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August 19, 1999 <br />MEMORANDUM <br />- 4 - 993 - 2057 <br />measurable impacts (i.e. moving from the negligible to very low rankings) were identified. <br />Specific monitoring and mitigation actions to reduce risk are addressed in subsequent <br />sections. <br />Table 1 presents the results of the qualitative hazard assessment (see second column). For <br />example, cavity collapse or roof failure mechanisms have the potential for high hazard <br />impacts for subsidence and groundwater contamination, but represent negligible hazards for <br />soil and surface water contamination. The exposure assessment as presented below <br />discusses how likely these hazards are to occur and other exposure issues. <br />6.0 EXPOSURE ASSESSMENT <br />The exposure assessment addresses the following key issues related to the potential hazards <br />identified above: <br />• Initiating events and likelihood <br />• Magnitude of exposure <br />• Duration of exposure <br />• Pathways <br />• Environment at risk <br />The exposure assessment is presented in column 3 on Table 1. As noted on Table 1 each <br />of the criteria presented above is qualitatively addressed for the potential hazards. <br />7.0 CONSEQUENCE ASSESSMENT <br />The consequence assessment reviews the elements of the exposure assessment and evaluates <br />the potential impacts or damages to the environment because of exposure of contaminants <br />or physical hazards. Note that the approach taken here has been to assess consequence <br />without regard to likelihood of a particular failure. Thus, a mechanism may have a high <br />consequence if it does happen although its likelihood may be negligible. In this case, the <br />overall risk will be negligible. The results of the consequence assessment are summarized <br />as one or range of the following risk descriptors: <br />• Negligible <br />• Very low <br />• Low <br />• Medium <br />\ \ GAI DEN1\ PROJECTS \WP \99 \205'T2057TM1.DOC Golder Associates <br />