Sampling, Measurement, and Monitoring
What this domain tests
This domain tests whether you can design a sampling or monitoring program that produces data fit for a stated decision. Items cover sampling design, representativeness, sample handling, field quality control, instrument calibration, detection limits, and monitoring frequency.
Core rules and concepts
- Sampling design follows the objective. Random or stratified random supports statistical inference; judgmental sampling targets known hot spots; systematic grids suit spatial coverage. Composite samples estimate average conditions but obscure peaks and are unsuitable for volatile analytes.
- Representativeness requires an appropriate location, timing, and physical handling. A sample that is not representative cannot be corrected later.
- Field quality control commonly includes duplicates, equipment blanks, trip blanks for volatile organics, matrix spikes, and temperature or preservation checks.
- Contamination control means clean equipment, dedicated or disposable tubing, background checks, and sampling least-contaminated locations first when a gradient is suspected.
- Monitoring design distinguishes baseline, compliance, performance, and closure monitoring. Each has a different frequency and decision rule.
- Detection and reporting limits should be below the regulatory or assessment threshold; otherwise the data cannot answer the question.
Worked example
A groundwater monitoring well must be sampled for volatile organic compounds and metals. Reasoning: purge by low-flow methods until pH, specific conductance, dissolved oxygen, oxidation-reduction potential, and turbidity stabilize, because stabilized indicator parameters indicate formation water rather than stagnant casing water. Sample volatile organics first, then metals, because volatiles are lost during handling and metals are less affected. Use new tubing, collect a trip blank and a field duplicate, fill volatile vials with no headspace, and chill and preserve according to the method. Record stabilization readings and purge volume. A full-credit answer explains why the order and the stabilization criteria matter, not just that they were followed.
Traps that cost marks
Compositing volatile samples; purging by fixed volume without checking stabilization; omitting a trip blank; collecting the duplicate from a different location and calling it precision; and setting a reporting limit above the regulatory threshold.