23-Chem-B2 Environmental Engineering · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. EGBC 04-Chem-B2 Environmental Engineering, December 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, dissolved air flotation, activated-sludge design, nutrient removal; 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; C. D. Cooper & F. C. Alley, Air Pollution Control: A Design Approach — fabric filtration, thermal oxidation, adsorption, 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 Canadian Council of Ministers of the Environment (CCME) Municipal Wastewater Effluent and Drinking Water Quality guidelines, and provincial air/water permitting practice (e.g. BC Environmental Management Act, Metro Vancouver air-quality bylaws), which govern effluent/emission limits and treatment-technology selection referenced throughout.
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.
Example and technology: dual-phase extraction (free-product recovery plus groundwater pump-and-treat) with oil–water separation and granular activated carbon (GAC) polishing. A former bunker-fuel or lubricating-oil storage yard, where a slow release has left heavy (low-volatility, largely insoluble, LNAPL-forming) hydrocarbons in the shallow soil and floating on and dissolved in the underlying drinking-water aquifer, is remediated by installing recovery wells screened across the water table. Each well pumps both the floating free product and contaminated groundwater; the combined stream passes through an oil–water separator (the recovered oil is recycled or disposed of) and then through GAC vessels, which strongly adsorb the dissolved and emulsified heavy-hydrocarbon fraction because of its high molecular weight and low solubility, before the treated water is reinjected or discharged under permit. Pumping also depresses the water table to create a capture zone, so the plume is hydraulically contained and cannot migrate toward drinking-water wells. The heavily impacted shallow source soil above the water table is excavated for off-site treatment or biopiling so it stops re-contaminating the aquifer. Volatilization-based methods (air stripping, soil-vapour extraction) are deliberately not chosen: heavy hydrocarbons have very low vapour pressures and Henry's-law constants, so they strip and vent poorly, whereas free-product recovery, hydraulic containment and adsorption do not depend on volatility.
Example: in-situ bioventing of a diesel-impacted vadose zone. Air injection wells push atmospheric oxygen into the unsaturated soil above a diesel spill, while extraction/monitoring wells confirm airflow distribution; the added oxygen stimulates indigenous aerobic, hydrocarbon-degrading bacteria already present in the soil to biodegrade the diesel fractions in place, avoiding the cost and disruption of excavation.
Sensitivity (S) is the smallest change in the measured pollutant concentration that produces a detectable, distinguishable change in the instrument's output signal (the slope of the response curve, $S=\Delta(\text{signal})/\Delta(\text{concentration})$). It matters for drinking-water/wastewater monitoring because many regulated parameters (e.g. residual chlorine, trace metals) must be tracked at low concentrations where an insufficiently sensitive method would report a flat, uninformative signal even as the true concentration varies meaningfully near a regulatory threshold; sensitivity must be matched to the concentration range and reporting limit specified by the applicable water-quality guideline, not just to the parameter's typical peak level.
Reliability (R) is the consistency of the instrument's response to the same true concentration across repeated measurements and over the extended, often largely unattended deployment periods typical of continuous water-quality monitoring (e.g. an online residual-chlorine analyzer between manual calibration checks). A monitoring program's regulatory and public-health value depends on continuous, gap-free records; an unreliable instrument that drifts or fails silently produces data gaps or plausible-looking but wrong values that can mask a real exceedance (e.g. an undetected chlorine-residual loss) or trigger a false alarm, so reliability is typically ensured by automated span/zero checks, redundant sensors at critical points, and a defined data-validation/QA program.
Accuracy (A) is how closely the instrument's reported concentration matches the true concentration, established by periodic calibration against a certified reference standard (e.g. a certified reference material or a parallel manual reference method such as Standard Methods titration for chlorine residual). Accuracy matters because water-quality objectives are absolute concentration thresholds — a precise but inaccurate (consistently biased) instrument can report a stable, plausible trend while every value is systematically wrong relative to the regulatory limit, a fundamentally more dangerous failure mode than simple measurement noise, since it can silently mask a real compliance violation.
Together, S, R and A define the overall defensibility of a water-quality monitoring program: sensitivity sets the floor of what changes can be meaningfully detected, reliability governs how representative and complete the resulting record is, and accuracy governs whether the reported values can be trusted against the regulatory threshold itself — a program strong in only one of the three still yields a poor overall picture of true water quality.
