18-Env-B4 Site Assessment and Remediation · December 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams; December 2017 — 04-Env-B4 / Site Assessment and Remediation. 3 hours duration; open-book exam (Casio or Sharp approved calculator only). The paper is split into Section A (five questions, candidates asked to answer four) and Section B (two questions, candidates asked to answer one), each question worth 20 marks. All seven required questions plus the second Section B option are solved below for completeness — eight questions in total.
Reference texts. Suthersan & Payne, Remediation Engineering: Design Concepts (CRC Press); Freeze & Cherry, Groundwater; Schwarzenbach, Gschwend & Imboden, Environmental Organic Chemistry; Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); American Petroleum Institute (API) publications on fuel-release site assessment and UST modelling; ASTM E1527 Standard Practice for Phase I Environmental Site Assessments and ASTM E1903 Standard Practice for Phase II ESA; Ontario Reg. 153/04 under the Environmental Protection Act (Record of Site Condition regime) and O.Reg. 406/19 (excess soil management); Transportation of Dangerous Goods Act/Regulations (Canada); CCME Canadian Environmental Quality Guidelines.
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.
Redevelopment and reuse (rather than simple containment or off-site removal) is the explicit community goal here, which changes the framing relative to a pure risk-management decision: the objective is to maximize the soil that stays on or near the property as usable fill, not merely to make the site "safe." The contaminant mix — hydrocarbons and PAHs (organic, biodegradable/destructible) alongside heavy metals (inorganic, only immobilizable, never destroyed) — means no single option treats everything, so the real question is which fraction goes where.
On-site treatment (in-situ and on-site ex-situ) — merits. Avoids transporting large soil volumes off-property, which is both the largest cost driver and the largest community-disruption factor (truck traffic through a residential/mixed-use redevelopment area) on a multi-property, railway-corridor-scale program. Supports the community's stated reuse goal directly — treated soil that meets the applicable standard can be placed back as engineered fill under the new development, consistent with Ontario's excess-soil reuse framework (O.Reg. 406/19), which specifically favours beneficial local reuse over landfilling. Organic contaminants (hydrocarbons, PAHs) are well suited to on-site biological treatment (land-farming, biopiles, in-situ bioremediation) or thermal desorption run as a mobile on-site unit, since these processes destroy or volatilize the contaminant rather than just moving it.
On-site treatment — challenges. Heavy metals cannot be destroyed on-site by any biological or thermal method — only stabilized/solidified or physically separated, so "on-site treatment" for the metals fraction really means immobilization, which still requires the metal to remain permanently on the property under a documented long-term management plan (institutional controls, capping, monitoring). Treatment times for biological methods are longer than excavation/disposal, which can conflict with development schedules. Space for staging biopiles/land-farming may be limited on a dense urban railway-corridor site, and heterogeneous fill material typical of century-old industrial/rail sites (mixed debris, ballast, foundations) complicates uniform treatment.
Off-site disposal/treatment — merits. Immediate, verifiable removal of the highest-risk material (fastest schedule, direct confirmation sampling of the open excavation); the only realistic option for soil so heavily impacted that no on-site technology can reach the applicable standard in a practical time frame; and appropriate for small, isolated hot spots where mobilizing on-site treatment equipment is not cost-effective.
Off-site disposal/treatment — challenges. Directly works against the stated community reuse goal — every truckload sent to landfill is soil that will never be reused locally, and Southern Ontario landfill capacity for contaminated soil is itself limited and increasingly costly; truck traffic and off-site handling create their own community and environmental (greenhouse-gas, road-wear) burden across a multi-site program; and it does not "solve" the metals problem, only relocates it to a landfill, which is not materially different from on-site stabilization in terms of long-term liability, but at far higher cost and disruption.
| Contaminant fraction | Recommended approach | Rationale |
|---|---|---|
| Hydrocarbons/PAHs (organic) | On-site treatment (biopile/land-farming or on-site thermal desorption) | Destructible; supports reuse goal; slower but scalable across the corridor |
| Heavy metals (inorganic) | On-site stabilization/solidification for bulk soil; off-site disposal only for the smallest, highest-concentration hot spots | Cannot be destroyed; immobilization allows reuse under a documented long-term management plan |
| Overall recommendation | On-site/on-property treatment as the primary strategy, off-site disposal reserved for hot spots and unmanageable volumes | Matches community reuse objective, minimizes truck traffic/cost across many sites, consistent with O.Reg. 406/19 |
Recommendation. For a multi-site, community-scale reuse program of this kind, on-site treatment should be the primary strategy, with off-site disposal reserved for a limited category of hot spots or volumes that on-site methods genuinely cannot handle in the available time and space. This is because the community's own objective — reuse, not just removal — is best served by keeping treated soil in place as engineered fill, the organic contaminant fraction (the majority of the listed contaminants) is genuinely destructible on-site, and the metals fraction can be made suitable for reuse under a documented stabilization and long-term management plan rather than trucked away at high cost with no net reduction in total contaminant mass in the province.
