Question 15 of 16: Risk Analysis for a Landfill Project

Question 15: Risk Analysis for a Landfill Project (7 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(1) Define scope and objectives — establish what decision the risk analysis informs (siting, design approval, operating permit renewal) and the receptors of concern (groundwater, surface water, air, human health, ecological). (2) Hazard identification — systematically list credible hazard events across the facility's life cycle: liner/leachate-collection failure, gas migration/explosion, slope instability, extreme-precipitation overtopping, fire, and post-closure long-term liner degradation. (3) Likelihood assessment — estimate the probability of each hazard event using site-specific data (geotechnical, hydrogeological, climate) combined with published failure-rate/performance data for engineered barrier systems. (4) Consequence assessment — for each hazard, estimate the magnitude of impact if it occurs (contaminant mass reaching a receptor, population/ecosystem exposed, remediation cost), typically via fate-and-transport modelling for groundwater/gas-migration pathways. (5) Risk characterization — combine likelihood and consequence (qualitatively via a risk matrix, or quantitatively as an expected-value/probabilistic estimate) to rank hazards by overall risk. (6) Risk mitigation and management — for unacceptable risks, identify and evaluate mitigation measures (redundant liner systems, enhanced monitoring, contingency/emergency response plans) and their cost-effectiveness at reducing risk to an acceptable level. (7) Documentation and communication — present the analysis, assumptions and residual risk transparently to the municipality, regulator and public, since siting/permitting decisions for a landfill are as much about demonstrated due diligence and stakeholder confidence as about the technical result itself.

Steps 3 and 4 (likelihood and consequence) are often the weakest link in practice, since defensible site-specific probability data for a rare event like a liner breach is genuinely scarce; a competent risk analysis states this data limitation explicitly and, where site-specific data is unavailable, uses a documented range (rather than a single point estimate) so the resulting risk ranking is not presented with more precision than the underlying data actually supports.