Ontario On-Site Sewage Systems Technical
Exam Questions and Verified Answers with
Rationales
Question 1
What is the minimum soil depth between the high groundwater table and the bottom
of an earth pit privy?
Correct Answer
900 mm
Question 2
How do you calculate the daily design sanitary sewage flow for a residential
occupancy?
Correct Answer
From Table 8.2.1.3.A.
Question 3
Which of the following systems has a leaching bed as a way to dispose waste?
Correct Answer
Class 4 system
Question 4
Who must sign the application for a building permit for an on-site sanitary sewage
system?
Correct Answer
the owner of the property
the agent for the owner
Page 1 of 227
,Question 5
What is the range of percolation time allowed for a shallow buried trench system?
Correct Answer
Between 1 min/cm and 125 min/cm
Question 6
Who investigates complaints about malfunctioning systems?
Correct Answer
the inspector
Page 2 of 227
,Question 7
The regulations stipulate that hydraulic conductivity of the covering material must not
be:
Correct Answer
less than 0.01 m/day
Question 1: What is the minimum required capacity for a septic tank serving a
single-family dwelling with up to three bedrooms under the Ontario Building Code
Part 8?
A. 2,000 litres
B. 2,700 litres
C. 3,600 litres
D. 4,500 litres
CORRECT ANSWER: C. 3,600 litres
Rationale: Under the Ontario Building Code, the minimum capacity for a septic tank
serving a residential house with up to three bedrooms is 3,600 litres, with an
additional 900 litres required for each bedroom beyond three.
Question 2: According to the Ontario Building Code, what is the minimum vertical
separation distance required between the bottom of an absorption trench and the
high water table or rock?
A. 0.3 metres
B. 0.6 metres
C. 0.9 metres
D. 1.2 metres
CORRECT ANSWER: D. 1.2 metres
Rationale: A minimum unsaturated soil depth of 1.2 metres is required beneath an
absorption trench to ensure proper biological treatment and filtration of effluent
before it reaches the groundwater table or bedrock.
Question 3: Which of the following describes the primary purpose of a percolation
test (perc test) when designing an on-site sewage system?
A. To measure the chemical concentration of wastewater constituents
B. To determine the rate at which soil absorbs clear water to gauge permeability
C. To measure the exact depth of the bedrock layer across the entire property
Page 3 of 227
, D. To calculate the daily design sewage flow based on occupancy rates
CORRECT ANSWER: B. To determine the rate at which soil absorbs clear water to
gauge permeability
Rationale: A percolation test measures the percolation rate ($T$-time) of water in
the soil, which directly governs the sizing and design of leaching beds and
absorption trenches.
Question 4: What is the minimum horizontal distance required under the Ontario
Building Code between a septic tank and a property line?
A. 1.2 metres
B. 3.0 metres
C. 5.0 metres
D. 15.0 metres
CORRECT ANSWER: A. 1.2 metres
Rationale: The Ontario Building Code specifies a minimum horizontal separation of
1.2 metres between a septic tank and a property line to allow for maintenance
access and prevent boundary conflicts.
Question 5: When calculating daily design sewage flow for a private residence, how
much daily flow must be allocated for each bedroom after the first three bedrooms?
A. 500 litres per day
B. 750 litres per day
C. 900 litres per day
D. 1,000 litres per day
CORRECT ANSWER: A. 500 litres per day
Rationale: For single-family dwellings, the design flow is calculated based on
occupancy, requiring specific allowances for bedrooms. Specifically, each bedroom
after the first three adds 500 litres per day to the base flow calculation.
Question 6: What is the minimum horizontal separation distance required between
a distribution pipe in a leaching bed and a drilled well with a watertight casing?
A. 5 metres
B. 10 metres
C. 15 metres
D. 30 metres
Page 4 of 227
Exam Questions and Verified Answers with
Rationales
Question 1
What is the minimum soil depth between the high groundwater table and the bottom
of an earth pit privy?
Correct Answer
900 mm
Question 2
How do you calculate the daily design sanitary sewage flow for a residential
occupancy?
Correct Answer
From Table 8.2.1.3.A.
Question 3
Which of the following systems has a leaching bed as a way to dispose waste?
Correct Answer
Class 4 system
Question 4
Who must sign the application for a building permit for an on-site sanitary sewage
system?
Correct Answer
the owner of the property
the agent for the owner
Page 1 of 227
,Question 5
What is the range of percolation time allowed for a shallow buried trench system?
Correct Answer
Between 1 min/cm and 125 min/cm
Question 6
Who investigates complaints about malfunctioning systems?
Correct Answer
the inspector
Page 2 of 227
,Question 7
The regulations stipulate that hydraulic conductivity of the covering material must not
be:
Correct Answer
less than 0.01 m/day
Question 1: What is the minimum required capacity for a septic tank serving a
single-family dwelling with up to three bedrooms under the Ontario Building Code
Part 8?
A. 2,000 litres
B. 2,700 litres
C. 3,600 litres
D. 4,500 litres
CORRECT ANSWER: C. 3,600 litres
Rationale: Under the Ontario Building Code, the minimum capacity for a septic tank
serving a residential house with up to three bedrooms is 3,600 litres, with an
additional 900 litres required for each bedroom beyond three.
Question 2: According to the Ontario Building Code, what is the minimum vertical
separation distance required between the bottom of an absorption trench and the
high water table or rock?
A. 0.3 metres
B. 0.6 metres
C. 0.9 metres
D. 1.2 metres
CORRECT ANSWER: D. 1.2 metres
Rationale: A minimum unsaturated soil depth of 1.2 metres is required beneath an
absorption trench to ensure proper biological treatment and filtration of effluent
before it reaches the groundwater table or bedrock.
Question 3: Which of the following describes the primary purpose of a percolation
test (perc test) when designing an on-site sewage system?
A. To measure the chemical concentration of wastewater constituents
B. To determine the rate at which soil absorbs clear water to gauge permeability
C. To measure the exact depth of the bedrock layer across the entire property
Page 3 of 227
, D. To calculate the daily design sewage flow based on occupancy rates
CORRECT ANSWER: B. To determine the rate at which soil absorbs clear water to
gauge permeability
Rationale: A percolation test measures the percolation rate ($T$-time) of water in
the soil, which directly governs the sizing and design of leaching beds and
absorption trenches.
Question 4: What is the minimum horizontal distance required under the Ontario
Building Code between a septic tank and a property line?
A. 1.2 metres
B. 3.0 metres
C. 5.0 metres
D. 15.0 metres
CORRECT ANSWER: A. 1.2 metres
Rationale: The Ontario Building Code specifies a minimum horizontal separation of
1.2 metres between a septic tank and a property line to allow for maintenance
access and prevent boundary conflicts.
Question 5: When calculating daily design sewage flow for a private residence, how
much daily flow must be allocated for each bedroom after the first three bedrooms?
A. 500 litres per day
B. 750 litres per day
C. 900 litres per day
D. 1,000 litres per day
CORRECT ANSWER: A. 500 litres per day
Rationale: For single-family dwellings, the design flow is calculated based on
occupancy, requiring specific allowances for bedrooms. Specifically, each bedroom
after the first three adds 500 litres per day to the base flow calculation.
Question 6: What is the minimum horizontal separation distance required between
a distribution pipe in a leaching bed and a drilled well with a watertight casing?
A. 5 metres
B. 10 metres
C. 15 metres
D. 30 metres
Page 4 of 227
