18-Env-B7 Environmental Sampling and Analysis · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2014 — 04-Env-B7 / Environmental Sampling and Analysis. 3 hours duration; open book (approved Sharp or Casio calculator only); t-distribution table supplied. Part A (Questions 1–3) is compulsory; Part B (Questions 4–6) asks for any two of three — all six are solved below for completeness. Each question is worth 20 marks.
Reference texts. Walpole, Myers, Myers & Ye, Probability & Statistics for Engineers and Scientists (statistical hypothesis testing, exploratory data analysis); Davis & Cornwell, Introduction to Environmental Engineering (6th ed.) (sampling design, QA/QC, environmental monitoring programs); U.S. EPA Guidance for Choosing a Sampling Design for Environmental Data Collection (QA/G-5S); Canadian Council of Ministers of the Environment (CCME) monitoring and reporting guidance.
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 level of a substance already present in the environment from natural sources or general, diffuse anthropogenic loading, independent of the specific point-source under investigation. It is the baseline against which a site's incremental impact is judged.
The lowest concentration of an analyte that an analytical method can reliably distinguish from instrument/method noise (i.e., from zero), reported with a stated statistical confidence (commonly 99%). It states what can be detected, not what can be accurately measured – that is the quantification limit (part f).
A grab sample is a single, discrete sample collected at one point in time and space; it represents only the conditions at that instant and location. A composite sample combines several grab samples – over time (e.g., hourly aliquots over a 24-hour period) and/or space – into one physical sample, often flow-proportioned, so a single analysis represents an average condition over the sampling period/area and smooths out short-term fluctuations that a single grab would miss or over-weight.
Colorimetric methods rely on a chemical reaction that develops a colour proportional to analyte concentration, read visually or with a simple field spectrophotometer – fast, inexpensive, and field-portable, but with modest sensitivity and vulnerability to interference from other coloured/turbid constituents in the matrix. Instrumental analysis (e.g., gas chromatography, ICP-MS, atomic absorption) uses dedicated laboratory instrumentation to achieve much lower detection limits, higher specificity, and better precision, at the cost of greater sample preparation, turnaround time, and technical skill.
A test that measures a sample's biological effect (typically toxicity) directly on a living test organism (e.g., Daphnia magna, fathead minnow, algae), yielding an endpoint such as $LC_{50}$ or $EC_{50}$. Unlike a chemical assay, a bioassay captures the integrated effect of every constituent present – including unmeasured or interacting compounds – rather than the concentration of one target analyte.
The Maximum Contaminant Level is a regulatory, health-based upper limit permitted for a contaminant in a given medium (e.g., a drinking-water standard). The Quantification Limit is an analytical-performance metric – the lowest concentration a method can measure with acceptable precision and accuracy (typically 3–10× the detection limit). MCL is a legal threshold set by policy; QL is a laboratory capability. A meaningful compliance comparison against an MCL requires the method's QL to sit comfortably below that MCL.
Assessment monitoring is exploratory/diagnostic – characterizing background conditions, delineating the extent of contamination, or determining whether a suspected impact exists at all. Compliance monitoring is routine, permit-mandated sampling carried out on a fixed schedule to demonstrate ongoing conformance with a regulatory limit (e.g., an effluent discharge permit) – its design and frequency are typically fixed by the regulator, not chosen by the investigator.
Quality Assurance is the overall management system – written SOPs, chain-of-custody procedures, personnel training, and periodic audits – that ensures data are collected, handled, and reported to a pre-defined data-quality objective. Quality Control is the set of specific technical checks used to verify that objective is actually being met day to day: field and laboratory blanks, duplicate samples, matrix spikes, and calibration against certified standards. QA is the plan; QC is the evidence the plan is working.
