CWEA Laboratory Analyst Grade 3 QA/QC Practice test with 150
Questions and Answers/Plus a Rationale Updated 2026
A+/Instant Download PDF
Table of Contents
•
1. Quality Assurance and Quality Control (QA/QC) Principles and Data Validation
•
2. Laboratory Operations, Safety, and Regulatory Compliance
•
3. Analytical Chemistry: Instrumental Analysis and Wet Chemistry Procedures
•
4. Microbiological Testing and Biohazard Controls
•
5. Sampling Strategies, Chain of Custody, and Sample Preservation
1. A CWEA Grade 3 Laboratory Analyst is validating a new batch of initial calibration
curves for total kjeldahl nitrogen (TKN) using automated colorimetry. The linear
calibration curve yields an 𝑅 2 value of 0.992, but the lowest calibration standard
demonstrates a percent recovery of 65%. Which of the following is the most
appropriate corrective action before analyzing environmental wastewater samples?
A. Accept the calibration curve since 𝑅 2 ≥ 0.990 meets standard laboratory operational
guidelines.
B. Reject the calibration curve, re-prepare calibration standards, and re-calibrate ensuring
the low standard recovery falls within 80%--120%.
,C. Exclude the lowest calibration standard from the regression analysis and raise the
practical quantitation limit (PQL).
D. Flag all sample results falling near the lowest calibration standard as estimated without
re-calibrating.
Answer: B [Reject the calibration curve, re-prepare calibration standards, and re-calibrate
ensuring the low standard recovery falls within 80%--120%.]
Rationale: Standard QA/QC protocols dictate that a high coefficient of determination (𝑅 2 )
alone does not validate a calibration curve if low-level accuracy is compromised; calibration
standards must meet recovery criteria (typically 80%–120%) across the entire reporting
range. Option A is incorrect because reliance on 𝑅 2 alone hides low-end non-linearity. Option
C is incorrect as arbitrarily removing data points without investigating preparation error
violates standard method validation guidelines. Option D is incorrect because reporting
unvalidated low-level data compromises data integrity.
2. During a routine daily control check for total suspended solids (TSS) analysis, a
laboratory analyst evaluates the laboratory fortified blank (LFB) recovery. The
acceptance criteria for LFB recovery is 85%--115%, but the measured recovery is
122%. What is the immediate required protocol?
A. Adjust all sample results downwards by 22% to correct for the positive analytical bias.
B. Identify the root cause of high bias, re-analyze the LFB along with the associated batch
of samples.
C. Qualify the sample data with a flag noting high LFB recovery and release the final data.
D. Re-slope the analytical balance and re-weigh the aluminum dish batch without re-filtering
samples.
Answer: B [Identify the root cause of high bias, re-analyze the LFB along with the
associated batch of samples.]
Rationale: An out-of-control LFB indicates a systemic positive bias in the preparation or
measurement process, requiring batch re-analysis after corrective action. Option A is
incorrect because mathematical correction of environmental data using QC spikes is strictly
prohibited under Standard Methods. Option C is incorrect because batch re-analysis is
required when QC fails due to systemic bias unless sample volume is depleted. Option D is
incorrect because balance recalibration alone does not address potential filter contamination
or oven temperature drift.
, 3. A Grade 3 Analyst is reviewing Shewhart control charts for Matrix Spike (MS)
duplicate recovery of Biochemical Oxygen Demand (𝐵𝑂𝐷5 ). The last six consecutive
matrix spike duplicates fell on the same side of the mean line, but within the upper
and lower control limits (±3𝜎). According to Westgard rules, how should this trend
be interpreted?
A. The system is in statistical control because all points reside within the ±3𝜎 control limits.
B. A run rule violation (Run Rule 6𝑥 or 7𝑥 ) has occurred, indicating potential systematic
drift or bias that requires investigation.
C. An error in standard preparation has occurred; the instrument must be immediately shut
down.
D. A random error has occurred; double the sample volume on the next analytical batch.
Answer: B [A run rule violation (Run Rule 6𝑥 or 7𝑥 ) has occurred, indicating potential
systematic drift or bias that requires investigation.]
Rationale: Westgard rules specify that six or seven consecutive quality control results on one
side of the mean represent a systematic bias or process shift, even if they remain inside the
3-sigma limits. Option A is incorrect because control chart evaluation involves trend analysis,
not merely absolute limit checks. Option C is incorrect because a systematic trend does not
necessarily mean immediate instrument failure, but rather warrants root-cause analysis.
Option D is incorrect because systematic trends cannot be resolved by arbitrarily increasing
sample volume.
4. An analyst performs a duplicate analysis on an influent sample for Chemical Oxygen
Demand (COD). Replicate 1 yields 450 mg/L and Replicate 2 yields 510 mg/L. What is
the Relative Percent Difference (RPD), and does it pass if the maximum laboratory
acceptance limit is 10%?
A. 6.25%; Pass
B. 12.5%; Fail
C. 13.3%; Fail
D. 11.8%; Fail
Answer: B [12.5%; Fail]
|𝑅1−𝑅2| |450−510| 60
Rationale: RPD is calculated as Mean
× 100 = 480
× 100 = 480 × 100 = 12.5%,
which exceeds the 10% limit and fails acceptance criteria. Options A, C, and D reflect
mathematical miscalculations of the RPD formula.
, 5. When constructing an Initial Demonstration of Capability (IDC) for Inductively
Coupled Plasma - Mass Spectrometry (ICP-MS) trace metal analysis, how many
replicate spikes of a mid-level standard must be processed, and what parameter is
evaluated to demonstrate precision?
A. 3 replicates; standard error of the mean
B. 4 replicates; standard deviation and percent relative standard deviation (%RSD)
C. 10 replicates; range between maximum and minimum recovery
D. 5 replicates; absolute bias of the mean recovery
Answer: B [4 replicates; standard deviation and percent relative standard deviation
(%RSD)]
Rationale: EPA methods (e.g., Method 200.8) and Standard Methods requirement for IDC
mandate the preparation and analysis of 4 clean matrix replicates spiked at a mid-range
concentration, assessing precision via %RSD. Options A, C, and D do not align with standard
EPA/TNI IDC guidelines.
6. In a wastewater laboratory certified under NELAP/TNI standards, what is the
maximum allowable holding time for an unpreserved sample designated for Total
Phenols testing before extraction or analysis?
A. 24 hours at 4∘ C
B. 48 hours unpreserved at 4∘ C (or 28 days if preserved with 𝐻2 𝑆𝑂4 to 𝑝𝐻 < 2 at 4∘ C)
C. 7 days unpreserved at 4∘ C
D. 14 days preserved with 𝑁𝑎𝑂𝐻 to 𝑝𝐻 > 12
Answer: B [48 hours unpreserved at 4∘ C (or 28 days if preserved with 𝐻2 𝑆𝑂4 to 𝑝𝐻 < 2 at
4∘ C)]
Rationale: Standard regulatory preservation requirements (40 CFR Part 136) specify that
unpreserved phenols must be analyzed within 48 hours, or acidified with 𝐻2 𝑆𝑂4 to 𝑝𝐻 < 2
and cooled to ≤ 6∘ C to extend holding time to 28 days. Options A, C, and D present incorrect
holding times or preservation reagents.
7. An analyst is performing a Method Detection Limit (MDL) study following 40 CFR Part
136 Appendix B (Revision 2). A total of 7 low-level spiked samples and 7 method
blanks are processed over multiple days. The calculated standard deviation (𝑆𝑠 ) of
Questions and Answers/Plus a Rationale Updated 2026
A+/Instant Download PDF
Table of Contents
•
1. Quality Assurance and Quality Control (QA/QC) Principles and Data Validation
•
2. Laboratory Operations, Safety, and Regulatory Compliance
•
3. Analytical Chemistry: Instrumental Analysis and Wet Chemistry Procedures
•
4. Microbiological Testing and Biohazard Controls
•
5. Sampling Strategies, Chain of Custody, and Sample Preservation
1. A CWEA Grade 3 Laboratory Analyst is validating a new batch of initial calibration
curves for total kjeldahl nitrogen (TKN) using automated colorimetry. The linear
calibration curve yields an 𝑅 2 value of 0.992, but the lowest calibration standard
demonstrates a percent recovery of 65%. Which of the following is the most
appropriate corrective action before analyzing environmental wastewater samples?
A. Accept the calibration curve since 𝑅 2 ≥ 0.990 meets standard laboratory operational
guidelines.
B. Reject the calibration curve, re-prepare calibration standards, and re-calibrate ensuring
the low standard recovery falls within 80%--120%.
,C. Exclude the lowest calibration standard from the regression analysis and raise the
practical quantitation limit (PQL).
D. Flag all sample results falling near the lowest calibration standard as estimated without
re-calibrating.
Answer: B [Reject the calibration curve, re-prepare calibration standards, and re-calibrate
ensuring the low standard recovery falls within 80%--120%.]
Rationale: Standard QA/QC protocols dictate that a high coefficient of determination (𝑅 2 )
alone does not validate a calibration curve if low-level accuracy is compromised; calibration
standards must meet recovery criteria (typically 80%–120%) across the entire reporting
range. Option A is incorrect because reliance on 𝑅 2 alone hides low-end non-linearity. Option
C is incorrect as arbitrarily removing data points without investigating preparation error
violates standard method validation guidelines. Option D is incorrect because reporting
unvalidated low-level data compromises data integrity.
2. During a routine daily control check for total suspended solids (TSS) analysis, a
laboratory analyst evaluates the laboratory fortified blank (LFB) recovery. The
acceptance criteria for LFB recovery is 85%--115%, but the measured recovery is
122%. What is the immediate required protocol?
A. Adjust all sample results downwards by 22% to correct for the positive analytical bias.
B. Identify the root cause of high bias, re-analyze the LFB along with the associated batch
of samples.
C. Qualify the sample data with a flag noting high LFB recovery and release the final data.
D. Re-slope the analytical balance and re-weigh the aluminum dish batch without re-filtering
samples.
Answer: B [Identify the root cause of high bias, re-analyze the LFB along with the
associated batch of samples.]
Rationale: An out-of-control LFB indicates a systemic positive bias in the preparation or
measurement process, requiring batch re-analysis after corrective action. Option A is
incorrect because mathematical correction of environmental data using QC spikes is strictly
prohibited under Standard Methods. Option C is incorrect because batch re-analysis is
required when QC fails due to systemic bias unless sample volume is depleted. Option D is
incorrect because balance recalibration alone does not address potential filter contamination
or oven temperature drift.
, 3. A Grade 3 Analyst is reviewing Shewhart control charts for Matrix Spike (MS)
duplicate recovery of Biochemical Oxygen Demand (𝐵𝑂𝐷5 ). The last six consecutive
matrix spike duplicates fell on the same side of the mean line, but within the upper
and lower control limits (±3𝜎). According to Westgard rules, how should this trend
be interpreted?
A. The system is in statistical control because all points reside within the ±3𝜎 control limits.
B. A run rule violation (Run Rule 6𝑥 or 7𝑥 ) has occurred, indicating potential systematic
drift or bias that requires investigation.
C. An error in standard preparation has occurred; the instrument must be immediately shut
down.
D. A random error has occurred; double the sample volume on the next analytical batch.
Answer: B [A run rule violation (Run Rule 6𝑥 or 7𝑥 ) has occurred, indicating potential
systematic drift or bias that requires investigation.]
Rationale: Westgard rules specify that six or seven consecutive quality control results on one
side of the mean represent a systematic bias or process shift, even if they remain inside the
3-sigma limits. Option A is incorrect because control chart evaluation involves trend analysis,
not merely absolute limit checks. Option C is incorrect because a systematic trend does not
necessarily mean immediate instrument failure, but rather warrants root-cause analysis.
Option D is incorrect because systematic trends cannot be resolved by arbitrarily increasing
sample volume.
4. An analyst performs a duplicate analysis on an influent sample for Chemical Oxygen
Demand (COD). Replicate 1 yields 450 mg/L and Replicate 2 yields 510 mg/L. What is
the Relative Percent Difference (RPD), and does it pass if the maximum laboratory
acceptance limit is 10%?
A. 6.25%; Pass
B. 12.5%; Fail
C. 13.3%; Fail
D. 11.8%; Fail
Answer: B [12.5%; Fail]
|𝑅1−𝑅2| |450−510| 60
Rationale: RPD is calculated as Mean
× 100 = 480
× 100 = 480 × 100 = 12.5%,
which exceeds the 10% limit and fails acceptance criteria. Options A, C, and D reflect
mathematical miscalculations of the RPD formula.
, 5. When constructing an Initial Demonstration of Capability (IDC) for Inductively
Coupled Plasma - Mass Spectrometry (ICP-MS) trace metal analysis, how many
replicate spikes of a mid-level standard must be processed, and what parameter is
evaluated to demonstrate precision?
A. 3 replicates; standard error of the mean
B. 4 replicates; standard deviation and percent relative standard deviation (%RSD)
C. 10 replicates; range between maximum and minimum recovery
D. 5 replicates; absolute bias of the mean recovery
Answer: B [4 replicates; standard deviation and percent relative standard deviation
(%RSD)]
Rationale: EPA methods (e.g., Method 200.8) and Standard Methods requirement for IDC
mandate the preparation and analysis of 4 clean matrix replicates spiked at a mid-range
concentration, assessing precision via %RSD. Options A, C, and D do not align with standard
EPA/TNI IDC guidelines.
6. In a wastewater laboratory certified under NELAP/TNI standards, what is the
maximum allowable holding time for an unpreserved sample designated for Total
Phenols testing before extraction or analysis?
A. 24 hours at 4∘ C
B. 48 hours unpreserved at 4∘ C (or 28 days if preserved with 𝐻2 𝑆𝑂4 to 𝑝𝐻 < 2 at 4∘ C)
C. 7 days unpreserved at 4∘ C
D. 14 days preserved with 𝑁𝑎𝑂𝐻 to 𝑝𝐻 > 12
Answer: B [48 hours unpreserved at 4∘ C (or 28 days if preserved with 𝐻2 𝑆𝑂4 to 𝑝𝐻 < 2 at
4∘ C)]
Rationale: Standard regulatory preservation requirements (40 CFR Part 136) specify that
unpreserved phenols must be analyzed within 48 hours, or acidified with 𝐻2 𝑆𝑂4 to 𝑝𝐻 < 2
and cooled to ≤ 6∘ C to extend holding time to 28 days. Options A, C, and D present incorrect
holding times or preservation reagents.
7. An analyst is performing a Method Detection Limit (MDL) study following 40 CFR Part
136 Appendix B (Revision 2). A total of 7 low-level spiked samples and 7 method
blanks are processed over multiple days. The calculated standard deviation (𝑆𝑠 ) of
