16-Civ-A3 Elementary Environmental Engineering · May 2018
Question 2 of 7: Water-Resource Management and Toxic Gases
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
Paper format. National Exams, May 2018 — 16-Civ-A3 Elementary Environmental Engineering. Three hours; closed book with one candidate-prepared 8½ × 11 double-sided aid sheet; approved Casio or Sharp calculator only. Seven problems are printed, each worth 20 marks, and any five constitute a complete paper (maximum 100 marks). All seven are solved here, because the set is intended as a study resource rather than an exam script. Section marks are shown in brackets at the left margin of each question and are reproduced from the final-page Marking Scheme.
Reference texts.
Davis, M.L. & Cornwell, D.A., Introduction to Environmental Engineering, 5th ed., McGraw-Hill — material and energy balances, reactor kinetics, hardness, disinfection, water and wastewater unit processes.
Masters, G.M. & Ela, W.P., Introduction to Environmental Engineering and Science, 3rd ed., Pearson — mass/energy balances on power plants, air-emission estimation, growth–pollution linkages.
Metcalf & Eddy / AECOM, Wastewater Engineering: Treatment and Resource Recovery, 5th ed., McGraw-Hill — wastewater unit processes and plant upgrading.
Crittenden, J.C. et al. (MWH), Water Treatment: Principles and Design, 3rd ed., Wiley — coagulation/flocculation, filtration, membranes, adsorption, disinfection.
Engineers Canada / EGBC Code of Ethics; Canadian Council of Ministers of the Environment (CCME) and the Guidelines for Canadian Drinking Water Quality (GCDWQ), Health Canada — professional duty and water-quality benchmarks.
Check: Problem 4(ii) quotes a rate constant as “20 dm6/mol2” with no time unit, and states the fundamental reaction 2A + B ⇌ C. It is solved as a forward-rate second-in-A/first-in-B rate law with $k=20\ \text{dm}^{6}\,\text{mol}^{-2}\,\text{s}^{-1}$ (the only reading that makes $-r_A=k\,C_A^{2}C_B$ dimensionally a rate); the time unit is taken as seconds per NOTE 1. Because no feed flow rate is supplied, the well-posed deliverable is the flow-independent space-time $\tau$ (with $V=\tau\,v_0$ for any stated feed basis), not an absolute volume.
Question 2: Water-Resource Management and Toxic Gases (20 marks)
Part (i) — Three water-resource-management strategies (10 marks)
Because the aquifer is under the influence of surface water (GUDI), supplies both drinking-water wells and irrigation, and receives subsurface septic discharge, the strategies must protect it against both nutrient/pathogen loading (short term) and drawdown/contaminant accumulation (long term).
Wellhead and aquifer source-protection zoning (non-technical / regulatory). Delineate capture zones by time-of-travel and impose land-use controls — setback distances between septic fields and wells, minimum lot sizes, restrictions on manure and fertilizer application within the recharge area, and mandatory septic inspection/pump-out by-laws. This protects the designated uses (potable and irrigation) at their most vulnerable pathway (the septic-to-well shortcut) and is durable over the long term.
Groundwater monitoring and abstraction management (technical + non-technical). Install a monitoring-well network for water levels, nitrate, chloride and bacteriological indicators, and license total withdrawals so pumping stays within the sustainable-yield / safe-yield of the aquifer. Managed abstraction prevents long-term overdraft and, near the surface-water boundary, prevents induced infiltration of poor-quality surface water or (in coastal settings) saline intrusion.
Decentralized-wastewater upgrading and managed aquifer recharge (technical). Replace or upgrade failing septic systems with enhanced nitrogen-removing units (or cluster treatment), and use stormwater/recharge basins or conservation of recharge area to sustain water levels. This attacks the dominant nutrient source directly and supports both short-term water quality and long-term water quantity.
Part (ii) — Three environmental issues in using toxic gases for chloramination (10 marks)
Acute toxic-release hazard (technical). Both Cl2 and NH3 are toxic, corrosive gases; an accidental release from cylinders, headers or the reaction system endangers workers and the surrounding community. This demands engineered containment: gas detection, automatic isolation, scrubber/absorption emergency systems, secondary containment and separation of the two gases (they must not be stored so a leak can mix them).
Formation of disinfection by-products and ecological discharge (technical). Chloramination lowers regulated trihalomethanes/haloacetic acids relative to free chlorine but introduces nitrogenous by-products (e.g. NDMA) and a persistent monochloramine residual. Chloramines are highly toxic to fish and to dialysis patients, so any discharge (filter backwash, main flushing) must be de-chlorinated before release to receiving waters.
Emergency planning, worker safety and public right-to-know (non-technical). Handling toxic gases triggers regulatory and management duties — WHMIS/SDS and operator training, an emergency-response plan coordinated with local responders, community notification and evacuation planning, and compliance with transport-of-dangerous-goods and environmental-emergency (E2) requirements. The non-technical barrier (procedures, training, notification) is as essential as the hardware.
