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Lecture.Packet.9.risk - CHAPTER 5 QUANTITATIVE RISK...

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CEE 440 © 2011 Charles J. Werth, University of Illinois at Urbana-Champaign. All rights reserved. 1 CHAPTER 5. QUANTITATIVE RISK ASSESSMENT (from LaGrega et al., p837-885) My teaching goals for this chapter are for you: 1) to learn what information is required to perform a risk assessment 2) to learn how to calculate the risk associated with a given chemical concentration 3) to appreciate the uncertainty associated with risk assessment RISK: probability of suffering harm or loss If the level of risk can be quantified we can calculate it as follows: (5.1) risk = (probability) * (severity of consequence)
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CEE 440 © 2011 Charles J. Werth, University of Illinois at Urbana-Champaign. All rights reserved. 2 Example: If Bob smashes his finger while loading boxes he loses 5 days of work Severity of Consequence = 5 days The likelihood of Bob smashing his finger is 10% Probability = 0.1 Hence, Risk = Risk must be divided into background and incremental risk: Background risk: occurs in the absence of a particular source of risk Incremental risk: caused by the source of risk 0.1 * 5 days = .5 person days lost Total risk: Background + Incremental
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CEE 440 © 2011 Charles J. Werth, University of Illinois at Urbana-Champaign. All rights reserved. 3 Example: U.S. Background Cancer risk = 0.25 Excess lifetime cancer risk deemed acceptable by the US EPA at Superfund sites = 1x10 -6 Total risk = 0.250001 Death/Cancer Risks Annual risk Uncertainty Motor Vehicle Accident 0.00024 10% Home Accidents 0.00011 10% Cigarette Smoking (pack/day) 0.0036 Factor of 3 Peanut butter (4 tsp./day) 8x10 -6 Factor of 3 Lifetime risk Uncertainty Drinking Water with EPA limit of TCE 1x10 -6 Factor of 10 to 100
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CEE 440 © 2011 Charles J. Werth, University of Illinois at Urbana-Champaign. All rights reserved. 4 Risk Assessments can affect: 1) 2) 3) 4) 5) waste treatment/disposal options remediation of contaminated site How clean is clean? What remediation technology do we use? How do we protect the people doing the cleaning? minimization of waste generation placement of new treatment facilities developing new products
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CEE 440 © 2011 Charles J. Werth, University of Illinois at Urbana-Champaign. All rights reserved. 5 Four Steps to Risk Assessment 1) 2) 3) 4) Hazard Identification: which chemicals important Exposure Assessment: where do chemicals go, who might be exposed and how Toxicology Assessment: determine numerical indices of toxicology for computing risk Risk Characterization: estimate the magnitude of risk, and the uncertainty of the estimate
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CEE 440 © 2011 Charles J. Werth, University of Illinois at Urbana-Champaign. All rights reserved. 6 5.1 HAZARD IDENTIFICATION The potential hazard a chemical represents can be evaluated based on concentration and "danger" One approach is outlined below: 1) Sort the contaminants by medium (i.e. soil, groundwater, etc.) 2) Tabulate mean and range of concentration values of each chemical at site 3) Identify reference doses for non-carcinogens and slope factors for carcinogens for each potential exposure route 4) Determine the toxicity scores for each chemical in each media: For non-carcinogens: TS = C max /RfD (5.2) where TS = toxicity score C max = maximum concentration RfD = chronic reference dose
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