CHMM Site Remediation 4 — Questions and Answers
Question 1: During a remedial action, an unexpected encounter with buried drums containing unknown waste triggers what immediate requirement under OSHA 29 CFR 1910.120?
- Immediately resume excavation
- Stop work, evaluate hazards, and implement emergency procedures per the site safety plan (Correct answer)
- Notify only the state environmental agency within 30 days
- Dispose of drums at the nearest landfill
Correct answer: Stop work, evaluate hazards, and implement emergency procedures per the site safety plan
HAZWOPER requires work to halt upon discovery of unexpected hazards, with evaluation and emergency response per the established site safety and health plan before continuing.
Question 2: A groundwater plume of hexavalent chromium Cr(VI) can be treated in situ by injecting which reagent to reduce it to less mobile Cr(III)?
- Sodium persulfate
- Ferrous sulfate or sodium bisulfite (Correct answer)
- Hydrogen peroxide
- Potassium permanganate
Correct answer: Ferrous sulfate or sodium bisulfite
Ferrous sulfate and sodium bisulfite are reductants that convert toxic Cr(VI) to Cr(III), which precipitates out of solution and is far less mobile and toxic.
Question 3: Which feasibility study criterion evaluates whether a proposed remedy can be reliably constructed, operated, and maintained as designed?
- Long-term effectiveness
- Implementability (Correct answer)
- Short-term effectiveness
- Overall protection of human health
Correct answer: Implementability
Implementability assesses technical and administrative feasibility, including contractor availability, equipment access, and regulatory approval for the proposed remedy.
Question 4: Soil washing is an ex situ remediation technology that concentrates contaminants into which fraction for further treatment or disposal?
- The coarse sand and gravel fraction
- The fine-grained silt and clay fraction (Correct answer)
- The intermediate gravel fraction
- The vapor phase
Correct answer: The fine-grained silt and clay fraction
Contaminants preferentially sorb to fine-grained particles; soil washing separates and concentrates the fine fraction, allowing the bulk of cleaner coarse material to be reused.
Question 5: Which performance monitoring metric best indicates whether a pump-and-treat system is achieving hydraulic containment of a dissolved contaminant plume?
- Effluent contaminant concentration trends
- Potentiometric surface maps showing inward hydraulic gradients toward extraction wells (Correct answer)
- Soil gas concentration data
- Surface water sampling results
Correct answer: Potentiometric surface maps showing inward hydraulic gradients toward extraction wells
Potentiometric maps demonstrating inward gradients toward extraction wells confirm that groundwater and dissolved contaminants are captured rather than migrating downgradient.
Question 6: A site assessment identifies arsenic at 25 mg/kg in residential soil. EPA's residential soil screening level for arsenic is 0.39 mg/kg. What is the most appropriate next step?
- Immediately excavate all soil on the property
- Conduct a baseline human health risk assessment to characterize actual risk (Correct answer)
- Issue a no-further-action determination
- File a criminal referral
Correct answer: Conduct a baseline human health risk assessment to characterize actual risk
Exceedance of a screening level triggers a risk assessment to determine actual exposure, bioavailability, and risk rather than triggering automatic remediation.
Question 7: Institutional controls (ICs) such as groundwater use restrictions are implemented primarily to address what limitation of a remedy?
- Insufficient regulatory funding
- Residual contamination that remains above unrestricted use levels, requiring exposure pathway management (Correct answer)
- Lack of site ownership documentation
- Inability to obtain contractor bids
Correct answer: Residual contamination that remains above unrestricted use levels, requiring exposure pathway management
ICs protect against exposure to residual contamination by restricting activities such as groundwater withdrawal, construction, or land use that could create new exposure pathways.
CHMM Site Remediation 4
During a remedial action, an unexpected encounter with buried drums containing unknown waste triggers what immediate requirement under OSHA 29 CFR 1910.120?