Risk Assessment Oil and Gas

EVOLUTION OF METHODOLOGICAL APPROACH

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3.5 EVOLUTION OF METHODOLOGICAL APPROACH
In general we have based our risk assessment approach on the model proposed in the draft guidance document for ecological risk assessment (U.S. EPA, 1996), but the very conduct of this exercise has allowed us to reexamine certain assumptions and work toward the further refinement of elements of the guidance document itself. We found it helpful to go somewhat beyond that document in tightening our definition of risk and formalizing the relationship between risk and uncertainty.
The Draft Guidance Document (U.S. EPA, 1996) proposes that a review and summary of uncertainty be the final step in a risk assessment. This invites treating analysis of the uncertainty as separable from the quantification of the risk itself, in a way that could reduce the usefulness of risk assessments to the decision process.
Note that in ecological applications it is almost inevitable that the uncertainties with respect to models and parameters will be quite high. Our example risk assessment is no exception in this regard. What is a decision maker to conclude from a careful and detailed risk assessment that, in its final section, states that there are large uncertainties in the analysis just presented?
• Ignore the uncertainty statement and accept the results of the risk characterization at face value?
• Dismiss the risk assessment “because it is too uncertain”?
• Ask the analysts to provide a “best estimate” of the risk, and accept that characterization at face value?
• Ask the analysts to provide a “worst-case estimate” of the risk, and then accept that characterization at face value?
All these options have a ring of plausibility, and experienced practitioners are doubtless aware of past instances where each came into play. But each leads to quite different implicit or explicit characterizations of the risk, so they cannot all be correct. This would seem to leave too much discretionary latitude for the influence of subjective elements in the conduct and interpretation of an ecological risk assessment.
It would be helpful if risk assessment practice removed this potential source of ambiguity

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by integrating the “uncertainty analysis” into the risk characterization itself. In this chapter we explain how we approached a rigorous, quantitative integration of uncertainty analysis in our risk characterization. This had later implications for our understanding of risk tolerance and uncertainty tolerance as they bear on risk management decisions that may be made as the result of a risk assessment. This also has implications for the way we propose to quantify the value of NSS
data in our risk assessment, as discussed in section 2.3.

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