Ontario On-Site Sewage Systems Technical Exam: 300
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.
SECTION 1: GENERAL REQUIREMENTS, CLASSIFICATION &
DEFINITIONS (Questions 1–50)
1. Which Ontario Building Code classification applies to a conventional sewage
system using a septic tank and subsurface leaching bed?
A) Class 1
B) Class 2
C) Class 4
D) Class 5
Rationale: A Class 4 sewage system is a leaching-bed system, including conventional
systems that treat sewage and discharge effluent into a subsurface disposal area.
2. Which sewage system classification specifically describes a system using a
holding tank to retain hauled sewage before collection?
A) Class 1
B) Class 2
C) Class 4
D) Class 5
Rationale: Class 5 systems use a holding tank for retention of hauled sewage at the site
where the sewage is produced before collection.
,3. Which type of sewage system classification includes a greywater system under
the Ontario Building Code?
A) Class 1
B) Class 2
C) Class 3
D) Class 4
Rationale: The 2024 OBC identifies a greywater system as a Class 2 sewage system within
the Part 8 classification framework.
4. A cesspool is being evaluated for classification under Part 8. Which sewage
system class correctly applies to this installation?
A) Class 1
B) Class 2
C) Class 3
D) Class 5
Rationale: Part 8 specifically identifies a cesspool as a Class 3 sewage system,
distinguishing it from leaching-bed and holding-tank systems.
5. Which statement best describes the general scope of Part 8 concerning private
on-site sewage systems in Ontario?
A) It addresses only septic tank manufacturing requirements
B) It addresses only sewage disposal after construction
C) It addresses design, construction, operation, and maintenance
D) It applies exclusively to municipal sewage treatment plants
Rationale: Part 8 establishes requirements covering the complete lifecycle of sewage
systems, including design, construction, operation, and maintenance.
6. Why is site evaluation an essential component before designing an on-site
sewage system?
A) It determines the property's assessed value
B) It identifies soil, groundwater, terrain, and site limitations
C) It determines the building's electrical service size
D) It establishes municipal property taxation
Rationale: Site evaluation identifies critical factors such as soil characteristics, groundwater
conditions, terrain, and other limitations that affect system design and placement.
7. Under the Ontario Building Code, what is the maximum daily design flow for
sewage systems covered under Part 8?
A) 5,000 litres per day
B) 10,000 litres per day
C) 15,000 litres per day
,D) 20,000 litres per day
Rationale: Part 8 of the OBC applies to on-site sewage systems with a design capacity of
10,000 litres per day or less.
8. Which Class of sewage system consists of a septic tank followed by a leaching
bed?
A) Class 1
B) Class 2
C) Class 3
D) Class 4
Rationale: A Class 4 sewage system is the most common type, consisting of a treatment
unit (septic tank) connected to a leaching bed constructed in accordance with OBC
requirements.
9. A Class 2 sewage system is designed to receive only:
A) Blackwater only
B) Greywater only
C) Both blackwater and greywater
D) Industrial waste only
Rationale: A Class 2 sewage system is defined as a greywater system, designed exclusively
for the treatment and disposal of greywater where the daily design flow is less than 1,000
L/day.
10. Which of the following is classified as a Class 1 sewage system under the
Ontario Building Code?
A) A chemical toilet or composting toilet
B) A greywater leaching pit
C) A septic tank with an absorption trench
D) A holding tank requiring regular pump-outs
Rationale: Class 1 systems are waterless closets including composting toilets, chemical
toilets, incinerating toilets, and privies. They do not discharge liquid effluent into the
ground.
11. Under OBC Part 8, what type of sewage system is classified as a Class 3 system?
A) Cesspool
B) Holding tank
C) Greywater system
D) Outhouse/Privy
Rationale: Article 8.1.2.1. of the Ontario Building Code classifies a cesspool as a Class 3
sewage system.
, 12. What is the classification of a sewage system consisting of a septic tank and a
leaching bed?
A) Class 2
B) Class 3
C) Class 4
D) Class 5
Rationale: Under Article 8.1.2.1., a Class 4 sewage system consists of a treatment unit
(such as a septic tank) and a leaching bed.
13. Which of the following best describes the purpose of an on-site wastewater
treatment system?
A) To treat and dispose of wastewater at the site where it is generated
B) To transport wastewater to a municipal treatment plant
C) To store wastewater indefinitely
D) To treat industrial waste only
Rationale: An on-site wastewater treatment system treats and disposes of wastewater at
the site where it is generated, typically for properties not connected to municipal sewers.
14. What is the maximum daily design flow for a Class 2 sewage system under the
OBC?
A) 500 L/day
B) 1,000 L/day
C) 2,000 L/day
D) 5,000 L/day
Rationale: The Ontario Building Code allows a maximum daily design flow of 1,000 L/day
for Class 2 systems.
15. Which document provides the minimum clearances for treatment units in
Ontario?
A) Table 8.2.1.5
B) Table 8.2.1.6.A
C) Table 8.2.1.3.A
D) Table 8.7.2.1
Rationale: Table 8.2.1.6.A provides the minimum clearances for treatment units (septic
tanks) under the Ontario Building Code.
16. Under Part 8, what is the minimum clearance from a septic tank to a well with
watertight casing to a depth of at least 6 m?
A) 5 m
B) 10 m
C) 15 m
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.
SECTION 1: GENERAL REQUIREMENTS, CLASSIFICATION &
DEFINITIONS (Questions 1–50)
1. Which Ontario Building Code classification applies to a conventional sewage
system using a septic tank and subsurface leaching bed?
A) Class 1
B) Class 2
C) Class 4
D) Class 5
Rationale: A Class 4 sewage system is a leaching-bed system, including conventional
systems that treat sewage and discharge effluent into a subsurface disposal area.
2. Which sewage system classification specifically describes a system using a
holding tank to retain hauled sewage before collection?
A) Class 1
B) Class 2
C) Class 4
D) Class 5
Rationale: Class 5 systems use a holding tank for retention of hauled sewage at the site
where the sewage is produced before collection.
,3. Which type of sewage system classification includes a greywater system under
the Ontario Building Code?
A) Class 1
B) Class 2
C) Class 3
D) Class 4
Rationale: The 2024 OBC identifies a greywater system as a Class 2 sewage system within
the Part 8 classification framework.
4. A cesspool is being evaluated for classification under Part 8. Which sewage
system class correctly applies to this installation?
A) Class 1
B) Class 2
C) Class 3
D) Class 5
Rationale: Part 8 specifically identifies a cesspool as a Class 3 sewage system,
distinguishing it from leaching-bed and holding-tank systems.
5. Which statement best describes the general scope of Part 8 concerning private
on-site sewage systems in Ontario?
A) It addresses only septic tank manufacturing requirements
B) It addresses only sewage disposal after construction
C) It addresses design, construction, operation, and maintenance
D) It applies exclusively to municipal sewage treatment plants
Rationale: Part 8 establishes requirements covering the complete lifecycle of sewage
systems, including design, construction, operation, and maintenance.
6. Why is site evaluation an essential component before designing an on-site
sewage system?
A) It determines the property's assessed value
B) It identifies soil, groundwater, terrain, and site limitations
C) It determines the building's electrical service size
D) It establishes municipal property taxation
Rationale: Site evaluation identifies critical factors such as soil characteristics, groundwater
conditions, terrain, and other limitations that affect system design and placement.
7. Under the Ontario Building Code, what is the maximum daily design flow for
sewage systems covered under Part 8?
A) 5,000 litres per day
B) 10,000 litres per day
C) 15,000 litres per day
,D) 20,000 litres per day
Rationale: Part 8 of the OBC applies to on-site sewage systems with a design capacity of
10,000 litres per day or less.
8. Which Class of sewage system consists of a septic tank followed by a leaching
bed?
A) Class 1
B) Class 2
C) Class 3
D) Class 4
Rationale: A Class 4 sewage system is the most common type, consisting of a treatment
unit (septic tank) connected to a leaching bed constructed in accordance with OBC
requirements.
9. A Class 2 sewage system is designed to receive only:
A) Blackwater only
B) Greywater only
C) Both blackwater and greywater
D) Industrial waste only
Rationale: A Class 2 sewage system is defined as a greywater system, designed exclusively
for the treatment and disposal of greywater where the daily design flow is less than 1,000
L/day.
10. Which of the following is classified as a Class 1 sewage system under the
Ontario Building Code?
A) A chemical toilet or composting toilet
B) A greywater leaching pit
C) A septic tank with an absorption trench
D) A holding tank requiring regular pump-outs
Rationale: Class 1 systems are waterless closets including composting toilets, chemical
toilets, incinerating toilets, and privies. They do not discharge liquid effluent into the
ground.
11. Under OBC Part 8, what type of sewage system is classified as a Class 3 system?
A) Cesspool
B) Holding tank
C) Greywater system
D) Outhouse/Privy
Rationale: Article 8.1.2.1. of the Ontario Building Code classifies a cesspool as a Class 3
sewage system.
, 12. What is the classification of a sewage system consisting of a septic tank and a
leaching bed?
A) Class 2
B) Class 3
C) Class 4
D) Class 5
Rationale: Under Article 8.1.2.1., a Class 4 sewage system consists of a treatment unit
(such as a septic tank) and a leaching bed.
13. Which of the following best describes the purpose of an on-site wastewater
treatment system?
A) To treat and dispose of wastewater at the site where it is generated
B) To transport wastewater to a municipal treatment plant
C) To store wastewater indefinitely
D) To treat industrial waste only
Rationale: An on-site wastewater treatment system treats and disposes of wastewater at
the site where it is generated, typically for properties not connected to municipal sewers.
14. What is the maximum daily design flow for a Class 2 sewage system under the
OBC?
A) 500 L/day
B) 1,000 L/day
C) 2,000 L/day
D) 5,000 L/day
Rationale: The Ontario Building Code allows a maximum daily design flow of 1,000 L/day
for Class 2 systems.
15. Which document provides the minimum clearances for treatment units in
Ontario?
A) Table 8.2.1.5
B) Table 8.2.1.6.A
C) Table 8.2.1.3.A
D) Table 8.7.2.1
Rationale: Table 8.2.1.6.A provides the minimum clearances for treatment units (septic
tanks) under the Ontario Building Code.
16. Under Part 8, what is the minimum clearance from a septic tank to a well with
watertight casing to a depth of at least 6 m?
A) 5 m
B) 10 m
C) 15 m
