights for factors; ; ranges and ratings; maps Alves, Calijuri, Lorentz, Souza, Silva, Azevedo Preliminary assessment of mineral extraction-related activities in the urban area of Ouro Preto, MG - page 389 Mapping; ; GIS 14/8/02 Waldemar Hachich 19

20 Misplaced Sakai, Tarumi Simple sensor for determination of chromium in the ground using chemiluminescence detection technique based on reaction of silicaimmobilized luminol and hydrogen peroxide - page 395 Junqueira, Palmeira Variations of leachate characteristics with time in na experimental waste cell - page 401 Almeida, Mesquita, Miranda, Barbosa Studies of channel sediments contaminated with organics and heavy metals - page 425 Almeida, Barbosa, Almeida, Mariz Geo-environmental investigation of a PCB plume contamination in a mangrove area - page /8/02 Waldemar Hachich 20

21 Lost? Marques, Calijuri, Lorentz, Souza, Azevedo, Carvalho Multi-criteria analysis for the identification of potential areas for marble and granite waste at Cachoeiro do Itapemirim, ES -page??? 14/8/02 Waldemar Hachich 21

22 Presentation available at: /8/02 Waldemar Hachich 22