CWEA Laboratory Analyst Grade 3 Sample Handling and Preservation
Exam with 150 Questions and Answers/Plus a Rationale Updated
2026 A+/Instant Download PDF
Table of Contents
•
1. Sample Collection Planning and Representativeness
•
2. Sample Containers, Materials, and Cleaning
•
3. Sample Preservation and Temperature Control
•
4. Holding Times and Regulatory Compliance
•
5. Chain of Custody and Sample Documentation
•
6. Field Sampling, Composite Sampling, and Automatic Samplers
•
7. Sample Receipt, Inspection, and Laboratory Acceptance
•
8. Sample Integrity, Contamination Control, and Quality Assurance
•
9. Parameter-Specific Handling and Preservation
•
10. Troubleshooting, Corrective Action, and Data Qualification
1. A wastewater treatment plant is investigating intermittent nitrification failure. A grab
sample from the aeration basin shows a substantially different ammonia
concentration from a sample collected by an automatic sampler over the same
period. The automatic sampler tubing was clean, but the sample container remained
unrefrigerated for several hours. Which factor most directly threatens the
representativeness of the automatic-sampler result?
,A. The sample was collected using an automatic sampler
B. The sample volume was larger than the grab sample
C. The extended period without appropriate temperature control may have allowed
biological and chemical changes
D. The aeration basin sample was collected manually
Answer: C [The extended period without appropriate temperature control may have
allowed biological and chemical changes]
Rationale: Proper preservation is intended to minimize biological activity, chemical reactions,
and other changes between collection and analysis. A is not inherently problematic, B does
not by itself invalidate representativeness, and D does not explain the preservation failure.
2. A laboratory receives an effluent sample for a compliance analysis requiring
refrigeration. The sampler recorded collection at 09:10, but the sample was not
placed into the laboratory refrigerator until 15:30. The sample temperature upon
receipt is 17°C. What is the most appropriate initial action?
A. Analyze it normally because the bottle is intact
B. Refrigerate it and automatically extend the holding time
C. Document the temperature excursion and evaluate acceptability against the applicable
method, permit, and QA plan
D. Recollect the sample without documenting the original condition
Answer: C [Document the temperature excursion and evaluate acceptability against the
applicable method, permit, and QA plan]
Rationale: Sample acceptance must be based on applicable preservation requirements and
documented quality procedures. A ignores a significant integrity concern, B cannot
retroactively restore sample integrity, and D destroys evidence needed for corrective action
and data evaluation.
3. A laboratory analyst is preparing containers for trace-metal sampling. A previous
batch of containers was cleaned using detergent and tap water only. What is the
greatest concern?
A. The bottles may become heavier after cleaning
B. Residual metals or other contaminants may contribute to measured concentrations
C. Detergent always increases dissolved oxygen
D. Tap water prevents acid preservation from working
Answer: B [Residual metals or other contaminants may contribute to measured
concentrations]
Rationale: Trace-metal containers require cleaning procedures appropriate for low-level
analysis so that background contamination does not bias results. A is irrelevant, C is
unrelated to container cleanliness, and D is not a general consequence of tap-water rinsing.
, 4. During preparation for a dissolved-metals sampling event, a field technician plans to
collect the sample, transport it to the laboratory, filter it several hours later, and then
acid-preserve it. What is the best correction?
A. Filter only after acid preservation
B. Freeze the sample before filtration
C. Filter the sample promptly in the field before preservation when the applicable method
requires dissolved-metal filtration
D. Leave the sample at ambient temperature until filtration
Answer: C [Filter the sample promptly in the field before preservation when the applicable
method requires dissolved-metal filtration]
Rationale: Applicable regulatory procedures specify immediate field filtration for dissolved
metals before preservation because preservation before filtration can change the
dissolved/particulate distribution. A can prevent appropriate separation, B may alter analyte
behavior, and D permits changes before filtration.
5. A compliance sample is collected at 11:45, and the laboratory receives it at 13:00.
The analyst notices that the sample was preserved immediately but the collection
time on the chain-of-custody form is missing. What is the primary concern?
A. The preservative is automatically invalid
B. The bottle must be discarded regardless of circumstances
C. The laboratory cannot reliably establish the beginning of the applicable holding period
D. The sample automatically becomes a composite sample
Answer: C [The laboratory cannot reliably establish the beginning of the applicable holding
period]
Rationale: Holding-time calculations depend on accurate collection information. A
preservation may still be technically correct, B is unnecessarily absolute, and D has no
relationship to missing collection time.
6. A plant collects a composite sample for an analyte with a required chemical
preservative. The automatic sampler adds aliquots every 30 minutes but does not
add preservative until the composite bottle is removed at the end of the sampling
period. Which approach is most defensible?
A. Always discard the sample
B. Ignore preservation because composite samples are exempt
C. Follow the applicable regulatory allowance for automated composite sampling and
document the preservation procedure used
D. Add preservative only after analysis
Answer: C [Follow the applicable regulatory allowance for automated composite sampling
and document the preservation procedure used]
, Rationale: Regulatory requirements recognize specific circumstances involving automated
composite samplers and preservation, including controlled cooling until compositing and
splitting when immediate preservation of each aliquot is impractical. A and B are overly
broad, while D is unacceptable.
7. A sample intended for volatile-organic analysis arrives with a large headspace in the
vial. The method requires a completely filled vial without headspace. What is the
most appropriate laboratory response?
A. Shake the vial vigorously to eliminate the headspace
B. Add laboratory water to fill it
C. Flag the sample for potential loss of volatile analytes and follow the method and
laboratory SOP for compromised vials
D. Transfer it to an open beaker
Answer: C [Flag the sample for potential loss of volatile analytes and follow the method
and laboratory SOP for compromised vials]
Rationale: Headspace can permit volatilization and compromise volatile-organic results. A
increases volatilization, B changes the sample matrix, and D provides no acceptable
preservation.
8. A sample for pH analysis arrives at the laboratory two hours after collection. The
project method requires prompt pH measurement because pH can change rapidly.
Which action is most appropriate?
A. Store it overnight and analyze it the following morning
B. Freeze it immediately
C. Analyze it promptly and document the elapsed time from collection to measurement
D. Adjust its pH to the expected field value
Answer: C [Analyze it promptly and document the elapsed time from collection to
measurement]
Rationale: pH is particularly susceptible to changes caused by gas exchange and biological or
chemical processes and is generally measured promptly. A risks unacceptable change, B
alters the sample, and D would destroy the validity of the measurement.
9. A laboratory receives a compliance sample with an intact bottle, correct label, and
sufficient volume, but the sample temperature exceeds the specified preservation
range. What should the analyst do first?
A. Immediately dilute the sample
B. Re-preserve the sample without documentation
C. Record the condition and evaluate it against the applicable acceptance criteria and
quality system
D. Change the collection date
Exam with 150 Questions and Answers/Plus a Rationale Updated
2026 A+/Instant Download PDF
Table of Contents
•
1. Sample Collection Planning and Representativeness
•
2. Sample Containers, Materials, and Cleaning
•
3. Sample Preservation and Temperature Control
•
4. Holding Times and Regulatory Compliance
•
5. Chain of Custody and Sample Documentation
•
6. Field Sampling, Composite Sampling, and Automatic Samplers
•
7. Sample Receipt, Inspection, and Laboratory Acceptance
•
8. Sample Integrity, Contamination Control, and Quality Assurance
•
9. Parameter-Specific Handling and Preservation
•
10. Troubleshooting, Corrective Action, and Data Qualification
1. A wastewater treatment plant is investigating intermittent nitrification failure. A grab
sample from the aeration basin shows a substantially different ammonia
concentration from a sample collected by an automatic sampler over the same
period. The automatic sampler tubing was clean, but the sample container remained
unrefrigerated for several hours. Which factor most directly threatens the
representativeness of the automatic-sampler result?
,A. The sample was collected using an automatic sampler
B. The sample volume was larger than the grab sample
C. The extended period without appropriate temperature control may have allowed
biological and chemical changes
D. The aeration basin sample was collected manually
Answer: C [The extended period without appropriate temperature control may have
allowed biological and chemical changes]
Rationale: Proper preservation is intended to minimize biological activity, chemical reactions,
and other changes between collection and analysis. A is not inherently problematic, B does
not by itself invalidate representativeness, and D does not explain the preservation failure.
2. A laboratory receives an effluent sample for a compliance analysis requiring
refrigeration. The sampler recorded collection at 09:10, but the sample was not
placed into the laboratory refrigerator until 15:30. The sample temperature upon
receipt is 17°C. What is the most appropriate initial action?
A. Analyze it normally because the bottle is intact
B. Refrigerate it and automatically extend the holding time
C. Document the temperature excursion and evaluate acceptability against the applicable
method, permit, and QA plan
D. Recollect the sample without documenting the original condition
Answer: C [Document the temperature excursion and evaluate acceptability against the
applicable method, permit, and QA plan]
Rationale: Sample acceptance must be based on applicable preservation requirements and
documented quality procedures. A ignores a significant integrity concern, B cannot
retroactively restore sample integrity, and D destroys evidence needed for corrective action
and data evaluation.
3. A laboratory analyst is preparing containers for trace-metal sampling. A previous
batch of containers was cleaned using detergent and tap water only. What is the
greatest concern?
A. The bottles may become heavier after cleaning
B. Residual metals or other contaminants may contribute to measured concentrations
C. Detergent always increases dissolved oxygen
D. Tap water prevents acid preservation from working
Answer: B [Residual metals or other contaminants may contribute to measured
concentrations]
Rationale: Trace-metal containers require cleaning procedures appropriate for low-level
analysis so that background contamination does not bias results. A is irrelevant, C is
unrelated to container cleanliness, and D is not a general consequence of tap-water rinsing.
, 4. During preparation for a dissolved-metals sampling event, a field technician plans to
collect the sample, transport it to the laboratory, filter it several hours later, and then
acid-preserve it. What is the best correction?
A. Filter only after acid preservation
B. Freeze the sample before filtration
C. Filter the sample promptly in the field before preservation when the applicable method
requires dissolved-metal filtration
D. Leave the sample at ambient temperature until filtration
Answer: C [Filter the sample promptly in the field before preservation when the applicable
method requires dissolved-metal filtration]
Rationale: Applicable regulatory procedures specify immediate field filtration for dissolved
metals before preservation because preservation before filtration can change the
dissolved/particulate distribution. A can prevent appropriate separation, B may alter analyte
behavior, and D permits changes before filtration.
5. A compliance sample is collected at 11:45, and the laboratory receives it at 13:00.
The analyst notices that the sample was preserved immediately but the collection
time on the chain-of-custody form is missing. What is the primary concern?
A. The preservative is automatically invalid
B. The bottle must be discarded regardless of circumstances
C. The laboratory cannot reliably establish the beginning of the applicable holding period
D. The sample automatically becomes a composite sample
Answer: C [The laboratory cannot reliably establish the beginning of the applicable holding
period]
Rationale: Holding-time calculations depend on accurate collection information. A
preservation may still be technically correct, B is unnecessarily absolute, and D has no
relationship to missing collection time.
6. A plant collects a composite sample for an analyte with a required chemical
preservative. The automatic sampler adds aliquots every 30 minutes but does not
add preservative until the composite bottle is removed at the end of the sampling
period. Which approach is most defensible?
A. Always discard the sample
B. Ignore preservation because composite samples are exempt
C. Follow the applicable regulatory allowance for automated composite sampling and
document the preservation procedure used
D. Add preservative only after analysis
Answer: C [Follow the applicable regulatory allowance for automated composite sampling
and document the preservation procedure used]
, Rationale: Regulatory requirements recognize specific circumstances involving automated
composite samplers and preservation, including controlled cooling until compositing and
splitting when immediate preservation of each aliquot is impractical. A and B are overly
broad, while D is unacceptable.
7. A sample intended for volatile-organic analysis arrives with a large headspace in the
vial. The method requires a completely filled vial without headspace. What is the
most appropriate laboratory response?
A. Shake the vial vigorously to eliminate the headspace
B. Add laboratory water to fill it
C. Flag the sample for potential loss of volatile analytes and follow the method and
laboratory SOP for compromised vials
D. Transfer it to an open beaker
Answer: C [Flag the sample for potential loss of volatile analytes and follow the method
and laboratory SOP for compromised vials]
Rationale: Headspace can permit volatilization and compromise volatile-organic results. A
increases volatilization, B changes the sample matrix, and D provides no acceptable
preservation.
8. A sample for pH analysis arrives at the laboratory two hours after collection. The
project method requires prompt pH measurement because pH can change rapidly.
Which action is most appropriate?
A. Store it overnight and analyze it the following morning
B. Freeze it immediately
C. Analyze it promptly and document the elapsed time from collection to measurement
D. Adjust its pH to the expected field value
Answer: C [Analyze it promptly and document the elapsed time from collection to
measurement]
Rationale: pH is particularly susceptible to changes caused by gas exchange and biological or
chemical processes and is generally measured promptly. A risks unacceptable change, B
alters the sample, and D would destroy the validity of the measurement.
9. A laboratory receives a compliance sample with an intact bottle, correct label, and
sufficient volume, but the sample temperature exceeds the specified preservation
range. What should the analyst do first?
A. Immediately dilute the sample
B. Re-preserve the sample without documentation
C. Record the condition and evaluate it against the applicable acceptance criteria and
quality system
D. Change the collection date
