Question 14 of 18: Engineering Calculations for Performance Criteria

Question 14: Engineering Calculations for Performance Criteria (9 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.

Part (a) — 14.1 Gas testing. Model predicted LFG generation using a first-order decay model (rate constant $k$, ultimate yield $L_0$) and compare against measured extraction-well flow rate and methane concentration (by portable GC or infrared analyzer) to compute the gas-collection system's actual collection efficiency. Compare perimeter probe methane readings against the regulatory action level (commonly 25% of the lower explosive limit at the property boundary, 100% LEL in any structure) and check that well-field vacuum/flow achieves the design capture radius at every well.

Part (b) — 14.2 Leachate control. Run a water-balance calculation (e.g. the HELP — Hydrologic Evaluation of Landfill Performance — method, combining precipitation, evapotranspiration, surface runoff and infiltration through the cover with the waste mass's field capacity) to estimate the leachate generation rate, and compare it against the leachate collection/pumping system's design capacity. Calculate the hydraulic head of leachate on the liner and confirm it stays below the regulatory maximum (commonly 300 mm) at every point on the base, and trend leachate quality (BOD, COD, ammonia-N) over time against the receiving treatment system's design or permit limits.

Part (c) — 14.3 Groundwater monitoring. Apply statistical trend analysis (e.g. the Mann-Kendall trend test or ANOVA comparison of upgradient versus downgradient wells, consistent with standard regulatory statistical-methods guidance) to the monitoring-well time series to detect a statistically significant increase in an indicator parameter. Use Darcy's law and estimated hydraulic conductivity/gradient to confirm the monitoring-well network's capture zone and travel time actually intercept a plume originating at the landfill before it reaches a receptor, and compare measured concentrations against the applicable regulatory groundwater-quality standard or established background concentration.