18-Env-B4 Site Assessment and Remediation · December 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams; December 2015 — 04-Env-B4 / Site Assessment and Remediation. 3 hours duration; open-book exam (any non-communicating calculator permitted). The paper is split into Section A (five questions, candidates asked to answer three) and Section B (three questions, candidates asked to answer two), each question worth 20 marks. All eight questions are solved below for completeness.
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.); Leeson & Hinchee (1997), Soil Bioventing: Principles and Practice (AFCEE); ASTM E1527 Standard Practice for Phase I Environmental Site Assessments and ASTM E1903 Standard Practice for Phase II ESA; American Petroleum Institute (API) publications on UST release modelling; Ontario Reg. 153/04 under the Environmental Protection Act (Record of Site Condition regime); BC Environmental Management Act / Contaminated Sites Regulation.
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 site geology is the controlling factor here: a 0.3 m gravel ballast layer bedded directly on low-permeability clay creates a shallow, laterally-continuous preferential pathway right beneath the tracks, while the underlying clay itself strongly limits vertical migration. That combination means the sampling program has to prioritize lateral delineation within the gravel and the clay/gravel interface over deep vertical borings, while still confirming the clay is intact (i.e., that crude has not found a fracture or utility trench and by-passed it) before it can reach the creek 200 m to the east.
Sampling extent and layout. Begin with a biased grid centred on the derailment site (the three ruptured tankers) and extend step-out sampling points radially and, more importantly, preferentially along the rail alignment and any drainage swale, since the gravel ballast will conduct free-phase product for tens of metres along the track bed even where it has not visibly surfaced. Sample at three depth horizons at each location: (1) surface/near-surface soil (0–0.3 m) to capture the initial pooled release and the fire-retardant foam residue; (2) the gravel ballast itself (0.3–0.6 m), the most mobile horizon; and (3) the top of the underlying clay (immediately below the gravel/clay contact), to confirm whether the clay has been breached. A biased judgmental grid (denser near the derailment, thinning outward) is more defensible here than a uniform grid, because the release geometry (tipped tankers at a fixed point) is known, unlike a diffuse or historical release.
Delineating toward the creek. Install a transect of soil borings/piezometers between the spill and the creek, with the closest pair straddling the gravel/clay interface (to catch lateral ballast-layer transport) and at least one located immediately adjacent to the creek bank to confirm (or rule out) surface-water impact. A background sample taken well upgradient/outside any plausible influence establishes the pre-spill baseline for both soil and, if a shallow water table exists, groundwater.
Parameters. Total petroleum hydrocarbons (TPH) as crude oil, BTEX (the mobile, toxic light fraction), and polycyclic aromatic hydrocarbons (PAHs, the persistent heavy fraction) at every location; field screening (photoionization detector headspace readings, visual sheen/staining) to triage and prioritize the fixed laboratory sample set, since 200,000 L covers a large area and PID screening lets the limited lab budget go to the highest-probability locations. Because fire-retardant foam (AFFF-type) was also released, add PFAS to the analyte list at the immediate spill footprint — a foam release is often overlooked as a separate contaminant source distinct from the crude oil itself.
| Element | Approach |
|---|---|
| Layout | Biased grid at derailment site + step-out along rail alignment/ballast; background location |
| Depths | 0–0.3 m surface; gravel ballast 0.3–0.6 m; top-of-clay interface |
| Creek pathway | Transect of borings/piezometers between spill and creek; bank-edge confirmation point |
| Parameters | TPH, BTEX, PAHs; PID field screening; PFAS at the foam-release footprint |
Collection, storage and shipping. Soil samples are collected with decontaminated stainless-steel hand augers/split-spoon samplers (dedicated or decontaminated between locations to avoid cross-contamination), placed directly into laboratory-supplied glass jars with Teflon-lined lids for TPH/PAH (no headspace requirement for semi-volatiles) and into VOA vials with zero headspace for BTEX, which is volatile and lost quickly from an open jar. Samples are labelled immediately (unique ID, depth, time, sampler initials) and logged on a chain-of-custody form that travels with the cooler from the moment of collection. All samples are placed on ice in an insulated cooler at 4 ± 2 °C immediately in the field and kept iced through transport; BTEX has a short regulatory holding time (14 days to analysis, and volatilization losses begin immediately if not chilled), so coolers are shipped same-day or overnight courier to an accredited (CALA/ISO 17025) laboratory, with a trip blank and field duplicate accompanying every shipment for QA/QC.
