ABC Technical Proficiency and Best Practices 3 — Questions and Answers
Question 1: A water operator calculates that the detention time in a clearwell is 2 hours. If the flow is 1.5 MGD, what is the approximate volume of the clearwell in gallons?
- 62,500 gallons
- 125,000 gallons (Correct answer)
- 3,000,000 gallons
- 180,000 gallons
Correct answer: 125,000 gallons
Detention time = Volume / Flow; 2 hr × (1,500,000 gpd ÷ 24 hr/day) = 125,000 gallons.
Question 2: Which indicator best reflects the biological health and stability of activated sludge?
- Settleable solids volume
- Sludge volume index (SVI) (Correct answer)
- Biochemical oxygen demand (BOD) of the influent
- Total suspended solids in the effluent
Correct answer: Sludge volume index (SVI)
SVI measures how well sludge settles and compacts; normal values (80–150 mL/g) indicate healthy, well-settling biological floc.
Question 3: What is the primary purpose of maintaining a chlorine residual in a drinking water distribution system?
- To improve taste and odor of finished water
- To provide continued disinfection protection against microbial contamination (Correct answer)
- To meet corrosion control treatment requirements
- To oxidize iron and manganese in the distribution mains
Correct answer: To provide continued disinfection protection against microbial contamination
A chlorine residual acts as a continuous disinfectant barrier, protecting water from microbial regrowth or contamination during distribution.
Question 4: When performing a jar test to optimize coagulation, the operator adjusts which variable to find the optimal dose?
- Filtration rate
- Coagulant concentration (Correct answer)
- Disinfectant contact time
- Sedimentation basin depth
Correct answer: Coagulant concentration
The jar test evaluates different coagulant doses to identify the concentration that produces the best floc formation and clarification.
Question 5: Under the Safe Drinking Water Act, which document must an operator maintain to demonstrate compliance with water quality standards?
- Annual Consumer Confidence Report (Correct answer)
- Operations and Maintenance Manual
- Operator Certification Record
- Comprehensive Facility Emergency Response Plan
Correct answer: Annual Consumer Confidence Report
The Annual Consumer Confidence Report (CCR) is a federally mandated document delivered to customers summarizing water quality data and compliance status.
Question 6: What operational adjustment would an operator make if the secondary clarifier sludge blanket level is rising dangerously high?
- Increase the waste activated sludge (WAS) pumping rate (Correct answer)
- Decrease the return activated sludge (RAS) pumping rate
- Reduce aeration basin dissolved oxygen
- Increase influent flow to the clarifier
Correct answer: Increase the waste activated sludge (WAS) pumping rate
Increasing WAS removes excess sludge from the system, lowering the blanket level in the secondary clarifier.
Question 7: Which chemical is most commonly used in the US to adjust pH upward during drinking water treatment to meet corrosion control requirements?
- Sulfuric acid
- Sodium fluoride
- Lime (calcium hydroxide) (Correct answer)
- Potassium permanganate
Correct answer: Lime (calcium hydroxide)
Lime raises water pH, reducing corrosivity and helping comply with Lead and Copper Rule corrosion control treatment requirements.
ABC Technical Proficiency and Best Practices 3
A water operator calculates that the detention time in a clearwell is 2 hours.
If the flow is 1.5 MGD, what is the approximate volume of the clearwell in gallons?