18-Env-B7 Environmental Sampling and Analysis · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams, May 2018 — 04-Env-B7, Environmental Sampling and Analysis (3 hours, closed book, approved non-programmable calculator only, statistical tables provided). The paper instructs "answer all 5 questions"; this solution answers all 5 in full.
Reference texts: Walpole, Myers, Myers & Ye, Probability & Statistics for Engineers and Scientists (sampling designs, hypothesis tests, EDA, ANOVA); Davis & Cornwell, Introduction to Environmental Engineering, ch. 2 (sampling protocol, QA/QC, monitoring program design).
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.
a) Background or baseline concentration. The concentration of a substance already present in an environmental medium from natural sources or general ambient conditions, established before (or independent of) the specific activity or contamination event being investigated. It is the reference point against which an incremental, human-caused increase is judged.
b) Censored data. Measurements for which the exact value is not known, only that it lies beyond some known bound — most commonly "left-censored" results reported only as below the laboratory's method detection or reporting limit ("< MDL", a non-detect); less commonly "right-censored" results above an instrument's calibrated range. Censored values must be flagged and handled with statistical methods suited to censored data, not silently substituted with zero or the detection limit itself.
c) Composite sample. A single physical sample formed by combining several discrete (grab) samples — from different locations, depths, or times — into one container before analysis. It yields an economical estimate of the average concentration over the composited space or time period, but the individual grab-to-grab variability is lost (a single high grab is diluted into the average and may go undetected).
d) Colorimetric analysis versus instrumental analysis. Colorimetric analysis infers concentration from the intensity of a color developed by a chemical reagent reacting with the analyte, read visually or with a simple single/dual-wavelength photometer — inexpensive, field-portable, and fast, but less precise and more susceptible to interferences. Instrumental analysis uses dedicated laboratory instrumentation (e.g. gas chromatography, ICP-MS, atomic absorption, HPLC) that separates and/or detects the analyte with much greater specificity, precision and lower detection limits, at higher capital cost and the need for trained laboratory staff.
e) Remote sensing. The acquisition of information about the earth's surface or an environmental condition without physical contact with the object being measured, typically from a satellite- or aircraft-mounted sensor measuring reflected or emitted electromagnetic radiation (optical, infrared, radar or LiDAR). It is used to characterize large-scale spatial and temporal environmental patterns — land use/land cover change, vegetation health (e.g. NDVI), sea-surface temperature, or turbidity plumes — that would be impractical to cover with point sampling alone.
f) Maximum Contaminant Level (MCL). The legally enforceable maximum permissible concentration of a specific contaminant in drinking water (or an analogous regulated medium), set by the applicable regulatory authority to protect public health with an appropriate margin of safety; exceedance triggers a mandatory regulatory response.
g) Assessment monitoring versus compliance monitoring. Assessment monitoring is diagnostic/exploratory — it characterizes baseline conditions or investigates the nature, extent and behaviour of contamination to inform a decision (e.g. is remediation needed, and where). Compliance monitoring is routine and enforcement-driven — it verifies ongoing conformance with a specific numeric limit set in a permit, licence or regulation, typically on a fixed schedule.
h) Data QA/QC. Quality Assurance (QA) is the overarching program of policies and procedures — written SOPs, a sampling and analysis plan, personnel training/certification, and use of an accredited laboratory — designed to ensure that data of known and adequate quality is produced. Quality Control (QC) is the set of specific technical checks executed to measure and control that quality as the data is generated: blanks, duplicates, spikes, and calibration standards. QA is the plan; QC is its verification in practice.
i) Bioassay. A test method that exposes a living organism (or its cells/tissues) to an environmental sample or condition and measures the resulting biological response — mortality, growth inhibition, reproductive impairment, or another sub-lethal endpoint — to assess the presence, potency or bioavailability of a toxicant, or the aggregate toxicity of a complex mixture that chemical analysis alone cannot characterize.
