OSSF Installer 1 License Exam Questions with 100% Correct Answers, Rationales (Texas
On-Site Sewage Facility Certification Prep)
Question 1: Under Texas Administrative Code Chapter 285, what is the minimum setback distance required between an OSSF
drainfield and a property line?
A. 5 feet
B. 10 feet
C. 15 feet
D. 25 feet
CORRECT ANSWER: B. 10 feet
Rationale: 30 TAC §285.32(4) requires a minimum 10-foot setback from any property line for OSSF components (septic tank,
drainfield, aerobic unit). This prevents encroachment issues and ensures adequate space for maintenance and repairs.
Question 2: Which soil texture class is most suitable for a conventional gravity-fed septic system drainfield?
A. Clay
B. Sandy clay loam
C. Pure sand
D. Peat
CORRECT ANSWER: B. Sandy clay loam
,Rationale: Sandy clay loam provides optimal percolation rates (0.6-2.0 inches/hour) for conventional systems. Pure clay has too-slow
percolation (<0.6 in/hr); pure sand may allow too-rapid flow (<0.1 in/hr) risking groundwater contamination; peat is unsuitable due
to high organic content and instability.
Question 3: What is the minimum required depth for a septic tank outlet tee below the liquid level?
A. 6 inches
B. 12 inches
C. 18 inches
D. 24 inches
CORRECT ANSWER: B. 12 inches
Rationale: 30 TAC §285.32(2)(A) requires outlet tees to extend at least 12 inches below the liquid level to prevent scum and floating
solids from exiting the tank and clogging the drainfield. This ensures only clarified effluent enters the absorption area.
Question 4: Under Texas rules, who is authorized to perform a soil evaluation for an OSSF permit application?
A. Any licensed contractor
B. A TCEQ-authorized site evaluator or professional engineer
C. The property owner
D. A certified plumber
CORRECT ANSWER: B. A TCEQ-authorized site evaluator or professional engineer
,Rationale: 30 TAC §285.30(3) requires soil evaluations to be conducted by a TCEQ-authorized site evaluator (ASE) or a licensed
professional engineer. This ensures accurate soil classification, percolation testing, and system design based on site-specific
conditions.
Question 5: What is the minimum required horizontal separation between a septic tank and a water well?
A. 25 feet
B. 50 feet
C. 100 feet
D. 150 feet
CORRECT ANSWER: C. 100 feet
Rationale: 30 TAC §285.32(1) mandates a minimum 100-foot horizontal separation between any OSSF component and a potable
water well. This critical setback prevents contamination of drinking water sources by pathogens or nutrients.
Question 6: Which component prevents solids from entering the drainfield in a conventional septic system?
A. Distribution box
B. Effluent filter
C. Grease trap
D. Pump chamber
CORRECT ANSWER: B. Effluent filter
, Rationale: An effluent filter installed on the septic tank outlet tee captures suspended solids and prevents them from clogging
drainfield pipes or soil pores. 30 TAC §285.32(2)(B) requires filters on new installations and recommends retrofitting existing systems.
Question 7: What is the maximum allowable slope for a conventional trench drainfield in Texas?
A. 10%
B. 15%
C. 20%
D. 25%
CORRECT ANSWER: C. 20%
Rationale: 30 TAC §285.32(5)(C) limits drainfield trench slopes to a maximum of 20% (approximately 11.3 degrees) to ensure even
effluent distribution and prevent channeling or surfacing. Steeper slopes require alternative designs like pressure distribution or
terraced trenches.
Question 8: Which test measures the rate at which water moves through soil for OSSF design?
A. Soil texture analysis
B. Percolation (perc) test
C. Moisture content test
D. Compaction test
CORRECT ANSWER: B. Percolation (perc) test
On-Site Sewage Facility Certification Prep)
Question 1: Under Texas Administrative Code Chapter 285, what is the minimum setback distance required between an OSSF
drainfield and a property line?
A. 5 feet
B. 10 feet
C. 15 feet
D. 25 feet
CORRECT ANSWER: B. 10 feet
Rationale: 30 TAC §285.32(4) requires a minimum 10-foot setback from any property line for OSSF components (septic tank,
drainfield, aerobic unit). This prevents encroachment issues and ensures adequate space for maintenance and repairs.
Question 2: Which soil texture class is most suitable for a conventional gravity-fed septic system drainfield?
A. Clay
B. Sandy clay loam
C. Pure sand
D. Peat
CORRECT ANSWER: B. Sandy clay loam
,Rationale: Sandy clay loam provides optimal percolation rates (0.6-2.0 inches/hour) for conventional systems. Pure clay has too-slow
percolation (<0.6 in/hr); pure sand may allow too-rapid flow (<0.1 in/hr) risking groundwater contamination; peat is unsuitable due
to high organic content and instability.
Question 3: What is the minimum required depth for a septic tank outlet tee below the liquid level?
A. 6 inches
B. 12 inches
C. 18 inches
D. 24 inches
CORRECT ANSWER: B. 12 inches
Rationale: 30 TAC §285.32(2)(A) requires outlet tees to extend at least 12 inches below the liquid level to prevent scum and floating
solids from exiting the tank and clogging the drainfield. This ensures only clarified effluent enters the absorption area.
Question 4: Under Texas rules, who is authorized to perform a soil evaluation for an OSSF permit application?
A. Any licensed contractor
B. A TCEQ-authorized site evaluator or professional engineer
C. The property owner
D. A certified plumber
CORRECT ANSWER: B. A TCEQ-authorized site evaluator or professional engineer
,Rationale: 30 TAC §285.30(3) requires soil evaluations to be conducted by a TCEQ-authorized site evaluator (ASE) or a licensed
professional engineer. This ensures accurate soil classification, percolation testing, and system design based on site-specific
conditions.
Question 5: What is the minimum required horizontal separation between a septic tank and a water well?
A. 25 feet
B. 50 feet
C. 100 feet
D. 150 feet
CORRECT ANSWER: C. 100 feet
Rationale: 30 TAC §285.32(1) mandates a minimum 100-foot horizontal separation between any OSSF component and a potable
water well. This critical setback prevents contamination of drinking water sources by pathogens or nutrients.
Question 6: Which component prevents solids from entering the drainfield in a conventional septic system?
A. Distribution box
B. Effluent filter
C. Grease trap
D. Pump chamber
CORRECT ANSWER: B. Effluent filter
, Rationale: An effluent filter installed on the septic tank outlet tee captures suspended solids and prevents them from clogging
drainfield pipes or soil pores. 30 TAC §285.32(2)(B) requires filters on new installations and recommends retrofitting existing systems.
Question 7: What is the maximum allowable slope for a conventional trench drainfield in Texas?
A. 10%
B. 15%
C. 20%
D. 25%
CORRECT ANSWER: C. 20%
Rationale: 30 TAC §285.32(5)(C) limits drainfield trench slopes to a maximum of 20% (approximately 11.3 degrees) to ensure even
effluent distribution and prevent channeling or surfacing. Steeper slopes require alternative designs like pressure distribution or
terraced trenches.
Question 8: Which test measures the rate at which water moves through soil for OSSF design?
A. Soil texture analysis
B. Percolation (perc) test
C. Moisture content test
D. Compaction test
CORRECT ANSWER: B. Percolation (perc) test
