CES Soil Contamination & Remediation 2 — Questions and Answers
Question 1: Which soil parameter most directly controls the bioavailability of heavy metals to plants?
- Soil pH (Correct answer)
- Soil texture
- Organic carbon content
- Cation exchange capacity
Correct answer: Soil pH
Soil pH is the single most influential factor controlling heavy metal solubility and plant bioavailability, with most metals becoming more soluble and bioavailable under acidic conditions.
Question 2: Pump-and-treat systems for groundwater contamination are often criticized primarily because:
- They are too expensive to install
- Contaminant rebound occurs after pumping ceases (Correct answer)
- They require too much energy
- They cannot remove dissolved contaminants
Correct answer: Contaminant rebound occurs after pumping ceases
Pump-and-treat systems frequently exhibit contaminant rebound, where concentrations rise back toward original levels when pumping stops, making complete aquifer restoration difficult.
Question 3: In the context of soil remediation, 'monitored natural attenuation' (MNA) relies on which of the following processes?
- Engineered injection of nutrients to stimulate biodegradation
- Natural physical, chemical, and biological processes to reduce contaminant concentrations (Correct answer)
- Installation of permeable reactive barriers
- Excavation of contaminated material to a controlled landfill
Correct answer: Natural physical, chemical, and biological processes to reduce contaminant concentrations
MNA relies on naturally occurring processes such as biodegradation, dispersion, dilution, sorption, and volatilization to achieve remediation goals without engineered intervention.
Question 4: What is the primary mechanism by which phytoremediation using hyperaccumulator plants removes metals from soil?
- Root exudates precipitate metals as insoluble compounds
- Plants translocate metals from roots to above-ground biomass which is then harvested (Correct answer)
- Mycorrhizal fungi degrade metal complexes in the rhizosphere
- Volatilization of metals from leaf surfaces
Correct answer: Plants translocate metals from roots to above-ground biomass which is then harvested
Hyperaccumulators translocate metals from roots through the xylem to shoots and leaves, and the metal-laden biomass is harvested and processed to remove the contaminant.
Question 5: The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) established which key fund for hazardous waste site cleanup?
- RCRA Trust Fund
- Superfund (Correct answer)
- TSCA Remediation Account
- EPA Emergency Reserve
Correct answer: Superfund
CERCLA established the Hazardous Substance Superfund, commonly known as 'Superfund,' to finance cleanup of sites where responsible parties cannot be identified or are unable to pay.
Question 6: Soil vapor extraction (SVE) is most effective for remediating contaminants with:
- High water solubility and low vapor pressure
- Low volatility and high adsorption to soil particles
- High Henry's Law constant and high vapor pressure (Correct answer)
- Low Henry's Law constant and high soil organic matter affinity
Correct answer: High Henry's Law constant and high vapor pressure
SVE works by drawing air through the unsaturated zone, so it is most effective for volatile contaminants characterized by high vapor pressure and a high Henry's Law constant (tendency to volatilize from water).
Question 7: Which of the following best describes the 'source zone' in a contaminated site conceptual site model (CSM)?
- The regulatory boundary of the affected property
- The area containing concentrated contaminant mass driving continued plume migration (Correct answer)
- The receptor location where exposure is assessed
- The down-gradient boundary of the dissolved plume
Correct answer: The area containing concentrated contaminant mass driving continued plume migration
The source zone is the area where concentrated contaminant mass, such as NAPLs or highly sorbed chemicals, acts as a long-term reservoir that sustains the dissolved-phase plume.
CES Soil Contamination & Remediation 2
Which soil parameter most directly controls the bioavailability of heavy metals to plants?