WTO Quality Monitoring 3 — Questions and Answers
Question 1: What is the action level for copper under the Lead and Copper Rule that triggers additional treatment requirements?
- 0.015 mg/L
- 1.3 mg/L (Correct answer)
- 0.005 mg/L
- 2.0 mg/L
Correct answer: 1.3 mg/L
The action level for copper is 1.3 mg/L; if exceeded at the 90th percentile of tap samples, the system must take corrective actions including public education.
Question 2: When using the Standard Methods titration to measure total alkalinity, what indicator is typically used?
- Phenolphthalein only
- Methyl orange only
- Bromocresol green-methyl red mixed indicator
- Both phenolphthalein and methyl orange or a mixed indicator (Correct answer)
Correct answer: Both phenolphthalein and methyl orange or a mixed indicator
Total alkalinity titration uses phenolphthalein to the P-alkalinity endpoint (pH 8.3) and then a mixed indicator to the T-alkalinity endpoint (pH 4.5).
Question 3: A distribution system sample shows a heterotrophic plate count (HPC) of 600 CFU/mL. What does this result suggest?
- The sample is microbiologically safe with no action needed
- There may be a loss of disinfectant residual or biological regrowth (Correct answer)
- Immediate public notification is required
- The sample must be re-collected as it exceeds the MCL
Correct answer: There may be a loss of disinfectant residual or biological regrowth
An HPC above 500 CFU/mL suggests potential loss of disinfectant residual or biological regrowth, though HPC itself has no federal MCL.
Question 4: Under the Stage 2 DBPR, what sampling approach replaced the running annual average used in Stage 1 for TTHM and HAA5 compliance?
- Single-point annual average
- Locational running annual average (LRAA) (Correct answer)
- System-wide running average
- Quarterly grab sampling at entry point only
Correct answer: Locational running annual average (LRAA)
Stage 2 DBPR uses the Locational Running Annual Average (LRAA), which evaluates compliance at each individual monitoring location rather than as a system-wide average.
Question 5: What is the primary purpose of continuous turbidity monitoring at individual filter effluent in a surface water treatment plant?
- To satisfy reporting requirements only
- To detect filter breakthrough and maintain Cryptosporidium removal credits (Correct answer)
- To adjust coagulant dosage in real time
- To measure color removal efficiency
Correct answer: To detect filter breakthrough and maintain Cryptosporidium removal credits
Individual filter effluent turbidity monitoring detects filter breakthrough early, protecting Cryptosporidium removal credits required under the LT2 Enhanced SWTR.
Question 6: Which water quality parameter, if too low, can cause corrosion of distribution system pipes and lead leaching?
- High pH
- Low pH and low alkalinity (Correct answer)
- High hardness
- High turbidity
Correct answer: Low pH and low alkalinity
Low pH combined with low alkalinity creates corrosive water conditions that can dissolve pipe materials and cause lead and copper to leach into drinking water.
Question 7: A fluoride concentration of 2.0 mg/L is detected in a community water system. What regulatory action is triggered?
- Nothing — 2.0 mg/L is below both the SMCL and MCL
- A secondary maximum contaminant level violation for aesthetic concerns only
- A primary MCL violation requiring public notification (Correct answer)
- Immediate treatment shutdown
Correct answer: A primary MCL violation requiring public notification
The primary MCL for fluoride is 4.0 mg/L, and 2.0 mg/L exceeds the secondary MCL (SMCL) of 2.0 mg/L, which triggers public notification about cosmetic dental fluorosis risk.
WTO Quality Monitoring 3
What is the action level for copper under the Lead and Copper Rule that triggers additional treatment requirements?