CEA Soil Contamination Assessment 4 — Questions and Answers
Question 1: Which quality assurance sample is used to detect potential cross-contamination between soil samples during field collection?
- Field blank
- Trip blank
- Equipment rinsate blank (Correct answer)
- Matrix spike duplicate
Correct answer: Equipment rinsate blank
Equipment rinsate (decontamination) blanks are collected by rinsing clean water through decontaminated sampling equipment to verify that cleaning was effective and no cross-contamination occurred.
Question 2: In soil contamination assessment, what is the primary purpose of a 'conceptual site model' (CSM)?
- To generate a 3D computer simulation of subsurface geology
- To summarize known and potential sources, pathways, and receptors in an integrated framework (Correct answer)
- To calculate the volume of contaminated soil requiring excavation
- To satisfy OSHA requirements for site health and safety planning
Correct answer: To summarize known and potential sources, pathways, and receptors in an integrated framework
A CSM integrates known and hypothesized sources, migration pathways, and potential receptors to guide site assessment and risk management decisions.
Question 3: Which soil sampling method provides the LEAST disturbance to sample stratigraphy and is preferred for lithological logging?
- Grab sampling with a hand auger
- Split-spoon sampling with standard penetration test (SPT)
- Shelby tube (thin-walled tube) sampling (Correct answer)
- Bulk bag sampling from stockpiled soil
Correct answer: Shelby tube (thin-walled tube) sampling
Shelby tube samplers recover relatively undisturbed cores that preserve stratigraphy, making them preferable for detailed lithological and stratigraphic logging.
Question 4: Under RCRA, which characteristic makes a contaminated soil a hazardous waste subject to full subtitle C management requirements?
- Total petroleum hydrocarbon concentration exceeds 500 mg/kg
- Soil is listed in 40 CFR Part 261 Subpart D as a listed hazardous waste
- Soil exhibits ignitability, corrosivity, reactivity, or toxicity as defined in 40 CFR Part 261 (Correct answer)
- Soil contains any detectable amount of a regulated contaminant
Correct answer: Soil exhibits ignitability, corrosivity, reactivity, or toxicity as defined in 40 CFR Part 261
Under RCRA, a solid waste is hazardous if it exhibits one of four characteristics—ignitability, corrosivity, reactivity, or toxicity—as defined in 40 CFR Part 261 Subparts C and D.
Question 5: What role does the 'vadose zone' play in soil contamination assessment?
- It represents the fully saturated zone below the water table where groundwater flows
- It is the unsaturated zone between the land surface and the water table, through which contaminants migrate to groundwater (Correct answer)
- It is the zone of capillary fringe saturation directly above the water table only
- It refers to bedrock formations below the saturated zone
Correct answer: It is the unsaturated zone between the land surface and the water table, through which contaminants migrate to groundwater
The vadose zone is the unsaturated region between the land surface and the water table; it is a critical pathway through which contaminants migrate downward to groundwater.
Question 6: Which statistical approach is most appropriate for determining whether site soil concentrations are significantly elevated above background?
- Simple arithmetic mean comparison
- Two-sample t-test or Wilcoxon rank-sum test comparing site and background data sets (Correct answer)
- Linear regression of concentration versus depth
- Chi-square test of sample distribution
Correct answer: Two-sample t-test or Wilcoxon rank-sum test comparing site and background data sets
A two-sample t-test (for normal data) or Wilcoxon rank-sum test (for non-normal data) is used to determine whether site concentrations are statistically distinguishable from background.
Question 7: For a carcinogenic contaminant in soil, the risk characterization step of a human health risk assessment calculates:
- Hazard quotient (HQ) by dividing exposure dose by the reference dose (RfD)
- Excess lifetime cancer risk (ELCR) by multiplying chronic daily intake by the cancer slope factor (Correct answer)
- Benchmark dose lower confidence limit (BMDL) from dose-response data
- Lethal concentration (LC50) from acute toxicity tests
Correct answer: Excess lifetime cancer risk (ELCR) by multiplying chronic daily intake by the cancer slope factor
Excess lifetime cancer risk (ELCR) is calculated by multiplying the chronic daily intake (CDI) by the chemical's cancer slope factor (CSF), expressing the incremental probability of developing cancer.
CEA Soil Contamination Assessment 4
Which quality assurance sample is used to detect potential cross-contamination between soil samples during field collection?