CEA Remediation Technologies 3 — Questions and Answers
Question 1: Thermal conductive heating (TCH) treats contaminated soil by:
- Injecting steam through horizontal wells to flush VOCs
- Using electrical resistance heating elements to conduct heat uniformly through soil (Correct answer)
- Burning contaminated material in a rotary kiln
- Applying radio-frequency energy exclusively to saturated zones
Correct answer: Using electrical resistance heating elements to conduct heat uniformly through soil
TCH uses steel heating elements inserted into the subsurface that conduct heat directly through soil, raising temperatures sufficiently to volatilize and destroy contaminants including DNAPLs.
Question 2: The primary goal of a soil vapor extraction (SVE) system is to:
- Remove dissolved-phase contaminants from groundwater
- Extract volatile and semi-volatile organic contaminants from the vadose zone (Correct answer)
- Biologically degrade petroleum hydrocarbons using forced-air injection
- Stabilize heavy metals in unsaturated soils using chemical amendments
Correct answer: Extract volatile and semi-volatile organic contaminants from the vadose zone
SVE applies a vacuum to extraction wells in the vadose zone, inducing airflow that volatilizes and removes VOCs from soil pores for above-ground treatment.
Question 3: Ex situ bioremediation using a slurry-phase bioreactor offers which advantage over land farming?
- Lower capital and operating costs
- Enhanced contact between microorganisms, nutrients, and contaminants due to mixing (Correct answer)
- No requirement for leachate collection
- Ability to treat highly chlorinated compounds without electron donors
Correct answer: Enhanced contact between microorganisms, nutrients, and contaminants due to mixing
Slurry-phase bioreactors mix contaminated soil with water and nutrients in a tank, maximizing contact and mass transfer, which accelerates biodegradation compared to static land farming.
Question 4: In phytoremediation, rhizofiltration specifically refers to:
- Plant uptake of contaminants into shoots and leaves for harvest
- The use of plant roots to absorb, concentrate, and precipitate contaminants from water (Correct answer)
- Breaking down contaminants in the root zone through microbial activity
- Containing contamination by hydraulic control using deep-rooted plants
Correct answer: The use of plant roots to absorb, concentrate, and precipitate contaminants from water
Rhizofiltration uses plant roots grown in contaminated water to adsorb and concentrate heavy metals or radionuclides, then harvested plant material is disposed of as hazardous waste.
Question 5: A remedial action objective (RAO) for a RCRA corrective action site must be based on:
- The lowest achievable concentration regardless of cost or technical feasibility
- Cleanup levels protective of human health and the environment, considering exposure pathways (Correct answer)
- Federal MCLs applicable only to drinking water standards
- The background concentration of the contaminant in pristine reference soils
Correct answer: Cleanup levels protective of human health and the environment, considering exposure pathways
RAOs define the cleanup goals needed to be protective of human health and the environment for current and reasonably anticipated future land and groundwater uses, considering all relevant exposure pathways.
Question 6: Pneumatic fracturing is used in remediation primarily to:
- Increase permeability of low-conductivity formations to improve contaminant extraction (Correct answer)
- Inject chemical oxidants at high pressure to destroy DNAPLs
- Stimulate aerobic biodegradation by forced air injection
- Extract free-phase NAPL from fractured bedrock using vacuum pressure
Correct answer: Increase permeability of low-conductivity formations to improve contaminant extraction
Pneumatic fracturing injects high-pressure air into tight, low-permeability formations (silts, clays) to create fractures that improve fluid flow and enhance SVE or other remediation technologies.
Question 7: Which document formally concludes a CERCLA remedial action and confirms cleanup goals have been achieved?
- Record of Decision (ROD)
- Remedial Design/Remedial Action (RD/RA) Work Plan
- Preliminary Assessment (PA)
- Closeout Report or Completion Report (Correct answer)
Correct answer: Closeout Report or Completion Report
A CERCLA Closeout Report (or Completion Report) documents that all remedial action objectives have been met, triggering the formal closeout of remedial activities and transitioning to long-term monitoring or deletion from the NPL.
CEA Remediation Technologies 3
Thermal conductive heating (TCH) treats contaminated soil by: