Question 1 of 5: General

Question 1: General (25 marks)

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.

1) Definitions (10 marks)

i) Water quality guideline vs. criteria. A water quality criterion is the scientifically derived concentration or narrative condition of a substance or parameter that is known, from toxicological and ecological research, to protect a designated water use (e.g. aquatic life, drinking water). A guideline is the numeric or narrative value that regulators (in Canada, the Canadian Council of Ministers of the Environment, CCME) publish based on that criterion as a recommended, generally non-enforceable benchmark for managing water quality. In short: the criterion is the underlying science, the guideline is the published management value derived from it — a guideline only becomes legally binding once it is adopted into a regulation or permit as an enforceable standard or objective.

ii) Non-point source pollution. Pollution that enters a water body from a diffuse area rather than a single identifiable outfall or pipe — agricultural runoff carrying nutrients/sediment/pesticides, urban stormwater, atmospheric deposition, and manure-field runoff are classic examples. Because it has no single discharge point, non-point pollution cannot be controlled by an end-of-pipe treatment device; it is managed instead through land-use practices (buffer strips, nutrient management plans, cover crops, erosion control).

iii) Self-purification capacity. The natural ability of a stream or lake to assimilate and break down an organic or nutrient load through dilution, sedimentation, reaeration, and microbial degradation, restoring the water body to its pre-discharge condition over distance/time without external treatment. It is bounded — the classic Streeter-Phelps dissolved-oxygen sag curve illustrates the balance between the deoxygenation rate of the added BOD load and the stream's own reaeration rate; loading beyond the self-purification capacity produces a DO sag below the water quality objective.

iv) Sludge retention time (SRT). Also called mean cell residence time (MCRT): the average time biological solids remain within a treatment system, computed as the mass of solids held in the system divided by the mass of solids wasted per day. SRT governs the degree of biological stabilization achieved and is deliberately decoupled from hydraulic retention time (HRT, the average time the liquid itself spends in the tank) in any process with solids recycle — a long SRT with a short HRT is exactly how activated-sludge and similar processes achieve high treatment efficiency in a compact tank.

v) Engineered wetland. A constructed treatment system that deliberately reproduces the physical, chemical and biological treatment processes of a natural wetland — settling, filtration through substrate, plant nutrient uptake, and microbial transformation (nitrification/denitrification, sulfate reduction) — under controlled hydraulic conditions. Built as either free-water-surface (open water, emergent vegetation) or subsurface-flow (water moves through a gravel/soil bed below grade) systems, engineered wetlands are used as a low-energy polishing step for agricultural runoff, lagoon effluent, or stormwater.

2) Nitrogen transformation pathways after swine manure land application (5 marks)

At least three pathways redistribute the organic and ammoniacal nitrogen applied in swine manure: mineralization, in which soil microbes convert organic-N to plant-available ammonium (NH₄⁺) over the growing season(s) following application; nitrification, the aerobic microbial oxidation of that ammonium first to nitrite then to nitrate (NO₃^-), which is mobile and available for either plant uptake or leaching; and denitrification, the anaerobic microbial reduction of nitrate to gaseous N₂O/N₂ under saturated or poorly aerated soil conditions, which is a genuine loss of nitrogen (and a greenhouse-gas emission pathway) from the field. A fourth pathway worth naming is ammonia volatilization, the direct loss of NH₃ gas to the atmosphere from surface-applied manure before it is incorporated into the soil — this is exactly the 30% volatilization factor used quantitatively in Question 5 below. Finally, some of the transformed nitrogen is captured by plant uptake (the design target of a nutrient-management plan) while any surplus nitrate that escapes uptake and denitrification is vulnerable to leaching to groundwater.

3) Windrow vs. static pile composting (5 marks)

Windrow composting (elongated piles turned mechanically on a schedule) gives the operator direct, hands-on control of aeration and temperature — turning breaks up channelling, re-homogenizes the mix, and reliably drives every part of the pile through the pathogen-kill temperature range. Its disadvantages are a larger land footprint per tonne processed, a heavier reliance on turning equipment and fuel/labour, and a higher risk of odour release each time the pile is opened and turned. Static pile composting (aerated static pile, ASP — a stationary pile aerated by blowers through a perforated pipe network) needs no turning equipment or labour, gives more consistent process control once commissioned, and — because the pile stays closed — has lower odour release and a smaller operating footprint. Its disadvantages are the up-front capital and ongoing energy cost of the blower/piping system, a greater risk of anaerobic dead zones or short-circuiting if the pile is poorly structured or under-aerated, and less flexibility to physically remix the material if a cold spot or excess moisture pocket develops partway through the process.

4) Deadstock incineration — environmental risks and mitigation (5 marks)

Risk 1 — air emissions. Combustion of animal carcasses releases particulate matter, odour, greenhouse gases, and — if combustion is incomplete or occurs at too low a temperature — dioxins/furans and other products of incomplete combustion. Mitigation: (a) operate the primary chamber with a secondary/afterburner chamber maintained above roughly 850 °C with adequate gas residence time to fully destroy organic combustion by-products, and (b) fit air-pollution-control equipment (baghouse filtration, wet or dry scrubbing) with a routine stack-emissions monitoring and maintenance program to keep particulate and acid-gas emissions within the facility's air permit.

Risk 2 — ash and residual contamination. Incinerator ash can concentrate heavy metals and, if combustion was incomplete, may retain viable pathogens; improperly stored or disposed ash risks leaching contaminants to soil and groundwater. Mitigation: (a) maintain strict temperature/residence-time process control (as above) so that ash is genuinely pathogen-free and combustion is complete before it ever leaves the chamber, and (b) handle and dispose of the ash through an approved pathway only — a permitted landfill cell or regulated land application at agronomic metal-loading rates — with covered on-site storage to prevent leachate generation between disposal events.