TCEQ OSSF Exam 2026–2027 | 150 Questions & Correct Answers
TEXAS COMMISSION ON ENVIRONMENTAL QUALITY
ON-SITE SEWAGE FACILITY (OSSF) EXAM
2026–2027
150 Questions and Correct Answers | Graded A+ | 100% Verified
Key Domains: OSSF Regulations, System Design and Installation, Soil Evaluation,
Maintenance Protocols, Environmental Safety, and Texas Administrative Code Compliance
INSTRUCTIONS
Each question is followed by four options (A–D). The correct answer is highlighted in
bold cyan along with a concise rationale explaining safety and operational reasoning,
code adherence, and why alternative options are less appropriate.
DOMAIN 1: OSSF Regulations and Licensing
Questions 1–25
1. Which Texas agency is the primary regulatory authority for On-Site Sewage Facilities (OSSF) in the
state?
A. Texas Department of State Health Services
B. Texas Commission on Environmental Quality (TCEQ)
C. Texas Parks and Wildlife Department
D. Texas Department of Agriculture
Answer: B
Rationale: TCEQ is the primary regulatory authority for OSSF systems under 30 TAC Chapter 285. The agency
establishes rules, oversees licensed installers, and enforces compliance for on-site sewage treatment systems across
Texas.
2. Under 30 TAC Chapter 285, what is the minimum acreage generally required for a standard OSSF
system utilizing a conventional subsurface absorption drainfield?
A. One-quarter acre B. One-half acre
C. Three-quarter acre D. One full acre
Answer: C
Rationale: Under 30 TAC 285.6, a minimum lot size of three-quarters of an acre is generally required for conventional
OSSF systems using a subsurface absorption area, ensuring adequate setback distances and suitable area for drainfield
placement and reserve area.
3. What type of TCEQ license is required to install, maintain, and repair standard OSSF systems in Texas?
A. Licensed Professional Engineer (PE) only
B. OSSF Installer or Apprentice license issued by TCEQ
1
, TCEQ OSSF Exam 2026–2027 | 150 Questions & Correct Answers
C. General Contractor license from the Texas Department of Licensing
D. No specific license is required for basic OSSF installation
Answer: B
Rationale: 30 TAC 285.31 requires that OSSF installation, maintenance, and repair work be performed by individuals
holding a valid OSSF Installer license or working under the direct supervision of a licensed installer as an apprentice.
PEs may design systems but installation requires an OSSF license.
4. At what minimum depth must an OSSF disposal field be installed below the ground surface to ensure
adequate soil treatment of effluent?
A. 6 inches below ground surface B. 12 inches below ground surface
C. 18 inches below ground surface D. 24 inches below ground surface
Answer: C
Rationale: 30 TAC 285.33(c)(4) requires a minimum of 18 inches of unsaturated soil beneath the disposal field trench
bottom to provide adequate treatment of effluent before it reaches any restrictive horizon, groundwater, or impervious
layer.
5. Which entity at the local level is authorized by TCEQ to administer the OSSF program and issue
construction permits within its jurisdiction?
A. County Tax Assessor-Collector office
B. Designated Representative (DR) such as a county or local health department
C. Local Water Control and Improvement District board
D. Municipal Utility District engineering department
Answer: B
Rationale: Under 30 TAC 285.9, TCEQ may designate local authorities as Designated Representatives (DRs) to
administer the OSSF program. DRs include county commissioners courts, local health departments, and other
authorized entities that can review plans and issue permits.
6. What is the maximum daily flow rate, in gallons per day, that a single-family residential OSSF system is
typically designed to treat under standard TCEQ design criteria?
A. 200 gallons per day B. 300 gallons per day
C. 400 gallons per day D. 500 gallons per day
Answer: C
Rationale: TCEQ design guidelines for single-family residential OSSF systems use a standard daily design flow of 400
gallons per day (gpd) per dwelling unit. This figure is used for calculating drainfield sizing and treatment component
capacity.
7. Under TCEQ rules, how many feet of horizontal separation must be maintained between an OSSF
disposal field and a private water supply well?
A. 50 feet B. 75 feet
C. 100 feet D. 150 feet
Answer: C
Rationale: 30 TAC 285.8 requires a minimum horizontal separation of 100 feet between an OSSF disposal field and a
water supply well. This setback distance helps prevent contamination of drinking water sources from inadequately
treated effluent.
8. What is the purpose of the reserve area requirement in OSSF system design under TCEQ regulations?
A. To provide additional space for future home expansion
2
, TCEQ OSSF Exam 2026–2027 | 150 Questions & Correct Answers
B. To designate an area of equal size to the initial disposal field for replacement in case of system failure
C. To create a buffer zone between the OSSF and property lines
D. To allow for installation of a second treatment unit
Answer: B
Rationale: 30 TAC 285.6(d) requires a reserve area of equal size to the initial disposal field. This reserve ensures that if
the primary system fails, land is available to install a replacement disposal area without requiring variances or
additional permitting.
9. Which TCEQ regulation specifically governs the permitting, construction, and operation of on-site
sewage facilities in Texas?
A. 30 TAC Chapter 290 B. 30 TAC Chapter 285
C. 30 TAC Chapter 210 D. 30 TAC Chapter 330
Answer: B
Rationale: 30 TAC Chapter 285 (Subchapter A: General Provisions through Subchapter F: Alternative Systems) is the
specific regulatory framework governing OSSF permitting, design, construction, installation, operation, and
maintenance in Texas. All OSSF work must comply with these rules.
10. When is a licensed OSSF Installer required to notify TCEQ or the Designated Representative before
beginning construction of an OSSF system?
A. At least 72 hours before construction begins
B. At least 48 hours before construction begins
C. No notification is required if the installer is licensed
D. Only notification from the property owner is required
Answer: B
Rationale: 30 TAC 285.36(d) requires the licensed installer to notify TCEQ or the Designated Representative at least 48
hours prior to the start of OSSF construction activities. This notification allows for scheduling of required inspections.
11. What category of OSSF system requires a licensed professional engineer (PE) or registered sanitarian to
prepare the design plans?
A. Any single-family residential system regardless of size
B. Large systems exceeding 500 gpd or systems serving multiple connections
C. Only aerobic treatment systems
D. Only conventional septic tank systems
Answer: B
Rationale: 30 TAC 285.5 requires that systems serving more than one dwelling or facility, or systems with design flows
exceeding 500 gpd, must have plans prepared and sealed by a licensed professional engineer or registered sanitarian to
ensure adequate design for larger-scale treatment requirements.
12. Under TCEQ rules, what is the minimum separation distance between an OSSF system and a surface
water body such as a lake or stream?
A. 25 feet B. 50 feet
C. 75 feet D. 100 feet
Answer: B
Rationale: 30 TAC 285.8 requires a minimum horizontal separation of 50 feet from an OSSF disposal field to surface
water bodies including lakes, ponds, streams, and irrigation canals. This protects surface water quality from potential
effluent discharge.
3
, TCEQ OSSF Exam 2026–2027 | 150 Questions & Correct Answers
13. What is the minimum depth below grade to which the bottom of a septic tank must be set according to
TCEQ standards?
A. 6 inches B. 12 inches
C. 18 inches D. 24 inches
Answer: C
Rationale: TCEQ requires that septic tanks be installed with a minimum burial depth. The tank bottom must be at least
18 inches below final ground surface grade to prevent structural damage from traffic or frost action and to maintain
adequate flow by gravity from the building sewer.
14. Which of the following OSSF system types is specifically defined as an alternative system under 30 TAC
Chapter 285?
A. Conventional septic tank and gravity drainfield
B. Aerobic treatment unit with surface irrigation
C. Standard gravity flow subsurface absorption system
D. Cesspool or privy
Answer: B
Rationale: Alternative OSSF systems under 30 TAC 285 Subchapter F include aerobic treatment units (ATUs),
mounds, evapotranspiration beds, constructed wetlands, and other non-conventional treatment methods. These systems
require additional design criteria and maintenance oversight compared to conventional systems.
15. What is the TCEQ requirement regarding the watertightness testing of a newly installed septic tank?
A. Watertightness testing is not required for residential septic tanks
B. The tank must be tested for watertightness before being backfilled and covered
C. Watertightness testing is only required for commercial installations
D. Only the inlet and outlet connections must be tested
Answer: B
Rationale: 30 TAC 285.36(f) requires that all septic tanks be tested for watertightness before backfilling. This ensures
the tank will not leak raw sewage into the surrounding soil or allow groundwater infiltration, which could overwhelm
the treatment system.
16. What is the minimum size, in gallons, for a two-compartment septic tank serving a three-bedroom
single-family residence under TCEQ guidelines?
A. 750 gallons B. 1,000 gallons
C. 1,250 gallons D. 1,500 gallons
Answer: B
Rationale: TCEQ design criteria require a minimum 1,000-gallon two-compartment septic tank for a standard three-
bedroom residence. Tank sizing is based on the number of bedrooms, with each additional bedroom typically adding
250 gallons of tank capacity.
17. Under TCEQ rules, who is responsible for ensuring that an OSSF system is properly maintained after
installation?
A. The TCEQ regional office
B. The licensed installer who built the system
C. The property owner or designated responsible party
D. The local county health department
Answer: C
4
TEXAS COMMISSION ON ENVIRONMENTAL QUALITY
ON-SITE SEWAGE FACILITY (OSSF) EXAM
2026–2027
150 Questions and Correct Answers | Graded A+ | 100% Verified
Key Domains: OSSF Regulations, System Design and Installation, Soil Evaluation,
Maintenance Protocols, Environmental Safety, and Texas Administrative Code Compliance
INSTRUCTIONS
Each question is followed by four options (A–D). The correct answer is highlighted in
bold cyan along with a concise rationale explaining safety and operational reasoning,
code adherence, and why alternative options are less appropriate.
DOMAIN 1: OSSF Regulations and Licensing
Questions 1–25
1. Which Texas agency is the primary regulatory authority for On-Site Sewage Facilities (OSSF) in the
state?
A. Texas Department of State Health Services
B. Texas Commission on Environmental Quality (TCEQ)
C. Texas Parks and Wildlife Department
D. Texas Department of Agriculture
Answer: B
Rationale: TCEQ is the primary regulatory authority for OSSF systems under 30 TAC Chapter 285. The agency
establishes rules, oversees licensed installers, and enforces compliance for on-site sewage treatment systems across
Texas.
2. Under 30 TAC Chapter 285, what is the minimum acreage generally required for a standard OSSF
system utilizing a conventional subsurface absorption drainfield?
A. One-quarter acre B. One-half acre
C. Three-quarter acre D. One full acre
Answer: C
Rationale: Under 30 TAC 285.6, a minimum lot size of three-quarters of an acre is generally required for conventional
OSSF systems using a subsurface absorption area, ensuring adequate setback distances and suitable area for drainfield
placement and reserve area.
3. What type of TCEQ license is required to install, maintain, and repair standard OSSF systems in Texas?
A. Licensed Professional Engineer (PE) only
B. OSSF Installer or Apprentice license issued by TCEQ
1
, TCEQ OSSF Exam 2026–2027 | 150 Questions & Correct Answers
C. General Contractor license from the Texas Department of Licensing
D. No specific license is required for basic OSSF installation
Answer: B
Rationale: 30 TAC 285.31 requires that OSSF installation, maintenance, and repair work be performed by individuals
holding a valid OSSF Installer license or working under the direct supervision of a licensed installer as an apprentice.
PEs may design systems but installation requires an OSSF license.
4. At what minimum depth must an OSSF disposal field be installed below the ground surface to ensure
adequate soil treatment of effluent?
A. 6 inches below ground surface B. 12 inches below ground surface
C. 18 inches below ground surface D. 24 inches below ground surface
Answer: C
Rationale: 30 TAC 285.33(c)(4) requires a minimum of 18 inches of unsaturated soil beneath the disposal field trench
bottom to provide adequate treatment of effluent before it reaches any restrictive horizon, groundwater, or impervious
layer.
5. Which entity at the local level is authorized by TCEQ to administer the OSSF program and issue
construction permits within its jurisdiction?
A. County Tax Assessor-Collector office
B. Designated Representative (DR) such as a county or local health department
C. Local Water Control and Improvement District board
D. Municipal Utility District engineering department
Answer: B
Rationale: Under 30 TAC 285.9, TCEQ may designate local authorities as Designated Representatives (DRs) to
administer the OSSF program. DRs include county commissioners courts, local health departments, and other
authorized entities that can review plans and issue permits.
6. What is the maximum daily flow rate, in gallons per day, that a single-family residential OSSF system is
typically designed to treat under standard TCEQ design criteria?
A. 200 gallons per day B. 300 gallons per day
C. 400 gallons per day D. 500 gallons per day
Answer: C
Rationale: TCEQ design guidelines for single-family residential OSSF systems use a standard daily design flow of 400
gallons per day (gpd) per dwelling unit. This figure is used for calculating drainfield sizing and treatment component
capacity.
7. Under TCEQ rules, how many feet of horizontal separation must be maintained between an OSSF
disposal field and a private water supply well?
A. 50 feet B. 75 feet
C. 100 feet D. 150 feet
Answer: C
Rationale: 30 TAC 285.8 requires a minimum horizontal separation of 100 feet between an OSSF disposal field and a
water supply well. This setback distance helps prevent contamination of drinking water sources from inadequately
treated effluent.
8. What is the purpose of the reserve area requirement in OSSF system design under TCEQ regulations?
A. To provide additional space for future home expansion
2
, TCEQ OSSF Exam 2026–2027 | 150 Questions & Correct Answers
B. To designate an area of equal size to the initial disposal field for replacement in case of system failure
C. To create a buffer zone between the OSSF and property lines
D. To allow for installation of a second treatment unit
Answer: B
Rationale: 30 TAC 285.6(d) requires a reserve area of equal size to the initial disposal field. This reserve ensures that if
the primary system fails, land is available to install a replacement disposal area without requiring variances or
additional permitting.
9. Which TCEQ regulation specifically governs the permitting, construction, and operation of on-site
sewage facilities in Texas?
A. 30 TAC Chapter 290 B. 30 TAC Chapter 285
C. 30 TAC Chapter 210 D. 30 TAC Chapter 330
Answer: B
Rationale: 30 TAC Chapter 285 (Subchapter A: General Provisions through Subchapter F: Alternative Systems) is the
specific regulatory framework governing OSSF permitting, design, construction, installation, operation, and
maintenance in Texas. All OSSF work must comply with these rules.
10. When is a licensed OSSF Installer required to notify TCEQ or the Designated Representative before
beginning construction of an OSSF system?
A. At least 72 hours before construction begins
B. At least 48 hours before construction begins
C. No notification is required if the installer is licensed
D. Only notification from the property owner is required
Answer: B
Rationale: 30 TAC 285.36(d) requires the licensed installer to notify TCEQ or the Designated Representative at least 48
hours prior to the start of OSSF construction activities. This notification allows for scheduling of required inspections.
11. What category of OSSF system requires a licensed professional engineer (PE) or registered sanitarian to
prepare the design plans?
A. Any single-family residential system regardless of size
B. Large systems exceeding 500 gpd or systems serving multiple connections
C. Only aerobic treatment systems
D. Only conventional septic tank systems
Answer: B
Rationale: 30 TAC 285.5 requires that systems serving more than one dwelling or facility, or systems with design flows
exceeding 500 gpd, must have plans prepared and sealed by a licensed professional engineer or registered sanitarian to
ensure adequate design for larger-scale treatment requirements.
12. Under TCEQ rules, what is the minimum separation distance between an OSSF system and a surface
water body such as a lake or stream?
A. 25 feet B. 50 feet
C. 75 feet D. 100 feet
Answer: B
Rationale: 30 TAC 285.8 requires a minimum horizontal separation of 50 feet from an OSSF disposal field to surface
water bodies including lakes, ponds, streams, and irrigation canals. This protects surface water quality from potential
effluent discharge.
3
, TCEQ OSSF Exam 2026–2027 | 150 Questions & Correct Answers
13. What is the minimum depth below grade to which the bottom of a septic tank must be set according to
TCEQ standards?
A. 6 inches B. 12 inches
C. 18 inches D. 24 inches
Answer: C
Rationale: TCEQ requires that septic tanks be installed with a minimum burial depth. The tank bottom must be at least
18 inches below final ground surface grade to prevent structural damage from traffic or frost action and to maintain
adequate flow by gravity from the building sewer.
14. Which of the following OSSF system types is specifically defined as an alternative system under 30 TAC
Chapter 285?
A. Conventional septic tank and gravity drainfield
B. Aerobic treatment unit with surface irrigation
C. Standard gravity flow subsurface absorption system
D. Cesspool or privy
Answer: B
Rationale: Alternative OSSF systems under 30 TAC 285 Subchapter F include aerobic treatment units (ATUs),
mounds, evapotranspiration beds, constructed wetlands, and other non-conventional treatment methods. These systems
require additional design criteria and maintenance oversight compared to conventional systems.
15. What is the TCEQ requirement regarding the watertightness testing of a newly installed septic tank?
A. Watertightness testing is not required for residential septic tanks
B. The tank must be tested for watertightness before being backfilled and covered
C. Watertightness testing is only required for commercial installations
D. Only the inlet and outlet connections must be tested
Answer: B
Rationale: 30 TAC 285.36(f) requires that all septic tanks be tested for watertightness before backfilling. This ensures
the tank will not leak raw sewage into the surrounding soil or allow groundwater infiltration, which could overwhelm
the treatment system.
16. What is the minimum size, in gallons, for a two-compartment septic tank serving a three-bedroom
single-family residence under TCEQ guidelines?
A. 750 gallons B. 1,000 gallons
C. 1,250 gallons D. 1,500 gallons
Answer: B
Rationale: TCEQ design criteria require a minimum 1,000-gallon two-compartment septic tank for a standard three-
bedroom residence. Tank sizing is based on the number of bedrooms, with each additional bedroom typically adding
250 gallons of tank capacity.
17. Under TCEQ rules, who is responsible for ensuring that an OSSF system is properly maintained after
installation?
A. The TCEQ regional office
B. The licensed installer who built the system
C. The property owner or designated responsible party
D. The local county health department
Answer: C
4
