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Every septic job is an excavation job. You dig for the tank, for the trenches, sometimes for a full bed. The exam pulls in a few general excavation rules from Part 4 and Part 9, and two Part 9 drainage rules, one of which is written for wells and leaching beds. The articles are short, so questions usually test a single word: "all", "continuously", "free of", "away from".
Design and construction of excavations (Part 4)
Excavations, and the supports for their sides, are designed to Subsection 4.2.4. and Subsection 4.2.5. (OBC Div. B 4.2.5.1.OBC Div. B 4.2.5.1. Design of Excavations(1) The design of excavations and of supports for the sides of excavations shall conform with Subsection 4.2.4. and with this Subsection. (See Note A-4.2.5.1.(1))).
During construction (OBC Div. B 4.2.5.2.OBC Div. B 4.2.5.2. Excavation Construction(1) Every excavation shall be undertaken in such a manner as to prevent movement that would cause damage to adjacent buildings at all phases of construction. (2) Material shall not be placed nor shall equipment be operated or placed in or adjacent to an excavation in a manner that may endanger the integrity of the…):
- Dig so that movement does not damage adjacent buildings at any stage.
- Do not place material or run or park equipment in or next to an excavation in a way that could endanger the excavation or its supports. A loaded excavator or a stockpile of septic stone at the edge of a deep tank hole is the classic example.
Water control, protection and backfill (Part 4)
| Topic | What the code requires |
|---|---|
| Water | Surface water, all groundwater, perched groundwater and especially artesian groundwater must be kept under control during excavation and construction (OBC Div. B 4.2.5.5.OBC Div. B 4.2.5.5. Control of Water Around Excavations(1) Surface water, all groundwater, perched groundwater and in particular artesian groundwater shall be kept under control at all phases of excavation and construction.) |
| Protection | All sides, supported or not, must be continuously maintained and protected from deterioration by construction activity, frost, rain and wind (OBC Div. B 4.2.5.7.OBC Div. B 4.2.5.7. Protection and Maintenance at Excavations(1) All sides of an excavation, supported and unsupported, shall be continuously maintained and protected from possible deterioration by construction activity or by the action of frost, rain and wind.) |
| Backfill | Place backfill to give lateral support to the adjacent soil and to prevent harmful movement; fill that supports a footing, foundation or slab must not be prone to harmful volume change with moisture or temperature (OBC Div. B 4.2.5.8.OBC Div. B 4.2.5.8. Backfilling(1) Where an excavation is backfilled, the backfill shall be placed so as to (a) provide lateral support to the soil adjacent to the excavation, and (b) prevent detrimental movements. (2) The material used as backfill or fill supporting a footing, foundation or a floor on grade shall be of a type that is not subject…) |
Know the definitions behind the water words. Artesian groundwater is a confined body of water under pressure (def.OBC Div. A 1.4.1.2.(1) Artesian groundwaterArtesian groundwater means a confined body of water under pressure in the ground.). Perched groundwater is a free-standing body of water extending to a limited depth (def.OBC Div. A 1.4.1.2.(1) Perched groundwaterPerched groundwater means a free standing body of water in the ground extending to a limited depth.). Both can flood a tank excavation and float an empty tank, which is why Part 8 also requires tanks to be anchored where groundwater may cause hydrostatic pressure (OBC Div. B 8.2.2.2.(6)OBC Div. B 8.2.2.2. Tanks(1) A tank that is used as a treatment unit in a Class 4 sewage system or a holding tank in a Class 5 sewage system shall conform to the requirements of CSA B66, "Design, material, and manufacturing requirements for prefabricated septic tanks and sewage holding tanks." (2) Material standards, access and construction…).
Part 9 application and excavation
Part 9 applies as set out in Division A, Subsection 1.3.3. (OBC Div. B 9.1.1.1.OBC Div. B 9.1.1.1. Application(1) The application of this Part shall be as described in Subsection 1.3.3. of Division A.). In practice, that is houses and small buildings of not more than 3 storeys and 600 m² building area in the listed occupancies (OBC Div. A 1.3.3.3.OBC Div. A 1.3.3.3. Application of Part 9(1) Subject to Article 1.3.3.3B., Part 9 of Division B applies to all buildings described in Article 1.1.1.1. of 3 storeys or less in building height, having a building area not exceeding 600 m², and used for major occupancies classified as (a) reserved (b) Group C, residential occupancies other than buildings used…).
The Part 9 excavation rules in Subsection 9.12.1. are simple. The syllabus excludes the termite sentence (9.12.1.1.(2)), so focus on these:
| Article | Rule |
|---|---|
| 9.12.1.1.(1) and (3)OBC Div. B 9.12.1.1. Removal of Topsoil and Organic Matter(1) The topsoil and vegetable matter in all unexcavated areas under a building shall be removed. (2) In localities where termite infestation is known to be a problem, all stumps, roots and other wood debris shall be removed from the soil to a depth of not less than 300 mm in unexcavated areas under a building. (3) The… | remove topsoil and vegetable matter in unexcavated areas under a building; the bottom of every excavation must be free of all organic material |
| 9.12.1.2.OBC Div. B 9.12.1.2. Standing Water(1) Excavations shall be kept free of standing water. | keep excavations free of standing water |
| 9.12.1.3.OBC Div. B 9.12.1.3. Protection from Freezing(1) The bottom of excavations shall be kept from freezing throughout the entire construction period. | keep the bottom of excavations from freezing throughout construction |
| 9.12.1.4.OBC Div. B 9.12.1.4. Precautions During Excavation(1) Every excavation shall be undertaken in such a manner to prevent damage to adjacent property, existing structures, utilities, roads and sidewalks at all stages of construction. (2) Material shall not be placed nor shall equipment be operated or placed in or adjacent to an excavation in a manner that may endanger… | prevent damage to adjacent property, existing structures, utilities, roads and sidewalks; do not place material or equipment where it endangers the excavation |
Compare the Part 4 and Part 9 versions of the "prevent damage" rule. Part 4 says adjacent buildings. Part 9 lists more: adjacent property, existing structures, utilities, roads and sidewalks.
Surface drainage and drainage away from wells or leaching beds
Section 9.14. covers both subsurface and surface drainage (OBC Div. B 9.14.1.1.OBC Div. B 9.14.1.1. Application(1) This Section applies to subsurface drainage and to surface drainage.). The two articles on the syllabus:
- Locate the building, or grade the site, so water does not collect at or near the building and does not harm adjacent properties (OBC Div. B 9.14.6.1.OBC Div. B 9.14.6.1. Surface Drainage(1) The building shall be located or the building site graded so that water will not accumulate at or near the building and will not adversely affect adjacent properties.).
- Surface drainage must be directed away from a water supply well or a leaching bed (OBC Div. B 9.14.6.2.OBC Div. B 9.14.6.2. Drainage away from Wells or Septic Disposal Beds(1) Surface drainage shall be directed away from the location of a water supply well or leaching bed.).
This last rule ties in with Part 8, which requires the surface of a leaching bed to shed water (OBC Div. B 8.7.2.1.(3)OBC Div. B 8.7.2.1. General Requirements(1) A leaching bed shall not be located (a) in an area that has an average slope that exceeds one unit vertically to four units horizontally, (b) in soil or leaching bed fill having a percolation time of, (i) less than 1 min, or greater than 125 min if constructed as a shallow buried trench, or (ii) less than 1 min…) and requires privies, greywater pits and cesspools to be graded so surface drainage is diverted away from them.
Worked example: regrading a backyard
A homeowner regrades so that roof water from the house and the driveway runs across the leaching bed toward the road ditch. This breaks 9.14.6.2., which requires surface drainage to be directed away from a leaching bed. It also risks the operation and maintenance rule that land near a sewage system must be kept in a condition that will not damage or impair it (OBC Div. B 8.9.3.2.(2)OBC Div. B 8.9.3.2. General(1) Every sewage system shall be maintained so that (a) the construction of the sewage system remains in accordance with (i) the basis on which the construction and use of the sewage system was approved or required under the Act or predecessor legislation, as the case may be, and (ii) the requirements of the…). The fix is a swale that carries the water around the bed.
Worked example: tank hole in spring
An installer digs a hole for a 4,500 L tank in April and finds water seeping in from a perched layer. Part 4 requires that perched groundwater be kept under control, and Part 9 requires that the excavation be kept free of standing water. Pump it out, keep it controlled, and anchor the tank if groundwater could lift it.
Common traps
- "All groundwater, perched groundwater and in particular artesian groundwater": artesian is the one named "in particular".
- Sides of an excavation must be protected whether or not they are supported.
- The bottom of every excavation must be free of all organic material (not just under footings).
- Drainage goes away from both the well and the leaching bed.
- The termite rule (9.12.1.1.(2)) is excluded from this exam.
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.
- Design and construction of excavations (Part 4)
Excavations, and the supports for their sides, are designed to Subsection 4.2.4. and Subsection 4.2.5..
- Water control, protection and backfill (Part 4)
Know the definitions behind the water words.
- Part 9 application and excavation
Part 9 applies as set out in Division A, Subsection 1.3.3.. In practice, that is houses and small buildings of not more than 3 storeys and 600 m² building area in the listed…
- Surface drainage and drainage away from wells or leaching beds
Section 9.14. covers both subsurface and surface drainage.
Usual exam traps
- "All groundwater, perched groundwater and in particular artesian groundwater": artesian is the one named "in particular".
- Sides of an excavation must be protected whether or not they are supported.
- The bottom of every excavation must be free of all organic material (not just under footings).
- Drainage goes away from both the well and the leaching bed.
- The termite rule (9.12.1.1.(2)) is excluded from this exam.
Practice this chapter
Questions on Excavation and site drainage, 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 4.2.5.1. Design of Excavations
Open OBC Div. B 4.2.5.1. in the code viewer(1)The design of excavations and of supports for the sides of excavations shall conform with Subsection 4.2.4. and with this Subsection. (See Note A-4.2.5.1.(1))
OBC Div. B 4.2.5.2. Excavation Construction
Open OBC Div. B 4.2.5.2. in the code viewer(1)Every excavation shall be undertaken in such a manner as to prevent movement that would cause damage to adjacent buildings at all phases of construction.
(2)Material shall not be placed nor shall equipment be operated or placed in or adjacent to an excavation in a manner that may endanger the integrity of the excavation or its supports.
OBC Div. B 4.2.5.5. Control of Water Around Excavations
Open OBC Div. B 4.2.5.5. in the code viewer(1)Surface water, all groundwater, perched groundwater and in particular artesian groundwater shall be kept under control at all phases of excavation and construction.
OBC Div. B 4.2.5.7. Protection and Maintenance at Excavations
Open OBC Div. B 4.2.5.7. in the code viewer(1)All sides of an excavation, supported and unsupported, shall be continuously maintained and protected from possible deterioration by construction activity or by the action of frost, rain and wind.
OBC Div. B 4.2.5.8. Backfilling
Open OBC Div. B 4.2.5.8. in the code viewer(1)Where an excavation is backfilled, the backfill shall be placed so as to
(a)provide lateral support to the soil adjacent to the excavation, and
(b)prevent detrimental movements.
(2)The material used as backfill or fill supporting a footing, foundation or a floor on grade shall be of a type that is not subject to detrimental volume change with changes in moisture content and temperature.
OBC Div. A 1.4.1.2.(1) Artesian groundwater
Open OBC Div. A 1.4.1.2.(1) in the code viewerArtesian groundwater means a confined body of water under pressure in the ground.
OBC Div. A 1.4.1.2.(1) Perched groundwater
Open OBC Div. A 1.4.1.2.(1) in the code viewerPerched groundwater means a free standing body of water in the ground extending to a limited depth.
OBC Div. B 8.2.2.2. Tanks
Open OBC Div. B 8.2.2.2. in the code viewer(1)A tank that is used as a treatment unit in a Class 4 sewage system or a holding tank in a Class 5 sewage system shall conform to the requirements of CSA B66, "Design, material, and manufacturing requirements for prefabricated septic tanks and sewage holding tanks."
(2)Material standards, access and construction methods and practices for a tank used for other Classes of sewage systems shall conform to the requirements of CSA B66, "Design, material, and manufacturing requirements for prefabricated septic tanks and sewage holding tanks."
(3)Sentence (2) does not apply to a tank that is an integral part of a prefabricated Class 1 sewage system.
(4)Access openings shall be located to facilitate the pumping of all compartments and the servicing of the inlet and outlet of each compartment not accessible by removal of the tank top or part of it.
(5)A tank shall not be covered by soil or leaching bed fill having a depth greater than the maximum depth of burial that the tank is designed to withstand.
(6)A tank shall be securely anchored when located in an area subject to flooding or where ground water levels may cause hydrostatic pressures.
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OBC Div. B 9.1.1.1. Application
Open OBC Div. B 9.1.1.1. in the code viewer(1)The application of this Part shall be as described in Subsection 1.3.3. of Division A.
OBC Div. A 1.3.3.3. Application of Part 9
Open OBC Div. A 1.3.3.3. in the code viewer(1)Subject to Article 1.3.3.3B., Part 9 of Division B applies to all buildings described in Article 1.1.1.1. of 3 storeys or less in building height, having a building area not exceeding 600 m², and used for major occupancies classified as
(a)reserved
(b)Group C, residential occupancies other than buildings used for retirement homes, (See Note A-9.1.1.1.(1) of Division B)
(c)Group D, business and personal services occupancies,
(d)Group E, mercantile occupancies, or
(e)Group F, Divisions 2 and 3, medium- and low-hazard industrial occupancies.
OBC Div. B 9.12.1.1. Removal of Topsoil and Organic Matter
Open OBC Div. B 9.12.1.1. in the code viewer(1)The topsoil and vegetable matter in all unexcavated areas under a building shall be removed.
(2)In localities where termite infestation is known to be a problem, all stumps, roots and other wood debris shall be removed from the soil to a depth of not less than 300 mm in unexcavated areas under a building.
(3)The bottom of every excavation shall be free of all organic material.
OBC Div. B 9.12.1.2. Standing Water
Open OBC Div. B 9.12.1.2. in the code viewer(1)Excavations shall be kept free of standing water.
OBC Div. B 9.12.1.3. Protection from Freezing
Open OBC Div. B 9.12.1.3. in the code viewer(1)The bottom of excavations shall be kept from freezing throughout the entire construction period.
OBC Div. B 9.12.1.4. Precautions During Excavation
Open OBC Div. B 9.12.1.4. in the code viewer(1)Every excavation shall be undertaken in such a manner to prevent damage to adjacent property, existing structures, utilities, roads and sidewalks at all stages of construction.
(2)Material shall not be placed nor shall equipment be operated or placed in or adjacent to an excavation in a manner that may endanger the integrity of the excavation or its supports.
OBC Div. B 9.14.1.1. Application
Open OBC Div. B 9.14.1.1. in the code viewer(1)This Section applies to subsurface drainage and to surface drainage.
OBC Div. B 9.14.6.1. Surface Drainage
Open OBC Div. B 9.14.6.1. in the code viewer(1)The building shall be located or the building site graded so that water will not accumulate at or near the building and will not adversely affect adjacent properties.
OBC Div. B 9.14.6.2. Drainage away from Wells or Septic Disposal Beds
Open OBC Div. B 9.14.6.2. in the code viewer(1)Surface drainage shall be directed away from the location of a water supply well or leaching bed.
OBC Div. B 8.7.2.1. General Requirements
Open OBC Div. B 8.7.2.1. in the code viewer(1)A leaching bed shall not be located
(a)in an area that has an average slope that exceeds one unit vertically to four units horizontally,
(b)in soil or leaching bed fill having a percolation time of,
(i)less than 1 min, or greater than 125 min if constructed as a shallow buried trench, or
(ii)less than 1 min, or greater than 50 min for all other leaching beds, or
(c)in or on an area that is subject to flooding that may be expected to cause damage to the leaching bed or impair the operation of the leaching bed.
(2)A leaching bed shall not be covered with any material having a hydraulic conductivity less than 0.01 m/day.
(3)The surface of the leaching bed shall be shaped to shed water and together with the side slopes of any raised portion, shall be protected against erosion in such a manner as to not inhibit the evaporation and transpiration of waters from the soil or leaching bed fill, and to not cause plugging of the distribution pipe.
(4)No part of a leaching bed shall be sloped steeper than 1 unit vertically to 4 units horizontally.
(5)A leaching bed shall be designed to be protected from compaction or any stress or pressure that may result in,
(a)the impairment or destruction of any pipe in the leaching bed, or
(b)the smearing of the soil or leaching bed fill.
OBC Div. B 8.9.3.2. General
Open OBC Div. B 8.9.3.2. in the code viewer(1)Every sewage system shall be maintained so that
(a)the construction of the sewage system remains in accordance with
(i)the basis on which the construction and use of the sewage system was approved or required under the Act or predecessor legislation, as the case may be, and
(ii)the requirements of the manufacturer of the sewage system, and
(b)all components of the sewage system function in their intended manner.
(2)The land in the vicinity of a sewage system shall be maintained in a condition that will not cause damage to, or impair the functioning of, the sewage system.