3
stormwater from eroding a reclamation cover and exposing
harmful materials, or an electronic monitoring array needs
to remain operational to capture incremental slope move-
ment which may lead to more consequential stability prob-
lems. A common theme in the analyses from the Mount
Polley (2015), Fundão (2016), and Brumadinho (2019)
tailings dam failures was that multiple, inter-dependent
system breakdowns and conditions led to eventual dam col-
lapse. Warning signs of system performance irregularities at
these sites were evident, that if addressed, may have averted
a complete system failure.
To further illustrate the point about long-term integ-
rity, after a tailings facility is closed it still must function
as a stable repository for tailings, however, the operating
requirements applied during mining to ensure a safe facility
may be less relevant after closure. The risk drivers present
during operations (e.g., water holding capacity, liquefac-
tion potential, seepage) may no longer be as critical to facil-
ity stability, replaced by closure related concerns such as
cap integrity, underdrain performance, or stormwater rout-
ing. While likely different, the potential failure modes and
consequences from a tailings facility’s non-performance
after closure still exist in some form and it may continue
to be a threat to human health and the environment. To
dismiss the importance of tailings impoundment integrity
based on a facility coming to the end of its operating life is
ill-advised, as this phase will be replaced by a state of func-
tional life that can extend in perpetuity.
The US Forest Service recently conducted a risk assess-
ment of a mine facility on National Forest System lands
using the Failure Modes and Effects Analysis (FMEA)
methodology. Mine features include a tailings storage facil-
ity, waste rock dumps, mine portals and shafts, a water
treatment facility, mill and administrative buildings, and
related mine infrastructure. The exercise focused strictly on
the post-closure time frame and did not limit the analysis
period to a specific future end date. The outcome of the
FMEA (unpublished) yielded interesting results. The exer-
cise identified that the risk drivers were not the extreme
events such as the Probable Maximum Flood or Maximum
Credible Earthquake, rather it was the smaller, chronic
events like seasonal storms that impacted ancillary struc-
tures and facilities such as diversion ditches, or it was the
failure of engineered systems such as underdrains and elec-
tronic monitoring stations that posed the greatest risk over
time.
The FMEA highlighted recurrent natural processes
(e.g., wildfire, storm runoff, vegetation succession, slope
creep, freeze-thaw cycling) were the principal drivers
behind eventual reclamation failure over an extended time
horizon. This is due to the incremental degradation of indi-
vidual component performance leading to more acute non-
performance and eventual system-wide breakdown. Not
surprisingly, simple periodic care and maintenance such as
cleaning diversion ditches, repairing rills and gullies, and
replacing electronic monitoring systems can reduce risk lev-
els and help avert eventual widespread facility failure. The
FMEA participants concluded that the natural processes
that drove risk would always be present and would slowly
degrade the reclaimed facilities over time. The only solution
to maintaining system performance was a commitment to
site care and maintenance, well, forever.
COST CONSIDERATIONS
Water treatment is often the most expensive ongoing post-
closure activity at a reclaimed mine site and can easily cost
millions of dollars per year, but even relatively simple, low-
cost care and maintenance activities such as site inspec-
tions, data retrieval, cleaning diversion ditches or minor
site regrading, can run tens of thousands of dollars per
year depending on site conditions. Often a third-party is
retained to oversee the annual care and maintenance work
adding an additional layer of cost. So, even without a water
treatment component, a site may require tens to hundreds
of thousands of dollars in annual care and maintenance to
ensure reclaimed facilities remain stable and function as
intended during the post-closure period.
Financing such annual costs when they occur would
likely be unsustainable for any length of time. Alternatively,
taking advantage of the time value of money to create a
trust account to finance the recurring out-year cost require-
ments can ensure funding will be available for ongoing
future care and maintenance. When faced with an open-
ended time frame, an interest-bearing account is likely the
most cost-effective means to fund LTCM.
A simple example can illustrate the effectiveness of this
concept. Assume an annual care and maintenance require-
ment of $50K USD and a discount rate of 3%. Running the
calculation to a future date when the Present Value of the
out-year annual expenditure drops below $1 yields a Net
Present Value (NPV) of $1.7M. The point in time when
this occurs is approximately 400 years in the future and is
effectively the same as running the calculation as a perpetual
fund calculation. Conversely, if one simply pays the $50K
per year, adjusts for inflation over this same time period,
the total cash outflow would be $6.6B. Increase the annual
care and maintenance to $500K, the NPV is $17.5M while
the non-discounted approach yields $322.7B. A one-time
payment of $17.5M is certainly a manageable sum for most
stormwater from eroding a reclamation cover and exposing
harmful materials, or an electronic monitoring array needs
to remain operational to capture incremental slope move-
ment which may lead to more consequential stability prob-
lems. A common theme in the analyses from the Mount
Polley (2015), Fundão (2016), and Brumadinho (2019)
tailings dam failures was that multiple, inter-dependent
system breakdowns and conditions led to eventual dam col-
lapse. Warning signs of system performance irregularities at
these sites were evident, that if addressed, may have averted
a complete system failure.
To further illustrate the point about long-term integ-
rity, after a tailings facility is closed it still must function
as a stable repository for tailings, however, the operating
requirements applied during mining to ensure a safe facility
may be less relevant after closure. The risk drivers present
during operations (e.g., water holding capacity, liquefac-
tion potential, seepage) may no longer be as critical to facil-
ity stability, replaced by closure related concerns such as
cap integrity, underdrain performance, or stormwater rout-
ing. While likely different, the potential failure modes and
consequences from a tailings facility’s non-performance
after closure still exist in some form and it may continue
to be a threat to human health and the environment. To
dismiss the importance of tailings impoundment integrity
based on a facility coming to the end of its operating life is
ill-advised, as this phase will be replaced by a state of func-
tional life that can extend in perpetuity.
The US Forest Service recently conducted a risk assess-
ment of a mine facility on National Forest System lands
using the Failure Modes and Effects Analysis (FMEA)
methodology. Mine features include a tailings storage facil-
ity, waste rock dumps, mine portals and shafts, a water
treatment facility, mill and administrative buildings, and
related mine infrastructure. The exercise focused strictly on
the post-closure time frame and did not limit the analysis
period to a specific future end date. The outcome of the
FMEA (unpublished) yielded interesting results. The exer-
cise identified that the risk drivers were not the extreme
events such as the Probable Maximum Flood or Maximum
Credible Earthquake, rather it was the smaller, chronic
events like seasonal storms that impacted ancillary struc-
tures and facilities such as diversion ditches, or it was the
failure of engineered systems such as underdrains and elec-
tronic monitoring stations that posed the greatest risk over
time.
The FMEA highlighted recurrent natural processes
(e.g., wildfire, storm runoff, vegetation succession, slope
creep, freeze-thaw cycling) were the principal drivers
behind eventual reclamation failure over an extended time
horizon. This is due to the incremental degradation of indi-
vidual component performance leading to more acute non-
performance and eventual system-wide breakdown. Not
surprisingly, simple periodic care and maintenance such as
cleaning diversion ditches, repairing rills and gullies, and
replacing electronic monitoring systems can reduce risk lev-
els and help avert eventual widespread facility failure. The
FMEA participants concluded that the natural processes
that drove risk would always be present and would slowly
degrade the reclaimed facilities over time. The only solution
to maintaining system performance was a commitment to
site care and maintenance, well, forever.
COST CONSIDERATIONS
Water treatment is often the most expensive ongoing post-
closure activity at a reclaimed mine site and can easily cost
millions of dollars per year, but even relatively simple, low-
cost care and maintenance activities such as site inspec-
tions, data retrieval, cleaning diversion ditches or minor
site regrading, can run tens of thousands of dollars per
year depending on site conditions. Often a third-party is
retained to oversee the annual care and maintenance work
adding an additional layer of cost. So, even without a water
treatment component, a site may require tens to hundreds
of thousands of dollars in annual care and maintenance to
ensure reclaimed facilities remain stable and function as
intended during the post-closure period.
Financing such annual costs when they occur would
likely be unsustainable for any length of time. Alternatively,
taking advantage of the time value of money to create a
trust account to finance the recurring out-year cost require-
ments can ensure funding will be available for ongoing
future care and maintenance. When faced with an open-
ended time frame, an interest-bearing account is likely the
most cost-effective means to fund LTCM.
A simple example can illustrate the effectiveness of this
concept. Assume an annual care and maintenance require-
ment of $50K USD and a discount rate of 3%. Running the
calculation to a future date when the Present Value of the
out-year annual expenditure drops below $1 yields a Net
Present Value (NPV) of $1.7M. The point in time when
this occurs is approximately 400 years in the future and is
effectively the same as running the calculation as a perpetual
fund calculation. Conversely, if one simply pays the $50K
per year, adjusts for inflation over this same time period,
the total cash outflow would be $6.6B. Increase the annual
care and maintenance to $500K, the NPV is $17.5M while
the non-discounted approach yields $322.7B. A one-time
payment of $17.5M is certainly a manageable sum for most