CEA Soil Contamination Assessment 5 — Questions and Answers
Question 1: Which in-situ soil remediation technology works by injecting steam or hot water into the subsurface to volatilize and remove contaminants?
- Soil vapor extraction (SVE)
- In-situ thermal treatment (ISTT) (Correct answer)
- Permeable reactive barrier (PRB)
- Monitored natural attenuation (MNA)
Correct answer: In-situ thermal treatment (ISTT)
In-situ thermal treatment (ISTT) uses steam injection, electrical resistance heating, or conductive heating to raise subsurface temperatures and volatilize contaminants for extraction.
Question 2: What is the significance of the 'total threshold limit concentration' (TTLC) in California's soil contamination regulations?
- It is the OSHA permissible exposure limit for field workers during soil excavation
- It is the state-specific total concentration threshold above which a soil is classified as hazardous waste (Correct answer)
- It is the groundwater protection criterion used to back-calculate soil cleanup goals
- It is the minimum detection limit required of certified laboratories in California
Correct answer: It is the state-specific total concentration threshold above which a soil is classified as hazardous waste
California's TTLC is a total concentration threshold; soils exceeding TTLC for listed constituents are classified as hazardous waste under California law.
Question 3: A brownfield redevelopment project proposes to convert an industrial site to a daycare facility. How does this change in land use affect soil cleanup standards?
- It has no effect; cleanup standards are media-specific and land-use independent
- It requires more stringent cleanup standards due to the sensitive receptor population and residential-equivalent exposure assumptions (Correct answer)
- It allows less stringent standards because daycare facilities are regulated as commercial, not residential
- It triggers RCRA subtitle C requirements regardless of contaminant concentrations
Correct answer: It requires more stringent cleanup standards due to the sensitive receptor population and residential-equivalent exposure assumptions
Sensitive receptors such as children at a daycare facility trigger more stringent, residential-type cleanup standards due to higher exposure frequencies, lower body weights, and greater susceptibility.
Question 4: Which document does EPA require to be completed before initiating a time-critical removal action at a contaminated soil site?
- Record of Decision (ROD)
- Action Memorandum (Correct answer)
- Remedial Design/Remedial Action (RD/RA) Work Plan
- Environmental Impact Statement (EIS)
Correct answer: Action Memorandum
An Action Memorandum documents the basis for and scope of a time-critical removal action and must be approved before cleanup activities begin under CERCLA.
Question 5: What is 'phytoremediation' and for which soil contaminants is it generally MOST effective?
- Use of microorganisms to break down organics; most effective for dense chlorinated solvents
- Use of plants to accumulate, degrade, or stabilize contaminants; most effective for metals and some organic compounds in shallow soils (Correct answer)
- Use of chemical oxidants injected into soil; most effective for recalcitrant petroleum hydrocarbons
- Use of electrokinetic gradients to mobilize ions; most effective for deep DNAPL sources
Correct answer: Use of plants to accumulate, degrade, or stabilize contaminants; most effective for metals and some organic compounds in shallow soils
Phytoremediation uses plants to hyperaccumulate metals or promote rhizosphere biodegradation of organics; it is best suited for shallow, diffuse contamination with metals such as lead, arsenic, or cadmium.
Question 6: During a soil contamination investigation, a field screening instrument shows a high PID reading in a boring at 8 feet bgs but laboratory confirmation shows low TPH concentrations. What is the MOST likely explanation?
- The laboratory used an incorrect extraction solvent
- The PID response was caused by naturally occurring biogenic gases or non-contaminant volatile compounds (Correct answer)
- The boring was not drilled deep enough to reach the contamination source zone
- Field screening instruments cannot detect petroleum hydrocarbons
Correct answer: The PID response was caused by naturally occurring biogenic gases or non-contaminant volatile compounds
PIDs respond to a wide range of volatile organic compounds including naturally occurring biogenic gases (methane, terpenes) that can produce elevated readings not confirmed by targeted laboratory analysis.
Question 7: What is the primary regulatory purpose of a 'soil management plan' (SMP) during construction at a contaminated brownfield site?
- To document the number of soil samples collected per acre of disturbance
- To establish procedures for identifying, handling, segregating, and disposing of contaminated soil encountered during grading and excavation (Correct answer)
- To certify that all contaminated soil has been removed prior to construction
- To satisfy NPDES permit requirements for stormwater discharge from the construction site
Correct answer: To establish procedures for identifying, handling, segregating, and disposing of contaminated soil encountered during grading and excavation
A soil management plan establishes worker protection protocols and procedures for identifying, segregating, and properly disposing of contaminated soil encountered during construction activities.
CEA Soil Contamination Assessment 5
Which in-situ soil remediation technology works by injecting steam or hot water into the subsurface to volatilize and remove contaminants?