Limiting Potential Failures - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 108

potential impacts of such a failure are considered. Thus, the second
classification scheme is a version of a risk assessment, according to the standard
definition. The committee concludes that using different hazard classification
methodologies for embankments and basins is inappropriate. Therefore, the
committee recommends that: (1) MSHA and OSM review activities related
to risk assessment for existing impoundments (including both
embankments and basins) to ensure that they are consistent and that they
distinguish appropriately between hazard and consequence assessment in
the methodologies adopted; and (2) MSHA and OSM establish a single,
consistent system, which should be used to assign both embankments and
basins to risk categories. The ranking should be based on the combination of
hazards and consequences, such as loss of life, cost, and environmental impact.
Proposed new impoundments should also be assigned to risk categories, based
on a combination of hazards and consequences, as was suggested for existing
impoundments. The committee believes that this can be accomplished using
qualitative risk assessment techniques.
A consistent risk assessment system would allow decisions on
impoundments to be based on their relative risks. The committee also
recommends that MSHA and OSM oversee a thorough assessment of
potential mitigation measures for those impoundments that fall in the
highest risk category and should determine which mitigation measures
should be applied to reduce this risk to an acceptable level.
Geotechnical engineering is used in the design and construction of waste
impoundments. Given the inevitable uncertainties in site characterization,
knowledge of material properties, and the need for use of idealized models to
describe both physical and human behavior, risk is inherent. Therefore,
managing risk is an essential consideration (Morgenstern, 1995).
Fortunately, powerful methods of risk management have evolved. The
observational method is the first line of defense in managing risk in the face of
identified uncertainties. This method involves the use of observation to review
performance and refine subsequent design, construction, or operation. Peck
(1969) identified the elements of the observational method as follows:
• Site exploration to establish (at a minimum) the general nature, pattern, and
properties of subsurface materials;
• Assessment of the most probable conditions and most unfavorable
deviations from these conditions;
• Establishment of the design based on a working hypothesis of anticipated
behavior under the most probable conditions;