7.7 Do Not Forget to Define Performance, Success and Failure Criteria
97
example, experts convene to look only at “credible failures”, without defining what
“credible” means; they neglect to properly define the system (see Chap. 8) and use
ill-conditioned binning exercises (FMEA, PIGs) with arbitrarily indexes and related
values. Any “safe dam statement” based on a blatantly censored and biased scenario
is obviously devoid of any meaning and unethical.
Part of this effort also goes in using a well-defined and clear glossary (https://www.
riskope.com/knowledge-centre/tool-box/glossary/). A clear example comes from a
relatively recent event in the Solomon Islands (https://www.riskope.com/2016/04/
20/solomon-islands-gold-mine-contaminated-water-spill-disaster/). In the case of
Solomon Islands’ Gold Ridge dam, arsenic, cyanide and reportedly selenium and
mercury are present in the tailings. Excess water accumulated behind the dam. The
Gold Ridge dam recently overflowed uncontrollably after heavy rain. In 2014 and
2015 the catastrophic flooding brought by Tropical Cyclone ITA (http://www.unocha.
org/top-stories/all-stories/solomon-islands-worst-flooding-history) and a close call
raised alarm at various levels. 8000 people live downstream. Tens of millions of
litres of contaminated water reportedly escaped from the dam via its weir.
1 That
event altered the life of the 8000 downstream residents. Indeed, health authorities in
the Solomon Islands released a statement advising downstream communities not to
use rivers for drinking, cooking or bathing.
The environmentalist point of view was obviously that the dam did not protect
the environment from the chemical contained in the tailings reservoir, therefore the
tailings dam has “failed” because of the weir. For the dam engineer the weir and
its associated spillway relieved the pressure and reduced the likelihood of a dam
collapse. The system worked perfectly! For dam engineers a dam failure is what we
have seen at Samarco or Mount Polley (see respectively Sects. 2.1 and 2.2). The weir
functioning was a success from the dam engineer point of view.
In the case of the Solomon Islands’ Gold Ridge dam it is obvious that a performance/success criteria should have been established for the level of contaminants
under normal storage conditions such that any discharged water through the weir
would meet “acceptable” levels. However, could a failure criteria be the exceedance
of water quality objectives at a specified point, i.e., just before the nearest drinking
water source downstream?
This leads to the question: what are the criteria for defining a tailings dam structural
failure?
For example has the dam “failed” if:
1. It continues to contain all material despite being damaged?
2. It contains spills, but all solid and water impacts are limited to
a. within property limits?
b. within an acceptable inundation or exceedance areas?
1 A weir is a structure built across a water course or on top of a dam allowing water to flow steadily
over its top. Weirs built on top (at the crest) of a dam are there to allow excess water accumulated
behind the dam to run away. That is, of course, without damaging the dam by uncontrolled overtopping.
97
example, experts convene to look only at “credible failures”, without defining what
“credible” means; they neglect to properly define the system (see Chap. 8) and use
ill-conditioned binning exercises (FMEA, PIGs) with arbitrarily indexes and related
values. Any “safe dam statement” based on a blatantly censored and biased scenario
is obviously devoid of any meaning and unethical.
Part of this effort also goes in using a well-defined and clear glossary (https://www.
riskope.com/knowledge-centre/tool-box/glossary/). A clear example comes from a
relatively recent event in the Solomon Islands (https://www.riskope.com/2016/04/
20/solomon-islands-gold-mine-contaminated-water-spill-disaster/). In the case of
Solomon Islands’ Gold Ridge dam, arsenic, cyanide and reportedly selenium and
mercury are present in the tailings. Excess water accumulated behind the dam. The
Gold Ridge dam recently overflowed uncontrollably after heavy rain. In 2014 and
2015 the catastrophic flooding brought by Tropical Cyclone ITA (http://www.unocha.
org/top-stories/all-stories/solomon-islands-worst-flooding-history) and a close call
raised alarm at various levels. 8000 people live downstream. Tens of millions of
litres of contaminated water reportedly escaped from the dam via its weir.
1 That
event altered the life of the 8000 downstream residents. Indeed, health authorities in
the Solomon Islands released a statement advising downstream communities not to
use rivers for drinking, cooking or bathing.
The environmentalist point of view was obviously that the dam did not protect
the environment from the chemical contained in the tailings reservoir, therefore the
tailings dam has “failed” because of the weir. For the dam engineer the weir and
its associated spillway relieved the pressure and reduced the likelihood of a dam
collapse. The system worked perfectly! For dam engineers a dam failure is what we
have seen at Samarco or Mount Polley (see respectively Sects. 2.1 and 2.2). The weir
functioning was a success from the dam engineer point of view.
In the case of the Solomon Islands’ Gold Ridge dam it is obvious that a performance/success criteria should have been established for the level of contaminants
under normal storage conditions such that any discharged water through the weir
would meet “acceptable” levels. However, could a failure criteria be the exceedance
of water quality objectives at a specified point, i.e., just before the nearest drinking
water source downstream?
This leads to the question: what are the criteria for defining a tailings dam structural
failure?
For example has the dam “failed” if:
1. It continues to contain all material despite being damaged?
2. It contains spills, but all solid and water impacts are limited to
a. within property limits?
b. within an acceptable inundation or exceedance areas?
1 A weir is a structure built across a water course or on top of a dam allowing water to flow steadily
over its top. Weirs built on top (at the crest) of a dam are there to allow excess water accumulated
behind the dam to run away. That is, of course, without damaging the dam by uncontrolled overtopping.