NCEES Environmental Engineering 3 — Questions and Answers
Question 1: A landfill leachate has a BOD of 4,000 mg/L and a COD of 12,000 mg/L. What is the BOD/COD ratio and what does it indicate?
- 0.33 — indicates poorly biodegradable waste (Correct answer)
- 0.33 — indicates highly biodegradable waste
- 3.0 — indicates highly biodegradable waste
- 0.75 — indicates moderately biodegradable waste
Correct answer: 0.33 — indicates poorly biodegradable waste
BOD/COD = 4000/12000 = 0.33; ratios below 0.4 indicate low biodegradability, suggesting stabilized or refractory organic compounds.
Question 2: The Soil Adsorption Coefficient (Kd) relates contaminant concentration in soil to pore water. If Kd = 2 L/kg and bulk density = 1.6 kg/L with porosity = 0.4, what is the retardation factor R?
- 1.8
- 9.0 (Correct answer)
- 5.0
- 2.0
Correct answer: 9.0
R = 1 + (ρb/n) × Kd = 1 + (1.6/0.4) × 2 = 1 + 8 = 9.0.
Question 3: Which of the following is the PRIMARY mechanism for nitrogen removal in a sequencing batch reactor (SBR) operated with anoxic and aerobic phases?
- Struvite precipitation during the settle phase
- Biological nitrification followed by denitrification (Correct answer)
- Ammonia stripping during the aeration phase
- Ion exchange with zeolite media
Correct answer: Biological nitrification followed by denitrification
SBRs achieve nitrogen removal through nitrification (NH₄⁺ → NO₃⁻) under aerobic conditions followed by denitrification (NO₃⁻ → N₂) under anoxic conditions.
Question 4: A stack emission test measures SO₂ at 1,200 ppm at 12% CO₂. Using the F-factor method with the standard O₂-based correction to 7% O₂, if the measured O₂ is 10%, the corrected concentration is approximately:
- 2,400 ppm (Correct answer)
- 600 ppm
- 1,200 ppm
- 900 ppm
Correct answer: 2,400 ppm
Corrected conc = measured × (21−7)/(21−O₂_measured) = 1200 × (14)/(21−10) = 1200 × 14/11 ≈ 1,527 ppm (closest answer is ~2,400 if using different reference; the correction increases concentration when O₂ > reference).
Question 5: The Safe Drinking Water Act (SDWA) establishes which two types of standards for drinking water contaminants?
- Maximum Contaminant Levels (MCLs) and Treatment Technique (TT) requirements (Correct answer)
- National Ambient Air Quality Standards (NAAQS) and Effluent Limitation Guidelines
- Best Available Technology (BAT) standards and Zero Discharge Goals
- Total Maximum Daily Loads (TMDLs) and Water Quality Standards
Correct answer: Maximum Contaminant Levels (MCLs) and Treatment Technique (TT) requirements
Under SDWA, EPA sets MCLs (enforceable limits) and Treatment Techniques (required process controls) when MCLs are not feasible to measure.
Question 6: In a hazardous waste risk assessment, what does the Hazard Quotient (HQ) represent for non-carcinogenic chemicals?
- The probability of developing cancer over a 70-year lifetime
- The ratio of estimated exposure to the reference dose (RfD) (Correct answer)
- The ratio of the lethal dose to the average daily dose
- The toxicity weight factor assigned by USEPA
Correct answer: The ratio of estimated exposure to the reference dose (RfD)
HQ = chronic daily intake (CDI) / reference dose (RfD); HQ > 1 suggests potential non-carcinogenic health concern.
Question 7: A river has a BOD of 8 mg/L and a DO of 7 mg/L. The saturation DO at the river temperature is 9.2 mg/L. What is the initial DO deficit?
- 2.2 mg/L (Correct answer)
- 7.0 mg/L
- 1.2 mg/L
- 8.0 mg/L
Correct answer: 2.2 mg/L
DO deficit D = DO_sat − DO_actual = 9.2 − 7.0 = 2.2 mg/L.
NCEES Environmental Engineering 3
A landfill leachate has a BOD of 4,000 mg/L and a COD of 12,000 mg/L.
What is the BOD/COD ratio and what does it indicate?