Managing Risk at Northern Contaminated Sites: Differentiating - PowerPoint PPT Presentation

Managing Risk at Northern Contaminated Sites: Differentiating Assessment-derived Uncertainty from Risk Assessment Conservatism in Remedial Action Planning RPIC Montreal 2016 Presented by: Francois Lauzon Prepared by: David Wilson Stantec Consulting Ltd. April 27, 2016

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

1 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

Definitions Risk Treasury Board (2010b): “the effect of uncertainty on • objectives” or “the expression of likelihood and impact of an event” [4] Uncertainty “Deep Treasury Board (2010a): “the state, even partial, of • Uncertainty”: deficiency of information related to understanding - uncertainty or knowledge of an event, its consequence, or about likelihood” [3] fundamental Environment Canada (2012): the “state of having • processes or limited knowledge where it is impossible to exactly assumptions [2] describe an existing state or future outcome” [1] Types of uncertainty: • Often forgotten: Aleatory or Exogenous Uncertainty - statistical • also includes variability and heterogeneity of the system (e.g., scenario and standard deviation of sample results) decision-rule Epistemic Uncertainty - model and parameter • uncertainty uncertainty (e.g., infiltration rate)

Building the Conceptual Site Model Phase CSM COCs* Terrestrial/ Land Climate/ Hydro- Aquatic Use Hydrology geology ESA I I(G) Historical land Identify surface Water wells SARA/aquatic use/SARA/ water (SW) species terrestrial species bodies ESA II C(G) Characterize soils Characterize SW Stratigraphy, Characterize (impacted and (impacted and groundwater SW and background) background) (GW) sediment ESA III D(G) Delineate soil Characterize SW Porosity/ Delineate SW impacts/ transport Gradients/ and sediment background GW Transport impacts HHERA C(SS) Define human Consider Characterize Characterize health and eco seasonality and GW exposure SW/sediment exposures trends exposure RAP D(SS) Risk mitigation (remedial options) / management measures * I(G) = Identify (generic guideline) C(G) = Characterize (generic guideline) D(G) = Delineate (generic guideline) C(SS) = Characterize (site-specific guideline) D(SS) = Delineate (site-specific guideline)

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 SOURCE e.g.s: NORTHERN SITE Quantification ‘MAGNIFIERS’ Background conditions Limited time/samples Parameter inclusion as poorly defined COC: Y/N/Unk. CSM not fully developed Limited site-specific physical system data Some COCs not Limited historical data Parameter inclusion as identified COC: Y/N/Unk. Impacts not delineated Risk assessment Impacted soil volume exposure scenarios not range: x m3 ± y m3 ‘typical’ Decision criteria not Identifying/engaging Identify reliance of defined stakeholders decisions on site challenging objectives 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]

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 •

2 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

Remedial Action Planning Objective: Reduce risk to acceptable • ESA levels as effectively and efficiently as possible Inputs: Site hazards posing • significant human health or ecological risks Outputs: Recommended remedial/risk • RAP management options that eliminate risk or reduce to acceptable levels

Risk Assessment Risk COPCs & resides Media here Reduce Uncertainty of Using Generic Criteria: • Screen out/in COCs Receptors Pathways • Eliminate non-existing pathways and receptors Define Site-specific Criteria: • Based upon site COC concentrations • For site receptors Dependencies: • Exposure scenarios: land use assumptions • Pathways: CSM

Remedial Options Analysis How do uncertainties affect the ROA? ESA-CSM or RA: Attributes: Uncertainties: Toxicity TRVs; Exposure duration RA Location Pathways/receptors Both Hazard Size/volume + / - ESA-CSM Stability Trend ESA-CSM Significant or not: elimination, reduction or management RO Technology RO Cost/Duration RO Technology/Cost/Duration

3 The Uncertainty (Risk) Budget “There are those who are so scrupulously afraid of doing wrong that they seldom venture to do anything” - Vauvenargues

The ESA Risk Budget Component Phase of Nature of Uncertainty Management of Definition Uncertainty Background II, III Nat. Var. – mean, S.D. Additional sampling Conditions Epistemic - 95% UCLM; High natural CSM: Land use I, II, III Epistemic - generic criteria Conservatism (lowest Deep - future intentions criteria) CSM: Terrestrial I, II (Preliminary) Nat. Var. - soil depth, grain Conservatism (e.g., Environment II, III (Mature) size, FOC, groundwater coarse grained); Epistemic - porosity additional sampling CSM: Aquatic I, II (Preliminary) Nat. Var. – seasonality, TDS/ Conservatism (e.g., Environment II, III (Mature) TSS, pH, species max values); Epistemic – flows (e.g., 7Q10) additional sampling COCS: I, II Epistemic - COCs > Tier 1 Gap analysis; Identification criteria not identified additional sampling COCs: II Nat. Var. - mean, S.D. Gap analysis; Characteri- Epistemic - generic vs. site- additional sampling zation specific criteria COCs: III Nat. Var. - extent in x, y, z , Gap analysis; Delineation duration in t additional sampling; Epistemic - qualifiers (L, M, H) contingency volume

The RA Risk Budget Component Nature of Uncertainty Management of Uncertainty Inputs Background Conditions As per ESA Reference sites 95% UCLM CSM: Land use Human health exposure Conservatism (chronic scenario; Applicable vs. acute exposure) pathways CSM: Terrestrial and Ecological exposure Modeled vs. measured aquatic environments scenario; Applicable concentrations pathways ESA COCs Nat. Var. – mean, S.D., 95% UCLM = EPC OR extent in x, y, z , duration max. conc. in t Models Human health dose TRV Conservatism (e.g. model published uncertainty factors for TRVs) Ecological dose model Species; Exposure area Conservatism (e.g. most and duration sensitive species; max. concentrations)

ESA and RA Risk Budgets Compared ESA RA How much of the COC – arsenic uncertainty is due Volume – 100 m 3 +/- 20 m 3 20% - to natural variability, 10% - Soil texture – undefined Sample results: to ESA-CSM models # samples: 7 used, to RA models 95% UCLM = N/a used, or to deeper Log-norm. mean = 136 mg/kg 10% - issues? Max. concentration = Find out: predict 367 mg/kg - 10% expected case, HH chronic TRVs: best case, and - 20% Ingestion 1.8 (mg/kg-d) -1 worst case values Inhalation 27 (mg/kg-d) -1 - 5% - 10% HH HQ – 1.6 (FN toddler) E.g. area of soil Eco subchronic TRVs: impacted with Dog 0.55 (mg/kg-d) UF: 3 - 50% arsenic - 10% Eco HQ – 10 (Masked shrew)

The Conservatism Cascade Component CSM: CSM: COCS: COCs: Background CSM: Land COCs: Terrestrial Aquatic Identifica- Characteri- Conditions use Delineation Environment Environment tion zation Not Future use GW Aquatic COCs not COCs not COCs not ESA enough unknown pathway species identified character delineated samples undefined undefined -ized to Max value Most GW Species COC list Charac- Delineation RA vs. mean sensitive pathway assumed assumed terization assumed use assumed present complete assumed Impact on Risk Error 1 2 2 2 1 1 1 Type* * 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)

4 Working with Risk “Fail to plan, plan to fail”

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 •