Level 3 · Advanced sample questions
5 free sample questions on laboratory for the Level 3 · Advanced wastewater treatment operator exam. Try each one, then open the answer to check your work.
The lab accepts BOD bottles with at least 2.0 mg/L DO depletion and at least 1.0 mg/L final DO. Four bottles from one sample have these initial/final DO readings: Bottle 1: 8.4/6.8; Bottle 2: 8.2/4.0; Bottle 3: 8.1/0.6; and Bottle 4: 8.0/3.0 mg/L. Which bottle results should be averaged?
Answer: B. Bottles 2 and 4
Bottle 1 has only 1.6 mg/L depletion, and Bottle 3 ends below 1.0 mg/L DO, so both fail the stated limits. Bottles 2 and 4 meet both the depletion and final-DO requirements and are the valid results to average.
A pH meter passes calibration at pH 4 and 7, but gives a stable high reading on two fresh pH 10 check buffers. Its temperature reading and compensation check pass. A second meter reads both buffers correctly. What should be evaluated before using the first meter for high-pH samples?
Answer: C. Electrode response above pH 7
The first meter works at pH 4 and 7 but shows the same high bias on two verified pH 10 buffers. With temperature effects and the buffers ruled out, its electrode response in the alkaline range must be evaluated before high-pH use.
An ammonia sample's matrix spike has low recovery. The calibration check, laboratory control sample, and a matrix spike on a different wastewater sample all pass. Which cause is most likely?
Answer: D. Interference from this sample's matrix
The calibration check, control sample, and spike from another wastewater sample all pass, so the method and reagents are working under other conditions. Low recovery limited to this sample points to interference from its specific matrix.
A laboratory SOP treats each group of four membrane-filtration samples as a separate batch and states that a failed closing blank invalidates that batch. The blank before Samples 1-4 is clean, but their closing blank has growth. Samples 5-8 use a new sterile setup and have clean opening and closing blanks. A valid repeat can be completed within holding time. Which samples require repeat analysis?
Answer: B. Samples 1-4 because their sterility check failed
The SOP makes each four-sample group a separate batch and states that a failed closing blank invalidates that batch. Therefore Samples 1-4 require repeat analysis, while the clean opening and closing blanks support Samples 5-8 as a separate valid batch.
A luminescent DO meter passes its zero check but fails an air-saturation check after being moved to a higher-elevation plant. Temperature is correct. The meter's pressure entry is 101.3 kPa, while a calibrated barometer at the plant reads 84.0 kPa. What should be corrected before repeating the check?
Answer: C. Enter the plant's barometric pressure
The meter's air-saturation value depends on local atmospheric pressure. Its stored pressure is sea-level pressure rather than the verified 84.0 kPa at the higher-elevation plant, so the correct barometric pressure should be entered before repeating the check.
Keep practicing
Operator Master has 22 Level 3 · Advanced laboratory questions, free.
More topics