ON-SITE WASTEWATER SYSTEM INSTALLER LICENSING EXAMINER
EXAM QUESTIONS AND ANSWERS (VERIFIED ANSWERS) PLUS
RATIONALE 2025/2026 Q&A/ INSTANDOWNLOAD PDF
1. Which of the following best describes the purpose of an on-site wastewater treatment
system?
A. To store rainwater for irrigation
B. To collect and treat household sewage on-site
C. To pump wastewater directly into nearby streams
D. To dispose of solid waste only
Correct answer: B — On-site wastewater systems are designed to collect, treat, and dispose of
household sewage safely on-site.
2. What is the primary function of a septic tank in a wastewater system?
A. Chlorination
B. Sedimentation and anaerobic digestion
C. Aeration and nitrification
D. Filtration through gravel
Correct answer: B — Septic tanks allow solids to settle and undergo anaerobic digestion before
effluent exits to the drainfield.
3. Which component typically follows the septic tank in a conventional system?
A. Distribution box and drainfield
B. Pump chamber
C. Chlorination unit
D. Grease trap
Correct answer: A — The effluent flows from the septic tank to a distribution box and then into
the drainfield trenches.
4. The soil percolation test measures:
A. Soil color
B. Rate of water absorption
C. Organic content of soil
D. Soil pH
Correct answer: B — Percolation tests determine how quickly soil absorbs water, critical for
drainfield design.
,5. Which soil type has the slowest percolation rate?
A. Sand
B. Silt
C. Clay
D. Loam
Correct answer: C — Clay has very small pores that restrict water movement, leading to slow
percolation.
6. The minimum separation distance between a septic tank and a private water well is
usually:
A. 5 feet
B. 25 feet
C. 50 feet
D. 100 feet
Correct answer: C — Most health codes require at least 50 feet to prevent groundwater
contamination.
7. In a gravity-fed system, effluent moves through the system by:
A. Pump pressure
B. Gravity flow
C. Capillary action
D. Air suction
Correct answer: B — Gravity-fed systems rely on natural slope and elevation for effluent
movement.
8. What is the main purpose of effluent filters in septic tanks?
A. Remove suspended solids before effluent enters the drainfield
B. Neutralize pH
C. Chlorinate the effluent
D. Add oxygen to the effluent
Correct answer: A — Effluent filters trap solids and prevent them from clogging the drainfield.
9. Which of the following signs may indicate drainfield failure?
A. Lush green grass over trenches
B. Slow household drains
C. Sewage odors near the system
D. All of the above
Correct answer: D — These are typical signs of overload or drainfield malfunction.
, 10. The scum layer in a septic tank primarily consists of:
A. Inorganic materials
B. Fats, oils, and grease
C. Heavy solids
D. Nitrates
Correct answer: B — The scum layer floats due to fats and oils that rise above the liquid level.
11. What is the typical retention time for wastewater in a septic tank?
A. 1 hour
B. 12 hours
C. 24–48 hours
D. 72 hours
Correct answer: C — Two days allow solids to settle and partial digestion to occur.
12. Which of the following ensures even distribution of effluent to drainfield trenches?
A. Check valve
B. Distribution box
C. Aerator
D. Vent pipe
Correct answer: B — The distribution box evenly disperses effluent to multiple drainfield lines.
13. The required trench depth for most conventional drainfields is approximately:
A. 6–12 inches
B. 18–36 inches
C. 4–5 feet
D. 6–8 feet
Correct answer: B — Trenches are usually 18–36 inches deep to maintain aerobic soil
conditions.
14. What is the primary treatment process occurring in the drainfield?
A. Sedimentation
B. Biological filtration and soil absorption
C. Chemical oxidation
D. Evaporation
Correct answer: B — Soil bacteria filter and biologically treat effluent as it percolates.
EXAM QUESTIONS AND ANSWERS (VERIFIED ANSWERS) PLUS
RATIONALE 2025/2026 Q&A/ INSTANDOWNLOAD PDF
1. Which of the following best describes the purpose of an on-site wastewater treatment
system?
A. To store rainwater for irrigation
B. To collect and treat household sewage on-site
C. To pump wastewater directly into nearby streams
D. To dispose of solid waste only
Correct answer: B — On-site wastewater systems are designed to collect, treat, and dispose of
household sewage safely on-site.
2. What is the primary function of a septic tank in a wastewater system?
A. Chlorination
B. Sedimentation and anaerobic digestion
C. Aeration and nitrification
D. Filtration through gravel
Correct answer: B — Septic tanks allow solids to settle and undergo anaerobic digestion before
effluent exits to the drainfield.
3. Which component typically follows the septic tank in a conventional system?
A. Distribution box and drainfield
B. Pump chamber
C. Chlorination unit
D. Grease trap
Correct answer: A — The effluent flows from the septic tank to a distribution box and then into
the drainfield trenches.
4. The soil percolation test measures:
A. Soil color
B. Rate of water absorption
C. Organic content of soil
D. Soil pH
Correct answer: B — Percolation tests determine how quickly soil absorbs water, critical for
drainfield design.
,5. Which soil type has the slowest percolation rate?
A. Sand
B. Silt
C. Clay
D. Loam
Correct answer: C — Clay has very small pores that restrict water movement, leading to slow
percolation.
6. The minimum separation distance between a septic tank and a private water well is
usually:
A. 5 feet
B. 25 feet
C. 50 feet
D. 100 feet
Correct answer: C — Most health codes require at least 50 feet to prevent groundwater
contamination.
7. In a gravity-fed system, effluent moves through the system by:
A. Pump pressure
B. Gravity flow
C. Capillary action
D. Air suction
Correct answer: B — Gravity-fed systems rely on natural slope and elevation for effluent
movement.
8. What is the main purpose of effluent filters in septic tanks?
A. Remove suspended solids before effluent enters the drainfield
B. Neutralize pH
C. Chlorinate the effluent
D. Add oxygen to the effluent
Correct answer: A — Effluent filters trap solids and prevent them from clogging the drainfield.
9. Which of the following signs may indicate drainfield failure?
A. Lush green grass over trenches
B. Slow household drains
C. Sewage odors near the system
D. All of the above
Correct answer: D — These are typical signs of overload or drainfield malfunction.
, 10. The scum layer in a septic tank primarily consists of:
A. Inorganic materials
B. Fats, oils, and grease
C. Heavy solids
D. Nitrates
Correct answer: B — The scum layer floats due to fats and oils that rise above the liquid level.
11. What is the typical retention time for wastewater in a septic tank?
A. 1 hour
B. 12 hours
C. 24–48 hours
D. 72 hours
Correct answer: C — Two days allow solids to settle and partial digestion to occur.
12. Which of the following ensures even distribution of effluent to drainfield trenches?
A. Check valve
B. Distribution box
C. Aerator
D. Vent pipe
Correct answer: B — The distribution box evenly disperses effluent to multiple drainfield lines.
13. The required trench depth for most conventional drainfields is approximately:
A. 6–12 inches
B. 18–36 inches
C. 4–5 feet
D. 6–8 feet
Correct answer: B — Trenches are usually 18–36 inches deep to maintain aerobic soil
conditions.
14. What is the primary treatment process occurring in the drainfield?
A. Sedimentation
B. Biological filtration and soil absorption
C. Chemical oxidation
D. Evaporation
Correct answer: B — Soil bacteria filter and biologically treat effluent as it percolates.
