Principles and Practice of Engineering
(PE) Environmental Examination
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the primary purpose of a sanitary sewer system?
A) Transport stormwater runoff
B) Convey domestic and industrial wastewater to a treatment facility
C) Provide irrigation water for agriculture
D) Recharge groundwater aquifers
Correct Answer: B
Rationale: Sanitary sewers are designed specifically to collect and transport
wastewater from residential, commercial, and industrial sources to a treatment
plant, not stormwater or irrigation.
2. Which of the following best describes biochemical oxygen demand (BOD)?
A) The amount of oxygen required to chemically oxidize organic matter
B) The amount of dissolved oxygen consumed by microorganisms during
decomposition of organic matter
C) The total oxygen content of a water sample
D) The oxygen demand of inorganic compounds only
Correct Answer: B
Rationale: BOD measures the oxygen used by aerobic bacteria to break down
organic matter over a specified period, typically 5 days at 20°C.
,3. A wastewater treatment plant uses activated sludge. What is the primary
biological process occurring in the aeration tank?
A) Anaerobic digestion
B) Nitrification only
C) Aerobic decomposition of organic matter by bacteria
D) Chemical precipitation of phosphates
Correct Answer: C
Rationale: Activated sludge relies on aerobic bacteria in the aeration tank to
consume organic pollutants, converting them into biomass, CO₂, and water.
4. What is the typical design hydraulic loading rate for a slow sand filter in
drinking water treatment?
A) 0.1–0.4 m³/m²·h
B) 1–2 m³/m²·h
C) 5–10 m³/m²·h
D) 15–20 m³/m²·h
Correct Answer: A
Rationale: Slow sand filters operate at very low hydraulic loading rates (0.1–0.4
m³/m²·h) to allow a biological layer (schmutzdecke) to form and trap particles.
5. Which air pollutant is primarily associated with photochemical smog
formation?
A) Sulfur dioxide (SO₂)
B) Carbon monoxide (CO)
C) Nitrogen oxides (NOx) and volatile organic compounds (VOCs)
D) Particulate matter (PM10)
,Correct Answer: C
Rationale: NOx and VOCs react in sunlight to form ground-level ozone and other
photochemical oxidants, which are the main components of smog.
6. The Safe Drinking Water Act (SDWA) regulates which of the following?
A) Discharges to surface waters
B) Public water supply systems
C) Hazardous waste landfills
D) Air emissions from industrial sources
Correct Answer: B
Rationale: SDWA establishes standards for drinking water quality in public
water systems and protects underground sources of drinking water.
7. What is the typical detention time for primary clarifiers in municipal
wastewater treatment?
A) 1–2 hours
B) 4–8 hours
C) 12–24 hours
D) 2–4 days
Correct Answer: A
Rationale: Primary clarifiers typically have detention times of 1 to 2 hours to
allow settleable solids to separate by gravity.
8. Which of the following is a common method for controlling particulate
emissions from industrial stacks?
A) Wet scrubber
B) Activated carbon adsorption
C) Thermal oxidizer
D) Selective catalytic reduction
, Correct Answer: A
Rationale: Wet scrubbers use liquid to capture particulate matter from gas
streams; the others are primarily for gaseous pollutants or VOCs.
9. The hydraulic conductivity of an aquifer is measured in which units?
A) m³/s
B) m/s
C) kg/m³
D) Pa·s
Correct Answer: B
Rationale: Hydraulic conductivity (K) has units of velocity (m/s or ft/day),
representing the ease with which water moves through porous media.
10. What is the primary cause of eutrophication in surface waters?
A) Heavy metal contamination
B) Excess nutrients (nitrogen and phosphorus)
C) Low dissolved oxygen
D) High salinity
Correct Answer: B
Rationale: Eutrophication is driven by nutrient enrichment, especially N and P,
which stimulates algal blooms and subsequent oxygen depletion.
11. In a municipal solid waste landfill, what is the main purpose of the
composite liner system?
A) To generate methane gas
B) To prevent leachate migration into groundwater
C) To stabilize waste volume
D) To promote aerobic decomposition
(PE) Environmental Examination
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the primary purpose of a sanitary sewer system?
A) Transport stormwater runoff
B) Convey domestic and industrial wastewater to a treatment facility
C) Provide irrigation water for agriculture
D) Recharge groundwater aquifers
Correct Answer: B
Rationale: Sanitary sewers are designed specifically to collect and transport
wastewater from residential, commercial, and industrial sources to a treatment
plant, not stormwater or irrigation.
2. Which of the following best describes biochemical oxygen demand (BOD)?
A) The amount of oxygen required to chemically oxidize organic matter
B) The amount of dissolved oxygen consumed by microorganisms during
decomposition of organic matter
C) The total oxygen content of a water sample
D) The oxygen demand of inorganic compounds only
Correct Answer: B
Rationale: BOD measures the oxygen used by aerobic bacteria to break down
organic matter over a specified period, typically 5 days at 20°C.
,3. A wastewater treatment plant uses activated sludge. What is the primary
biological process occurring in the aeration tank?
A) Anaerobic digestion
B) Nitrification only
C) Aerobic decomposition of organic matter by bacteria
D) Chemical precipitation of phosphates
Correct Answer: C
Rationale: Activated sludge relies on aerobic bacteria in the aeration tank to
consume organic pollutants, converting them into biomass, CO₂, and water.
4. What is the typical design hydraulic loading rate for a slow sand filter in
drinking water treatment?
A) 0.1–0.4 m³/m²·h
B) 1–2 m³/m²·h
C) 5–10 m³/m²·h
D) 15–20 m³/m²·h
Correct Answer: A
Rationale: Slow sand filters operate at very low hydraulic loading rates (0.1–0.4
m³/m²·h) to allow a biological layer (schmutzdecke) to form and trap particles.
5. Which air pollutant is primarily associated with photochemical smog
formation?
A) Sulfur dioxide (SO₂)
B) Carbon monoxide (CO)
C) Nitrogen oxides (NOx) and volatile organic compounds (VOCs)
D) Particulate matter (PM10)
,Correct Answer: C
Rationale: NOx and VOCs react in sunlight to form ground-level ozone and other
photochemical oxidants, which are the main components of smog.
6. The Safe Drinking Water Act (SDWA) regulates which of the following?
A) Discharges to surface waters
B) Public water supply systems
C) Hazardous waste landfills
D) Air emissions from industrial sources
Correct Answer: B
Rationale: SDWA establishes standards for drinking water quality in public
water systems and protects underground sources of drinking water.
7. What is the typical detention time for primary clarifiers in municipal
wastewater treatment?
A) 1–2 hours
B) 4–8 hours
C) 12–24 hours
D) 2–4 days
Correct Answer: A
Rationale: Primary clarifiers typically have detention times of 1 to 2 hours to
allow settleable solids to separate by gravity.
8. Which of the following is a common method for controlling particulate
emissions from industrial stacks?
A) Wet scrubber
B) Activated carbon adsorption
C) Thermal oxidizer
D) Selective catalytic reduction
, Correct Answer: A
Rationale: Wet scrubbers use liquid to capture particulate matter from gas
streams; the others are primarily for gaseous pollutants or VOCs.
9. The hydraulic conductivity of an aquifer is measured in which units?
A) m³/s
B) m/s
C) kg/m³
D) Pa·s
Correct Answer: B
Rationale: Hydraulic conductivity (K) has units of velocity (m/s or ft/day),
representing the ease with which water moves through porous media.
10. What is the primary cause of eutrophication in surface waters?
A) Heavy metal contamination
B) Excess nutrients (nitrogen and phosphorus)
C) Low dissolved oxygen
D) High salinity
Correct Answer: B
Rationale: Eutrophication is driven by nutrient enrichment, especially N and P,
which stimulates algal blooms and subsequent oxygen depletion.
11. In a municipal solid waste landfill, what is the main purpose of the
composite liner system?
A) To generate methane gas
B) To prevent leachate migration into groundwater
C) To stabilize waste volume
D) To promote aerobic decomposition
