1999-08-23_HYDROLOGY - M1999051 - Laserfiche WebLink

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August 1999 1: \99\2057\20571in.xis TABLE I RISK ASSESSMENT SUMMARY \� Cavity: Subsidence and Loss of Containment Initiating events and likelihood: Negligible likelihood. Under normal operations roof is stable. Provided fluid control pad remains is in place this will protect from upward solutioning. Salt roof barrier fluid pad volume is monitored. Magnitude of exposure: Medium Duration of exposure: Long - once aquifer contacted difficult to reverse Pathways: High risk due to direct pathway to aquifers Environment at risk: B Groove aquifer 1) Loss of solution control leads to thinning roof, possible collapse and connection to B Groove Subsidence - Negligible to High Hazard Groundwater - Negligible to High Hazard Soil - Negligible Surface Water - Negligible 2) Loss of structural integrity of oil shale during nahcolite leaching potential loss of cavity support Subsidence - Negligible to High Hazard Groundwater - Negligible to High Hazard Soil - Negligible Surface Water - Negligible 3) Coalescing of cavities Subsidence - Negligible to High Hazard Groundwater - Negligible to High Hazard Soil - Negligible Surface Water - Negligible 4) Collapse of Pillars Subsidence - Negligible to High Hazard Groundwater - Negligible to High Hazard Soil - Negligible Surface Water - Negligible 5) Fluid conducting fault or fracture connection between cavity and overlying lower aquifer Subsidence - Negligible Hazard Groundwater - Negligible to High Hazard Soil - Negligible Surface Water - Negligible Initiating events and likelihood: High likelihood. Evidence from Shell test suggests that oil shale will rubblize and most likely lose much structural integrity. Magnitude of exposure: Medium Duration of exposure: Long - once aquifer contacted difficult to reverse Pathways: High risk due to direct pathway to aquifers Environment at risk: B Groove aquifer Initiating events and likelihood: Very low likelihood at pilot scale. Uncontrolled lateral solutioning of lower resource bed could lead to collapse of web and connection to adjacent cavity. At the pilot scale the likelihood is low due to the wide separation on pilot cavities. Monitoring of adjacent cavities will give an early warning. Magnitude of exposure: Negligible to Medium: Cavity coalescence will not necessarily lead to instability. Duration of exposure: Negligible to Long - once cavities are coalesced cannot reverse. Pathways: High risk due to direct pathway to aquifers Environment at risk: B Groove aquifer and surface Initiating events and likelihood: Negligible likelihood. Uncontrolled lateral solution (or wall collapse) could lead to overloading of pillar and collapse. Negligible likelihood due to size of lateral pillars and cavity fluid internal supporting pressure Magnitude of exposure: Negligible to Medium Duration of exposure: Long Pathways: High risk due to direct pathway to aquifers Environment at risk: B Groove aquifer and surface Initiating events and likelihood: Negligible likelihood. No evidence of fluid conducting faults. Presence of possibly conducting fault or fracture will be detected during drilling, or by loss of fluid pad. Undetected fault would be unlikely to effect subsidence. Magnitude of exposure: Negligible since fault may be detected prior to solution operations or by real time pad monitoring Duration of exposure: Negligible Pathways: High risk due to direct pathway to aquifers Environment at risk: B Groove aquifer Negligible to high due to potential for contamination to aquifer N N Negligible consequence: While Permit Application states that oil shale matrix remains intact and resists cavern collapse (p.D -18) 'the stability ajtalyses of Agapito shows that the cavern is stable with only internal fluid pr ure, and that the only contribution of the insoluble solids in the cavity is to preve topalled'material from falling out of the walls. Negligible to high consequence due to potential for contamination o aquifer Negligible to high consequence due to potential for contaminationto aquifer Negligible consequence due to negligible magnitude and duration t f exposure Negligible risk due to negligible probability of occurrence i Negligible risk due to negligible consequence Very low risk due to very low probability of occurrence, and low magnitude of potential releases to the environment thereby minimizing potential for exposure Recommended Mitigation: Cross - borehole tomography, or some similar technique, should be used from a central pillar hole to identify solution "fingers". In addition, volume changes in the cavity will be monitored from solution inflow /outflow balance. Negligible risk due to negligible probability of occurrence Negligible risk due to negligible probability of occurrence and negligible magnitude and duration of potential releases to the environment Footnotes to Table 1: Risk Assessment Components: Potential Failure Mechanisms: All identified potential mechanisms are included, regardless of likelihood of occurrence Hazard Assessment: An assessment of "what can happen ?" ranked according to risk to the environment (see Table 2) Exposure Assessment: Assessment of the likelihood and extent of any exposure. Consequence Assessment: An evaluation of the consequence of any exposure, regardless of how likely it is. Risk Characterization: An evaluation of the overall risk to the environment of the identified failure mechanism, based on the evaluation of hazard, exposure and consequence. 1 of 5 Golder Associates 993 -2057