CEA Remediation Technologies 4 — Questions and Answers
Question 1: Dual-phase extraction (DPE) simultaneously removes which two phases from the subsurface?
- Dissolved-phase and solid-phase contaminants
- Soil vapor and groundwater (or NAPL) (Correct answer)
- Free-phase LNAPL and DNAPL
- Heavy metals and radionuclides from saturated soils
Correct answer: Soil vapor and groundwater (or NAPL)
DPE uses a high-vacuum system to extract both soil vapor from the vadose zone and contaminated groundwater (or free-phase NAPL) from the saturated zone through a single extraction well.
Question 2: The primary distinction between LNAPL and DNAPL behavior in the subsurface is that DNAPLs:
- Dissolve more rapidly into groundwater due to higher solubility
- Sink below the water table because their density exceeds that of water (Correct answer)
- Volatilize more readily in the vadose zone
- Are immiscible with soil moisture but miscible with groundwater
Correct answer: Sink below the water table because their density exceeds that of water
DNAPLs (dense non-aqueous phase liquids) have specific gravity greater than 1.0, causing them to penetrate the water table and migrate downward until reaching an impermeable layer or residual saturation.
Question 3: Which amendment is most commonly injected to stimulate enhanced reductive dechlorination (ERD) of chlorinated ethenes?
- Sodium persulfate as an oxidant
- Emulsified vegetable oil (EVO) as an electron donor (Correct answer)
- Calcium peroxide (CaO2) as an oxygen-releasing compound
- Potassium permanganate as a chemical oxidant
Correct answer: Emulsified vegetable oil (EVO) as an electron donor
EVO provides a slow-release carbon substrate that sustains anaerobic conditions and electron donor supply, enabling dehalorespiring bacteria (like Dehalococcoides) to reductively dechlorinate PCE and TCE to ethene.
Question 4: Solidification/stabilization (S/S) technology treats contaminated material by:
- Vaporizing contaminants at high temperatures and condensing them for off-site disposal
- Immobilizing contaminants within a solid matrix to reduce leachability and mobility (Correct answer)
- Chemically oxidizing organics and precipitating metals in a reactor vessel
- Biologically degrading contaminants using aerobic microorganisms in place
Correct answer: Immobilizing contaminants within a solid matrix to reduce leachability and mobility
S/S uses binders (cement, lime, pozzolans) to physically encapsulate or chemically fix contaminants, reducing their solubility and preventing leaching rather than destroying them.
Question 5: A Treatability Study is conducted during CERCLA remediation to:
- Characterize the nature and extent of contamination at a site
- Evaluate the performance and cost-effectiveness of candidate remedial technologies before full-scale implementation (Correct answer)
- Calculate the cancer slope factor for site-specific risk assessment
- Determine the responsible parties liable under CERCLA Section 107
Correct answer: Evaluate the performance and cost-effectiveness of candidate remedial technologies before full-scale implementation
Treatability studies (bench-scale or pilot-scale) test how well specific technologies work for site-specific conditions, providing data to support technology selection in the Feasibility Study.
Question 6: In the context of vapor intrusion (VI) mitigation, sub-slab depressurization (SSD) works by:
- Sealing all cracks in the foundation slab with epoxy injection
- Creating negative pressure beneath the slab to prevent soil vapors from entering the building (Correct answer)
- Injecting clean air under the slab to dilute vapor concentrations
- Installing activated carbon adsorption units in the HVAC return air stream
Correct answer: Creating negative pressure beneath the slab to prevent soil vapors from entering the building
SSD installs suction points through the foundation slab and draws air from the sub-slab environment, maintaining negative pressure that prevents soil vapors from migrating into the building interior.
Question 7: Which performance metric best indicates that in situ chemical oxidation (ISCO) is actively destroying organic contaminants in the target treatment zone?
- Rising dissolved oxygen concentrations with no change in ORP
- Temporary increase in contaminant concentrations followed by rapid decline (oxidant push-pull) (Correct answer)
- Decrease in hydraulic conductivity indicating pore clogging
- Increase in total dissolved solids without corresponding decrease in target VOCs
Correct answer: Temporary increase in contaminant concentrations followed by rapid decline (oxidant push-pull)
A push-pull test showing initial concentration increase (as the oxidant mobilizes sorbed mass) followed by sharp decline confirms that ISCO is actively oxidizing the target contaminants in the treatment zone.
CEA Remediation Technologies 4
Dual-phase extraction (DPE) simultaneously removes which two phases from the subsurface?