Question 6 of 7: Air Toxics Control, Environmental Quality Standards/Guidelines and Solid Waste Management

Question 6: Air Toxics Control, Environmental Quality Standards/Guidelines and Solid Waste Management (20 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.

(i) Control Methods for Benzene and Methylene Chloride Emissions

(ii) Environmental Quality Standards versus Guidelines

The key difference is legal enforceability. An environmental quality standard is a legally binding numeric or narrative limit set in regulation or a permit, with defined compliance obligations and enforcement consequences (orders, penalties) for exceedance. An environmental quality guideline is a science-based recommended value or target that is not, by itself, legally binding — it represents best professional judgment of a protective level but carries no automatic penalty for exceedance unless separately incorporated into a permit or regulation.

Standards are superior where certainty, consistency and enforceability are paramount — e.g., a discharge permit limit for a specific facility, where the regulator needs a clear, defensible legal threshold to compel compliance and to prosecute non-compliance. Guidelines are superior where flexibility and rapid updating in response to evolving science are more valuable than rigid enforceability — e.g., ambient water-quality or soil guidelines used to screen a very wide range of site conditions and contaminants, where a single legally-fixed numeric standard for every substance and every context would be impractical to develop and maintain, and where the guideline can be revised quickly as new toxicological data emerge without the delay of a formal regulatory amendment process.

(iii) Extending Landfill Life from 10 to 20 Years

Three strategies to extend the existing landfill’s life from a 10-year to a 20-year horizon:

1. Waste diversion through enhanced recycling and organics diversion. Implementing (or expanding) mandatory curbside/commercial recycling and a separate organics (food waste/yard waste) collection stream for composting or anaerobic digestion removes a large fraction — organics alone are often 30–40% of the municipal waste stream by weight — of material that would otherwise consume landfill airspace. Implementation requires new collection infrastructure (bins, trucks, routing), a processing facility (composting pad or digester), and public education/enforcement to achieve high participation and low contamination rates.
2. Waste-to-energy (WTE) or landfill-gas-to-energy. Combusting the residual, non-divertible waste fraction in a WTE facility dramatically reduces the volume requiring landfilling (typically by roughly 90% by volume), directly extending site life, while also generating recoverable energy; alternatively (or in addition), capturing landfill gas from the existing site for energy recovery does not reduce airspace consumption but improves the environmental performance of the extended-life site. Implementation of WTE requires significant capital investment, an air-emissions permit and control train, and a long-term supply agreement to justify the facility, so it suits a jurisdiction planning multi-decade waste management, not just a stop-gap.
3. Optimized landfill operations — compaction and cell design. Increasing in-place waste density through more aggressive compaction equipment/practice, minimizing daily cover soil volume (e.g., using alternative daily cover materials or tarps instead of a full soil layer), and, where geotechnically and regulator-approved, vertical expansion (increasing final cell height) all increase the effective airspace utilized per tonne of waste without acquiring new land. Implementation is comparatively low-cost and can begin immediately (equipment/procedure changes), but vertical expansion specifically requires a geotechnical stability and leachate/gas-management review and a permit amendment before proceeding.

Combining all three — diversion to reduce the incoming tonnage, WTE/energy recovery to shrink the residual volume, and operational optimization to use the remaining airspace more efficiently — gives the city several independent, additive levers, which is generally more robust than relying on any single strategy to double the site’s remaining life.