CWEA Laboratory Analyst Grade 3 Certification Exam | Latest
Update 2026/2027 | 200 Practice Questions & Detailed
Solutions | Laboratory Analyst III Complete Q&A Guide | A+
Graded
Question 1
A laboratory analyst is performing a BOD₅ test and observes that the dissolved oxygen depletion is 0.8
mg/L. What is the most appropriate corrective action?
A) Report the result as zero
B) Increase incubation temperature
C) Decrease dilution factor
D) Increase sample volume in dilution to achieve proper DO depletion
Answer: D) Increase sample volume in dilution to achieve proper DO depletion
Explanation: Acceptable BOD depletion is 2.0–7.0 mg/L; insufficient depletion (<2.0 mg/L) requires
increasing the sample concentration to obtain measurable oxygen demand.
Question 2
What is the main purpose of using a blank sample in chemical analysis?
A) To calibrate instruments
B) To provide a control for contamination
C) To standardize the reagents
D) To increase the concentration of analytes
,Answer: B) To provide a control for contamination
Explanation: A blank sample contains all reagents except the analyte of interest and is used to detect
any contamination or background interference.
Question 3
In the BOD determination, which of the following restrictions applies regarding acceptance of analysis
values?
A) The blank must not deplete more than 0.2 mg/L dissolved oxygen
B) Samples must deplete at least 2 mg/L and have at least 1 mg/L dissolved oxygen remaining
C) The blank must not deplete more than 0.5 mg/L dissolved oxygen
D) Samples must deplete at least 0.5 mg/L and have at least 3 mg/L dissolved oxygen remaining
Answer: A) The blank must not deplete more than 0.2 mg/L dissolved oxygen
Explanation: In BOD determination, the blank must not deplete more than 0.2 mg/L dissolved oxygen,
and samples must deplete at least 2.0 mg/L and have at least 1.0 mg/L dissolved oxygen remaining.
Question 4
Which parameter is most commonly used to assess organic pollution in wastewater?
A) pH
B) Biochemical Oxygen Demand (BOD)
C) Turbidity
D) Conductivity
,Answer: B) Biochemical Oxygen Demand (BOD)
Explanation: BOD is the most commonly used parameter to assess organic pollution in wastewater,
measuring the amount of dissolved oxygen consumed by microorganisms during the decomposition of
organic matter.
Question 5
Which of the following is the most appropriate method for preparing a sample for microbiological
analysis of wastewater?
A) Centrifugation followed by filtration
B) Direct plating without dilution
C) Serial dilution and plating
D) Evaporation of water
Answer: C) Serial dilution and plating
Explanation: Serial dilution and plating ensures that bacterial colonies are countable and prevents
overgrowth, which can obscure results. Direct plating or evaporation could result in inaccurate counts.
Question 6
What does COLOR measure in wastewater analysis?
A) The pH level of the sample
B) The amount of color units (CU) in a sample
, C) The turbidity of the sample
D) The conductivity of the sample
Answer: B) The amount of color units (CU) in a sample
Explanation: Color in wastewater is measured in color units (CU) and is caused by natural metallic ions
(Fe & Mg) and industrial wastes.
Question 7
Total suspended solids (TSS) in wastewater are measured using which technique?
A) Filtration and gravimetric analysis
B) Spectrophotometry
C) Titration
D) Colorimetry
Answer: A) Filtration and gravimetric analysis
Explanation: TSS is determined by filtering a known volume of sample, drying the filter, and weighing the
retained solids gravimetrically.
Question 8
The most accurate method for measuring residual chlorine in wastewater is:
A) Colorimetric DPD method
Update 2026/2027 | 200 Practice Questions & Detailed
Solutions | Laboratory Analyst III Complete Q&A Guide | A+
Graded
Question 1
A laboratory analyst is performing a BOD₅ test and observes that the dissolved oxygen depletion is 0.8
mg/L. What is the most appropriate corrective action?
A) Report the result as zero
B) Increase incubation temperature
C) Decrease dilution factor
D) Increase sample volume in dilution to achieve proper DO depletion
Answer: D) Increase sample volume in dilution to achieve proper DO depletion
Explanation: Acceptable BOD depletion is 2.0–7.0 mg/L; insufficient depletion (<2.0 mg/L) requires
increasing the sample concentration to obtain measurable oxygen demand.
Question 2
What is the main purpose of using a blank sample in chemical analysis?
A) To calibrate instruments
B) To provide a control for contamination
C) To standardize the reagents
D) To increase the concentration of analytes
,Answer: B) To provide a control for contamination
Explanation: A blank sample contains all reagents except the analyte of interest and is used to detect
any contamination or background interference.
Question 3
In the BOD determination, which of the following restrictions applies regarding acceptance of analysis
values?
A) The blank must not deplete more than 0.2 mg/L dissolved oxygen
B) Samples must deplete at least 2 mg/L and have at least 1 mg/L dissolved oxygen remaining
C) The blank must not deplete more than 0.5 mg/L dissolved oxygen
D) Samples must deplete at least 0.5 mg/L and have at least 3 mg/L dissolved oxygen remaining
Answer: A) The blank must not deplete more than 0.2 mg/L dissolved oxygen
Explanation: In BOD determination, the blank must not deplete more than 0.2 mg/L dissolved oxygen,
and samples must deplete at least 2.0 mg/L and have at least 1.0 mg/L dissolved oxygen remaining.
Question 4
Which parameter is most commonly used to assess organic pollution in wastewater?
A) pH
B) Biochemical Oxygen Demand (BOD)
C) Turbidity
D) Conductivity
,Answer: B) Biochemical Oxygen Demand (BOD)
Explanation: BOD is the most commonly used parameter to assess organic pollution in wastewater,
measuring the amount of dissolved oxygen consumed by microorganisms during the decomposition of
organic matter.
Question 5
Which of the following is the most appropriate method for preparing a sample for microbiological
analysis of wastewater?
A) Centrifugation followed by filtration
B) Direct plating without dilution
C) Serial dilution and plating
D) Evaporation of water
Answer: C) Serial dilution and plating
Explanation: Serial dilution and plating ensures that bacterial colonies are countable and prevents
overgrowth, which can obscure results. Direct plating or evaporation could result in inaccurate counts.
Question 6
What does COLOR measure in wastewater analysis?
A) The pH level of the sample
B) The amount of color units (CU) in a sample
, C) The turbidity of the sample
D) The conductivity of the sample
Answer: B) The amount of color units (CU) in a sample
Explanation: Color in wastewater is measured in color units (CU) and is caused by natural metallic ions
(Fe & Mg) and industrial wastes.
Question 7
Total suspended solids (TSS) in wastewater are measured using which technique?
A) Filtration and gravimetric analysis
B) Spectrophotometry
C) Titration
D) Colorimetry
Answer: A) Filtration and gravimetric analysis
Explanation: TSS is determined by filtering a known volume of sample, drying the filter, and weighing the
retained solids gravimetrically.
Question 8
The most accurate method for measuring residual chlorine in wastewater is:
A) Colorimetric DPD method
