ETC Environmental Site Assessment & Investigation 2 — Questions and Answers
Question 1: What does the term 'conceptual site model' (CSM) represent in environmental investigation and remediation?
- A three-dimensional physical scale model of the site built for regulatory presentations
- A systematic description of contaminant sources, release mechanisms, transport pathways, and potential receptors at a site (Correct answer)
- A computer simulation model used to predict groundwater flow
- A regulatory document submitted to EPA describing the planned investigation approach
Correct answer: A systematic description of contaminant sources, release mechanisms, transport pathways, and potential receptors at a site
The CSM is a living document that synthesizes all known information about contamination sources, release history, transport pathways (soil, groundwater, vapor), exposure points, and potential receptors into a coherent site understanding that guides investigation and remediation decisions.
Question 2: In direct push technology (DPT) soil sampling using a Geoprobe, what is the key advantage over conventional hollow-stem auger drilling?
- DPT can collect samples from deeper formations than HSA methods
- DPT is faster, generates minimal waste, and reduces cross-contamination between vertical intervals (Correct answer)
- DPT provides continuous core samples with better lithologic detail than HSA
- DPT requires no drilling permits in most US states unlike HSA
Correct answer: DPT is faster, generates minimal waste, and reduces cross-contamination between vertical intervals
DPT advances small-diameter probes without drilling fluid or cuttings generation, enabling rapid collection of discrete soil and groundwater samples with minimal waste and reduced risk of cross-contaminating different depth intervals.
Question 3: A potentiometric surface map is constructed from water level measurements in multiple monitoring wells. What does this map depict?
- The concentration distribution of contaminants across the site
- The hydraulic head distribution showing groundwater flow direction and gradient (Correct answer)
- The depth to the bottom of the aquifer across the site
- The distribution of water table elevation above sea level only in unconfined aquifers
Correct answer: The hydraulic head distribution showing groundwater flow direction and gradient
A potentiometric surface map contours hydraulic head values across the site, showing groundwater flow direction (perpendicular to contour lines, from high to low head) and the hydraulic gradient driving that flow.
Question 4: What is the significance of a 'data gap' identified during a Phase II investigation, and what action is typically required?
- Data gaps indicate the investigation is complete and no further sampling is needed
- Data gaps represent areas of insufficient information that prevent completing the CSM or making a remediation decision, requiring additional investigation (Correct answer)
- Data gaps are minor omissions that do not affect site characterization conclusions
- Data gaps are only significant when found by regulatory reviewers
Correct answer: Data gaps represent areas of insufficient information that prevent completing the CSM or making a remediation decision, requiring additional investigation
Data gaps are identified when existing data are insufficient to characterize contamination extent, define the CSM, or support a remediation decision; they drive the design of additional investigation rounds or field activities.
Question 5: Which type of geophysical survey is most commonly used to locate buried drums, underground storage tanks, and metallic debris at contaminated sites?
- Ground Penetrating Radar (GPR)
- Electromagnetic (EM) Induction Survey (Correct answer)
- Seismic Refraction Survey
- Electrical Resistivity Tomography (ERT)
Correct answer: Electromagnetic (EM) Induction Survey
Electromagnetic induction surveys detect variations in soil conductivity and magnetic susceptibility caused by metallic objects, making them highly effective for locating buried drums, USTs, and metallic debris prior to intrusive investigation.
Question 6: A site investigation reveals that contamination extends beneath an active building. What sampling approach is used to evaluate whether subsurface vapors are entering the building interior?
- Passive soil gas sampling using Summa canisters at the property boundary
- Sub-slab soil gas sampling and indoor air sampling as part of a vapor intrusion assessment (Correct answer)
- Collection of outdoor air samples at the building perimeter
- Wipe sampling of interior surfaces for semi-volatile organic compounds
Correct answer: Sub-slab soil gas sampling and indoor air sampling as part of a vapor intrusion assessment
Vapor intrusion assessment involves collecting sub-slab soil gas samples immediately beneath the building foundation and indoor air samples to evaluate whether subsurface VOC vapors are migrating into the occupied building.
ETC Environmental Site Assessment & Investigation 2
What does the term 'conceptual site model' (CSM) represent in environmental investigation and remediation?