OSSF Installer I Certification Exam Study Guide |
Comprehensive Practice Exam Question Bank with Verified
Answers, Detailed Rationales | (New Texas On-Site Sewage
Facility Certification Prep) |Latest Update 2026/2027
Question 1
Total suspended solids that settle out when left standing are called:
A. Dissolved solids
B. Suspended solids
C. Settleable solids
D. Floatable solids
Answer: C
Rationale: Settleable solids are the portion of suspended solids that will settle out of wastewater
when left standing, typically measured in a cone-shaped Imhoff cone.
Question 2
Detention time tanks are sized to provide approximately:
A. Two to three hours
B. Two to three weeks
C. Two to three months
D. Two to three days
Answer: D
Rationale: Septic tanks are designed to provide approximately 2 to 3 days of detention time to
allow for proper settling and digestion of solids.
Question 3
Hookworms, ringworms, and tapeworms are three examples of what?
A. Bacteria
B. Viruses
C. Parasites/Helminthes
D. Protozoa
Answer: C
Rationale: Hookworms, ringworms, and tapeworms are parasitic worms (helminths) that can be
transmitted through wastewater and contaminated soil.
pg. 1
,Question 4
What is the measurement "30 inches" inside a septic tank referring to?
A. The total height of the tank
B. The liquid depth of the tank
C. The width of the tank
D. The depth of the scum layer
Answer: B
Rationale: The liquid depth of a septic tank shall be at least 30 inches to provide adequate
detention time and settling capacity.
Question 5
The house and the septic tank must have what provided between them?
A. A pump
B. A two-way cleanout
C. A grease trap
D. A dosing tank
Answer: B
Rationale: A two-way cleanout must be provided between the house and the septic tank to allow
for access and cleaning of the house sewer line.
Question 6
What is the distance all three types of wells must be from an OSSF component?
A. 30 feet
B. 50 feet
C. 75 feet
D. 100 feet
Answer: B
Rationale: A 50-foot setback is required between all types of wells (public, private, pressure
cemented) and OSSF components to prevent groundwater contamination.
Question 7
What is the distance a pressure cemented well must be from an OSSF component?
A. 30 feet
B. 50 feet
C. 75 feet
D. 100 feet
pg. 2
,Answer: B
Rationale: Pressure cemented wells require a 50-foot setback from OSSF components.
Question 8
The ability to absorb water is the most critical characteristic of what?
A. The septic tank
B. The drainfield
C. The soil
D. The piping
Answer: C
Rationale: Soil's ability to absorb water (permeability) is the most critical characteristic for
determining suitability for an OSSF drainfield.
Question 9
The septic tank must be set back how many feet from a pressure cemented well?
A. 30 feet
B. 50 feet
C. 75 feet
D. 100 feet
Answer: B
Rationale: A 50-foot setback is required between a septic tank and a pressure cemented well.
Question 10
The septic tank and drainfield must be set back how many feet from a private water line?
A. 5 feet
B. 10 feet
C. 15 feet
D. 20 feet
Answer: B
Rationale: A 10-foot setback is required between private water lines and both the septic tank and
drainfield.
Question 11
The slope of the house sewer pipe shall be no less than how many inches fall per foot of pipe?
A. 1/16 inch
B. 1/8 inch
pg. 3
, C. 1/4 inch
D. 1/2 inch
Answer: B
Rationale: The slope of the house sewer pipe must be no less than 1/8 inch per foot to ensure
proper drainage and prevent solids from settling.
Question 12
What percentage of the total volume must be taken up by the first tank in a three-tank system?
A. One-quarter
B. One-third
C. One-half
D. Two-thirds
Answer: C
Rationale: In a three-tank system, the first tank must contain approximately one-half of the total
volume to allow for primary settling.
Question 13
Precipitation, percolation, and runoff are three ways in which what happens?
A. The water supply is replenished
B. Wastewater is treated
C. Soil is formed
D. Bacteria are destroyed
Answer: A
Rationale: Precipitation (rain), percolation (water moving through soil), and runoff are the three
primary ways the water supply is replenished.
Question 14
The reserve capacity volume of a pumping chamber must be equal to how many day's flow?
A. One-quarter day
B. One-third day
C. One-half day
D. One day
Answer: B
Rationale: The reserve capacity of a pumping chamber must be at least one-third of the daily
wastewater flow to provide adequate storage during pump failure.
pg. 4
Comprehensive Practice Exam Question Bank with Verified
Answers, Detailed Rationales | (New Texas On-Site Sewage
Facility Certification Prep) |Latest Update 2026/2027
Question 1
Total suspended solids that settle out when left standing are called:
A. Dissolved solids
B. Suspended solids
C. Settleable solids
D. Floatable solids
Answer: C
Rationale: Settleable solids are the portion of suspended solids that will settle out of wastewater
when left standing, typically measured in a cone-shaped Imhoff cone.
Question 2
Detention time tanks are sized to provide approximately:
A. Two to three hours
B. Two to three weeks
C. Two to three months
D. Two to three days
Answer: D
Rationale: Septic tanks are designed to provide approximately 2 to 3 days of detention time to
allow for proper settling and digestion of solids.
Question 3
Hookworms, ringworms, and tapeworms are three examples of what?
A. Bacteria
B. Viruses
C. Parasites/Helminthes
D. Protozoa
Answer: C
Rationale: Hookworms, ringworms, and tapeworms are parasitic worms (helminths) that can be
transmitted through wastewater and contaminated soil.
pg. 1
,Question 4
What is the measurement "30 inches" inside a septic tank referring to?
A. The total height of the tank
B. The liquid depth of the tank
C. The width of the tank
D. The depth of the scum layer
Answer: B
Rationale: The liquid depth of a septic tank shall be at least 30 inches to provide adequate
detention time and settling capacity.
Question 5
The house and the septic tank must have what provided between them?
A. A pump
B. A two-way cleanout
C. A grease trap
D. A dosing tank
Answer: B
Rationale: A two-way cleanout must be provided between the house and the septic tank to allow
for access and cleaning of the house sewer line.
Question 6
What is the distance all three types of wells must be from an OSSF component?
A. 30 feet
B. 50 feet
C. 75 feet
D. 100 feet
Answer: B
Rationale: A 50-foot setback is required between all types of wells (public, private, pressure
cemented) and OSSF components to prevent groundwater contamination.
Question 7
What is the distance a pressure cemented well must be from an OSSF component?
A. 30 feet
B. 50 feet
C. 75 feet
D. 100 feet
pg. 2
,Answer: B
Rationale: Pressure cemented wells require a 50-foot setback from OSSF components.
Question 8
The ability to absorb water is the most critical characteristic of what?
A. The septic tank
B. The drainfield
C. The soil
D. The piping
Answer: C
Rationale: Soil's ability to absorb water (permeability) is the most critical characteristic for
determining suitability for an OSSF drainfield.
Question 9
The septic tank must be set back how many feet from a pressure cemented well?
A. 30 feet
B. 50 feet
C. 75 feet
D. 100 feet
Answer: B
Rationale: A 50-foot setback is required between a septic tank and a pressure cemented well.
Question 10
The septic tank and drainfield must be set back how many feet from a private water line?
A. 5 feet
B. 10 feet
C. 15 feet
D. 20 feet
Answer: B
Rationale: A 10-foot setback is required between private water lines and both the septic tank and
drainfield.
Question 11
The slope of the house sewer pipe shall be no less than how many inches fall per foot of pipe?
A. 1/16 inch
B. 1/8 inch
pg. 3
, C. 1/4 inch
D. 1/2 inch
Answer: B
Rationale: The slope of the house sewer pipe must be no less than 1/8 inch per foot to ensure
proper drainage and prevent solids from settling.
Question 12
What percentage of the total volume must be taken up by the first tank in a three-tank system?
A. One-quarter
B. One-third
C. One-half
D. Two-thirds
Answer: C
Rationale: In a three-tank system, the first tank must contain approximately one-half of the total
volume to allow for primary settling.
Question 13
Precipitation, percolation, and runoff are three ways in which what happens?
A. The water supply is replenished
B. Wastewater is treated
C. Soil is formed
D. Bacteria are destroyed
Answer: A
Rationale: Precipitation (rain), percolation (water moving through soil), and runoff are the three
primary ways the water supply is replenished.
Question 14
The reserve capacity volume of a pumping chamber must be equal to how many day's flow?
A. One-quarter day
B. One-third day
C. One-half day
D. One day
Answer: B
Rationale: The reserve capacity of a pumping chamber must be at least one-third of the daily
wastewater flow to provide adequate storage during pump failure.
pg. 4
