18-Env-B4 Site Assessment and Remediation · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Reference texts: Davis & Cornwell, Introduction to Environmental Engineering, 6th ed.; Freeze & Cherry, Groundwater, 1979; Fetter, Contaminant Hydrogeology, 2nd ed.; LaGrega, Buckingham & Evans, Hazardous Waste Management, 2nd ed.; Suthersan, Remediation Engineering: Design Concepts, 2nd ed.; Leeson & Hinchee (AFCEE), Principles and Practices of Bioventing, 1997; CSA Z768/Z769 (Phase I/II ESA); BC Environmental Management Act & Contaminated Sites Regulation.
The paper instructs candidates to answer any THREE of the FIVE questions in Section A and any TWO of the THREE questions in Section B. All eight questions are answered in full below, since this solution set is used as a complete study resource.
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.
This site presents two chemically very different waste streams in close proximity — inorganic metal-bearing plating liquids/sludge and a chlorinated solvent (PCE) — and the sampling program has to be designed so that neither contaminates the other's data set.
Where to sample. Each of the three plating-liquid tanks is sampled at multiple depths (top, mid, near-bottom), since metals commonly settle and stratify in standing liquid; a composite of these depths, plus a separate bottom-sediment grab if a settled layer is visible, characterizes the tank honestly rather than just its surface. The PCE tank is sampled and handled entirely separately from the metals tanks, because PCE (SG > 1) is a DNAPL and any spillage or historic leakage would sink and migrate independently of the metals plume — soil and, if present, groundwater directly beneath and downgradient of that specific tank pad need dedicated attention, sampled to depth rather than assumed to stop at the surface. The sludge pit is cored at several locations and multiple depths, since decades of intermittent discharge typically leave a stratified deposit rather than a homogeneous one; core logs should record any visual layering. Finally, the concrete pads and any floor drains, sumps or cracks beneath all five source areas are sampled (wipe samples on concrete, soil borings beneath and downgradient of the pads) to check for historic leakage into the underlying soil, which is usually the actual remediation driver, not the tank contents themselves.
How samples are collected. Liquids are collected with dedicated or thoroughly decontaminated bailers/depth samplers — equipment is never carried directly from the PCE tank to a metals tank (or vice versa) without a full decontamination sequence, and disposable equipment is preferable given the contaminant mix. Sludge and soil are collected with decontaminated stainless-steel trowels or split-spoon samplers. Metals samples go into HDPE or glass containers preserved with nitric acid to pH < 2 and held at 4°C; the PCE sample goes into a glass VOA vial filled to zero headspace, cooled to 4°C with no chemical preservative, and analyzed within the short volatile-organics holding time (7 days unpreserved for water, 14 days for soil) because PCE will volatilize out of any headspace or through a plastic container wall.
Storage and shipping. All samples are placed in an iced cooler immediately on collection and kept at 4°C ± 2°C, out of direct sunlight, with minimal jostling to avoid disturbing settled solids. Because the waste streams may exhibit hazardous-waste characteristics (corrosivity for the plating liquids, a listed solvent for PCE), shipment to a CALA-accredited analytical laboratory follows Transportation of Dangerous Goods (TDG) packaging and labelling requirements, with a signed chain-of-custody form accompanying the cooler at every transfer of possession. Field QA/QC samples — a trip blank and an equipment rinsate blank for the VOC (PCE) samples, plus field duplicates for both waste streams — are submitted alongside the primary samples so the lab data can be defended.
