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Descriptors for Qualitative Risk Characterization. A consistent set of descriptors are developed for the risk characterization based on a combination of those used for hazard, exposure, and consequence. The descriptors for the risk characterization are used to compare the relative risks of the failure modes. Table 4 presents the basis for the final description of the risk characterization. The risk characterization is determined by considering the contributions from the hazard, exposure and consequence assessments. Consider the first row in Table 4: if the hazard is negligible to high, leading to a negligible to very low exposure, resulting in a negligible consequence, then the risk associated with such a failure mode will be negligible. A site specific example of such a failure mode is cyanide usage in the mill: the hazard is high because of the concentrated form of the cyanide, however, due to the precautions used in the mill, as well as the potential limited volume of release and long release pathway, the potential exposure of the aquatic ecosystem due to the presence of cyanide in the mill is negligible. Because exposure is negligible, the consequences are negligible. The overall risk characterization for cyanide release from the mill is, therefore, negligible. A review of Table 4 shows that although the descriptor used for hazard assessment varies over a wide range, those for the exposure and consequence assessments vary over a narrower range. For example, in the first row: for a risk to be characterized as negligible the consequence must be negligible, and the exposure could be negligible to very low. However, the hazard can be negligible to high because the potential, magnitude and duration of release, as well as release pathway can reduce the high hazard in a negligible to very low exposure. DISCUSSION OF RESULTS The qualitative risk assessment for the example project considered 36 individual failure modes. These 36 failure modes were a subset of the potential release mechanisms identified in Table 1. All failure modes were evaluated as the two examples shown in Appendix A. It was concluded that of the 36 failure modes the following may result in higher risks: • sediment releases during construction and operations in the Mine Area; • ARD releases during operations, reclamation and closure in the Mine Area; and, • tailings release from the three tailings impoundments during operations. These failure mechanisms also consist of more complex systems and have higher uncertainties associated with the respective parameters controlling the potential failures and releases. For example, ARD can only be discharged during operations if failures occur in the interception, containment of runoff, and the subsequent treatment and discharge of the water. This system of controls is complex and contains many parameters that can impact the reliability of clean water discharge. This risk assessment was performed to decide if the project design was successful in reducing risks, and to determine if residual or unacceptable risks exist. It was concluded from 2Area: Phase: System /activity: Failure mode: QUALITATIVE ENVIRONMENTAL RISK ASSESSMENT FOR MINE DEVELOPMENT 29 the results of this study that the risk associated with a majority of the failure modes could be characterized as negligible. The highest risks were characterized as very low to low and this is the case for only 10 percent of the failure modes. The risk assessment determined that the management and control systems built into the design could be successful in reducing risks when implemented at the proposed mine project. CONCLUSIONS Qualitative risk assessment can be used to evaluate the environmental impacts of a project. It can be used to document the evaluation and decision - making process, express the relative risk and select those failure modes or release mechanisms which pose the biggest risk. A four step process is proposed. Five descriptors are used to describe the relative level of hazard, exposure, consequence and risk. Development of these descriptors is a major part of a qualitative risk assessment. They must be developed on a site specific basis. The application of qualitative environmental risk assessment is demonstrated for the proposed development of a mine in an environmentally sensitive setting. It can be concluded that: • a qualitative environmental risk assessment can be successfully applied to mining projects; • site - specific descriptors can be developed to describe the relative hazards, exposures, consequences and finally risk; and, • failure mechanisms posing the highest risks can be selected for possible quantitative risk assessments. REFERENCES Kaplan, S., and B.J. Garrick (1981) On the quantitative definition of risk, Risk Analysis, Vol. 1, No. 1, pp 11 -27. Smith, D.A. (1987). Mining America, The Industry and the Environment, 1800 -1980. University Press of Kansas, 210 pp. Van Zyl, D. (1987) Health risk assessment and geotechnical perspective. In Geotechnical Practice for Waste Disposal. Richard D. Woods (Ed.) ASCE, pp 812 -831. APPENDIX A EXAMPLE QUALITATIVE RISK ASSESSMENTS FOR TWO INDIVIDUAL FAILURE SCENARIOS A.1 Failure Scenario 1 MINE Construction Construction of onsite facilities Sediment release to local drainages Hazard Assessment a. Hazard Description and Qualitative Assessment Hazards are sediment and possibly heavy metals. Only small surface areas will be exposed during construction. It is expected that at most 2,0000 of sediment can be released. Based on Table 2 this