OSSF INSTALLER
LICENSE EXAM PREP (2026
EDITION)
Texas On-Site Sewage Facility Certification Study
Guide
Exam-Aligned Questions, Verified Answers &
Detailed Rationales
✓ Texas OSSF regulatory framework and installer responsibilities
✓ Overview of OSSF Installer I licensing scope
✓ Conventional septic system components and operation
✓ Aerobic treatment unit (ATU) system design and function
✓ Septic tank sizing, compartments, and installation standards
✓ Pretreatment requirements and effluent filtration
✓ Soil texture classification and field identification methods
✓ Soil morphology indicators, including redoximorphic features
✓ Seasonal high water table and restrictive horizon identification
✓ Percolation testing principles and long-term acceptance rates (LTAR)
✓ Drainfield trench construction requirements
Disclaimer:
This study guide is an independent exam preparation resource.
It is not affiliated with or endorsed by TCEQ, and questions are practice-based, not copied from the
official exam.
This study guide is an independent educational resource and is not affiliated with or endorsed by any academic institution. It is intended for exam
preparation purposes only.
1
© 2026. All rights reserved. Unauthorized distribution is prohibited.
, _____1. Which state agency is primarily responsible for the adoption and enforcement of rules
regarding on-site sewage facilities in Texas?
A) Texas Department of State Health Services
B) Texas Parks and Wildlife Department
C) Texas Commission on Environmental Quality – Correct answer✅✅
D) Railroad Commission of Texas
_____2. What is the primary function of the pretreatment component in a standard on-site
sewage facility?
A) To distribute effluent evenly into the soil
B) To reduce the concentration of pathogens and suspended solids – Correct answer✅✅
C) To introduce oxygen directly into the groundwater table
D) To evaporate wastewater through surface vegetation
_____3. According to state regulations, what is the minimum required depth of suitable soil
beneath a conventional subsurface soil absorption system before encountering a restrictive
horizon or groundwater?
A) 12 inches
B) 24 inches
C) 36 inches
D) 48 inches – Correct answer✅✅
_____4. During a soil morphology evaluation, a redoximorphic feature characterized by grey
matrix colors with prominent redox concentrations is observed at 18 inches. What does this
indicate regarding the site?
A) The soil is highly aerobic and well-drained
B) A seasonal high water table or saturated zone is present – Correct answer✅✅
C) The soil contains an abundance of organic matter suitable for treatment
D) The area is entirely devoid of clay particles
_____5. An installer is laying perforated distribution piping for a gravity-flow drainfield. What
is the standard minimum slope required to ensure adequate effluent movement without leaving
solids behind?
A) 1 inch per 100 feet
B) 1/8 inch per foot
C) 1/4 inch per foot – Correct answer✅✅
D) 1/2 inch per foot
_____6. Which of the following soil textures is classified as having the highest percolation rate
and therefore the lowest wastewater treatment capability?
A) Sandy loam
B) Clay loam
C) Sand – Correct answer✅✅
D) Silty clay
This study guide is an independent educational resource and is not affiliated with or endorsed by any academic institution. It is intended for exam
preparation purposes only.
2
© 2026. All rights reserved. Unauthorized distribution is prohibited.
, _____7. A property owner wants to install an aerobic treatment unit with surface application.
What is the minimum required setback distance from the spray dispersal area to a public water
supply well?
A) 50 feet
B) 100 feet
C) 150 feet – Correct answer✅✅
D) 300 feet
_____8. What is the standard minimum effective depth of a two-compartment septic tank
required for residential use under current guidelines?
A) 750 gallons
B) 1,000 gallons – Correct answer✅✅
C) 1,500 gallons
D) 2,000 gallons
_____9. In an aerobic treatment system, what is the specific role of the aeration chamber?
A) To separate heavy solids from the liquid stream
B) To provide an environment for aerobic bacteria to decompose organic matter – Correct
answer✅✅
C) To store clarified effluent before it is pumped to the dispersal field
D) To disinfect the wastewater using ultraviolet light
_____10. When installing a distribution box for a conventional drainfield, what critical step must
be taken to ensure hydraulic equilibrium across all laterals?
A) Sealing all joints with hydraulic cement
B) Leveling the box perfectly on a stable compacted base – Correct answer✅✅
C) Installing a check valve on the inlet pipe
D) Backfilling with gravel before setting the box
_____11. Which type of on-site sewage facility system is most appropriate for a lot with a shallow
seasonal high water table and clay soils, assuming adequate surface area is available?
A) Standard gravity drainfield
B) Evapotranspiration bed – Correct answer✅✅
C) Subsurface sand filter
D) Cesspool
_____12. A maintenance provider reports that an aerobic system alarm is continuously sounding
despite the aerator functioning normally. What is the most probable cause?
A) The chlorinator is empty
B) The water level in the pump tank is abnormally high – Correct answer✅✅
C) The trash tank needs to be pumped
D) The spray heads are clogged
_____13. What is the primary purpose of an effluent screen or filter installed on the outlet baffle
of a septic tank?
A) To increase the retention time of the wastewater
This study guide is an independent educational resource and is not affiliated with or endorsed by any academic institution. It is intended for exam
preparation purposes only.
3
© 2026. All rights reserved. Unauthorized distribution is prohibited.
, B) To prevent large solids from entering and clogging the drainfield – Correct
answer✅✅
C) To introduce anaerobic bacteria into the effluent
D) To measure the volume of wastewater leaving the tank
_____14. Select all that apply. According to installation standards, which of the following
materials are explicitly prohibited from use in the construction of an on-site sewage facility
dispersal system?
A) Perforated PVC pipe meeting ASTM standards
B) Clay drainage tiles – Correct answer✅✅
C) Automobile tires – Correct answer✅✅
D) Corrugated polyethylene tubing with slotted openings
_____15. An installer is excavating a trench for a subsurface drainfield in sandy loam soil. What
is the minimum required depth of aggregate or approved gravel surrounding the perforated
piping?
A) 2 inches above and below the pipe
B) 6 inches above and 2 inches below the pipe
C) 2 inches above and 6 inches below the pipe – Correct answer✅✅
D) 4 inches above and 4 inches below the pipe
_____16. Under what specific condition is an installer permitted to use a single-compartment
septic tank for a new residential installation?
A) When the daily wastewater flow is calculated to be less than 500 gallons
B) When the tank is manufactured from high-density polyethylene
C) When local regulations specifically permit it or it is for a replacement system only –
Correct answer✅✅
D) When the system utilizes a drip dispersal field
_____17. What constitutes a "restrictive horizon" in the context of a soil evaluation for an OSSF?
A) A layer of organic matter at the surface
B) A zone with a bulk density that limits root penetration and water movement – Correct
answer✅✅
C) A stratum of highly permeable gravel
D) An area with an elevated concentration of nitrates
_____18. A site has a calculated long-term acceptance rate of 0.4 gallons per day per square foot.
If a three-bedroom home generates 360 gallons of wastewater per day, what is the minimum
required absorption area?
A) 600 square feet
B) 900 square feet – Correct answer✅✅
C) 1,200 square feet
D) 1,500 square feet
_____19. Which of the following disinfection methods is most commonly utilized in aerobic
treatment units prior to surface spray irrigation?
A) Ozonation
This study guide is an independent educational resource and is not affiliated with or endorsed by any academic institution. It is intended for exam
preparation purposes only.
4
© 2026. All rights reserved. Unauthorized distribution is prohibited.
LICENSE EXAM PREP (2026
EDITION)
Texas On-Site Sewage Facility Certification Study
Guide
Exam-Aligned Questions, Verified Answers &
Detailed Rationales
✓ Texas OSSF regulatory framework and installer responsibilities
✓ Overview of OSSF Installer I licensing scope
✓ Conventional septic system components and operation
✓ Aerobic treatment unit (ATU) system design and function
✓ Septic tank sizing, compartments, and installation standards
✓ Pretreatment requirements and effluent filtration
✓ Soil texture classification and field identification methods
✓ Soil morphology indicators, including redoximorphic features
✓ Seasonal high water table and restrictive horizon identification
✓ Percolation testing principles and long-term acceptance rates (LTAR)
✓ Drainfield trench construction requirements
Disclaimer:
This study guide is an independent exam preparation resource.
It is not affiliated with or endorsed by TCEQ, and questions are practice-based, not copied from the
official exam.
This study guide is an independent educational resource and is not affiliated with or endorsed by any academic institution. It is intended for exam
preparation purposes only.
1
© 2026. All rights reserved. Unauthorized distribution is prohibited.
, _____1. Which state agency is primarily responsible for the adoption and enforcement of rules
regarding on-site sewage facilities in Texas?
A) Texas Department of State Health Services
B) Texas Parks and Wildlife Department
C) Texas Commission on Environmental Quality – Correct answer✅✅
D) Railroad Commission of Texas
_____2. What is the primary function of the pretreatment component in a standard on-site
sewage facility?
A) To distribute effluent evenly into the soil
B) To reduce the concentration of pathogens and suspended solids – Correct answer✅✅
C) To introduce oxygen directly into the groundwater table
D) To evaporate wastewater through surface vegetation
_____3. According to state regulations, what is the minimum required depth of suitable soil
beneath a conventional subsurface soil absorption system before encountering a restrictive
horizon or groundwater?
A) 12 inches
B) 24 inches
C) 36 inches
D) 48 inches – Correct answer✅✅
_____4. During a soil morphology evaluation, a redoximorphic feature characterized by grey
matrix colors with prominent redox concentrations is observed at 18 inches. What does this
indicate regarding the site?
A) The soil is highly aerobic and well-drained
B) A seasonal high water table or saturated zone is present – Correct answer✅✅
C) The soil contains an abundance of organic matter suitable for treatment
D) The area is entirely devoid of clay particles
_____5. An installer is laying perforated distribution piping for a gravity-flow drainfield. What
is the standard minimum slope required to ensure adequate effluent movement without leaving
solids behind?
A) 1 inch per 100 feet
B) 1/8 inch per foot
C) 1/4 inch per foot – Correct answer✅✅
D) 1/2 inch per foot
_____6. Which of the following soil textures is classified as having the highest percolation rate
and therefore the lowest wastewater treatment capability?
A) Sandy loam
B) Clay loam
C) Sand – Correct answer✅✅
D) Silty clay
This study guide is an independent educational resource and is not affiliated with or endorsed by any academic institution. It is intended for exam
preparation purposes only.
2
© 2026. All rights reserved. Unauthorized distribution is prohibited.
, _____7. A property owner wants to install an aerobic treatment unit with surface application.
What is the minimum required setback distance from the spray dispersal area to a public water
supply well?
A) 50 feet
B) 100 feet
C) 150 feet – Correct answer✅✅
D) 300 feet
_____8. What is the standard minimum effective depth of a two-compartment septic tank
required for residential use under current guidelines?
A) 750 gallons
B) 1,000 gallons – Correct answer✅✅
C) 1,500 gallons
D) 2,000 gallons
_____9. In an aerobic treatment system, what is the specific role of the aeration chamber?
A) To separate heavy solids from the liquid stream
B) To provide an environment for aerobic bacteria to decompose organic matter – Correct
answer✅✅
C) To store clarified effluent before it is pumped to the dispersal field
D) To disinfect the wastewater using ultraviolet light
_____10. When installing a distribution box for a conventional drainfield, what critical step must
be taken to ensure hydraulic equilibrium across all laterals?
A) Sealing all joints with hydraulic cement
B) Leveling the box perfectly on a stable compacted base – Correct answer✅✅
C) Installing a check valve on the inlet pipe
D) Backfilling with gravel before setting the box
_____11. Which type of on-site sewage facility system is most appropriate for a lot with a shallow
seasonal high water table and clay soils, assuming adequate surface area is available?
A) Standard gravity drainfield
B) Evapotranspiration bed – Correct answer✅✅
C) Subsurface sand filter
D) Cesspool
_____12. A maintenance provider reports that an aerobic system alarm is continuously sounding
despite the aerator functioning normally. What is the most probable cause?
A) The chlorinator is empty
B) The water level in the pump tank is abnormally high – Correct answer✅✅
C) The trash tank needs to be pumped
D) The spray heads are clogged
_____13. What is the primary purpose of an effluent screen or filter installed on the outlet baffle
of a septic tank?
A) To increase the retention time of the wastewater
This study guide is an independent educational resource and is not affiliated with or endorsed by any academic institution. It is intended for exam
preparation purposes only.
3
© 2026. All rights reserved. Unauthorized distribution is prohibited.
, B) To prevent large solids from entering and clogging the drainfield – Correct
answer✅✅
C) To introduce anaerobic bacteria into the effluent
D) To measure the volume of wastewater leaving the tank
_____14. Select all that apply. According to installation standards, which of the following
materials are explicitly prohibited from use in the construction of an on-site sewage facility
dispersal system?
A) Perforated PVC pipe meeting ASTM standards
B) Clay drainage tiles – Correct answer✅✅
C) Automobile tires – Correct answer✅✅
D) Corrugated polyethylene tubing with slotted openings
_____15. An installer is excavating a trench for a subsurface drainfield in sandy loam soil. What
is the minimum required depth of aggregate or approved gravel surrounding the perforated
piping?
A) 2 inches above and below the pipe
B) 6 inches above and 2 inches below the pipe
C) 2 inches above and 6 inches below the pipe – Correct answer✅✅
D) 4 inches above and 4 inches below the pipe
_____16. Under what specific condition is an installer permitted to use a single-compartment
septic tank for a new residential installation?
A) When the daily wastewater flow is calculated to be less than 500 gallons
B) When the tank is manufactured from high-density polyethylene
C) When local regulations specifically permit it or it is for a replacement system only –
Correct answer✅✅
D) When the system utilizes a drip dispersal field
_____17. What constitutes a "restrictive horizon" in the context of a soil evaluation for an OSSF?
A) A layer of organic matter at the surface
B) A zone with a bulk density that limits root penetration and water movement – Correct
answer✅✅
C) A stratum of highly permeable gravel
D) An area with an elevated concentration of nitrates
_____18. A site has a calculated long-term acceptance rate of 0.4 gallons per day per square foot.
If a three-bedroom home generates 360 gallons of wastewater per day, what is the minimum
required absorption area?
A) 600 square feet
B) 900 square feet – Correct answer✅✅
C) 1,200 square feet
D) 1,500 square feet
_____19. Which of the following disinfection methods is most commonly utilized in aerobic
treatment units prior to surface spray irrigation?
A) Ozonation
This study guide is an independent educational resource and is not affiliated with or endorsed by any academic institution. It is intended for exam
preparation purposes only.
4
© 2026. All rights reserved. Unauthorized distribution is prohibited.
