AQS Remediation & Mitigation Strategies 2 — Questions and Answers
Question 1: Which soil vapor extraction (SVE) design parameter most directly controls the radius of influence at a contaminated site?
- Soil permeability and applied vacuum (Correct answer)
- Depth of contamination only
- Groundwater table elevation
- Carbon content of native soil
Correct answer: Soil permeability and applied vacuum
Soil permeability and the applied vacuum together determine how far the pressure gradient extends, defining the SVE radius of influence.
Question 2: In a bioventing system for petroleum hydrocarbon remediation, the primary goal of air injection is to:
- Volatilize contaminants to the surface
- Supply oxygen to stimulate indigenous aerobic microorganisms (Correct answer)
- Lower the water table to expose the smear zone
- Dilute contaminant concentrations in situ
Correct answer: Supply oxygen to stimulate indigenous aerobic microorganisms
Bioventing delivers oxygen to the vadose zone to enhance aerobic biodegradation of hydrocarbons by native bacteria.
Question 3: A permeable reactive barrier (PRB) using zero-valent iron (ZVI) remediates chlorinated solvents primarily through:
- Adsorption onto iron surfaces
- Reductive dechlorination via electron donation (Correct answer)
- Oxidative destruction by iron oxides
- pH adjustment that precipitates contaminants
Correct answer: Reductive dechlorination via electron donation
ZVI donates electrons to chlorinated ethenes, sequentially removing chlorine atoms through reductive dechlorination.
Question 4: When designing an air pollution control system, the pressure drop across a fabric filter (baghouse) is primarily important because it affects:
- Particulate collection efficiency only
- Fan energy consumption and filtration velocity (Correct answer)
- Chemical reactivity of captured dust
- Stack exit temperature
Correct answer: Fan energy consumption and filtration velocity
Pressure drop determines the energy required to move air through the system and governs actual filtration velocity (air-to-cloth ratio).
Question 5: Which in situ chemical oxidation (ISCO) reagent is most appropriate when treating a site with high natural organic matter (NOM) content?
- Potassium permanganate due to high NOM demand tolerance
- Hydrogen peroxide due to low reactivity with NOM
- Persulfate activated with heat or alkali (Correct answer)
- Ozone due to its selectivity for contaminants over NOM
Correct answer: Persulfate activated with heat or alkali
Persulfate, particularly when thermally or alkaline-activated, is less quenched by NOM than permanganate or Fenton's reagent and is preferred at high-NOM sites.
Question 6: A wet scrubber's removal efficiency for gaseous pollutants is governed primarily by which parameter?
- Liquid-to-gas ratio and mass transfer coefficient (Correct answer)
- Particulate size distribution of the gas stream
- Exhaust stack height above grade
- Ambient humidity at the facility boundary
Correct answer: Liquid-to-gas ratio and mass transfer coefficient
Gas-phase absorption efficiency depends on how much liquid contacts the gas (L/G ratio) and the ease of transfer between phases (mass transfer coefficient).
Question 7: During natural attenuation monitoring for a BTEX plume, which field parameter most directly indicates active aerobic biodegradation?
- Increasing dissolved oxygen downgradient of source
- Decreasing dissolved oxygen near the contaminant source (Correct answer)
- Rising pH in the source zone
- Stable sulfate concentrations throughout the plume
Correct answer: Decreasing dissolved oxygen near the contaminant source
Dissolved oxygen depletion near the source zone indicates it is being consumed by aerobic microorganisms degrading BTEX compounds.
AQS Remediation & Mitigation Strategies 2
Which soil vapor extraction (SVE) design parameter most directly controls the radius of influence at a contaminated site?