Question 4 of 5: Terminology — Definitions

Question 4: Terminology — Definitions (20 marks)

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) BACI (Before-After-Control-Impact) design. A monitoring design for establishing whether a specific development, discharge or remediation actually caused an environmental change, by sampling on two crossed factors: time (before the activity begins and after it begins) and place (the impact site and one or more unaffected control/reference sites). The effect attributable to the activity is not the raw before-to-after change at the impact site — that change also contains any region-wide shift in climate, flow or upstream land use — but the interaction between the two factors: the change at the impact site over and above the change measured at the control site over the same period. Statistically this is the interaction term of a two-factor ANOVA on the (Before/After) × (Control/Impact) design, tested exactly as in Question 2. Its strength is that differencing removes both the pre-existing site-to-site difference and any regional temporal trend; its practical requirements are genuine pre-activity baseline data (which must be planned before the activity starts, and often is not) and control sites that are truly comparable to the impact site. Replicated variants — multiple control sites and multiple sampling times (BACIPS / "beyond-BACI") — are used to avoid pseudo-replication and to distinguish a persistent impact from a transient pulse.

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.