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Water & Wastewater Operator (WPI/ABC Class I) — Practice Exam

WT lab: practice questions

Our Water/Wastewater Operator bank has 17 questions on this topic. Here are 5 of them with answers; the full mock exam draws from every topic, like the real one.

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Question 1 · Water Treatment Class I

What does a jar test show the operator?

  1. Which coagulant dose and conditions give the best floc and settled water
  2. Lead levels at the tap
  3. The chlorine residual, lead levels and the bacteria count in the settled water
  4. The chlorine residual and lead levels
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A. Which coagulant dose and conditions give the best floc and settled water — It is a process control test.

Question 2 · Water Treatment Class I

What does a high heterotrophic plate count (HPC) suggest in a distribution sample?

  1. Good disinfection
  2. High hardness
  3. Too much chlorine, high fluoride and low turbidity
  4. Bacterial regrowth, often with low residual or stagnant water
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D. Bacterial regrowth, often with low residual or stagnant water — HPC is a general indicator of water quality.

Question 3 · Water Treatment Class I

How should a pH meter be calibrated?

  1. With distilled water only, adjusting the meter to read 7.0
  2. With at least two standard buffers that bracket the expected pH
  3. With distilled water only, adjusting the meter until it reads exactly 7.0 before each use
  4. It never needs calibration
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B. With at least two standard buffers that bracket the expected pH — Common buffers are 4, 7 and 10.

Question 4 · Water Treatment Class I

Why should pH be measured immediately in the field?

  1. Labs can't measure pH
  2. pH is stable for weeks, so it can be measured at the lab later
  3. pH changes as gases such as CO₂ leave or enter the sample
  4. pH only matters at night
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C. pH changes as gases such as CO₂ leave or enter the sample — pH has a very short holding time.

Question 5 · Water Treatment Class I

Why are bacteriological sample bottles supplied with sodium thiosulfate?

  1. To preserve dissolved metals and lower the sample pH so bacteria grow faster in the lab
  2. To preserve metals and adjust the pH of the sample
  3. To neutralize chlorine so it doesn't keep killing bacteria before analysis
  4. To add nutrients for the bacteria
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C. To neutralize chlorine so it doesn't keep killing bacteria before analysis — Residual chlorine would give false negatives.

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