Limiting Potential Failures - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 97

downstream-type dams (S.Vick, consultant, personal communication, 2001).
The preponderance of failures occurred during active operation of the
impoundment with surface water on the tailings deposit. By contrast, only a few
failures occurred for inactive impoundments subsequent to water removal upon
abandonment. These were caused mostly by overtopping attributable to
inadequate post-closure spillways (S.Vick, consultant, personal communication,
2001). Slope instability and earthquake effects dominate failure causes for
upstream-type dams. However, seepage, overtopping, and foundation instability
are other important considerations.
In recognition of the need to improve the design and construction of
tailings dams, a number of guides to good practice have been prepared (e.g.,
ICOLD, 1989b, 1994, 1995a, b, 1996). Frequency of failure has declined during
the past decade, which has been attributed to more rigorous engineering and
regulations (Cambridge, 2001).
The failure at Buffalo Creek ( Sidebar 1.3 ) was a pivotal experience in U.S.
practice with regard to the need to improve design and regulation of coal waste
embankments. Since MSHA was established, there have been no incidents of
embankment instability, other than overtopping of starter dams early in
construction. Nevertheless, it is prudent not to be complacent.
Worldwide experience with upstream-constructed tailings dams indicates
that many, particularly those with wide subaerial beaches, have performed well
in significant seismic events, when subjected to intense rainfall, and sometimes
in spite of questionable operating practices. Davies and Martin (2000) outline
the requirements for construction of a safe upstream tailings dam. Unless
alternative processing and disposal methods are adopted on a large scale
( Chapter 7 ), embankments in the future will likely be higher than in the past.
Given this challenge, and given the fact that some modern dams in other
extractive industries have failed, the committee concludes that it is essential
that MSHA and OSM stay current by ensuring that design criteria reflect the
latest experience from all segments of the mining industry. Although the
committee has not identified any deficiencies, it is a matter of due diligence that
MSHA, OSM, and industry employ the best available current technology. The
committee recommends that MSHA and OSM continue to adopt and
promote the best available technology and practices with regard to the site
evaluation, design, construction, and operation of impoundments. For
example, MSHA and OSM should commission periodic reviews of existing
technical procedures and practices, with particular attention to the basin. Results
of the reviews should be disseminated to industry. Based on the outcome,
MSHA and OSM may have to revise guidelines to establish minimum
expectations and levels