1|Page
OSSF INSTALLER 1 ACTUAL EXAM
PREP 2026 |QUESTIONS AND VERIFIED
ANSWERS |ALREADY A GRADED | NEW
AND REVISED
1. In the hydrologic cycle, water moves from the surface into the
atmosphere primarily by
A. Infiltration
B. Condensation
C. Evaporation
D. Sublimation
Water moves by evaporation from soil and water surfaces.
2. Which soil characteristic most directly affects wastewater
absorption rate?
A. Color
B. Texture
C. Temperature
D. Magnetism
Texture controls pore size and flow capability; it is critical in site
evaluation.
3. What is the primary purpose of an on-site sewage facility (OSSF)
system?
A. Aesthetic enhancement
B. Stormwater control
C. Safe treatment and disposal of wastewater
D. Water purification for drinking
OSSF protect public health by treating wastewater before
disposal.
4. A certified Installer I may construct which of the following
systems?
A. Aerobic treatment unit with advanced treatment
,2|Page
B. Standard absorptive drainfield systems
C. Secondary treatment mound systems designed by an engineer
D. Commercial wastewater treatment plant
Installer I level is limited to basic systems; advanced systems
often require higher certification or engineering design.
5. A soil with high clay content typically has
A. High permeability
B. High porosity and rapid percolation
C. Slow percolation rate
D. Excellent drainage characteristics
Clay reduces infiltration and slows acceptance rates.
6. If potable water lines are within the prescribed setback distance of
a septic tank, what must the installer do?
A. Reduce setback by half
B. Redirect the water line
C. Maintain minimum regulatory separation distances
D. No action required
Regulations require specific protections between sewage systems
and water supplies.
7. The best definition of “authorization to construct” is
A. Verbal consent from owner
B. Insurance approval
C. Permit approval to begin installation
D. Oral agreement with health official
It is the formal permit issued allowing construction.
8. Which microorganism group is most responsible for organic waste
decomposition in OSSFs?
A. Algae
B. Parasites
C. Bacteria
D. Fungi
Bacteria dominate biochemical decomposition in septic systems.
9. The term “restrictive horizon” refers to
A. Bedrock only
B. A clay surface layer
,3|Page
C. A subsurface layer that limits wastewater movement
D. Topsoil layer
This layer impedes infiltration and must be considered during
site evaluation.
10. The minimum liquid depth required in a properly functioning
septic tank is typically
A. 12 inches
B. 30 inches
C. 6 inches
D. 48 inches
Industry standards prescribe a minimum liquid depth to ensure
sufficient biological treatment.
11. Water flowing back into the house from an OSS system is
most likely caused by
A. Excessive chlorination
B. System overload or blockage
C. High groundwater only
D. Low percolation soils
Backflow usually results from hydraulic overload or obstruction.
12. What is a “designated representative” in OSSF practice?
A. Homeowner’s agent
B. Truck driver
C. Licensed individual authorized to review permits and
inspections
D. Real estate agent
A designated representative holds authority to enforce codes
under regulatory delegation.
13. Which of the following is NOT a common symptom of a
failing OSSF?
A. Pooling effluent on surface
B. Strong sewage odors
C. Clear water draining properly
D. Increased vegetation over drainfield due to moisture
Effluent pooling and odors indicate failures; clear drainage is
normal, not a symptom of failure.
, 4|Page
14. The slope formula is calculated as
A. (Distance ÷ elevation) × 100
B. (Elevation change ÷ distance) × 100
C. Elevation minus distance
D. Distance times elevation
Slope is percent rise over run.
15. Minimum setback from a drainfield to a private well is
usually
A. 10 feet
B. 50 feet
C. 100 feet
D. 200 feet
Minimum separation is required to protect water supplies.
16. Which type of tank outlet prevents solids from entering the
drainfield?
A. Open pipe
B. Effluent filter
C. Overflow pipe
D. Manhole cover
Effluent filters remove solids to prevent drainfield clogging.
17. What is the purpose of a percolation test?
A. Determine groundwater contamination
B. Identify septic tank size
C. Measure soil absorption rate
D. Calculate water usage
Perc tests evaluate how quickly soil absorbs water, guiding
system design.
18. The first step when inspecting a failed drainfield is to
A. Replace the entire system
B. Add chemicals to the tank
C. Identify source and cause of failure
D. Ignore minor pooling
Diagnosis must precede remediation to avoid unnecessary costs.
19. Which safety equipment is required when entering a confined
septic tank?
OSSF INSTALLER 1 ACTUAL EXAM
PREP 2026 |QUESTIONS AND VERIFIED
ANSWERS |ALREADY A GRADED | NEW
AND REVISED
1. In the hydrologic cycle, water moves from the surface into the
atmosphere primarily by
A. Infiltration
B. Condensation
C. Evaporation
D. Sublimation
Water moves by evaporation from soil and water surfaces.
2. Which soil characteristic most directly affects wastewater
absorption rate?
A. Color
B. Texture
C. Temperature
D. Magnetism
Texture controls pore size and flow capability; it is critical in site
evaluation.
3. What is the primary purpose of an on-site sewage facility (OSSF)
system?
A. Aesthetic enhancement
B. Stormwater control
C. Safe treatment and disposal of wastewater
D. Water purification for drinking
OSSF protect public health by treating wastewater before
disposal.
4. A certified Installer I may construct which of the following
systems?
A. Aerobic treatment unit with advanced treatment
,2|Page
B. Standard absorptive drainfield systems
C. Secondary treatment mound systems designed by an engineer
D. Commercial wastewater treatment plant
Installer I level is limited to basic systems; advanced systems
often require higher certification or engineering design.
5. A soil with high clay content typically has
A. High permeability
B. High porosity and rapid percolation
C. Slow percolation rate
D. Excellent drainage characteristics
Clay reduces infiltration and slows acceptance rates.
6. If potable water lines are within the prescribed setback distance of
a septic tank, what must the installer do?
A. Reduce setback by half
B. Redirect the water line
C. Maintain minimum regulatory separation distances
D. No action required
Regulations require specific protections between sewage systems
and water supplies.
7. The best definition of “authorization to construct” is
A. Verbal consent from owner
B. Insurance approval
C. Permit approval to begin installation
D. Oral agreement with health official
It is the formal permit issued allowing construction.
8. Which microorganism group is most responsible for organic waste
decomposition in OSSFs?
A. Algae
B. Parasites
C. Bacteria
D. Fungi
Bacteria dominate biochemical decomposition in septic systems.
9. The term “restrictive horizon” refers to
A. Bedrock only
B. A clay surface layer
,3|Page
C. A subsurface layer that limits wastewater movement
D. Topsoil layer
This layer impedes infiltration and must be considered during
site evaluation.
10. The minimum liquid depth required in a properly functioning
septic tank is typically
A. 12 inches
B. 30 inches
C. 6 inches
D. 48 inches
Industry standards prescribe a minimum liquid depth to ensure
sufficient biological treatment.
11. Water flowing back into the house from an OSS system is
most likely caused by
A. Excessive chlorination
B. System overload or blockage
C. High groundwater only
D. Low percolation soils
Backflow usually results from hydraulic overload or obstruction.
12. What is a “designated representative” in OSSF practice?
A. Homeowner’s agent
B. Truck driver
C. Licensed individual authorized to review permits and
inspections
D. Real estate agent
A designated representative holds authority to enforce codes
under regulatory delegation.
13. Which of the following is NOT a common symptom of a
failing OSSF?
A. Pooling effluent on surface
B. Strong sewage odors
C. Clear water draining properly
D. Increased vegetation over drainfield due to moisture
Effluent pooling and odors indicate failures; clear drainage is
normal, not a symptom of failure.
, 4|Page
14. The slope formula is calculated as
A. (Distance ÷ elevation) × 100
B. (Elevation change ÷ distance) × 100
C. Elevation minus distance
D. Distance times elevation
Slope is percent rise over run.
15. Minimum setback from a drainfield to a private well is
usually
A. 10 feet
B. 50 feet
C. 100 feet
D. 200 feet
Minimum separation is required to protect water supplies.
16. Which type of tank outlet prevents solids from entering the
drainfield?
A. Open pipe
B. Effluent filter
C. Overflow pipe
D. Manhole cover
Effluent filters remove solids to prevent drainfield clogging.
17. What is the purpose of a percolation test?
A. Determine groundwater contamination
B. Identify septic tank size
C. Measure soil absorption rate
D. Calculate water usage
Perc tests evaluate how quickly soil absorbs water, guiding
system design.
18. The first step when inspecting a failed drainfield is to
A. Replace the entire system
B. Add chemicals to the tank
C. Identify source and cause of failure
D. Ignore minor pooling
Diagnosis must precede remediation to avoid unnecessary costs.
19. Which safety equipment is required when entering a confined
septic tank?
