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ENVIRONMENTAL ENGINEER – PE ENVIRONMENTAL
EXAM QUESTIONS AND VERIFIED ANSWERS WITH
RATIONALES JUST RELEASED
ENVIRONMENTAL ENGINEER – PE ENVIRONMENTAL EXAM
1. A groundwater sample has a pH of 6.3 and alkalinity of 120 mg/L as CaCO₃. What is the approximate
concentration of carbonate species (HCO₃⁻) present?
A) 120 mg/L
B) 146 mg/L
C) 100 mg/L
D) 61 mg/L
Rationale: At pH 6.3, the dominant carbonate species is bicarbonate (HCO₃⁻). Alkalinity at this pH ≈
[HCO₃⁻] as CaCO₃, so to convert HCO₃⁻ (61 g/eq) to mg/L HCO₃⁻: 120 * (61/50) ≈ 146 mg/L.
2. For a completely mixed activated sludge system without primary clarification, the food-to-
microorganism ratio is calculated using which influent parameter?
A) Total suspended solids
B) Biochemical oxygen demand
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C) Volatile suspended solids in the aeration tank
D) Total organic carbon
Rationale: F/M = (Influent BOD₅, lb/day) / (MLVSS in aeration tank, lb). BOD is the food source; MLVSS
represents the microorganism mass.
3. A stack emits 150 g/s of SO₂ at an effective stack height of 60 m. Wind speed is 3 m/s. Using the
Gaussian dispersion model, the ground-level concentration directly downwind (x=2 km, y=0) with
stability class D is most affected by which parameter?
A) Emission temperature
B) Stack diameter
C) Vertical dispersion coefficient (σz)
D) Ambient relative humidity
Rationale: In Gaussian plume, downwind concentration is inversely proportional to σy and σz. σz
controls vertical spread, critical for ground-level impact at 2 km.
4. Which of the following is the primary mechanism for removal of dissolved organic matter in a slow
sand filter?
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A) Straining
B) Electrostatic attraction
C) Biological degradation in the schmutzdecke
D) Chemical precipitation
Rationale: Slow sand filters develop a biological layer (schmutzdecke) on top, where microorganisms
degrade dissolved organic matter.
5. A hazardous waste site has a TCE concentration of 5 mg/L in groundwater. What is the approximate
theoretical detention time required in a granular activated carbon column if the equilibrium capacity is
0.2 g TCE/g GAC and the empty bed contact time is 10 min?
A) 10 min
B) 20 min
C) 30 min
D) 40 min
Rationale: EBCT is independent of concentration; it is a hydraulic parameter. For a given carbon column,
EBCT is fixed by design. Extra time is not needed for capacity calculation.
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6. Which air pollutant is most likely to cause acid rain when combined with atmospheric moisture?
A) Carbon monoxide
B) Lead
C) Nitrogen dioxide
D) Particulate matter (PM10)
Rationale: NO₂ reacts with water to form nitric acid; SO₂ forms sulfuric acid. Both cause acid rain.
7. In a sanitary landfill, leachate generation rate is primarily controlled by:
A) Compaction of waste
B) Precipitation and evapotranspiration
C) Daily cover soil type
D) Gas collection system efficiency
Rationale: Water balance: precipitation minus evapotranspiration and runoff equals percolation, which
becomes leachate.
8. A wastewater treatment plant uses chlorine for disinfection. If the chlorine residual is 1.0 mg/L after
30 minutes contact at pH 7, the required Ct value for 99.9% inactivation of Giardia is most likely:
ENVIRONMENTAL ENGINEER – PE ENVIRONMENTAL
EXAM QUESTIONS AND VERIFIED ANSWERS WITH
RATIONALES JUST RELEASED
ENVIRONMENTAL ENGINEER – PE ENVIRONMENTAL EXAM
1. A groundwater sample has a pH of 6.3 and alkalinity of 120 mg/L as CaCO₃. What is the approximate
concentration of carbonate species (HCO₃⁻) present?
A) 120 mg/L
B) 146 mg/L
C) 100 mg/L
D) 61 mg/L
Rationale: At pH 6.3, the dominant carbonate species is bicarbonate (HCO₃⁻). Alkalinity at this pH ≈
[HCO₃⁻] as CaCO₃, so to convert HCO₃⁻ (61 g/eq) to mg/L HCO₃⁻: 120 * (61/50) ≈ 146 mg/L.
2. For a completely mixed activated sludge system without primary clarification, the food-to-
microorganism ratio is calculated using which influent parameter?
A) Total suspended solids
B) Biochemical oxygen demand
, Page 2 of 112
C) Volatile suspended solids in the aeration tank
D) Total organic carbon
Rationale: F/M = (Influent BOD₅, lb/day) / (MLVSS in aeration tank, lb). BOD is the food source; MLVSS
represents the microorganism mass.
3. A stack emits 150 g/s of SO₂ at an effective stack height of 60 m. Wind speed is 3 m/s. Using the
Gaussian dispersion model, the ground-level concentration directly downwind (x=2 km, y=0) with
stability class D is most affected by which parameter?
A) Emission temperature
B) Stack diameter
C) Vertical dispersion coefficient (σz)
D) Ambient relative humidity
Rationale: In Gaussian plume, downwind concentration is inversely proportional to σy and σz. σz
controls vertical spread, critical for ground-level impact at 2 km.
4. Which of the following is the primary mechanism for removal of dissolved organic matter in a slow
sand filter?
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A) Straining
B) Electrostatic attraction
C) Biological degradation in the schmutzdecke
D) Chemical precipitation
Rationale: Slow sand filters develop a biological layer (schmutzdecke) on top, where microorganisms
degrade dissolved organic matter.
5. A hazardous waste site has a TCE concentration of 5 mg/L in groundwater. What is the approximate
theoretical detention time required in a granular activated carbon column if the equilibrium capacity is
0.2 g TCE/g GAC and the empty bed contact time is 10 min?
A) 10 min
B) 20 min
C) 30 min
D) 40 min
Rationale: EBCT is independent of concentration; it is a hydraulic parameter. For a given carbon column,
EBCT is fixed by design. Extra time is not needed for capacity calculation.
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6. Which air pollutant is most likely to cause acid rain when combined with atmospheric moisture?
A) Carbon monoxide
B) Lead
C) Nitrogen dioxide
D) Particulate matter (PM10)
Rationale: NO₂ reacts with water to form nitric acid; SO₂ forms sulfuric acid. Both cause acid rain.
7. In a sanitary landfill, leachate generation rate is primarily controlled by:
A) Compaction of waste
B) Precipitation and evapotranspiration
C) Daily cover soil type
D) Gas collection system efficiency
Rationale: Water balance: precipitation minus evapotranspiration and runoff equals percolation, which
becomes leachate.
8. A wastewater treatment plant uses chlorine for disinfection. If the chlorine residual is 1.0 mg/L after
30 minutes contact at pH 7, the required Ct value for 99.9% inactivation of Giardia is most likely:
