ETC Environmental Monitoring & Instrumentation 2 — Questions and Answers
Question 1: A field technician uses a combustible gas indicator (CGI) and observes a reading of 10% LEL in a utility vault. What action should be taken?
- The space is safe to enter for normal work
- Ventilate the space and continue monitoring before entry (Correct answer)
- The space must be evacuated immediately as it is above the UEL
- A reading of 10% LEL is normal background and can be ignored
Correct answer: Ventilate the space and continue monitoring before entry
A 10% LEL reading indicates a measurable combustible gas presence; standard practice requires forced ventilation and continued monitoring to trend whether concentrations are rising or falling before permitting entry.
Question 2: Which EPA method is the standard for measuring total metals in water samples using inductively coupled plasma mass spectrometry (ICP-MS)?
- EPA Method 200.8 (Correct answer)
- EPA Method 8270
- EPA Method 624
- EPA Method 9040
Correct answer: EPA Method 200.8
EPA Method 200.8 is the standard aqueous method for determining trace elements in water by ICP-MS, providing low detection limits for metals like arsenic, lead, and mercury.
Question 3: What is the significance of measuring oxidation-reduction potential (ORP) in a groundwater sample during field monitoring?
- ORP indicates the presence of petroleum hydrocarbons
- ORP characterizes the redox environment, which determines which contaminant degradation pathways are occurring (Correct answer)
- ORP measures the concentration of heavy metals in solution
- ORP is used to calibrate pH meters in the field
Correct answer: ORP characterizes the redox environment, which determines which contaminant degradation pathways are occurring
ORP (measured in millivolts) indicates whether subsurface conditions are oxidizing or reducing, which directly controls natural attenuation processes such as aerobic biodegradation, sulfate reduction, or methanogenesis.
Question 4: When collecting a low-flow groundwater sample, what field parameter stability criteria typically indicates the sample is representative of aquifer conditions?
- Three successive readings of pH within ±0.1 unit, conductance within ±3%, DO within ±0.3 mg/L, and ORP within ±10 mV (Correct answer)
- Two identical pH readings taken 1 minute apart
- When the turbidity drops below 50 NTU
- When the pumping rate stabilizes at the target flow rate
Correct answer: Three successive readings of pH within ±0.1 unit, conductance within ±3%, DO within ±0.3 mg/L, and ORP within ±10 mV
Low-flow sampling protocols require stabilization of pH (±0.1), specific conductance (±3%), dissolved oxygen (±0.3 mg/L), and ORP (±10 mV) across at least three consecutive readings before sample collection.
Question 5: A technician uses an XRF (X-ray fluorescence) analyzer on soil at a brownfield site. What primary advantage does XRF offer compared to laboratory analysis?
- XRF provides legally defensible data for regulatory reporting
- XRF gives real-time, non-destructive elemental analysis enabling rapid site-wide screening (Correct answer)
- XRF detects organic compounds like PCBs and PAHs
- XRF is more accurate than ICP-OES for low-concentration metals
Correct answer: XRF gives real-time, non-destructive elemental analysis enabling rapid site-wide screening
Portable XRF provides immediate, non-destructive elemental (metals) analysis in the field, allowing technicians to screen hundreds of locations per day and guide confirmatory sampling without waiting for laboratory turnaround.
Question 6: What is the purpose of a 'trip blank' in groundwater or soil vapor sampling quality assurance?
- To verify the sampling pump is working correctly
- To detect cross-contamination or VOC introduction from sampling equipment or field environment during sample transport (Correct answer)
- To calibrate the laboratory's GC/MS instrument
- To measure background concentrations in the sampling area
Correct answer: To detect cross-contamination or VOC introduction from sampling equipment or field environment during sample transport
A trip blank (typically a VOC-free water vial prepared in the lab and carried through all sample handling steps) checks for contamination introduced from the field environment, equipment, or transport containers.
ETC Environmental Monitoring & Instrumentation 2
A field technician uses a combustible gas indicator (CGI) and observes a reading of 10% LEL in a utility vault.
What action should be taken?