NCEES Environmental Engineering 4 — Questions and Answers
Question 1: In the Streeter-Phelps model for river oxygen sag, the critical point occurs where:
- BOD equals the initial dissolved oxygen concentration
- The deoxygenation rate equals the reaeration rate (Correct answer)
- Dissolved oxygen reaches saturation after the outfall
- The river velocity equals the settling velocity of solids
Correct answer: The deoxygenation rate equals the reaeration rate
At the critical point (minimum DO), deoxygenation and reaeration rates are equal, so the DO deficit is at its maximum.
Question 2: A groundwater plume contains TCE at 500 µg/L. The EPA MCL for TCE is 5 µg/L. A pump-and-treat system reduces the concentration to 10 µg/L after 5 years but stalls due to back-diffusion. This behavior is best described as:
- Preferential flow through macropores causing bypass
- Tailing and rebound from matrix diffusion in low-permeability zones (Correct answer)
- Precipitation of TCE as a solid phase in the aquifer
- Volatilization of TCE into the vadose zone
Correct answer: Tailing and rebound from matrix diffusion in low-permeability zones
Back-diffusion from low-permeability matrix materials causes tailing (slow concentration decrease) and rebound after pumping, a well-documented limitation of pump-and-treat.
Question 3: Which coagulant is commonly used in water treatment and functions by forming aluminum hydroxide floc that sweeps particles from suspension?
- Sodium hypochlorite
- Alum (aluminum sulfate) (Correct answer)
- Ferrous sulfate without pH adjustment
- Potassium permanganate
Correct answer: Alum (aluminum sulfate)
Alum (Al₂(SO₄)₃) hydrolyzes to form Al(OH)₃ floc, which adsorbs and enmeshes suspended particles in a process called sweep flocculation.
Question 4: The RCRA Subtitle C program regulates hazardous waste from:
- Cradle to grave — generation, transport, treatment, storage, and disposal (Correct answer)
- Only the final disposal in permitted landfills
- Underground storage tanks containing petroleum products
- Non-hazardous industrial solid waste at municipal facilities
Correct answer: Cradle to grave — generation, transport, treatment, storage, and disposal
RCRA Subtitle C establishes a cradle-to-grave tracking system covering generation, transportation, treatment, storage, and disposal of hazardous waste.
Question 5: A municipal solid waste landfill uses a composite liner system. Which configuration meets the minimum RCRA Subtitle D requirements?
- 2-ft compacted clay layer alone
- 60-mil HDPE geomembrane overlying a 2-ft compacted clay layer with hydraulic conductivity ≤ 1×10⁻⁷ cm/s (Correct answer)
- Compacted clay liner with a leachate collection system above it
- Geomembrane alone with a leak detection system
Correct answer: 60-mil HDPE geomembrane overlying a 2-ft compacted clay layer with hydraulic conductivity ≤ 1×10⁻⁷ cm/s
RCRA Subtitle D requires a composite liner: a 60-mil HDPE geomembrane in direct contact with at least 2 ft of compacted soil with k ≤ 1×10⁻⁷ cm/s.
Question 6: For an air stripping tower designed to remove VOCs from groundwater, Henry's Law constant (H) is critical. A contaminant with H < 10⁻⁵ atm·m³/mol is generally considered:
- Highly strippable and easy to air strip
- Difficult to air strip; another treatment technology should be considered (Correct answer)
- Appropriate for granular activated carbon adsorption only
- Suitable for biological treatment in a packed bed reactor
Correct answer: Difficult to air strip; another treatment technology should be considered
Low Henry's Law constants indicate low volatility from the aqueous phase, making air stripping ineffective for contaminants with H < 10⁻⁵ atm·m³/mol.
Question 7: Under the National Environmental Policy Act (NEPA), which document requires the most thorough environmental review?
- Categorical Exclusion (CE)
- Environmental Assessment (EA)
- Finding of No Significant Impact (FONSI)
- Environmental Impact Statement (EIS) (Correct answer)
Correct answer: Environmental Impact Statement (EIS)
An Environmental Impact Statement (EIS) is the most comprehensive NEPA document, required for major federal actions significantly affecting the environment.
NCEES Environmental Engineering 4
In the Streeter-Phelps model for river oxygen sag, the critical point occurs where: