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CWEA Grade 2 Lab Analyst Practice Test (2026)
Instructions: Choose the best answer for each question.
Domain 1: Microbiology & Pathogens (20 Questions)
1. The standard test for enumerating total coliforms in drinking water using the membrane
filtration method requires incubating the m-Endo medium at:
A) 20°C for 24 hours
B) 35°C ± 0.5°C for 24 hours
C) 44.5°C ± 0.2°C for 48 hours
D) 55°C for 18 hours
Answer: B
Rationale: Total coliforms are incubated at 35°C ± 0.5°C for 24 hours on m-Endo agar. Fecal
coliforms (or E. coli) are incubated at the higher 44.5°C temperature to select for thermotolerant
organisms.
2. A Gram-negative, rod-shaped bacterium that produces a metallic green sheen on m-Endo
agar is indicative of:
A) Salmonella species
B) Pseudomonas aeruginosa
C) Coliform bacteria (especially E. coli)
D) Staphylococcus aureus
Answer: C
Rationale: Coliforms ferment lactose, producing aldehydes that react with the dyes in m-Endo
agar to create the characteristic metallic green sheen. This is the classic confirmation step in the
membrane filtration test.
3. What is the primary purpose of the confirmed test in the Most Probable Number (MPN)
method?
A) To provide a rapid screening of all bacteria
B) To verify the presence of coliforms from positive presumptive tubes
C) To determine the exact number of bacteria per milliliter
D) To test for chlorine residual
Answer: B
Rationale: The MPN process has three phases: Presumptive (lauryl tryptose broth), Confirmed
(brilliant green lactose bile broth), and Completed. The confirmed test re-inoculates positive
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tubes to verify that gas production was indeed due to coliform bacteria, eliminating false
positives from other gas-producing organisms.
4. Which organism is an indicator of recent (human or animal) fecal pollution and is the most
specific coliform for this purpose?
A) Total Coliforms
B) Fecal Coliforms (E. coli)
C) Clostridium perfringens
D) Fecal Streptococci
Answer: B
Rationale: While total coliforms can include environmental bacteria, E. coli is a specific species
that lives in the intestinal tract of warm-blooded animals. Its presence strongly indicates recent
fecal contamination.
5. A heterotrophic plate count (HPC) is used to:
A) Detect the presence of pathogens like Giardia
B) Measure the general bacterial population in water (including non-coliforms)
C) Test for heavy metals in industrial wastewater
D) Quantify the amount of suspended solids
Answer: B
Rationale: HPC (formerly Standard Plate Count) is a broad-spectrum test that grows aerobic and
facultative bacteria on a nutrient-rich medium (like R2A or Trypticase Soy Agar). It measures
overall bacterial "biomass" and is used to assess changes in water quality and biofilm formation.
6. In wastewater microbiology, the protozoan Opercularia is typically an indicator of:
A) High organic loading and poor sludge health
B) Excellent treatment and a healthy, stabilized biomass
C) Anaerobic conditions in the digester
D) The presence of filamentous bacteria and foaming
Answer: A
Rationale: In activated sludge microscopy, Opercularia (a stalked ciliate) is a hardy organism
that thrives in high-organic-load conditions. Its presence often indicates that the aeration basin
is being overloaded. In contrast, Vorticella and Epistylis are common indicators of healthy, well-
treated effluent.
7. What is the appropriate temperature and time for the fecal coliform test using the
membrane filtration method?
A) 35°C for 24 hours
B) 44.5°C ± 0.2°C for 24 hours
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C) 44.5°C ± 0.2°C for 48 hours
D) 35°C for 48 hours
Answer: B
Rationale: Fecal coliforms are thermotolerant. To differentiate them from total coliforms, m-FC
medium is incubated at the elevated temperature of 44.5°C for 24 hours. (Note: Some labs use
m-ColiBlue24, which is incubated at 35°C and gives both total and E. coli counts.)
Domain 2: Chemistry & Inorganic Analysis (20 Questions)
8. The BOD bottle used for the 5-day biochemical oxygen demand test must be incubated at:
A) 20°C ± 1°C in total darkness
B) 30°C ± 1°C with light exposure
C) 35°C ± 0.5°C in a water bath
D) 4°C ± 2°C for preservation
Answer: A
Rationale: Standard Methods 5210 requires the BOD test to be incubated at 20°C ± 1°C for 5
days in the dark. Darkness is strictly required to prevent photosynthetic algae from producing
oxygen, which would artificially lower the calculated BOD result.
9. In the Winkler titration method for Dissolved Oxygen (DO), what is the purpose of adding
manganous sulfate and alkaline iodide-azide?
A) To precipitate out the chlorine residual
B) To fix the oxygen in the sample by forming a brown manganese dioxide precipitate
C) To lower the pH of the sample for the titration step
D) To buffer the sample against temperature changes
Answer: B
Rationale: The "fixation" step is critical. MnSO₄ reacts with the NaOH in the alkaline iodide-azide
to form Mn(OH)₂. This then reacts with the dissolved oxygen to create a brown MnO(OH)₂
precipitate. This "fixes" the oxygen so it doesn't escape before the titration.
10. A waste stream has a pH of 9.5. To neutralize it for discharge, you should add:
A) Sodium hydroxide (NaOH)
B) Sulfuric acid (H₂SO₄)
C) Hydrochloric acid (HCl)
D) Ammonia (NH₃)
Answer: B
Rationale: pH 9.5 is alkaline (basic). To neutralize it, you must add an acid. In wastewater
CWEA Grade 2 Lab Analyst Practice Test (2026)
Instructions: Choose the best answer for each question.
Domain 1: Microbiology & Pathogens (20 Questions)
1. The standard test for enumerating total coliforms in drinking water using the membrane
filtration method requires incubating the m-Endo medium at:
A) 20°C for 24 hours
B) 35°C ± 0.5°C for 24 hours
C) 44.5°C ± 0.2°C for 48 hours
D) 55°C for 18 hours
Answer: B
Rationale: Total coliforms are incubated at 35°C ± 0.5°C for 24 hours on m-Endo agar. Fecal
coliforms (or E. coli) are incubated at the higher 44.5°C temperature to select for thermotolerant
organisms.
2. A Gram-negative, rod-shaped bacterium that produces a metallic green sheen on m-Endo
agar is indicative of:
A) Salmonella species
B) Pseudomonas aeruginosa
C) Coliform bacteria (especially E. coli)
D) Staphylococcus aureus
Answer: C
Rationale: Coliforms ferment lactose, producing aldehydes that react with the dyes in m-Endo
agar to create the characteristic metallic green sheen. This is the classic confirmation step in the
membrane filtration test.
3. What is the primary purpose of the confirmed test in the Most Probable Number (MPN)
method?
A) To provide a rapid screening of all bacteria
B) To verify the presence of coliforms from positive presumptive tubes
C) To determine the exact number of bacteria per milliliter
D) To test for chlorine residual
Answer: B
Rationale: The MPN process has three phases: Presumptive (lauryl tryptose broth), Confirmed
(brilliant green lactose bile broth), and Completed. The confirmed test re-inoculates positive
, Page |2
tubes to verify that gas production was indeed due to coliform bacteria, eliminating false
positives from other gas-producing organisms.
4. Which organism is an indicator of recent (human or animal) fecal pollution and is the most
specific coliform for this purpose?
A) Total Coliforms
B) Fecal Coliforms (E. coli)
C) Clostridium perfringens
D) Fecal Streptococci
Answer: B
Rationale: While total coliforms can include environmental bacteria, E. coli is a specific species
that lives in the intestinal tract of warm-blooded animals. Its presence strongly indicates recent
fecal contamination.
5. A heterotrophic plate count (HPC) is used to:
A) Detect the presence of pathogens like Giardia
B) Measure the general bacterial population in water (including non-coliforms)
C) Test for heavy metals in industrial wastewater
D) Quantify the amount of suspended solids
Answer: B
Rationale: HPC (formerly Standard Plate Count) is a broad-spectrum test that grows aerobic and
facultative bacteria on a nutrient-rich medium (like R2A or Trypticase Soy Agar). It measures
overall bacterial "biomass" and is used to assess changes in water quality and biofilm formation.
6. In wastewater microbiology, the protozoan Opercularia is typically an indicator of:
A) High organic loading and poor sludge health
B) Excellent treatment and a healthy, stabilized biomass
C) Anaerobic conditions in the digester
D) The presence of filamentous bacteria and foaming
Answer: A
Rationale: In activated sludge microscopy, Opercularia (a stalked ciliate) is a hardy organism
that thrives in high-organic-load conditions. Its presence often indicates that the aeration basin
is being overloaded. In contrast, Vorticella and Epistylis are common indicators of healthy, well-
treated effluent.
7. What is the appropriate temperature and time for the fecal coliform test using the
membrane filtration method?
A) 35°C for 24 hours
B) 44.5°C ± 0.2°C for 24 hours
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C) 44.5°C ± 0.2°C for 48 hours
D) 35°C for 48 hours
Answer: B
Rationale: Fecal coliforms are thermotolerant. To differentiate them from total coliforms, m-FC
medium is incubated at the elevated temperature of 44.5°C for 24 hours. (Note: Some labs use
m-ColiBlue24, which is incubated at 35°C and gives both total and E. coli counts.)
Domain 2: Chemistry & Inorganic Analysis (20 Questions)
8. The BOD bottle used for the 5-day biochemical oxygen demand test must be incubated at:
A) 20°C ± 1°C in total darkness
B) 30°C ± 1°C with light exposure
C) 35°C ± 0.5°C in a water bath
D) 4°C ± 2°C for preservation
Answer: A
Rationale: Standard Methods 5210 requires the BOD test to be incubated at 20°C ± 1°C for 5
days in the dark. Darkness is strictly required to prevent photosynthetic algae from producing
oxygen, which would artificially lower the calculated BOD result.
9. In the Winkler titration method for Dissolved Oxygen (DO), what is the purpose of adding
manganous sulfate and alkaline iodide-azide?
A) To precipitate out the chlorine residual
B) To fix the oxygen in the sample by forming a brown manganese dioxide precipitate
C) To lower the pH of the sample for the titration step
D) To buffer the sample against temperature changes
Answer: B
Rationale: The "fixation" step is critical. MnSO₄ reacts with the NaOH in the alkaline iodide-azide
to form Mn(OH)₂. This then reacts with the dissolved oxygen to create a brown MnO(OH)₂
precipitate. This "fixes" the oxygen so it doesn't escape before the titration.
10. A waste stream has a pH of 9.5. To neutralize it for discharge, you should add:
A) Sodium hydroxide (NaOH)
B) Sulfuric acid (H₂SO₄)
C) Hydrochloric acid (HCl)
D) Ammonia (NH₃)
Answer: B
Rationale: pH 9.5 is alkaline (basic). To neutralize it, you must add an acid. In wastewater
