Ontario On-Site Sewage Systems Technical Exam
Practice Questions & Verified Answers
This specialized engineering preparation resource provides 300 targeted practice
questions and verified answers designed specifically for the Ontario On-Site Sewage
Systems technical qualification exam. It delivers comprehensive coverage of the Ontario
Building Code (OBC) Part 8, including soil percolation testing, design flows, septic tank
sizing, leaching bed layouts, and treatment unit technologies. Licensed designers,
installers, and building officials will master critical hydraulic calculations, soil
classification methods, and environmental compliance parameters to pass their
proctored Ministry certification.
1. What is the minimum required distance from a septic tank to a drilled well with
a watertight casing to a depth of at least 6 metres?
A) 5 m
B) 10 m
C) 15 m
D) 30 m
Rationale: OBC Table 8.2.1.6.A requires a minimum horizontal distance of 15 m from a
treatment unit to a well with watertight casing to a depth of at least 6 m.
2. For a non-residential occupancy, the septic tank working capacity must be at
least how many times the daily design sanitary sewage flow?
A) 1.5 times
B) 2 times
C) 3 times
D) 4 times
Rationale: For non-residential occupancies, the septic tank capacity is determined by
tripling the daily design sewage flow (3 × Q).
,3. What is the minimum liquid depth required for a septic tank under the Ontario
Building Code?
A) 500 mm
B) 1,000 mm
C) 1,200 mm
D) 1,500 mm
Rationale: The OBC requires a minimum liquid depth of 1,000 mm in a septic tank to
ensure proper settling and digestion.
4. Which of the following best describes the purpose of a distribution box in a
leaching bed system?
A) To store effluent until it is pumped
B) To evenly distribute effluent to the distribution pipes
C) To filter solids from the effluent
D) To provide aeration to the effluent
Rationale: A distribution box receives effluent from the septic tank and distributes it
equally to each distribution pipe in the leaching bed.
5. What is the minimum required thickness of sand fill below the distribution pipes
in a Type A dispersal bed?
A) 150 mm
B) 300 mm
C) 450 mm
D) 600 mm
Rationale: A Type A dispersal bed requires a minimum of 450 mm of sand fill below the
distribution pipes to provide adequate treatment.
6. What is the maximum allowable slope for a leaching bed area according to the
OBC?
,A) 1 unit vertical to 2 units horizontal
B) 1 unit vertical to 3 units horizontal
C) 1 unit vertical to 4 units horizontal
D) 1 unit vertical to 5 units horizontal
Rationale: The OBC prohibits a leaching bed in an area with an average slope exceeding 1
unit vertical to 4 units horizontal.
7. What is the minimum required clearance from a holding tank to a property line?
A) 1 m
B) 2 m
C) 3 m
D) 5 m
Rationale: The OBC requires a minimum clearance of 3 m from a holding tank (Class 5) to
a property line.
8. Which class of sewage system is defined as a greywater system under the
Ontario Building Code?
A) Class 1
B) Class 2
C) Class 3
D) Class 4
Rationale: A Class 2 sewage system is defined as a greywater system designed to treat and
dispose of greywater only.
9. What is the maximum daily design flow for a Class 2 greywater system?
A) 500 L/day
B) 1,000 L/day
C) 2,000 L/day
D) 5,000 L/day
, Rationale: The OBC permits a maximum daily design flow of 1,000 L/day for Class 2
greywater systems.
10. When conducting a percolation test, how long must clay soils be allowed to
swell before testing?
A) 1 hour
B) 4 hours
C) 12 hours
D) 24 hours
Rationale: At least 12 hours must be allowed for swelling in clay soils to achieve a
stabilized percolation rate.
11. What is the minimum number of percolation test holes required for a site
evaluation?
A) 1
B) 2
C) *3*
D) 5
Rationale: A minimum of three percolation test holes must be dug, suitably spaced, to
accurately evaluate the leaching bed area.
12. Which of the following is a Class 1 sewage system?
A) Composting toilet
B) Septic tank and leaching bed
C) Cesspool
D) Holding tank
Rationale: Class 1 systems are waterless closets including composting toilets, chemical
toilets, incinerating toilets, and privies.
Practice Questions & Verified Answers
This specialized engineering preparation resource provides 300 targeted practice
questions and verified answers designed specifically for the Ontario On-Site Sewage
Systems technical qualification exam. It delivers comprehensive coverage of the Ontario
Building Code (OBC) Part 8, including soil percolation testing, design flows, septic tank
sizing, leaching bed layouts, and treatment unit technologies. Licensed designers,
installers, and building officials will master critical hydraulic calculations, soil
classification methods, and environmental compliance parameters to pass their
proctored Ministry certification.
1. What is the minimum required distance from a septic tank to a drilled well with
a watertight casing to a depth of at least 6 metres?
A) 5 m
B) 10 m
C) 15 m
D) 30 m
Rationale: OBC Table 8.2.1.6.A requires a minimum horizontal distance of 15 m from a
treatment unit to a well with watertight casing to a depth of at least 6 m.
2. For a non-residential occupancy, the septic tank working capacity must be at
least how many times the daily design sanitary sewage flow?
A) 1.5 times
B) 2 times
C) 3 times
D) 4 times
Rationale: For non-residential occupancies, the septic tank capacity is determined by
tripling the daily design sewage flow (3 × Q).
,3. What is the minimum liquid depth required for a septic tank under the Ontario
Building Code?
A) 500 mm
B) 1,000 mm
C) 1,200 mm
D) 1,500 mm
Rationale: The OBC requires a minimum liquid depth of 1,000 mm in a septic tank to
ensure proper settling and digestion.
4. Which of the following best describes the purpose of a distribution box in a
leaching bed system?
A) To store effluent until it is pumped
B) To evenly distribute effluent to the distribution pipes
C) To filter solids from the effluent
D) To provide aeration to the effluent
Rationale: A distribution box receives effluent from the septic tank and distributes it
equally to each distribution pipe in the leaching bed.
5. What is the minimum required thickness of sand fill below the distribution pipes
in a Type A dispersal bed?
A) 150 mm
B) 300 mm
C) 450 mm
D) 600 mm
Rationale: A Type A dispersal bed requires a minimum of 450 mm of sand fill below the
distribution pipes to provide adequate treatment.
6. What is the maximum allowable slope for a leaching bed area according to the
OBC?
,A) 1 unit vertical to 2 units horizontal
B) 1 unit vertical to 3 units horizontal
C) 1 unit vertical to 4 units horizontal
D) 1 unit vertical to 5 units horizontal
Rationale: The OBC prohibits a leaching bed in an area with an average slope exceeding 1
unit vertical to 4 units horizontal.
7. What is the minimum required clearance from a holding tank to a property line?
A) 1 m
B) 2 m
C) 3 m
D) 5 m
Rationale: The OBC requires a minimum clearance of 3 m from a holding tank (Class 5) to
a property line.
8. Which class of sewage system is defined as a greywater system under the
Ontario Building Code?
A) Class 1
B) Class 2
C) Class 3
D) Class 4
Rationale: A Class 2 sewage system is defined as a greywater system designed to treat and
dispose of greywater only.
9. What is the maximum daily design flow for a Class 2 greywater system?
A) 500 L/day
B) 1,000 L/day
C) 2,000 L/day
D) 5,000 L/day
, Rationale: The OBC permits a maximum daily design flow of 1,000 L/day for Class 2
greywater systems.
10. When conducting a percolation test, how long must clay soils be allowed to
swell before testing?
A) 1 hour
B) 4 hours
C) 12 hours
D) 24 hours
Rationale: At least 12 hours must be allowed for swelling in clay soils to achieve a
stabilized percolation rate.
11. What is the minimum number of percolation test holes required for a site
evaluation?
A) 1
B) 2
C) *3*
D) 5
Rationale: A minimum of three percolation test holes must be dug, suitably spaced, to
accurately evaluate the leaching bed area.
12. Which of the following is a Class 1 sewage system?
A) Composting toilet
B) Septic tank and leaching bed
C) Cesspool
D) Holding tank
Rationale: Class 1 systems are waterless closets including composting toilets, chemical
toilets, incinerating toilets, and privies.
