ABC Field Test and Inspection Procedures 2 — Questions and Answers
Question 1: When collecting a water sample for bacteriological analysis, what is the minimum flush time before sample collection from a chlorinated distribution tap?
- 30 seconds
- 2–3 minutes (Correct answer)
- 10 minutes
- No flushing required
Correct answer: 2–3 minutes
Taps must be flushed 2–3 minutes to clear standing water and obtain a representative distribution sample.
Question 2: A Hach DR spectrophotometer reads a chlorine residual of 0.00 mg/L in a distribution sample. The first troubleshooting step should be:
- Replace the reagent powder pillow and re-test (Correct answer)
- Report a chlorine deficiency immediately
- Collect a new sample from a different tap
- Check the meter's wavelength setting
Correct answer: Replace the reagent powder pillow and re-test
Depleted or expired DPD reagent is the most common cause of a falsely zero chlorine reading.
Question 3: What field parameter is used to estimate the carbonate-bicarbonate equilibrium and corrosivity of a water supply?
- Turbidity (NTU)
- Langelier Saturation Index (LSI) (Correct answer)
- Total dissolved solids (TDS)
- Conductivity (µS/cm)
Correct answer: Langelier Saturation Index (LSI)
The Langelier Saturation Index indicates whether water will tend to deposit scale or corrode pipe materials.
Question 4: Which instrument measures the dissolved oxygen concentration directly without the need for chemical titration?
- Colorimeter
- Membrane electrode DO meter (Correct answer)
- Winkler titration kit
- Nephelometer
Correct answer: Membrane electrode DO meter
A membrane electrode (polarographic or galvanic) DO meter measures oxygen electrochemically in the field.
Question 5: During a wastewater effluent inspection, the inspector notices a persistent oily sheen on the receiving stream. The FIRST regulatory concern is:
- Elevated BOD loading
- Violation of oil and grease discharge limits (Correct answer)
- Excessive nutrient loading
- High suspended solids concentration
Correct answer: Violation of oil and grease discharge limits
An oily sheen indicates a possible oil and grease permit exceedance and must be documented and reported.
Question 6: A composite sample for wastewater analysis is best described as:
- A single grab collected at peak flow
- Multiple grab samples combined proportionally over time or flow (Correct answer)
- A 24-hour average calculated from lab results
- A sample filtered before collection
Correct answer: Multiple grab samples combined proportionally over time or flow
Composite samples integrate flow or time variations, providing a more representative average concentration than a single grab.
Question 7: What is the maximum holding time for a chlorine residual field measurement once the sample is collected?
- 15 minutes
- 6 hours
- 24 hours
- Immediately — analyze on-site only (Correct answer)
Correct answer: Immediately — analyze on-site only
Chlorine residual degrades rapidly after collection and must be measured immediately at the sampling point.
ABC Field Test and Inspection Procedures 2
When collecting a water sample for bacteriological analysis, what is the minimum flush time before sample collection from a chlorinated distribution tap?