NCEES Environmental Engineering 5 — Questions and Answers
Question 1: In a biological phosphorus removal system (Enhanced Biological Phosphorus Removal, EBPR), phosphorus uptake occurs in which reactor zone?
- Anaerobic zone — where PAOs release phosphorus
- Anoxic zone — where denitrification drives phosphorus uptake
- Aerobic zone — where PAOs take up excess phosphorus (Correct answer)
- Sludge thickener — where phosphorus concentrates
Correct answer: Aerobic zone — where PAOs take up excess phosphorus
Phosphorus accumulating organisms (PAOs) release phosphorus under anaerobic conditions and then take up excess luxury phosphorus under aerobic conditions.
Question 2: A 500-acre watershed with a runoff curve number (CN) of 75 receives 3.5 inches of rainfall. Using the NRCS method, what is the potential maximum retention S?
- 1.33 inches
- 3.33 inches (Correct answer)
- 5.00 inches
- 2.50 inches
Correct answer: 3.33 inches
S = (1000/CN) − 10 = (1000/75) − 10 = 13.33 − 10 = 3.33 inches.
Question 3: A facility emits 50 g/s of a pollutant from a stack. Using a simple Gaussian dispersion model, doubling the wind speed while keeping all else constant will:
- Double the ground-level concentration downwind
- Have no effect on ground-level concentration
- Halve the ground-level concentration downwind (Correct answer)
- Quadruple the ground-level concentration downwind
Correct answer: Halve the ground-level concentration downwind
In the Gaussian plume model, centerline concentration is inversely proportional to wind speed (C ∝ Q/u), so doubling u halves the concentration.
Question 4: Which unit operation is MOST appropriate for removing dissolved heavy metals (e.g., cadmium, lead) from industrial wastewater before discharge?
- Dissolved air flotation (DAF)
- Chemical precipitation followed by clarification (Correct answer)
- Reverse osmosis without pretreatment
- Trickling filter biological treatment
Correct answer: Chemical precipitation followed by clarification
Raising pH causes heavy metals to precipitate as hydroxides (e.g., Cd(OH)₂), which are then removed by clarification or filtration.
Question 5: The Toxic Characteristic Leaching Procedure (TCLP) is used to:
- Measure the total concentration of metals in a solid waste sample
- Simulate leaching of hazardous constituents from waste in a landfill environment (Correct answer)
- Determine the biodegradability of organic waste under aerobic conditions
- Assess the ignitability of liquid hazardous waste
Correct answer: Simulate leaching of hazardous constituents from waste in a landfill environment
TCLP uses an acidic extraction fluid to simulate leachate formation in a co-disposal landfill setting and determines if a waste is hazardous by toxicity characteristic.
Question 6: A stormwater detention basin is sized for the 100-year storm event. Its PRIMARY environmental function in an urban watershed is to:
- Remove dissolved nitrogen and phosphorus from runoff through biological uptake
- Attenuate peak discharge rates to pre-development conditions (Correct answer)
- Provide tertiary treatment equivalent to a municipal WWTP
- Reduce total runoff volume through infiltration to the water table
Correct answer: Attenuate peak discharge rates to pre-development conditions
Detention basins (dry or wet) are designed primarily to reduce peak flow rates, releasing stored runoff slowly after the storm peak has passed.
Question 7: In the context of Superfund (CERCLA) cleanup, which document presents the analysis of remedial alternatives and recommends a preferred remedy for a contaminated site?
- Remedial Investigation (RI)
- Feasibility Study (FS) (Correct answer)
- Record of Decision (ROD)
- Remedial Action Plan (RAP)
Correct answer: Feasibility Study (FS)
The Feasibility Study (FS) evaluates and compares remedial alternatives against nine criteria and recommends a preferred remedy prior to the formal ROD.
NCEES Environmental Engineering 5
In a biological phosphorus removal system (Enhanced Biological Phosphorus Removal, EBPR), phosphorus uptake occurs in which reactor zone?