HIC Water Quality & Sampling 2 — Questions and Answers
Question 1: What is the maximum contaminant level (MCL) for total coliform bacteria in public water systems under the Revised Total Coliform Rule?
- Zero — no coliform-positive samples allowed in systems with <1,000 monthly samples (Correct answer)
- 1 CFU per 100 mL
- 5% of monthly samples may be positive
- 2 NTU turbidity threshold
Correct answer: Zero — no coliform-positive samples allowed in systems with <1,000 monthly samples
The Revised Total Coliform Rule sets an MCL violation when coliform-positive samples exceed 5% in a month for large systems, but for systems with fewer than 40 monthly samples, any positive triggers an E. coli follow-up.
Question 2: Which sampling technique is required when collecting a bacteriological water sample from a tap to ensure accurate results?
- Collect after running water for 5 minutes
- Flame or sanitize the tap, run cold water 2-3 minutes, then collect without touching the faucet interior (Correct answer)
- Collect the first-draw sample immediately without flushing
- Collect from the hot water tap only
Correct answer: Flame or sanitize the tap, run cold water 2-3 minutes, then collect without touching the faucet interior
Sanitizing the tap and flushing 2-3 minutes removes biofilm and stagnant water, yielding a representative distribution system sample.
Question 3: A health inspector finds turbidity in a filtered public water system exceeds 1 NTU in more than 5% of measurements in a month. What does this indicate?
- A treatment technique violation under the Surface Water Treatment Rule (Correct answer)
- An MCL violation for turbidity requiring immediate boil-water notice
- A monitoring-only violation with no public notice required
- An acceptable turbidity level for surface water systems
Correct answer: A treatment technique violation under the Surface Water Treatment Rule
Exceeding 1 NTU in more than 5% of monthly measurements constitutes a treatment technique violation under the Surface Water Treatment Rule.
Question 4: What holding time and temperature are required for bacteriological water samples collected for total coliform analysis?
- 24 hours at 10°C or below (Correct answer)
- 6 hours at room temperature
- 48 hours at 4°C
- 72 hours on ice
Correct answer: 24 hours at 10°C or below
Standard Methods specify a 24-hour maximum holding time at ≤10°C for total coliform samples to preserve sample integrity.
Question 5: Under the Lead and Copper Rule, first-draw lead samples must be collected after water has been stagnant for at least how long?
- 4 hours
- 6 hours (Correct answer)
- 8 hours
- 12 hours
Correct answer: 6 hours
The Lead and Copper Rule requires a minimum 6-hour stagnation period before first-draw sampling to capture lead leaching from plumbing.
Question 6: Which chemical is typically added to sample containers before collection of a chlorinated water sample for bacteriological testing?
- Hydrochloric acid
- Sodium thiosulfate (Correct answer)
- Sodium hypochlorite
- Ascorbic acid
Correct answer: Sodium thiosulfate
Sodium thiosulfate neutralizes residual chlorine in the sample bottle, preventing continued disinfection from killing bacteria during transit.
Question 7: What is the action level (AL) for lead in drinking water under the EPA Lead and Copper Rule?
- 5 ppb
- 10 ppb
- 15 ppb (Correct answer)
- 25 ppb
Correct answer: 15 ppb
The EPA action level for lead is 15 µg/L (ppb); if exceeded at more than 10% of first-draw samples, the system must take corrective action.
HIC Water Quality & Sampling 2
What is the maximum contaminant level (MCL) for total coliform bacteria in public water systems under the Revised Total Coliform Rule?