RPIC Montreal 2016 Presented by: Francois Lauzon Prepared by: David Wilson Stantec Consulting Ltd. April 27, 2016 Managing Risk at Northern Contaminated Sites: Differentiating Assessment-derived Uncertainty from Risk Assessment Conservatism in Remedial Action Planning
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RPIC Montreal 2016
Presented by: Francois Lauzon
Prepared by: David Wilson
Stantec Consulting Ltd.
April 27, 2016
Managing Risk at Northern Contaminated Sites: Differentiating Assessment-derived Uncertainty from Risk Assessment Conservatism in Remedial Action Planning
Agenda
1 Uncertainty in Site and Risk Assessment
2 Role of Risk Assessment in Remedial Action Planning
3 The Uncertainty (Risk) Budget
4 Working with Risk
5 Case Example
Uncertainty in Site and Risk Assessment
“Risk is like fire: If controlled it will help you; if uncontrolled it will rise up and destroy you” - Theodore Roosevelt
1
Definitions Risk • Treasury Board (2010b): “the effect of uncertainty on
objectives” or “the expression of likelihood and impact of an event” [4]
Uncertainty • Treasury Board (2010a): “the state, even partial, of
deficiency of information related to understanding or knowledge of an event, its consequence, or likelihood” [3]
• Environment Canada (2012): the “state of having limited knowledge where it is impossible to exactly describe an existing state or future outcome” [1]
• Types of uncertainty:
• Aleatory or Exogenous Uncertainty - statistical variability and heterogeneity of the system (e.g., standard deviation of sample results)
• Epistemic Uncertainty - model and parameter uncertainty (e.g., infiltration rate)
“Deep Uncertainty”: - uncertainty
about fundamental processes or assumptions [2]
Often forgotten: also includes scenario and decision-rule uncertainty
Building the Conceptual Site Model Phase CSM
COCs* Terrestrial/ Land Use
Climate/ Hydrology
Hydro-geology
Aquatic
ESA I I(G) Historical land use/SARA/
terrestrial species
Identify surface water (SW)
bodies
Water wells SARA/aquatic species
ESA II C(G) Characterize soils (impacted and background)
Uncertainty and the CSM How should it be developed? [5] Dealing with uncertainty: • Understand the data by doing exploratory analysis
• Identify and quantify uncertainty – revisions to the CSM are expected
• Question assumptions
• Supplement data where needed, re-analyze, update the CSM
[6] SAP = sampling and analysis plan
Sources of Uncertainty
Uncertainty is generally identified within a phase but is often not carried to a subsequent phase (e.g., from ESA to ROA/RAP; from RA to ROA/RAP; from ROA to RAP; from ROA/RAP to Cost) [7]
SOURCE e.g.s: NORTHERN SITE ‘MAGNIFIERS’
Quantification
Background conditions poorly defined
Limited time/samples
Parameter inclusion as COC: Y/N/Unk.
CSM not fully developed
Limited site-specific physical system data
Some COCs not identified
Limited historical data
Parameter inclusion as COC: Y/N/Unk.
Impacts not delineated
Risk assessment exposure scenarios not ‘typical’
Impacted soil volume range: x m3 ± y m3
Decision criteria not defined
Identifying/engaging stakeholders challenging
Identify reliance of decisions on site objectives
Characterizing Uncertainty
Aleatory or Exogenous Uncertainty • Measures of statistical variability:
o standard deviation (parametric and non-parametric)/ standard error; variogram
• Bayesian probabilities
Epistemic Uncertainty • Model sensitivity analysis
• Monte Carlo simulation
Deep Uncertainty • Expert judgment
• Pairwise comparison of significance
Role of Risk Assessment in Remedial Action Planning
"Reality is that which, when you stop believing in it, doesn’t go away“ - Philip K. Dick
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Remedial Action Planning
Objective: • Reduce risk to acceptable
levels as effectively and efficiently as possible
Inputs: • Site hazards posing
significant human health or ecological risks
Outputs: • Recommended remedial/risk
management options that eliminate risk or reduce to acceptable levels
ESA
RAP
Risk Assessment
Reduce Uncertainty of Using Generic Criteria: • Screen out/in COCs • Eliminate non-existing
pathways and receptors Define Site-specific Criteria: • Based upon site COC
concentrations • For site receptors Dependencies: • Exposure scenarios: land
* Assuming a site is contaminated, Type 1 = false negative (i.e., incorrectly assuming site is clean, and Type 2 = false positive (i.e., incorrectly assuming site is contaminated)
1 2 2 2 1 1 1
Working with Risk
“Fail to plan, plan to fail”
4
Revisiting the CSM Post-RA
The Dynamic CSM • Before beginning the ROA, update the CSM based upon the
RA results
Investments in Uncertainty Reduction • Best approach for a given hazard still unclear (i.e.,
remediate vs. risk manage)?
• Is the information needed for ROA (application of selection criteria) available?
Managing Residual Uncertainty (Risk) • Define triggers and thresholds in the LTMP
Mitigating Uncertainty
Exogenous Uncertainty • Variability is due to spatial, temporal, or individual randomness and
cannot be decreased by further data collection: it’s impact can only be (and should be) managed
Epistemic and Deep Uncertainties • Rank first by risk significance (e.g., hazardous vs. non-hazardous,
COC HQs), then by magnitude • Work down ranking, and answer the questions:
• Does the uncertainty span a decision threshold? [e.g., remediate or risk manage; on-site or off-site disposal]
• Worth investing in reduction of uncertainty (mitigate), or better to manage? [Cost-benefit analysis]
• What is the source of uncertainty? [Where should the investment in uncertainty reduction be made?]
Reducing and Managing Uncertainty based upon Source ESA (COCs): • Additional sampling
• Additional analysis (e.g., time series analysis)
• Monitor inputs to remedial option (RO) or risk management approach (RMA) and compare to design criteria
RA: • Development of short-term TRVs
• Use of measured vs. modeled concentrations in vegetation and animal tissues
Uncertainty in Technology Performance: • Monitor outputs of RO or RMA and compare to
performance prediction
Case Study
“Everything that can be counted does not necessarily count; everything that counts cannot necessarily be counted” - Albert Einstein
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Case Study Example Scenario: gold mining site decommissioned to the standard of the day in the late 1980’s: arsenic impacts in sediments and surface water adjacent to a tailings containment area (TCA) and flooded underground workings. Best option for the TCA?
Assessment History: Phase Scope Ph I/II ESA - historical 2010 - identification of APECs
- limited test pits/boreholes - soil. tailings and WR samples
Ph III ESA - characterization of AECs 2013 - additional boreholes
- SW, GW and sediment samples - background soil samples
- SSRTs = 44,800±9,400 m3 - remedial action required - can options be evaluated? N
Cont’d: - need to know if the aquatic environment is being impacted - additional assessment of aquatic environment required
RA Uncertainty Budget: undertake a similar process - Uncertainty in inputs - Uncertainty in models
Conclude options analysis: - assessment shows impacts above Tier 1 but RA shows non-toxic to benthic invertebrates - Class A cost estimate achievable within uncertainty? Y
2012
References References 1. Environment Canada. 2012. Federal Contaminated Sites Action Plan
2. Committee on Decision Making Under Uncertainty (CDMU). 2013. Environmental Decisions in the Face of Uncertainty. Board on Population Health and Public Health Practice. National Academy of Sciences. ISBN 978-0-309-13034-9.
3. TBS. 2010a. Framework for the Management of Risk. 4. TBS. 2010b. Guide to Integrated Risk Management. 5. Maheux, P., Lauzon, F., Wilson, D., Sundaram, S., Bouchard, M. 2012.
Developing a Good Conceptual Model for Federal Contaminated Sites – Common Shortfalls and Data Needs. Pres. at the RPIC Federal Contaminated Sites National Workshop, Toronto, Ontario.
6. Evolving Conceptual Site Models (CSMs) in Real-time for Cost Effective Projects, Kira P. Lynch, US Army Corps Seattle District.
7. Wilson, D. 2015. Advancements in Managing Uncertainty in Remedial Options Analysis and Remedial Action Plan Development for Northern Sites. Pres. at the RPIC Federal Contaminated Sites Regional Workshop, Edmonton, Alberta.