WIR SCHAFFEN WISSEN – HEUTE FÜR MORGEN
Risk Assessment of Coal Combustion
Residue Disposal Impoundment Closure
Rebecca Lordan :: Guest PhD Student :: Paul Scherrer Institut
International Disaster and Risk Conference, Davos Switzerland, August 2016
• Combine CCR and Tailings facility data into one database
Assumption based on 3 major shared attributes:
1. Materials share property: non-Newtonian fluids –
affects stability, destructive power, etc.
2. Wastes not economically valuable to operating firm
3. Management/engineering practices and problems
similar: stabilizing water balance, closure, etc.
• Analyze active facility risks to help assess long-term risks
• Consider the influence of Social-Technical Nexus on risks
What information are closure & liability policies decisions
How do closure & liability policy decisions affect safety?
Coal Combustion Residue: where is it?
• Mapping of coal plants by number of surface
• total = 952
• average number per site = 2-3
• total sites = 383
5-14 impoundments Lordan et al., 2016
• Considering U.S. data only
• Data come from tailings and
• 185 incidents and counting...
55 CCR incidents
130 tailings incidents
Results: Active Site Incidents
Type of Release/Incident
1940 1950 1960 1970 1980 1990 2000 2010
Volume to Height Ratio (million liters/ meters)
Type of Release/Incident
Mapping active incidents to closure risk
• In so much as closure mitigates active risks, it’s only partially effective…
must also have endurance and cope with long-term hazards!
• Must map the actions of closure to risks:
For example, for dry closure, the materials are “de-watered”:
Improves stability, reduces risk of soil liquefaction, can make facility
less sensitive to weather cycles (e.g. freezing, thawing…).
• Must consider long-term risks: physical, chemical, biological, and social
• Can closure provide endurance and cope with long-term hazards?
• Industry Argues: “Walk-Away” Closure (i.e. no maintenance or monitoring)
• Facilities in process of being closed provide data that shows “walk-away”
closure not possible
Continuing contamination of soil and water
Cover systems not behaving as anticipated
We still want to close these facilities!
• Reduce risks of
(e.g. dam breaches)
• Reduce exposure
of people to
• Stabilizes land for remediation and alternative future uses
General Closure Methods
Clean Closure Dry Closure Wet Closure
Relationship between costs and risks not necessarily inverse or specific
to one type of closure…. dependent on many factors
What do the costs and risks depend on?
Based on our research, we created this word cloud to highlight some of the
key factors in assessing risk and costs for closure.
Cover Closure Methods
Unlined Cap in Place Closure Lined Cap in Place Closure
• The most common cause of dam failure caused by water balance
(e.g. structural/slope instability, foundation)
• Common cause of releases was seepage and leaking to surrounding
media (e.g. “seepage,” “spill” and “other release” on graphs)
• Releases from surface impoundments inevitable, but may not
exceed background or “tolerable” limits
• Availability of data subject to both detection and reporting
• There are many “technical unknowns” in the management and
closure of CCR facilities – to both industry and the public
How heterogeneous ash materials will settle and compact over
How to dewater and stabilize extremely large impoundments
How to prevent infiltration of precipitation in ash
• Investigating the social components of long-term coal waste
storage and closure
How do limited liability and financial assurance influence
• Estimating the potential liability of the facilities that are
If the U.S. Government ends up “holding the bag” because
the coal industry doesn’t close or properly manage the
facilities, how much will remediation cost?
Future Work – Linking Social with Technical
Social & Political Factors
• Mapping of coal plants over median income. What role
might location play in the social distribution of impacts?
Wir schaffen Wissen – heute für morgen
Paul Scherrer Institut (PSI)
Assessment Group (TAG)
University of Chicago
Thank you for
Hinweis der Redaktion
Bankruptcy in the coal mining sector is leaving many waste facilities to be cared for by government – liabilities discharged in bankruptcy court – slows down care and closure
Situation and incentives of coal electricity utilities eerily similar with decline of coal to mining incidents – want to understand liability might have to take on as well as how closure can reduce risks
Give examples of non-newtonian fluids: ketchup
Three main different raising techniques: upstream, downstream, centerline
So, what we’re doing is looking at the existing sites and the data about incidents they have had
Explain difference between tailings and CCR
Technique, costs, benefits, risks
Explain each type of closure
Say self-generated, and based on literature review
Result from combustion of coal – all coal
CCRs: fly ash, bottom ash, boiler slag, flue gas desulphurization gypsum
Different coals have different contents of ash and sulfur – ash content can range from 3-49 %
Sulphur content can range from <1% to >3% -- more sulfur means more gypsum waste