Water Quality Monitoring and Laboratory Analysis
What a candidate must know
This domain blends sampling discipline with analytical method awareness. Know proper sampling technique: representative locations, clean and appropriate containers, preservation (cooling, acidification for metals, dechlorination for bacteriological samples), holding times, and chain-of-custody documentation. Understand the meaning of turbidity (NTU), residual chlorine measurement, pH, alkalinity, hardness, and the coliform indicator concept, including total coliform, fecal coliform, and E. coli and what a positive result triggers. Learn quality control vocabulary: blanks, duplicates, spikes, calibration, and control charts. Understand the difference between precision and accuracy, and why a method's detection limit matters. Recognize that chlorine residual decays over time and with temperature, so field readings should be taken promptly.
Traps
Watch for questions that reverse preservation rules (metals are acidified, not bacteriological samples) or that confuse accuracy with precision. A frequent trap is treating a single positive coliform result as automatically confirming contamination without addressing repeat sampling and the presence or absence of E. coli.
Rule of thumb
Sample the system, not the tap: choose sites representative of the distribution system, not the closest convenient faucet. Worked example: a sample reads 0.8 mg/L free chlorine in the field but 0.3 mg/L at the lab two hours later; the difference is decay, so field residual is the value of record for compliance at the point of sampling.