18-Env-B7 Environmental Sampling and Analysis · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams, May 2017 — 04-Env-B7, Environmental Sampling and Analysis (3 hours, closed book, approved non-programmable calculator only, statistical tables provided). The paper instructs "answer all 4 questions in Part A and any 2 questions in Part B"; as a study resource this solution answers all 7 questions in full, including all three Part B questions.
Reference texts: Walpole, Myers, Myers & Ye, Probability & Statistics for Engineers and Scientists (sampling designs, hypothesis tests, EDA/boxplots, 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 that is naturally present, or present prior to the activity under investigation, established by sampling an unaffected reference or up-gradient location; it is the yardstick against which a potentially impacted (down-gradient or on-site) result is compared to determine whether a real impact has occurred.
b) Censored data. Measurements that are known only to lie above or (far more commonly in environmental work) below a threshold — typically the laboratory's method detection limit (MDL) or reporting limit — rather than as an exact numeric value; a censored result is reported as "<MDL" and requires specialized statistical methods (e.g. Kaplan–Meier, regression-on-order-statistics) rather than simple substitution to summarize correctly.
c) Composite sample. A single sample formed by physically combining several discrete grab samples (collected across different locations, depths, or times) into one container before analysis; it yields one analytical result representing the spatially/temporally averaged condition of the combined grabs, reducing analytical cost at the expense of losing information about the variability among the individual grabs.
d) Colorimetric analysis versus instrumental analysis. Colorimetric analysis is a rapid, low-cost field or screening method in which a reagent produces a colour change proportional to analyte concentration, read visually or with a simple hand-held photometer — convenient but with higher detection limits and lower precision/selectivity. Instrumental analysis (e.g. atomic absorption, ICP-MS, GC-MS) uses dedicated laboratory instrumentation to achieve much lower detection limits, higher precision and specificity, at higher cost and turnaround time; colorimetric methods are typically used for field screening/triage, with instrumental methods reserved for definitive, defensible results.
e) Hotspots. Localized areas within a site that exhibit contaminant concentrations significantly elevated above the surrounding background or site-average level, often driven by a discrete source (a spill point, a buried drum, a former process area); hotspots are the reason purely random (SRS) sampling designs can under-represent risk, motivating judgmental or adaptive-cluster sampling in areas suspected of contamination.
f) Maximum Contaminant Level (MCL). The legally enforceable maximum concentration of a specific contaminant permitted in a regulated medium (most commonly drinking water), set by the responsible regulatory body (in Canada, the Guidelines for Canadian Drinking Water Quality published by Health Canada, adopted provincially) to protect human health with an appropriate margin of safety; exceeding the MCL triggers a required regulatory or corrective response.
g) Assessment monitoring versus compliance monitoring. Assessment monitoring is investigative: it characterizes the nature, extent and magnitude of contamination (or confirms/denies a suspected release), often at increased spatial/temporal density and with a broader analyte list. Compliance monitoring is routine and ongoing: it demonstrates, on a fixed schedule against a fixed analyte list and limit (e.g. an MCL or discharge permit condition), that a facility continues to meet its regulatory obligations; assessment monitoring is typically triggered by, or precedes, a change to the compliance monitoring program.
h) Data QA/QC. The complete set of planned and documented procedures — field blanks, trip blanks, duplicates, spikes, chain-of-custody, laboratory accreditation and calibration — that together ensure reported environmental data are of known, defensible quality and are traceable from field collection through to the final reported result (see also Question 4).
