CEA Remediation Technologies 2 — Questions and Answers
Question 1: Which remediation technology uses electricity to move contaminants through soil toward electrodes for extraction?
- Electrokinetic remediation (Correct answer)
- Electrodialysis reversal
- Galvanic isolation
- Capacitive deionization
Correct answer: Electrokinetic remediation
Electrokinetic remediation applies a low-level DC current to drive charged contaminants (metals, some organics) through saturated soils toward cathode or anode electrodes for removal.
Question 2: Monitored Natural Attenuation (MNA) relies on which primary naturally occurring processes?
- Precipitation, dilution, and volatilization only
- Biodegradation, dispersion, dilution, sorption, and volatilization (Correct answer)
- Thermal desorption and photolysis
- Electroosmosis and electromigration
Correct answer: Biodegradation, dispersion, dilution, sorption, and volatilization
MNA depends on a combination of biodegradation, dispersion, dilution, sorption, and volatilization to reduce contaminant mass, toxicity, and mobility without active intervention.
Question 3: In situ chemical reduction (ISCR) using zero-valent iron (ZVI) is most effective for treating which class of contaminants?
- Polycyclic aromatic hydrocarbons (PAHs)
- Chlorinated solvents such as TCE and PCE (Correct answer)
- Petroleum hydrocarbons (BTEX)
- Nitrate in drinking water wells
Correct answer: Chlorinated solvents such as TCE and PCE
ZVI dehalogenates chlorinated solvents (e.g., TCE, PCE) via reductive dechlorination, converting them to less toxic or non-toxic end products.
Question 4: A permeable reactive barrier (PRB) is best described as:
- A surface cap that prevents infiltration of rainwater into contaminated soil
- A subsurface wall of reactive material that treats groundwater as it flows through (Correct answer)
- An above-ground pump-and-treat system with ion exchange resin
- A series of injection wells that circulate heated steam
Correct answer: A subsurface wall of reactive material that treats groundwater as it flows through
A PRB is an in situ passive system placed perpendicular to groundwater flow; reactive media (such as ZVI or activated carbon) treat contaminants as groundwater passes through naturally.
Question 5: Surfactant-enhanced aquifer remediation (SEAR) improves contaminant removal primarily by:
- Increasing soil pH to mobilize heavy metals
- Lowering interfacial tension to solubilize or mobilize NAPLs (Correct answer)
- Elevating groundwater temperature to volatilize organics
- Introducing electron acceptors to stimulate aerobic biodegradation
Correct answer: Lowering interfacial tension to solubilize or mobilize NAPLs
Surfactants reduce interfacial tension between NAPLs and water, increasing NAPL solubility and mobility so contaminants can be more effectively flushed and extracted.
Question 6: Which metric is used to evaluate the effectiveness of in situ bioremediation by tracking the ratio of reduced to oxidized forms of a redox indicator?
- Total organic carbon (TOC) loading rate
- Eh (redox potential) or ORP measured in millivolts (Correct answer)
- Biochemical oxygen demand (BOD) at 5 days
- Hydraulic conductivity gradient
Correct answer: Eh (redox potential) or ORP measured in millivolts
Oxidation-reduction potential (ORP/Eh) measures the electron activity in groundwater, indicating whether conditions are aerobic, anoxic, or anaerobic—key for assessing bioremediation progress.
Question 7: During a pump-and-treat operation, the 'tailing' effect refers to:
- An increase in contaminant concentrations after pumping begins
- Persistently low but non-zero contaminant concentrations that are slow to decline despite continued pumping (Correct answer)
- Rebound of contaminant levels after pumping stops
- The lag time before pumping affects water table elevation
Correct answer: Persistently low but non-zero contaminant concentrations that are slow to decline despite continued pumping
Tailing is the gradual, asymptotic decrease in extracted contaminant concentrations as the more accessible mass is removed, leaving back-diffusion from low-permeability zones as the continuing source.
CEA Remediation Technologies 2
Which remediation technology uses electricity to move contaminants through soil toward electrodes for extraction?