16-Civ-A3 Elementary Environmental Engineering · May 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Exams, May 2015 — 98-Civ-A3 Environmental Engineering. Three hours; closed book with one candidate-prepared double-sided aid sheet and an approved Casio or Sharp calculator. Seven problems of 20 marks each; any five constitute a complete paper and only the first five answers in the work book are marked, for a maximum of 100 marks. The complete Marking Scheme is printed on page 8 and is reproduced against each question below. All seven problems are solved here, because this set is a study resource rather than an examination script.
Reference texts.
Check: compound naming in Problem 1(i). The question names the spilled liquid “dipropylene glycol” but gives its formula as C3H8O2 and its quantity as 38 kg (500 mol). C3H8O2 has a molar mass of 76.09 g/mol, and 38 000 g / 500 mol = 76.0 g/mol — so the formula, the mass and the mole count agree exactly with each other. It is the name that is wrong: C3H8O2 is propylene glycol (dipropylene glycol is C6H14O3, 134.2 g/mol). The solution therefore uses the self-consistent set (500 mol, 76.09 g/mol) and notes the naming slip, as NOTE 1 on page 1 invites. Nothing in the answer depends on the name.
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 question asks for a 3×3 matrix in which each cell carries two impacts and two corresponding engineering solutions. The matrix below is organised with the three infrastructure sectors as rows and the three drivers as columns, following the layout printed with the question.
| Sector | (a) Urban growth | (b) Increased water demands | (c) Higher energy use |
|---|---|---|---|
| Atmospheric emissions | I1: Traffic growth raises NOx, fine particulate (PM2.5) and ground-level ozone, creating an urban smog burden and measurable excess respiratory mortality. I2: Loss of vegetated land plus waste heat produces the urban heat island, raising summer temperatures several degrees and accelerating photochemical ozone formation. S1: Transit-oriented compact development with rapid transit, active-transport networks and electrified bus fleets, so that trips are avoided rather than merely cleaned. S2: Green infrastructure — urban forest canopy targets, green and high-albedo roofs — combined with district energy to cut both the heat island and combustion emissions. |
I1: Pumping, treatment and distribution of a larger flow raise electricity demand, and where that electricity is fossil-generated the water system's carbon intensity rises with it. I2: Long-distance transfers and deep-well pumping to meet demand add further emissions, while expanded aeration at the wastewater plant releases nitrous oxide, a greenhouse gas some 273 times as potent as CO2. S1: Demand-side management — universal metering, volumetric pricing, high-efficiency fixture retrofits and pressure management — which reduces the energy demand by reducing the flow. S2: Energy optimisation of the plants themselves: variable-frequency pump drives, fine-bubble aeration with dissolved-oxygen control, and on-site generation from digester biogas. |
I1: Fossil combustion for power and heat emits CO2, SO2 and NOx; the acid gases produce acid deposition that has damaged Canadian Shield lakes for decades. I2: Mercury and other trace metals released from coal combustion deposit on watersheds and bioaccumulate as methylmercury in fish, driving consumption advisories. S1: Displace combustion with low-carbon supply — hydro, wind and solar generation, coal phase-out (as Ontario completed in 2014), and building-envelope and process efficiency that reduces demand outright. S2: Where combustion remains, flue-gas desulphurisation, selective catalytic reduction, fabric filters and activated-carbon injection for mercury, backed by CCME Canada-Wide Standards. |
| Water and wastewater infrastructure | I1: Imperviousness rises with development, so runoff volume and peak flow increase sharply while baseflow declines, causing stream-channel erosion, habitat loss and urban flooding. I2: Growth loads existing collection systems beyond capacity, producing combined sewer overflows and sanitary sewer overflows of untreated sewage to the receiving water. S1: Low-impact development and stormwater source control — bioswales, permeable pavement, rain gardens, infiltration trenches and end-of-pipe wet ponds — designed to hold the post-development runoff regime at pre-development levels. S2: Capacity staging through a master servicing plan: sewer separation, inflow-and-infiltration reduction, real-time control and off-line storage tunnels, with plant expansion triggered by an assimilative-capacity study of the receiver. |
I1: Higher withdrawals lower lake and river levels and draw down aquifers, reducing instream flow below the requirement for aquatic habitat and, in coastal aquifers, inducing saline intrusion. I2: Greater water use produces proportionally greater wastewater flow, which dilutes influent strength while increasing hydraulic load, degrading treatment performance and raising nutrient loading to the receiver. S1: Integrated water-resource management with permitted allocation, non-revenue-water reduction through district metering and leak detection (many systems lose 15 to 30 % of production), and drought contingency triggers. S2: Fit-for-purpose supply — water reuse and reclaimed water for irrigation and cooling, rainwater harvesting, and dual-plumbed non-potable systems — so that potable-quality water is not spent on non-potable uses. |
I1: Thermoelectric generation withdraws very large cooling flows and returns heated water, causing thermal pollution that lowers dissolved oxygen and shifts aquatic community structure, with entrainment and impingement losses at the intake. I2: Energy extraction and conversion contaminate water directly — hydraulic-fracturing flowback, oil-sands process water, and coal-ash pond leachate carrying arsenic, selenium and boron. S1: Closed-cycle cooling towers or dry cooling instead of once-through intakes, with fish-friendly intake velocities and screens, and diffuser design that meets the thermal criterion at the edge of the mixing zone. S2: Zero-liquid-discharge and closed-loop process water for energy facilities, engineered containment with leachate collection for ash and tailings, and hydrogeological monitoring networks under provincial approval. |
| Solid waste management | I1: Waste generation scales with population and affluence while landfill siting becomes progressively harder near a growing city, forcing long-haul transport with its own emissions and cost. I2: Landfill leachate and gas: leachate carries ammonia, chloride, metals and organic contaminants toward ground water, and landfill gas is roughly half methane, a short-lived climate forcer with about 28 times the warming potential of CO2. S1: Divert at source — extended producer responsibility, curbside recycling and organics collection with centralised composting or anaerobic digestion, and disposal bans on divertible material — which extends the life of existing capacity. S2: Engineered containment for the residual: composite liners, leachate collection and treatment, active landfill-gas collection with energy recovery or flaring, progressive capping, and long-term post-closure monitoring under the provincial waste regulation. |
I1: Water and wastewater treatment themselves generate residuals — alum sludge, softening sludge, spent media and screenings — whose volume scales directly with the treated flow and which require disposal. I2: Higher wastewater flows generate more biosolids, whose land application can transfer nutrients, metals, pathogens and emerging contaminants such as PFAS and pharmaceuticals to soil and ground water. S1: Residuals minimisation and beneficial reuse: coagulant recovery, dewatering to reduce haulage volume, and use of softening sludge in agricultural liming or cement manufacture. S2: Biosolids stabilisation to a Class A standard by thermophilic digestion, composting or thermal drying, managed under a nutrient management plan with loading limits and setbacks per CCME biosolids guidance. |
I1: Energy production generates very large residual streams — coal fly ash and bottom ash, and mine tailings — whose impoundments pose long-term geotechnical and contaminant risk, as the Mount Polley tailings dam failure of 2014 demonstrated. I2: The energy transition creates new waste streams that current systems handle poorly: lithium-ion batteries, photovoltaic modules and wind-turbine blades, all with 20 to 25 year service lives arriving in bulk. S1: Convert waste to energy where diversion has been exhausted — landfill-gas utilisation, anaerobic digestion of organics, and modern energy-from-waste with full air-pollution control — recovering value from what remains. S2: Design for circularity: beneficial use of fly ash as a supplementary cementing material, dry-stack tailings instead of wet impoundment, and extended producer responsibility schemes with design-for-disassembly requirements for batteries and modules. |
Three themes run through the whole matrix and are worth stating explicitly, because they are what an examiner is looking for beyond the individual cells. First, the strongest engineering solution in almost every cell is a demand-side measure — compact development, water conservation, waste diversion, energy efficiency — because avoiding a unit of demand removes the impact at every downstream stage simultaneously, whereas an end-of-pipe control only relocates it. Second, the three sectors are coupled: water systems are large electricity consumers, energy systems are large water consumers, and both generate solid residuals, so a solution adopted in one row changes the loading in another and the sectors cannot be optimised in isolation. This is the water–energy–waste nexus. Third, every control listed operates inside a Canadian regulatory frame — CCME Canada-Wide Standards and environmental quality guidelines, provincial environmental compliance approvals, the federal Wastewater Systems Effluent Regulations, and municipal master servicing and solid-waste plans — so the engineer's task is to select the option that meets the statutory requirement at least whole-life cost while remaining resilient to further growth.
