16-Civ-A3 Elementary Environmental Engineering · December 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Exams, December 2016 — 98-Civ-A3 Environmental Engineering. Three hours; closed book with one candidate-prepared 8 × 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 below.
Reference texts.
Check: The page-1 marking scheme on this paper is not reliable as printed, but the mark figures printed in the left margin of each question page are internally consistent — every problem's sub-part marks sum to exactly 20, and the parts of the scheme that are given agree with them. The margin figures are adopted throughout: Q1 (6, 7, 7); Q2 (9, 6, 5); Q3 (7, 7, 6); Q4 (10, 10); Q5 (10, 10); Q6 (10, 10); Q7 (5, 6, 3, 3, 3).
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 process: secondary aluminium production — the manufacture of extruded aluminium window and curtain-wall framing from recovered scrap. Aluminium is chosen because it demonstrates all three criteria unusually clearly and because the numbers are dramatic: producing a tonne of primary aluminium by the Bayer and Hall-Héroult route consumes roughly 14 to 16 MWh of electricity and generates about 12 tonnes of CO2-equivalent along with 1.5 tonnes of caustic bauxite residue, whereas remelting a tonne of clean scrap consumes about 0.7 MWh — a saving of about 95 % — and the metal suffers no loss of properties on recycling, so it can cycle indefinitely.
Method 1 — use waste materials and minimise virgin input (criterion 1). The plant is designed to run on a charge of 85 to 95 % post-consumer and post-industrial scrap: recovered window frames from building demolition, extrusion butt-ends and offcuts returned from the fabricators, and sorted alloy scrap. Three engineering measures make this achievable rather than aspirational. Alloy segregation at source is the first — scrap is sorted by alloy family using laser-induced breakdown spectroscopy or X-ray fluorescence rather than being downcycled into a single mixed casting alloy, which is what preserves the ability to make wrought extrusion billet rather than only castings. Second, closed-loop take-back agreements with fabricators and demolition contractors return identified alloy directly to the smelter, so the composition is known and the melt requires minimal dilution with primary metal. Third, the product is designed for disassembly — mechanical fasteners instead of adhesives, and thermal breaks and gaskets that can be separated — so that at end of life the aluminium can be recovered clean. Only the small amount of primary metal needed to correct alloy chemistry remains as virgin input.
Method 2 — create outputs usable by other processes (criterion 2). Every residual stream is engineered to be a feedstock rather than a waste. The dross skimmed from the melt, which is 40 to 70 % metallic, is processed in a rotary salt furnace to recover the metal, and the residual salt cake is treated to recover the flux salts for reuse and the non-metallic oxide fraction for use as a cement kiln raw material and refractory filler. The anodising line's spent caustic etch is recovered as aluminium hydroxide, saleable to the water-treatment industry as a coagulant precursor and to the flame-retardant market, and the rinse waters are recycled through ion exchange. Machining swarf is compacted, degreased and returned to the furnace. The furnace flue gas passes through a heat exchanger before its baghouse, and the captured filter dust is returned to the salt furnace. The design intent throughout is that no stream leaves the site without an identified receiving process — the industrial-ecology principle that one process's residue is another's raw material.
Method 3 — minimise energy and source it renewably (criterion 3). Energy demand is first reduced and then decarbonised, in that order, because reducing demand is cheaper per tonne of carbon than supplying it cleanly. Demand reduction comes from regenerative burners on the melting furnace, which recover flue-gas heat to preheat combustion air and cut fuel use by 30 to 50 %; from scrap preheating using furnace exhaust, which also burns off organic coatings before charging; from insulated, well-sealed furnaces with oxygen-trim combustion control; and from casting billet close to final section so less extrusion and machining energy is needed downstream. Supply-side decarbonisation follows: siting the plant on a hydroelectric or wind-rich grid — in a Canadian context British Columbia, Manitoba or Québec, whose grids are more than 90 % renewable — procuring the balance under renewable power purchase agreements, installing rooftop solar for the ancillary loads, and displacing natural gas in the homogenising and ageing ovens with electric resistance or induction heating where practicable.
Assessing whether the result is truly sustainable requires a life-cycle assessment carried out to ISO 14040 and 14044, with the system boundary drawn from cradle to cradle rather than cradle to gate, so that the credit for the material's recovery at end of life is counted and the burdens of collection and sorting are counted against it. The honest conclusion for this example is that the process approaches but does not attain a closed loop: collection rates for post-consumer building aluminium run around 90 to 95 % rather than 100 %, some metal is lost to oxidation at each remelt, and alloying elements accumulate over successive cycles and eventually constrain the alloys that can be made. Sustainability in practice is therefore a direction of travel measured by declining virgin input, declining energy per tonne and declining residual to landfill, rather than an absolute state that a process either has or has not reached.
The figure supplied with the question is a monitoring-well hydrograph, and reading it correctly is the starting point of the assessment because it establishes all three of the quantities an EIA needs before it can evaluate any proposal.
Three readings follow from the record. The baseline condition is the water table at the start of the period, about 2.5 to 3 m below ground surface, which is the reference state against which change is judged. The normal variability is the seasonal oscillation of roughly one metre either side of the local mean, driven by spring recharge from snowmelt and by summer drawdown from irrigation and evapotranspiration; this is the envelope of natural fluctuation, and a change lying inside it is not an impact. The current trend is the steady decline of about 0.65 m per year, some 5.3 m over the record, which lies entirely outside the range of normal variability and is the finding that triggers the assessment. The distinction is the analytical heart of the answer: an impact is a change that can be shown to lie outside natural variability, and it is only because the trend is large relative to the seasonal envelope that a decline can be attributed to abstraction rather than to a run of dry years. The trend also implies that abstraction exceeds recharge, so the aquifer is being mined rather than used sustainably.
| EIA process step | Main issues to resolve | Actions necessary |
|---|---|---|
| 1. Project description and screening | Define the undertaking — new or expanded wells, artificial recharge, or a supply alternative — and determine whether it is subject to assessment under the applicable federal or provincial trigger and to a provincial water-licence approval. | Describe the works, abstraction rates and duration; screen against the Impact Assessment Act project list and provincial water legislation; identify Indigenous rights and treaty interests engaged and begin consultation at this stage, not later. |
| 2. Scoping | Decide which valued components matter — drinking water supply and quality, baseflow to streams and wetlands, aquatic and riparian habitat, domestic and agricultural well users, and land subsidence — and set spatial and temporal boundaries. | Hold public and Indigenous engagement to identify local concerns and traditional knowledge; set the study area to the modelled cone of depression plus the recharge zone; set the assessment horizon to at least the project life plus recovery time. |
| 3. Baseline characterisation | The single monitoring hydrograph is not enough to distinguish pumping-induced decline from a climatic drought, nor to map the extent of the affected area. | Extend the well network across the aquifer; log stratigraphy and run pumping tests for transmissivity and storativity; sample water chemistry and isotopes to date the water and identify recharge sources; compile precipitation and streamflow records over the same period so climate can be separated from abstraction; census all existing users and their withdrawals. |
| 4. Impact prediction | How far will the water table fall, over what area, and what are the consequences for wells, streams and water quality? | Build and calibrate a numerical groundwater flow model (for example MODFLOW) against the observed hydrograph; run scenarios for present, increased and reduced abstraction against wet, normal and dry climate sequences including climate-change projections; quantify the water balance to compare abstraction with sustainable recharge. |
| 5. Impact evaluation and significance | Determine whether predicted effects are significant — wells going dry, higher pumping costs and energy use, loss of stream baseflow and fish habitat, saline or contaminated water drawn in from adjacent formations, and land subsidence with consequent damage to infrastructure. | Judge significance against the natural variability envelope and against thresholds such as well screen depth, ecological baseflow requirements and drinking-water quality guidelines; assess cumulative effects of all users together, not the proposed increment in isolation. |
| 6. Mitigation — increasing available water quantity | The objective the question sets: raise the water table and make supply sustainable, in the standard order of avoid, reduce, restore, compensate. | Demand side: leak detection and mains renewal, metering and conservation pricing, efficient irrigation such as drip and scheduling, and reuse of treated wastewater for irrigation. Supply side: managed aquifer recharge through infiltration basins and injection wells using treated surface water or stormwater; rainwater harvesting; redistributing and re-screening wells to spread the drawdown; conjunctive use of surface water in wet seasons to rest the aquifer; and protecting the recharge zone from paving and contamination through land-use control. |
| 7. Follow-up, monitoring and adaptive management | Predictions carry real uncertainty, so the assessment must be verified in operation and the plan must be able to change. | Maintain the monitoring well network with telemetered continuous water-level and quality logging; set trigger levels that mandate specified reductions in abstraction when reached; report publicly each year; and review the water licence on a fixed cycle against the observed response. |
The test of success is directly readable from the same hydrograph that raised the alarm: the objective is to flatten the trend line to a zero long-term slope, so that the record shows only the seasonal oscillation about a stable mean and abstraction has been brought back within the aquifer's recharge. Recovery of the several metres already lost will follow slowly and only if recharge exceeds abstraction for a sustained period, which is why the earlier the trend is detected the cheaper the remedy. This is also the clearest illustration of why baseline monitoring has value long before any project is proposed — without eight years of record there would have been no way to demonstrate that the decline is real, that it is outside natural variability, and that it is attributable to abstraction rather than to weather.
