AWWA Water Quality Testing 3 — Questions and Answers
Question 1: Which organism is used as an indicator for fecal contamination in distribution system monitoring under the Total Coliform Rule?
- Escherichia coli (Correct answer)
- Giardia lamblia
- Cryptosporidium parvum
- Pseudomonas aeruginosa
Correct answer: Escherichia coli
E. coli is the definitive fecal indicator; its presence in a distribution sample triggers immediate investigation and public notification requirements.
Question 2: What is the Maximum Contaminant Level (MCL) for total trihalomethanes (TTHMs) in a community water system?
- 80 µg/L (Correct answer)
- 10 µg/L
- 100 µg/L
- 50 µg/L
Correct answer: 80 µg/L
EPA's Stage 2 Disinfectants and Disinfection Byproducts Rule sets the MCL for TTHMs at 80 µg/L as a locational running annual average.
Question 3: A water sample shows high UV absorbance at 254 nm (UVA254). What does this indicate?
- Elevated natural organic matter (NOM) concentration (Correct answer)
- High turbidity from inorganic particulates
- Elevated chlorine residual
- Presence of heavy metals
Correct answer: Elevated natural organic matter (NOM) concentration
UV absorbance at 254 nm is a surrogate measure of aromatic natural organic matter, which is a precursor to disinfection byproduct formation.
Question 4: Which disinfection method is most effective at inactivating Cryptosporidium oocysts in drinking water?
- Ultraviolet (UV) irradiation (Correct answer)
- Chlorination
- Chloramination
- Ozonation at low doses
Correct answer: Ultraviolet (UV) irradiation
Cryptosporidium oocysts are highly resistant to chemical disinfectants, but UV irradiation at adequate doses effectively inactivates them by damaging their DNA.
Question 5: What is the purpose of heterotrophic plate count (HPC) testing in drinking water?
- Assess general microbial quality and treatment effectiveness (Correct answer)
- Detect specific pathogens like Legionella
- Measure chlorine demand of the water
- Identify specific coliform genera
Correct answer: Assess general microbial quality and treatment effectiveness
HPC measures the total culturable bacteria in water and serves as an indicator of overall microbiological quality and the adequacy of treatment and distribution system maintenance.
Question 6: When calculating chlorine CT values for Giardia inactivation, what does the 'C' represent?
- Residual disinfectant concentration in mg/L (Correct answer)
- Contact time in minutes
- Chlorine dose applied in mg/L
- Cumulative flow volume in gallons
Correct answer: Residual disinfectant concentration in mg/L
In the CT concept, C is the residual disinfectant concentration measured at the outlet of the contact chamber, expressed in mg/L.
Question 7: Which water quality parameter is measured using the SPADNS colorimetric method in a water treatment laboratory?
- Fluoride (Correct answer)
- Nitrate
- Chlorine residual
- Manganese
Correct answer: Fluoride
The SPADNS method uses a dye reagent that reacts with fluoride to form a complex, producing a color change proportional to fluoride concentration.
AWWA Water Quality Testing 3
Which organism is used as an indicator for fecal contamination in distribution system monitoring under the Total Coliform Rule?