Onsite Wastewater System Installer Licensing
Exam Questions With Correct Answers
(Verified Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf
1. What is the primary function of a septic tank in an onsite
wastewater system?
A. To filter all bacteria from wastewater
B. To store water for irrigation
C. To separate solids from liquids and partially treat wastewater
D. To aerate the wastewater
Rationale: The septic tank allows solids to settle to the bottom as
sludge and oils to float as scum, providing primary treatment before
the effluent moves to the drainfield.
2. What type of soil is generally considered ideal for a conventional
drainfield?
A. Clay
B. Sand
, C. Rock
D. Loamy soil
Rationale: Loamy soils provide adequate drainage while retaining
enough moisture for microbial activity, which is essential for proper
treatment.
3. Which of the following is a common sign that a septic system is
failing?
A. Green lawn above the drainfield
B. Slow draining sinks
C. Sewage backup in the home
D. Excessive rainfall
Rationale: Sewage backup in the home indicates the system is unable
to process wastewater efficiently, often due to clogging or system
overload.
4. How often should a typical residential septic tank be pumped?
A. Every year
B. Every 10 years
C. Every 3–5 years
D. Only when problems occur
Rationale: Regular pumping prevents solids from accumulating
excessively, which can lead to system failure.
, 5. What is the purpose of a distribution box in a conventional septic
system?
A. To aerate wastewater
B. To evenly distribute effluent to the drainfield lines
C. To treat wastewater biologically
D. To measure water usage
Rationale: A distribution box ensures that each drainfield trench
receives an equal amount of effluent, preventing overload of one
section.
6. Which factor is most critical when determining the size of a
drainfield?
A. Proximity to the house
B. Soil percolation rate and daily wastewater flow
C. Depth of groundwater only
D. Type of septic tank
Rationale: Proper sizing depends on how fast the soil absorbs water
and the volume of wastewater generated, ensuring the system
functions safely.
7. What is a key requirement for the location of a drainfield?
A. It must be shaded at all times
B. It must be a minimum distance from wells, property lines, and
, water bodies
C. It should be on a slope of 20% or more
D. It must be under a driveway
Rationale: Proper setbacks protect water sources and prevent
contamination of adjacent properties.
8. What is the function of a riser on a septic tank?
A. To increase sludge capacity
B. To aerate effluent
C. To provide access for inspection and pumping
D. To filter solids
Rationale: Risers extend the septic tank access to the surface, making
maintenance easier without excavation.
9. What is the most common cause of drainfield failure?
A. Tree roots
B. Excess rainfall
C. Excessive solids entering the drainfield
D. Improper tank size
Rationale: Solids in the effluent can clog the soil pores, leading to
hydraulic failure of the drainfield.
Exam Questions With Correct Answers
(Verified Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf
1. What is the primary function of a septic tank in an onsite
wastewater system?
A. To filter all bacteria from wastewater
B. To store water for irrigation
C. To separate solids from liquids and partially treat wastewater
D. To aerate the wastewater
Rationale: The septic tank allows solids to settle to the bottom as
sludge and oils to float as scum, providing primary treatment before
the effluent moves to the drainfield.
2. What type of soil is generally considered ideal for a conventional
drainfield?
A. Clay
B. Sand
, C. Rock
D. Loamy soil
Rationale: Loamy soils provide adequate drainage while retaining
enough moisture for microbial activity, which is essential for proper
treatment.
3. Which of the following is a common sign that a septic system is
failing?
A. Green lawn above the drainfield
B. Slow draining sinks
C. Sewage backup in the home
D. Excessive rainfall
Rationale: Sewage backup in the home indicates the system is unable
to process wastewater efficiently, often due to clogging or system
overload.
4. How often should a typical residential septic tank be pumped?
A. Every year
B. Every 10 years
C. Every 3–5 years
D. Only when problems occur
Rationale: Regular pumping prevents solids from accumulating
excessively, which can lead to system failure.
, 5. What is the purpose of a distribution box in a conventional septic
system?
A. To aerate wastewater
B. To evenly distribute effluent to the drainfield lines
C. To treat wastewater biologically
D. To measure water usage
Rationale: A distribution box ensures that each drainfield trench
receives an equal amount of effluent, preventing overload of one
section.
6. Which factor is most critical when determining the size of a
drainfield?
A. Proximity to the house
B. Soil percolation rate and daily wastewater flow
C. Depth of groundwater only
D. Type of septic tank
Rationale: Proper sizing depends on how fast the soil absorbs water
and the volume of wastewater generated, ensuring the system
functions safely.
7. What is a key requirement for the location of a drainfield?
A. It must be shaded at all times
B. It must be a minimum distance from wells, property lines, and
, water bodies
C. It should be on a slope of 20% or more
D. It must be under a driveway
Rationale: Proper setbacks protect water sources and prevent
contamination of adjacent properties.
8. What is the function of a riser on a septic tank?
A. To increase sludge capacity
B. To aerate effluent
C. To provide access for inspection and pumping
D. To filter solids
Rationale: Risers extend the septic tank access to the surface, making
maintenance easier without excavation.
9. What is the most common cause of drainfield failure?
A. Tree roots
B. Excess rainfall
C. Excessive solids entering the drainfield
D. Improper tank size
Rationale: Solids in the effluent can clog the soil pores, leading to
hydraulic failure of the drainfield.
