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2014-03-07_REVISION - M1988112 (3)
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2014-03-07_REVISION - M1988112 (3)
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Last modified
8/24/2016 5:40:49 PM
Creation date
3/11/2014 1:22:25 PM
Metadata
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Template:
DRMS Permit Index
Permit No
M1988112
IBM Index Class Name
REVISION
Doc Date
3/7/2014
Doc Name
Tailing dam report TR33
From
DRMS
To
McClure & Eggleston, LLC
Type & Sequence
TR33
Email Name
WHE
GRM
Media Type
D
Archive
No
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to the dam, the higher the gradients will be acting along an internally developing erosion <br />feature and more likely that the erosion "pipe" will breach through to the ponded area. <br />5. If breach occurs during or following a large flood event, a large volume of saturated <br />tailing may be mobilized, as the breach would occur near the maximum section of the <br />dam. <br />Based on the positive and adverse factors listed, PFM -2 was assigned to a preliminary screening <br />Category of II. <br />PFM -2 was further evaluated by semi - quantitative risk analysis. Table 7 summarizes the nodes <br />on the event tree leading to failure, and the estimated range of probabilities associated with each <br />node. The probability range was bounded by the worst -case (major, assume 500 -year recurrence <br />interval) flood loading condition and the normal operating (static) pool conditions. The <br />probabilities for these triggering events are assumed to be 0.002 for a major flood event that <br />impounds water to 1 for the normal operating condition. The node probability for initiation of a <br />piping / internal erosion potential failure mode was estimated from empirical data that are <br />summarized in the U.S. Bureau of Reclamation Best Practices Manual (USBR, 2012). For <br />internal erosion or piping involving a pipe penetration through a dam, the statistical initiating <br />probability ranges from 4 x 10-4 to 1.5 X 10 (USBR, Ch. 26, Tables 26 -19). Subsequent nodes <br />on the event tree were assigned a descriptive probability and value as summarized on Table 4. <br />The consequences of this potential failure mode are believed to be significant if the breach <br />occurs when the impoundment is storing a significant amount of floodwater, because the stored <br />water and saturated tailing would be released through a breach that likely occurs through the <br />maximum section of the dam. Consequence categories (defined on Table 5) were assigned as a <br />range from 4 for breaches associated with piping that occurs during or following a major flood <br />event and impoundment of a flood pool, to 1 for an event that occurs under the normal operating <br />pool, as the volume of water and tailing released would likely be much lower under the normal <br />conditions. Similar to the discussion under PFM -1 (Section 5.3.1), the assignment of Category 4 <br />is considered conservative for this tailing storage facility as compared to a water retention dam. <br />The results are graphed on Figure 19 presented at the end of this section. These results indicate <br />that risks are well below established risk guidelines. This is primarily due to the very low <br />probability (likelihood) of this potential failure mode developing in a tailing impoundment, <br />which does not normally contain a large free water surface. <br />San Luis Project Miller Geotechnical Consultants <br />Tailing Dam Data Report 47 February 2014 <br />
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