23-Chem-B2 Environmental Engineering · May 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. EGBC 04-Chem-B2 Environmental Engineering, May 2014, 3 hours, closed-book with a candidate-prepared double-sided 8½×11-inch aid sheet. Seven problems, each worth 20 marks; candidates attempt any five, and only the first five answers in the workbook are marked. All seven problems are solved below as a complete study resource.
Reference texts: G. Tchobanoglous, F. L. Burton & H. D. Stensel (Metcalf & Eddy), Wastewater Engineering: Treatment and Reuse (4th ed., McGraw-Hill) — BOD kinetics, nutrient removal, activated-sludge design, sedimentation design; M. L. Davis & D. A. Cornwell, Introduction to Environmental Engineering (5th ed., McGraw-Hill) — drinking-water treatment, air pollution control, ion exchange, reverse osmosis, soil remediation, air quality modelling; C. D. Cooper & F. C. Alley, Air Pollution Control: A Design Approach — particulate/gas/vapour control, thermal/catalytic oxidation, odour control; S. P. Turner, Workbook of Atmospheric Dispersion Estimates (2nd ed., CRC Press) — the Gaussian plume model and Pasquill–Gifford stability classes. Canadian context follows the Canadian Environmental Protection Act (CEPA 1999), the Guidelines for Canadian Drinking Water Quality (Health Canada), the Canadian Council of Ministers of the Environment (CCME) Municipal Wastewater Effluent guidelines, and provincial air/water permitting practice (e.g. BC Environmental Management Act and Metro Vancouver air-quality bylaws).
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.
The scenario is a former tank-farm or pipeline-spill site where light crude oil has impacted the near-surface soil, and the requirement is to treat the excavated soil and return it to the same excavation (“dig-and-treat-in-place”) so the site can be redeveloped for residential use, which carries a stringent (residential/agricultural) clean-up criterion.
1 — Site characterization and delineation. A phased environmental site investigation (borehole/test-pit sampling on a grid, laboratory analysis for total petroleum hydrocarbon fractions F1–F4 and BTEX) delineates the horizontal and vertical extent of contamination above the applicable residential-land-use soil criterion, and confirms whether groundwater is also impacted, since that changes the remediation approach.
2 — Excavation and staged stockpiling. Contaminated soil is excavated to the delineated extent, segregated by contamination level (light vs. heavy impact) onto lined, covered stockpile pads to prevent cross-contamination of clean soil, rainwater infiltration, and volatile emissions during the interim period before treatment.
3 — Ex-situ treatment (biopiling / land-farming, appropriate for light crude). Because light crude oil (predominantly lighter, more biodegradable F1/F2 fractions) is well suited to biological treatment, the stockpiled soil is formed into aerated biopiles with nutrient (N, P) amendment and moisture control to stimulate indigenous hydrocarbon-degrading bacteria; this is markedly cheaper than thermal desorption and appropriate given the lighter (more readily bio-available) contamination compared with a heavy-hydrocarbon case.
4 — Confirmatory sampling of treated soil. Periodic sampling of the biopile confirms hydrocarbon concentrations have fallen below the residential-land-use criterion before the soil is approved for replacement; treatment continues (extended aeration/nutrient cycles) if criteria are not yet met.
5 — Backfill/replacement and confirmatory verification sampling of the excavation. Once both the excavation base/walls (confirmatory samples showing no residual contamination left behind) and the treated soil meet the residential criterion, the treated soil is placed back into the excavation and compacted; final verification samples from the reinstated ground confirm the site is suitable for residential development.
6 — Regulatory closure documentation. A remediation completion report, referencing the applicable provincial contaminated-sites regulation (e.g. BC Environmental Management Act Contaminated Sites Regulation) and the confirmatory sampling data, is filed to obtain a certificate of compliance before residential redevelopment proceeds.
Sensitivity (S) is the smallest change in the measured parameter that produces a discernible change in instrument response (the slope of the calibration curve near the operating range). It matters because ambient air-quality parameters (e.g. trace SO₂, O₃) and low-level water-quality contaminants often need to be resolved at concentrations close to the regulatory limit; an instrument with sensitivity too coarse for the parameter's regulatory range cannot demonstrate compliance even if it is otherwise well calibrated, since real changes below its sensitivity threshold are simply invisible to it.
Reliability (R) is the consistency (repeatability/reproducibility) of the instrument's response to the same input over repeated measurements and over time, including in field conditions (temperature swings, vibration, power fluctuation) rather than only in a controlled lab. It matters because a compliance or public-health decision built on a single unreliable reading cannot be trusted — an unreliable instrument might occasionally read correctly by chance, but a monitoring program needs the same input to reliably produce the same (or a tightly-bounded) output every time, which is what supports statistical process control and trend analysis over a continuous monitoring record.
Accuracy (A) is how close the measured value is to the true value, typically established by comparison against a certified reference standard or a reference method. It matters because sensitivity and reliability alone do not guarantee correctness — an instrument can be very sensitive and very reliable while being consistently biased (e.g. a poorly calibrated zero/span), reliably reporting a wrong number; accuracy is what a regulator ultimately relies on when comparing a reported concentration against a legal limit, so periodic calibration against traceable reference standards (and participation in inter-laboratory proficiency testing) is what maintains it over the life of the instrument.
Why all three matter together. A monitoring program strong in only one or two of these three dimensions still gives a poor picture of true performance: high sensitivity with poor accuracy detects small changes around a biased (wrong) baseline; high accuracy with poor reliability might be correct on the calibration bench but drift or scatter in field service; and high reliability with poor sensitivity consistently and repeatably fails to detect a real exceedance. Ambient air-quality and drinking/receiving-water monitoring programs are therefore specified (and audited) against all three simultaneously, not any single one in isolation.
