ABC Technical Proficiency and Best Practices 2 — Questions and Answers
Question 1: When calibrating a dissolved oxygen meter, which action ensures the most accurate reading before field use?
- Submerge the probe in saturated salt solution
- Allow the probe to air-equilibrate at ambient temperature and pressure (Correct answer)
- Zero the meter using deionized water
- Calibrate only at the lab regardless of field conditions
Correct answer: Allow the probe to air-equilibrate at ambient temperature and pressure
Air-equilibrating at ambient conditions accounts for local barometric pressure and temperature, ensuring accurate dissolved oxygen calibration.
Question 2: A wastewater plant operator notices the return activated sludge (RAS) rate is too high. What is the most likely operational consequence?
- Improved BOD removal efficiency
- Increased sludge age in the aeration basin
- Washout of mixed liquor suspended solids from the secondary clarifier (Correct answer)
- Excessive sludge blanket buildup in the aeration basin
Correct answer: Washout of mixed liquor suspended solids from the secondary clarifier
Excessive RAS flow can hydraulically overload the secondary clarifier, causing MLSS washout and poor effluent quality.
Question 3: In a water distribution system, the purpose of a pressure-reducing valve (PRV) is to:
- Increase pressure in low-pressure zones
- Prevent backflow from service connections
- Protect downstream piping from excess upstream pressure (Correct answer)
- Regulate chlorine residual in the distribution system
Correct answer: Protect downstream piping from excess upstream pressure
PRVs maintain downstream pressure within safe limits, protecting pipes, meters, and fixtures from overpressure damage.
Question 4: Which safety practice is most critical when entering a confined space at a water treatment facility?
- Wearing a hard hat and steel-toed boots only
- Testing the atmosphere for oxygen, flammable gases, and toxic vapors before entry (Correct answer)
- Having a coworker watch from outside the entrance
- Ensuring the space was last entered within 24 hours without incident
Correct answer: Testing the atmosphere for oxygen, flammable gases, and toxic vapors before entry
Atmospheric testing is the primary safety requirement before confined space entry to detect oxygen deficiency, flammable, or toxic hazards.
Question 5: What does a high turbidity reading in treated drinking water most directly indicate?
- Excessive chlorine demand
- Possible passage of pathogens through filtration (Correct answer)
- High total dissolved solids concentration
- Inadequate corrosion control treatment
Correct answer: Possible passage of pathogens through filtration
High turbidity in finished water suggests filtration inefficiency, which can allow pathogens including Cryptosporidium to pass through.
Question 6: An operator observes a sudden drop in filter run time. Which of the following is the MOST likely cause?
- Increased backwash frequency
- Reduction in source water temperature
- Coagulation or flocculation process upset (Correct answer)
- Decreased influent flow rate
Correct answer: Coagulation or flocculation process upset
Poor coagulation or flocculation results in poorly formed floc that penetrates and prematurely clogs filter media, reducing run time.
Question 7: When collecting a bacteriological sample for compliance monitoring, the operator must:
- Flush the tap for at least 10 minutes before collection
- Use a sterile container with sodium thiosulfate for dechlorination (Correct answer)
- Collect the sample at a location with the highest chlorine residual
- Refrigerate the sample for at least 2 hours before analysis
Correct answer: Use a sterile container with sodium thiosulfate for dechlorination
Sodium thiosulfate neutralizes residual chlorine, preventing continued disinfection that would kill bacteria during transport and falsely lower counts.
ABC Technical Proficiency and Best Practices 2
When calibrating a dissolved oxygen meter, which action ensures the most accurate reading before field use?