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

WT treatment: operation: practice questions

Our Water/Wastewater Operator bank has 6 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 should an operator do if the chlorine residual leaving the plant drops below the required minimum?

  1. Wait until the next day's sample to see whether the residual recovers
  2. Wait until the next day's sample to see whether the residual has recovered on its own
  3. Correct the feed immediately, increase monitoring and notify the state as required
  4. Turn off the high-service pumps permanently
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C. Correct the feed immediately, increase monitoring and notify the state as required — Under 0.2 mg/L for more than 4 hours is a violation for surface water systems.

Question 2 · Water Treatment Class I

Raw water turbidity suddenly rises after a storm. What is the first operational response?

  1. Turn off coagulant feed
  2. Run jar tests and adjust coagulant dose as needed
  3. Turn off the coagulant feed until the turbidity drops back down
  4. Increase filter rates
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B. Run jar tests and adjust coagulant dose as needed — Changing raw water needs new dose decisions.

Question 3 · Water Treatment Class I

Why should operators trend data such as turbidity and residuals?

  1. Trends reveal developing problems before they cause violations
  2. Trends set customer rates
  3. Trends replace lab tests and are only needed for monthly reports
  4. Trends are only for reports
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A. Trends reveal developing problems before they cause violations — Identifying trends and abnormal operation is a listed task.

Question 4 · Water Treatment Class I

Why is a sudden rise in filtration rate harmful?

  1. It reduces head loss
  2. It cleans the filter and lowers the head loss
  3. It can dislodge captured particles and cause turbidity breakthrough
  4. It improves water quality
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C. It can dislodge captured particles and cause turbidity breakthrough — Change filter rates gradually.

Question 5 · Water Treatment Class I

Filter effluent turbidity rises right after a backwash. What is a common fix?

  1. Use filter-to-waste or a filter aid polymer during ripening
  2. Skip the next backwash
  3. Turn off the coagulant feed and increase the filtration rate
  4. Turn off coagulant
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A. Use filter-to-waste or a filter aid polymer during ripening — Ripening turbidity spikes are common.

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