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Values this chapter turns on
- of sewage system under Part 8
- 5 classes
- of sewage system under Part 8
- minimum thickness for Part 8 soil
- 100 mm
- minimum thickness for Part 8 soil
- max share of daily design flow from laundry
- 20%
- max share of daily design flow from laundry
- drain down time for sizing a grease interceptor
- 60 s
- drain down time for sizing a grease interceptor
Section 8.1. is short, but almost every Part 8 question depends on it. It tells you what "soil" means in Part 8, sorts every sewage system into one of five classes, and limits what may be sent into a system. Learn the five classes cold. Many scenario questions are really asking "which class is this?".
Scope and the Part 8 meaning of soil
Part 8's scope is set by Division A, Subsection 1.3.3. (OBC Div. B 8.1.1.1.OBC Div. B 8.1.1.1. Scope(1) The scope of this Part shall be as described in Subsection 1.3.3. of Division A.), which applies it to the design, construction, operation and maintenance of all sewage systems and to buildings built near them (OBC Div. A 1.3.3.2A.OBC Div. A 1.3.3.2A. Application of Part 8(1) Subject to Article 1.3.3.3B., Part 8 of Division B applies to the design, construction, operation and maintenance of all sewage systems and to the construction of buildings in the vicinity of sewage systems.).
Italic words are defined in Division A 1.4.1.2. and in the Building Code Act, except that Part 8 has its own definition of soil (OBC Div. B 8.1.1.2.OBC Div. B 8.1.1.2. Definitions(1) Except as provided in Sentence (2), words that appear in italics are defined in Article 1.4.1.2. of Division A and in the Building Code Act, 1992. (2) In this Part, Soil means in-situ, naturally occurring, unconsolidated mineral or organic material, at the earth's surface that is at least 100 mm thick and capable…). In Part 8, soil is:
- in-situ, naturally occurring, unconsolidated mineral or organic material at the earth's surface,
- at least 100 mm thick,
- capable of supporting plant growth,
- including material compacted or cemented by soil forming processes,
- but not displaced material such as gravel dumps, mine spoils or similar deposits.
So a pile of trucked-in gravel is not "soil" for Part 8. Material placed to build a bed is "leaching bed fill", which has its own definition (def.OBC Div. A 1.4.1.2.(1) Leaching bed fillLeaching bed fill means unconsolidated material suitable for the construction of a leaching bed, placed in the area of the leaching bed in order to obtain the required unsaturated zone below the distribution pipes or leaching chambers and the required lateral extent such that the effluent is absorbed.).
The five classes
Every sewage system falls into one class (OBC Div. B 8.1.2.1.OBC Div. B 8.1.2.1. Classification of Systems(1) All sewage systems shall be classed as one of the following: (a) Class 1 — a chemical toilet, an incinerating toilet, a recirculating toilet, a self-contained portable toilet and all forms of privy including a portable privy, an earth pit privy, a pail privy, a privy vault and a composting toilet system, (b) Class…):
| Class | What it is | Where the rules are |
|---|---|---|
| 1 | Chemical, incinerating, recirculating and self-contained portable toilets, and all privies (portable, earth pit, pail, privy vault) and composting toilet systems | Section 8.3. |
| 2 | Greywater system | Section 8.4. |
| 3 | Cesspool | Section 8.5. |
| 4 | Leaching bed system (treatment unit plus leaching bed) | Sections 8.6. and 8.7. |
| 5 | System that uses a holding tank to keep hauled sewage on site until it is collected by a hauled sewage system | Section 8.8. |
Operation and maintenance of every class is governed by Section 8.9. (OBC Div. B 8.1.2.2.OBC Div. B 8.1.2.2. Operation and Maintenance(1) Operation and maintenance of sewage systems shall comply with Section 8.9.).
Memory aid: the number rises as the system gets more "engineered", except Class 5, which is the holding tank fallback. A composting toilet is Class 1, not Class 4, even though it treats waste.
Worked example: classify the system
| Situation | Class |
|---|---|
| Outhouse over a pit at a hunting camp | 1 (earth pit privy) |
| Rented portable toilets at a fair | 1 (portable privy) |
| Pit taking only kitchen sink and shower water at a cottage | 2 (greywater) |
| Covered pit receiving the contents of a privy | 3 (cesspool) |
| Septic tank and trenches for a house | 4 |
| Tank pumped out by a hauler for a seasonal trailer office on a tiny lot | 5 |
Limitations on discharge
The basic rule: a sewage system is designed and built to receive only sanitary sewage of domestic origin (OBC Div. B 8.1.3.1.(1)OBC Div. B 8.1.3.1. Discharge(1) Except as provided in Sentences (2) to (6), the sewage system shall be designed and constructed to receive only sanitary sewage of domestic origin. (See Note A-8.1.3.1.(1)) (2) Where laundry waste is not more than 20% of the total daily design sanitary sewage flow, it may discharge to a sewage system. (3) Where…). Then come the exceptions, each with a condition:
| Waste | Allowed if |
|---|---|
| Laundry waste | it is not more than 20% of the total daily design sanitary sewage flow |
| Industrial process waste water | treated to the contaminant levels of domestic sanitary sewage, and the treatment unit and system are designed to good engineering practice (to a leaching bed) |
| Restaurant kitchen waste water | it has passed through an operating grease interceptor, and the system is designed to good engineering practice (to a leaching bed) |
| Kitchen waste with a garbage grinder | the system was designed to accept it |
| Water softener and iron filter discharge | the system was designed to accept it |
| Storm sewage | never |
The grease interceptor required for restaurant waste must have a minimum flow rate per Sentence 7.4.4.3.(8) using a 60 second drain down time, and must conform to CSA B481.1 or B481.2 (Sentence (8)). You only need to know which standards are named, not what they contain.
Worked example: laundromat on a septic
A small motel has a total daily design flow of 5,000 L, of which laundry waste is estimated at 1,200 L. The limit is 20% of 5,000 L = 1,000 L. At 1,200 L the laundry waste exceeds the limit, so it may not discharge to the sewage system as designed.
Worked example: sump pump into the septic
A homeowner wants to run the basement sump pump (rain and snow melt water) into the septic tank. Storm sewage is water discharged from a surface because of rainfall, snow melt or snowfall (def.OBC Div. A 1.4.1.2.(1) Storm sewageStorm sewage means water that is discharged from a surface as a result of rainfall, snow melt or snowfall.), and it shall not be discharged into a sewage system (Sentence 8.1.3.1.(7)). The answer is no, with no exceptions.
Common traps
- Part 8 soil must be at least 100 mm thick and support plant growth. Gravel dumps and mine spoils are excluded.
- A cesspool is Class 3, and it only takes Class 1 contents (Chapter 7).
- A leaching bed system is Class 4, whatever the treatment unit.
- The laundry limit is 20% of the total daily design flow, not of the tank size.
- Softener and grinder waste are allowed only if the system was designed for them.
- There is no exception at all for storm sewage.
Chapter review
Chapter at a glance
One line per section: the idea to carry into the exam. Then the answers that most often catch candidates out.
- Scope and the Part 8 meaning of soil
Part 8's scope is set by Division A, Subsection 1.3.3., which applies it to the design, construction, operation and maintenance of all sewage systems and to buildings built near…
- The five classes
Operation and maintenance of every class is governed by Section 8.9..
- Limitations on discharge
The basic rule: a sewage system is designed and built to receive only sanitary sewage of domestic origin.
Usual exam traps
- Part 8 soil must be at least 100 mm thick and support plant growth. Gravel dumps and mine spoils are excluded.
- A cesspool is Class 3, and it only takes Class 1 contents (Chapter 7).
- A leaching bed system is Class 4, whatever the treatment unit.
- The laundry limit is 20% of the total daily design flow, not of the tank size.
- Softener and grinder waste are allowed only if the system was designed for them.
- There is no exception at all for storm sewage.
Practice this chapter
Questions on Part 8 general: scope, application, definitions and limitations, in the exam format, every answer explained and cited to its article. Sign in to start; a free account gets the free questions.
Code cited in this chapter
Based on the official 2024 Building Code Compendium on ontario.ca.
© King's Printer for Ontario, 2024. Reproduced with permission.
OBC Div. B 8.1.1.1. Scope
Open OBC Div. B 8.1.1.1. in the code viewer(1)The scope of this Part shall be as described in Subsection 1.3.3. of Division A.
OBC Div. A 1.3.3.2A. Application of Part 8
Open OBC Div. A 1.3.3.2A. in the code viewer(1)Subject to Article 1.3.3.3B., Part 8 of Division B applies to the design, construction, operation and maintenance of all sewage systems and to the construction of buildings in the vicinity of sewage systems.
OBC Div. B 8.1.1.2. Definitions
Open OBC Div. B 8.1.1.2. in the code viewer(1)Except as provided in Sentence (2), words that appear in italics are defined in Article 1.4.1.2. of Division A and in the Building Code Act, 1992.
(2)In this Part,
Soil means in-situ, naturally occurring, unconsolidated mineral or organic material, at the earth's surface that is at least 100 mm thick and capable of supporting plant growth, and includes material compacted or cemented by soil forming processes, but does not include displaced materials such as gravel dumps, mine spoils, or like deposits.
OBC Div. A 1.4.1.2.(1) Leaching bed fill
Open OBC Div. A 1.4.1.2.(1) in the code viewerLeaching bed fill means unconsolidated material suitable for the construction of a leaching bed, placed in the area of the leaching bed in order to obtain the required unsaturated zone below the distribution pipes or leaching chambers and the required lateral extent such that the effluent is absorbed.
OBC Div. B 8.1.2.1. Classification of Systems
Open OBC Div. B 8.1.2.1. in the code viewer(1)All sewage systems shall be classed as one of the following:
(a)Class 1 — a chemical toilet, an incinerating toilet, a recirculating toilet, a self-contained portable toilet and all forms of privy including a portable privy, an earth pit privy, a pail privy, a privy vault and a composting toilet system,
(b)Class 2 — a greywater system,
(c)Class 3 — a cesspool,
(d)Class 4 — a leaching bed system, or
(e)Class 5 — a system that requires or uses a holding tank for the retention of hauled sewage at the site where it is produced prior to its collection by a hauled sewage system.
OBC Div. B 8.1.2.2. Operation and Maintenance
Open OBC Div. B 8.1.2.2. in the code viewer(1)Operation and maintenance of sewage systems shall comply with Section 8.9.
OBC Div. B 8.1.3.1. Discharge
Open OBC Div. B 8.1.3.1. in the code viewer(1)Except as provided in Sentences (2) to (6), the sewage system shall be designed and constructed to receive only sanitary sewage of domestic origin. (See Note A-8.1.3.1.(1))
(2)Where laundry waste is not more than 20% of the total daily design sanitary sewage flow, it may discharge to a sewage system.
(3)Where industrial process waste water is treated to the contaminant levels found in domestic sanitary sewage, it may discharge to a leaching bed provided the treatment unit and sewage system are designed in accordance with good engineering practice. (See Note A-8.1.3.1.(3))
(4)Where kitchen waste water from a restaurant has passed through an operating grease interceptor, it may discharge to a leaching bed provided the sewage system has been designed in accordance with good engineering practice.
(5)Waste water from a kitchen equipped with a garbage grinder may be directed to the sewage system provided the system has been designed to accept such waste water.
(6)Water softener and iron filter discharge may be directed to the sewage system provided the system has been designed to accept such discharges.
(7)Storm sewage shall not be discharged into a sewage system.
(8)The interceptor required in Sentence (4) shall
(a)have a minimum flow rate as required by Sentence 7.4.4.3.(8) using a 60 second drain down time, and
(b)conform to,
(i)CSA B481.1, "Testing and rating of grease interceptors using lard," or
(ii)CSA B481.2, "Testing and rating of grease interceptors using oil."
OBC Div. A 1.4.1.2.(1) Storm sewage
Open OBC Div. A 1.4.1.2.(1) in the code viewerStorm sewage means water that is discharged from a surface as a result of rainfall, snow melt or snowfall.