CEA Soil Contamination Assessment 3 — Questions and Answers
Question 1: What does the term 'NAPL' refer to in the context of soil and groundwater contamination?
- Non-Aqueous Phase Liquid (Correct answer)
- Natural Attenuating Petroleum Layer
- Neutralized Acid Percolate Level
- Non-Adsorptive Pollutant Leachate
Correct answer: Non-Aqueous Phase Liquid
NAPL stands for Non-Aqueous Phase Liquid, referring to contaminants such as petroleum products or chlorinated solvents that exist as a separate liquid phase from water.
Question 2: Which method is used to determine the bioavailability of metals in contaminated soil for ecological risk assessment purposes?
- Total acid digest (EPA Method 3050B)
- Toxicity Characteristic Leaching Procedure (TCLP)
- Sequential extraction procedures (Correct answer)
- X-ray fluorescence (XRF) screening
Correct answer: Sequential extraction procedures
Sequential extraction procedures fractionate metals into operationally defined fractions (exchangeable, carbonate-bound, etc.) to estimate bioavailable versus non-bioavailable forms.
Question 3: Under CERCLA, what document formally identifies the extent of soil contamination and recommended cleanup actions at a Superfund site?
- Remedial Investigation / Feasibility Study (RI/FS) (Correct answer)
- RCRA Facility Assessment (RFA)
- Environmental Site Assessment Phase II Report
- Corrective Measures Study (CMS)
Correct answer: Remedial Investigation / Feasibility Study (RI/FS)
The Remedial Investigation/Feasibility Study (RI/FS) characterizes the nature and extent of contamination and evaluates cleanup alternatives under CERCLA.
Question 4: A soil sample is collected from a leaking underground storage tank (LUST) site. Which analytical suite is MOST appropriate as a first-tier screen?
- TCLP metals and SVOCs
- Total petroleum hydrocarbons (TPH) and BTEX compounds (Correct answer)
- Pesticides and PCBs
- Dioxins and furans
Correct answer: Total petroleum hydrocarbons (TPH) and BTEX compounds
TPH and BTEX (benzene, toluene, ethylbenzene, xylene) are the primary contaminants of concern at LUST sites and are the standard first-tier analytical parameters.
Question 5: What is 'contaminant plume diving' and why is it important during soil and groundwater assessment?
- A plume that migrates laterally due to preferential pathways at constant depth
- A dissolved-phase plume that sinks below the water table due to density differences
- A vapor plume that descends into the capillary fringe
- A DNAPL mass that releases dissolved-phase contamination that migrates downward (Correct answer)
Correct answer: A DNAPL mass that releases dissolved-phase contamination that migrates downward
DNAPL (dense NAPL) sinks through the saturated zone and serves as a long-term source releasing dissolved-phase contamination that can extend deep into the aquifer.
Question 6: Which of the following best defines the 'action level' in the context of a soil contamination assessment?
- The detection limit of the analytical laboratory instrument
- The contaminant concentration that triggers a regulatory response or cleanup obligation (Correct answer)
- The maximum allowable soil disturbance during field sampling
- The minimum number of samples required by the state environmental agency
Correct answer: The contaminant concentration that triggers a regulatory response or cleanup obligation
An action level is the contaminant concentration in soil (or other media) at or above which regulatory agencies require investigation or remediation.
Question 7: A soil borings program reveals contamination that increases with depth. What does this pattern most likely suggest?
- Surface runoff as the primary source
- Atmospheric deposition as the source
- A subsurface source such as a buried tank or pipeline leak (Correct answer)
- Naturally elevated background concentrations
Correct answer: A subsurface source such as a buried tank or pipeline leak
Contamination that increases with depth typically indicates a subsurface source (e.g., buried tank, pipeline) rather than surface deposition or runoff.
CEA Soil Contamination Assessment 3
What does the term 'NAPL' refer to in the context of soil and groundwater contamination?