Laserfiche WebLink
30 RISK ASSESSMENT /MANAGEMENT <br />results in a low hazard for sediment <br />release. <br />Exposure Assessment <br />b. Possible failure mechanisms <br />Sediment release due to: <br />inadequate sedimentation capacity <br />design, unprotected areas - no <br />sediment control facilities <br />constructed (human error), failure <br />of sediment structures: <br />under normal design flood <br />(design /construction error), <br />under runoff event exceeding <br />design flood. <br />c. Possible initiating events <br />Natural events: <br />high precipitation event. <br />Site specific events: <br />bare surfaces with no erosion <br />control or sediment collection. <br />Design, construction or maintenance <br />events: <br />inadequate capacity, poor <br />construction, sediment dam filling <br />up. <br />d. Potential for release <br />During the construction phase it is <br />expected that the potential of release <br />will be low, assuming that good <br />construction control is practiced. <br />e. Magnitude of release <br />Low because of construction <br />practices proposed <br />f. Duration of release <br />Very short to days depending on: <br />precipitation event, <br />quality of construction <br />supervision and facility <br />inspection. <br />g. Pathways <br />Overland and small creeks to nearby <br />wetlands and adjacent river. <br />h. Ecosystems at risk <br />Forested drainages in the mine area to <br />aquatic ecosystems in surrounding creeks <br />and wetland, or if major event, to nearby <br />river. <br />i. Exposure Description and Qualitative <br />Assessment <br />Construction will take place in the close <br />proximity of water courses and any release <br />of sediment could be directly discharged <br />to the streams and will impact aquatic <br />ecosystems. There is a very low <br />probability of a sediment release due to a <br />significant precipitation event occurring <br />coupled with poor construction practices <br />during the short construction period. <br />Therefore, due to low potential of release <br />it is not expected that the concentration <br />of sediment will exceed 1,000 mg /l. <br />According to Table 2 there will be a low <br />exposure. <br />Consequence Assessment <br />j. Consequence Description and Qualitative <br />Assessment <br />Possible consequences are: <br />slight accretion of streambeds <br />causing spawning habitat degradation <br />and slight ( <5 %) reduction in fish <br />productivity <br />Based on Table 3 the consequences are <br />therefore very low. <br />Risk Characterization <br />k. Risk Description and Qualitative <br />Characterization <br />The low hazard posed by the sediments <br />combined with a low exposure will lead to <br />very low consequences to the aquatic <br />ecosystem. The overall risk therefore is <br />very low (row 2 of Table 4). <br />Protect Specific Considerations <br />1. Management /Control Systems in Final Design <br />Phasing of project construction to prevent <br />unprotected soil surfaces, construction of <br />sediment collection structures. <br />m. Mitigation /Compensation and Contingency <br />Careful scheduling and supervision during <br />construction, construct sediment <br />collection structures first, remove <br />sediment if structures fill up, quickly <br />stabilize erodible surfaces and slopes. <br />n. Recommendations <br />Practice good construction scheduling and <br />control to eliminate areas unprotected by <br />sediment or runoff control. <br />A.2 Failure Scenario 2 <br />MINE <br />Operations (all phases) <br />through Reclamation <br />System /activity: Water management, control and <br />treatment facilities <br />Failure mode: ARfl: release to drainages <br />Area: <br />Phase: <br />Hazard Assessment <br />a. Hazard Description and Qualitative <br />Assessment <br />The hazard is acidic water in ARD. Due to <br />the potential for low pH ( <3.8) in ARD, <br />the hazard is medium to high according to <br />Table 2. <br />Exposure Assessment <br />b. Possible failure mechanisms <br />Release of ARD or contaminated water from <br />water management, control and treatment <br />facilities consisting of drainage and <br />runoff from waste rock stockpile and open <br />pit, to drainage collection, to holding <br />pond, to water treatment plant, to <br />constructed wetland, finally release to <br />creek. Water treatment takes place in <br />plant, polishing in wetlands and treated <br />water is released to creek. Releases can <br />be due to: <br />ditch failure, holding pond failure, <br />water treatment not adequate, <br />wetland filter not functioning or <br />damaged, seepage to groundwater. <br />c. Possible initiating events <br />Natural events: <br />high precipitation, earthquake. <br />Site specific events: <br />waste rock stockpile neutralization <br />inadequate, collection ditch break <br />or collapse, pipe break, overtopping <br />or breach in holding pond, <br />embankment failure, water treatment <br />plant failure, wetland failure. <br />Design, construction or maintenance <br />failure: <br />ditch undersized, water treatment <br />plant capacity low, system doesn't <br />work, holding pond inadequate, <br />construction poor, human error, <br />vandalism, wetland inadequate or <br />fails, pit failure, slope failure of <br />waste rock stockpile. <br />d. Potential for release <br />The relative risk of release is very low <br />to low due to the proposed design of the <br />