18-Env-B4 Site Assessment and Remediation · May 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2014 — 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); Gavaskar, Gupta, Sass, Janosy & O'Sullivan, Design Guidance for Application of Permeable Reactive Barriers for Groundwater Remediation (Battelle/EPA, 2000); ASTM E1527 Standard Practice for Phase I Environmental Site Assessments and ASTM E1903 Standard Practice for Phase II ESA; Mercer & Cohen (1990), “A review of immiscible fluids in the subsurface,” Journal of Contaminant Hydrology; Freeze & Cherry, Groundwater; Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); 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.
Arriving as the environmental first responder, the priority order is safety, source control, containment, and then clean-up initiation — with the wetland 2 km downgradient as the governing sensitive receptor because both the ground-surface slope and the water-table gradient point directly toward it, meaning it is threatened by overland flow, shallow interflow, and eventual groundwater migration alike.
Before any environmental action, the site is secured: eliminate ignition sources, establish exclusion zones, and monitor ambient vapour concentrations (crude oil headspace can contain flammable and toxic light ends). The source itself is then controlled — if any product remains in the punctured tanker, it is off-loaded to a vacuum truck or a patch/plug is applied to stop further release, since every additional litre released increases both the footprint and the eventual clean-up burden.
Given the 2 km travel distance to the wetland, the immediate priority is to stop the spill from ever reaching that pathway rather than to intercept it partway there. This means constructing earthen berms, sandbag/absorbent booms, or trenches downgradient of the pooled oil, oriented perpendicular to the surface-water flow path toward the wetland, to contain surface runoff on-site; deploying sorbent pads/booms and, if rain threatens, an impermeable cover over the exposed pool to limit both further infiltration and overland wash-off; and, if any drainage ditch or culvert exists along the rail right-of-way that could act as a preferential conduit south toward the wetland, blocking or diverting it immediately. Because the water table is also sloped toward the wetland, an interceptor trench or temporary well point between the source and the wetland provides an early-warning and capture point for any oil that does reach groundwater, buying time for a permanent remedy to be designed.
Gross free-product and heavily contaminated soil should be excavated and removed as soon as practicable (hot-spot removal), since this both eliminates a continuing source of infiltration/dissolution and is the single most effective way to shrink the eventual remediation footprint; excavated soil and any recovered free product are contained (lined bins, vacuum-truck storage) pending characterization and off-site disposal or treatment. In parallel, the responder should notify the appropriate regulatory spill line (e.g., BC's Environmental Emergency Program, or the equivalent under the Environmental Management Act) and affected stakeholders (the railway, the municipality, and any downstream landowners including whoever manages the wetland), and commission an expedited site characterization — including at least one monitoring point between the spill and the wetland — to confirm containment is holding and to inform the design of any longer-term remedy (e.g., pump-and-treat, or a permeable reactive barrier of the type analyzed in Question B-1, should dissolved-phase hydrocarbons reach groundwater and threaten the wetland via base flow).
