ETC Soil & Groundwater Remediation 2 — Questions and Answers
Question 1: What is the difference between LNAPL and DNAPL in groundwater contamination scenarios?
- LNAPL sinks below the water table; DNAPL floats on top
- LNAPL floats on the water table; DNAPL sinks below it (Correct answer)
- LNAPL dissolves readily; DNAPL does not dissolve
- LNAPL is always petroleum; DNAPL is always chlorinated solvents
Correct answer: LNAPL floats on the water table; DNAPL sinks below it
Light Non-Aqueous Phase Liquids (LNAPLs) have densities less than water and float on the water table, while Dense Non-Aqueous Phase Liquids (DNAPLs) are denser than water and sink below it.
Question 2: In groundwater monitoring, what is the purpose of a 'sentinel well' placed downgradient of a remediation system?
- To inject clean water to dilute the plume
- To detect contaminant migration beyond the treatment zone (Correct answer)
- To measure the aquifer pumping rate
- To collect representative background samples
Correct answer: To detect contaminant migration beyond the treatment zone
Sentinel wells serve as early warning indicators to detect whether contamination is migrating past the capture zone of a pump-and-treat or containment system.
Question 3: Which EPA guidance document provides the framework for evaluating risk at contaminated sites to establish cleanup levels protective of human health?
- ASTM E1527 Phase I ESA Standard
- EPA Risk Assessment Guidance for Superfund (RAGS) (Correct answer)
- RCRA Corrective Action Plan
- OSHA Process Safety Management Standard
Correct answer: EPA Risk Assessment Guidance for Superfund (RAGS)
EPA's Risk Assessment Guidance for Superfund (RAGS) provides the standard framework for conducting baseline human health risk assessments that determine remediation goals at contaminated sites.
Question 4: Enhanced bioremediation of chlorinated solvents often involves injecting an electron donor such as vegetable oil or molasses. What process does this stimulate?
- Aerobic oxidation of contaminants
- Anaerobic reductive dechlorination (Correct answer)
- Chemical hydrolysis of chlorinated bonds
- Photolytic degradation of solvents
Correct answer: Anaerobic reductive dechlorination
Electron donor injection creates anaerobic conditions that stimulate reductive dechlorination, in which microorganisms sequentially remove chlorine atoms from compounds like PCE and TCE.
Question 5: What does the term 'plume diving' describe in a groundwater contamination scenario?
- Contaminant sinking into deeper aquifer units due to density or recharge (Correct answer)
- Rapid spread of contamination along preferential flow paths
- Natural attenuation reducing contaminant concentrations vertically
- A remediation strategy using deep injection wells
Correct answer: Contaminant sinking into deeper aquifer units due to density or recharge
Plume diving occurs when a dissolved contaminant plume is driven downward into deeper aquifer zones due to recharge events, density differences, or aquifer heterogeneity.
Question 6: Which type of soil boring technique uses a hollow stem to advance through soil while simultaneously collecting continuous soil samples?
- Direct Push Technology (DPT)
- Hollow-Stem Auger (HSA) (Correct answer)
- Rotary Air Blast (RAB)
- Cable Tool Drilling
Correct answer: Hollow-Stem Auger (HSA)
Hollow-stem auger drilling advances a continuous-flight auger with a hollow center, allowing soil sample collection and well installation without removing the auger from the borehole.
ETC Soil & Groundwater Remediation 2
What is the difference between LNAPL and DNAPL in groundwater contamination scenarios?