Design standards: flows, clearances and tanks (On-site Sewage Systems)

Last updated October 22, 2026

Values this chapter turns on

minimum working capacity of any septic tank: 3,600 L; minimum working capacity of any septic tank
minimum percolation test locations, use the highest: 3 tests; minimum percolation test locations, use the highest
percolation time below which well clearances grow: 10 min; percolation time below which well clearances grow
minimum size of a septic tank first compartment: 2,400 L; minimum size of a septic tank first compartment

Section 8.2. is the engine room of this exam. Nearly every sizing question starts with the total daily design sanitary sewage flow (call it Q), and nearly every siting question ends in a clearance table. This chapter shows how to find Q, how to read the clearance tables, and how tanks are built and sized.

Site evaluation and percolation time

A site evaluation is required on every site where a new or replacement sewage system is installed (OBC Div. B 8.2.1.2.(1)). The percolation time (T) is found either by percolation tests or by classifying the soil, using the Unified Soil Classification System in MMAH Supplementary Standard SB-6 or the USDA Soil Texture Classification (Sentence (2)).

If you use percolation tests, test at least 3 locations, spaced to represent the leaching bed area, and design with the highest result (Sentence (3)). Using the average or the lowest is the classic wrong answer. SB-6 is covered in Chapter 9.

Practice this topic

Daily design flow (Q)

Residential occupancies: Q is at least the value from Table 8.2.1.3.-A (OBC Div. B 8.2.1.3.(1)).
All other occupancies: Q is at least the value from Table 8.2.1.3.-B (Sentence (2)).
A building with more than one establishment: add the flows of each establishment (Sentence (3)).
An occupancy not listed in Table 8.2.1.3.-B: the highest metered flow from at least 3 similar establishments is acceptable (Sentence (4)).

Reading Table 8.2.1.3.-A for a house

The "Dwellings" rows of Table 8.2.1.3.-A give a base flow by number of bedrooms. A 3 bedroom dwelling is 1,600 L, for example. Below the base rows are "additional flow" rows for bedrooms over 5, for finished floor area over 200 m² (in 10 m² steps, with a lower rate per step in each higher area band), and for each fixture unit over 20.

How to use it:

Start with the bedroom flow.
Work out each permitted additional flow separately: by finished area, by fixture units, and by bedrooms over 5 where that applies.
Note (2) to the table says that where more than one calculation is permitted, use the one giving the highest flow. In practice, add the largest of the additional flows to the bedroom flow.
Floor area is the total finished area, excluding a finished basement (Note (3)), and each 10 m² "or part of it" counts as a full step.

Worked example: a larger house

A 4 bedroom house has 255 m² of finished area above grade (plus a finished basement) and 24 fixture units.

Step	Working	Flow
Base, 4 bedrooms	from the table	2,000 L
Area	255 - 200 = 55 m², which is 6 steps (5 full plus a part) x 100 L	600 L
Fixture units	24 - 20 = 4 x 50 L	200 L
Q	2,000 + the larger extra (600)	2,600 L

The basement area is ignored. Adding both extras (2,800 L) or ignoring the "part of it" step (2,500 L) are the usual mistakes.

Reading Table 8.2.1.3.-B

Table 8.2.1.3.-B groups establishments under headings, each with a unit (per seat, per employee per 8 hour shift, per 9.25 m² and so on). Find the heading, pick the right row, and multiply. Where the table offers more than one way to calculate (for example an office per employee or per 9.3 m²), Note (3) says use the calculation giving the highest flow. Occupant loads come from Subsection 3.1.17. (Note (1)).

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Clearances

Where T is 10 min or more, every component must meet the clearances in Article 8.2.1.5. or 8.2.1.6., unless shown to be unnecessary. Where T is less than 10 min (fast soils), the distances to wells, lakes, ponds, reservoirs, rivers, springs and streams must be increased to make up for it (OBC Div. B 8.2.1.4.). No building may be built closer to a sewage system than these clearances, and two systems on one lot must not overlap.

There are four clearance tables. Pick the right one by class and component:

Table	Applies to
8.2.1.5.	Class 1, 2 and 3 systems (privies, greywater systems, cesspools)
8.2.1.6.-A	Treatment units (septic tanks and other units)
8.2.1.6.-B	Centre line of distribution pipe or leaching chambers
8.2.1.6.-C	Holding tanks

A few values to anchor your reading (look up the rest in the code):

Item	To a structure	To a property line
Treatment unit	1.5 m	3 m
Distribution pipe or leaching chamber	5 m	3 m
Holding tank	1.5 m	3 m

For distribution pipe, wells are split into two rows: a well with a watertight casing to a depth of at least 6 m, and any other well. The second distance is double the first. Table 8.2.1.5. splits wells and springs the same way, using separate columns.

Raised beds increase the distances

Where a leaching bed is raised above original grade, the distances in Column 2 of Table 8.2.1.6.-B are increased by twice the height the bed is raised (OBC Div. B 8.7.4.2.(11), referenced from 8.2.1.6.(2)).

Practice this topic

Tanks

Subsection 8.2.2. applies to any tank in a sewage system (OBC Div. B 8.2.2.1.). General rules (OBC Div. B 8.2.2.2.):

Class 4 treatment tanks and Class 5 holding tanks conform to CSA B66.
Access openings must allow pumping of every compartment and servicing of each inlet and outlet not reachable by removing the top.
Do not bury a tank deeper than its design burial depth.
Anchor it securely where flooding or groundwater could cause hydrostatic pressure.

Septic tank sizing

OBC Div. B 8.2.2.3. sets the minimum working capacity:

Occupancy	Minimum working capacity
Residential	the greater of 3,600 L and 2 x Q
Non-residential	the greater of 3,600 L and 3 x Q

Every septic tank has at least 2 compartments. The first is at least 1.3 x Q and never less than 2,400 L. Each later compartment is at least 50% of the first.

Other septic tank rules:

With multiple tanks in series, the first tank is never under 3,600 L working capacity, the pipe between tanks slopes at least 2%, and connections use flexible watertight seals.
Partitions extend at least 150 mm above the outlet liquid level. Air openings between compartments total at least 3 times the inlet pipe area. Liquid passes between compartments through an outlet-type device, or through openings centred at about 40% of liquid depth with a total area 3 to 5 times the inlet pipe area.
Liquid depth at least 1,000 mm, or 900 mm where excavation is in rock or to avoid groundwater problems.
Access openings not more than 300 mm below grade; deeper tanks need risers to within 300 mm of the surface.

Holding tanks

A holding tank must allow complete removal of settled solids, and must have a working capacity of at least 9,000 L. Connected tanks count as one tank, but any part that cannot drain completely does not count (OBC Div. B 8.2.2.4.). Residential holding tanks also need 7 days' capacity (Chapter 10).

Practice this topic

Common traps

Three percolation tests minimum, use the highest T.
Clearances are increased (not relaxed) where T is under 10 min.
Distribution pipe to a structure is 5 m; a tank to a structure is 1.5 m.
Raised beds add twice the raise height.
Non-residential tanks use 3 x Q, residential 2 x Q, with 3,600 L as the floor.
First compartment floor is 2,400 L; whole-tank floor is 3,600 L.

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.

Chapter at a glance: the key idea in each section
Section	Key idea
Site evaluation and percolation time	A site evaluation is required on every site where a new or replacement sewage system is installed.
Daily design flow (Q)	The "Dwellings" rows of give a base flow by number of bedrooms.
Clearances	Where T is 10 min or more, every component must meet the clearances in Article 8.2.1.5. or 8.2.1.6., unless shown to be unnecessary.
Tanks	Subsection 8.2.2. applies to any tank in a sewage system.

Site evaluation and percolation time
A site evaluation is required on every site where a new or replacement sewage system is installed.
Daily design flow (Q)
The "Dwellings" rows of give a base flow by number of bedrooms.
Clearances
Where T is 10 min or more, every component must meet the clearances in Article 8.2.1.5. or 8.2.1.6., unless shown to be unnecessary.
Tanks
Subsection 8.2.2. applies to any tank in a sewage system.

Usual exam traps

Three percolation tests minimum, use the highest T.
Clearances are increased (not relaxed) where T is under 10 min.
Distribution pipe to a structure is 5 m; a tank to a structure is 1.5 m.
Raised beds add twice the raise height.
Non-residential tanks use 3 x Q, residential 2 x Q, with 3,600 L as the floor.
First compartment floor is 2,400 L; whole-tank floor is 3,600 L.

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Questions on Design standards: flows, clearances and tanks, in the exam format, every answer explained and cited to its article. Sign in to start; a free account gets the free questions.

Practice this chapter On-site Sewage Systems calculations

Code cited in this chapter

Based on the official 2024 Building Code Compendium on ontario.ca.

OBC Div. B 8.2.1.2. Site Evaluation
(1)A site evaluation shall be conducted on every site where a new or replacement sewage system is to be installed. (See Note A-8.2.1.2.(1))
(2)The percolation time shall be determined by
(a)conducting percolation tests, or
(b)classifying the soil according to one of the following methods,
(i)the Unified Soil Classification System as described in MMAH Supplementary Standard SB-6, "Percolation Time and Soil Descriptions," or
(ii)the Soil Texture Classification as described in Chapter 3 of USDA, "Soil Survey Manual." (See Note A-8.2.1.2.(2))
(3)Where the percolation time is determined by a percolation test, there shall be a minimum of 3 locations selected, suitably spaced to accurately evaluate the leaching bed area, with the highest percolation time of the tests being used. (See Note A-8.2.1.2.(3))
Open OBC Div. B 8.2.1.2. in the code viewer
OBC Div. B 8.2.1.3. Sewage System Design Flows
(1)For residential occupancies, the total daily design sanitary sewage flow shall be at least the value determined in accordance with Table 8.2.1.3.-A. (See Note A-8.2.1.3.(1) and (2))
(2)For all other occupancies, the total daily design sanitary sewage flow shall be at least the value determined in accordance with Table 8.2.1.3.-B. (See Note A-8.2.1.3.(1) and (2))
(3)Where a building contains more than one establishment, the total daily design sanitary sewage flow shall be the sum of the total daily design sanitary sewage flow for each establishment.
(4)Where an occupancy is not listed in Table 8.2.1.3.-B, the highest of metered flow data from at least 3 similar establishments shall be acceptable for determining the total daily design sanitary sewage flow.
Open OBC Div. B 8.2.1.3. in the code viewer
OBC Div. B Table 8.2.1.3-A. Residential Occupancy — Forming Part of Sentence 8.2.1.3.(1)
Table 8.2.1.3.-A Residential Occupancy — Forming Part of Sentence 8.2.1.3.(1) Residential Occupancy | Volume, litres Apartments, Condominiums, Other Multi-family Dwellings - per person[1] | 275 Boarding Houses (a) Per person, (i) with meals and laundry facilities, or, | 200 Boarding Houses (a) Per person, (ii) without meal or laundry facilities, and | 150 Boarding Houses (b) Per non-resident staff per 8 hour shift | 40 Boarding School - per person | 300 Dwellings (a) 1 bedroom dwelling | 750 Dwellings (b) 2 bedroom dwelling | 1,100 Dwellings (c) 3 bedroom dwelling | 1,600 Dwellings (d) 4 bedroom dwelling | 2,000 Dwellings (e) 5 bedroom dwelling | 2,500 Dwellings (f) Additional flow for[2] (i) each bedroom over 5, | 500 Dwellings (f) Additional flow for[2] (f) (ii) (A) each 10 m² (or part of it) over 200 m² up to 400 m²[3], | 100 Dwellings (f) Additional flow for[2] (f) (ii) (B) each 10 m² (or part of it) over 400 m² up to 600 m²[3], and | 75 Dwellings (f) Additional flow for[2] (f) (ii) (C) each 10 m² (or part of it) over 600 m²[3], or | 50 Dwellings (f) Additional flow for[2] (iii) each fixture unit over 20 fixture units | 50 Hotels and Motels (excluding bars and restaurants) (a) Regular, per room | 250 Hotels and Motels (excluding bars and restaurants) (b) Resort hotel, cottage, per person | 500 Hotels and Motels (excluding bars and restaurants) (c) Self service laundry, add per machine | 2,500 Work Camp/Construction Camp, semi-permanent per worker | 250 Notes to Table 8.2.1.3.-A: (1) The occupant load shall be calculated using Subsection 3.1.17. (2) Where multiple calculations of sanitary sewage volume is permitted, the calculation resulting in the highest flow shall be used in determining the design daily sanitary sewage flow. (3) Total finished area, excluding the area of the finished basement.
Open OBC Div. B Table 8.2.1.3-A. in the code viewer
OBC Div. B Table 8.2.1.3-B. Airports, Bus Terminals, Train Stations, Dock/Port Facilities (Food Services excluded)
Airports, Bus Terminals, Train Stations, Dock/Port Facilities (Food Services excluded) Establishments[1] | Volume, litres (a) Per passenger, and | 20 (b) Per employee per 8 hour shift | 40 Assembly Hall — per seat Establishments[1] | Volume, litres (a) No food service, or | 8 (b) Food service provided | 36 Barber Shop/Beauty Salon Establishments[1] | Volume, litres per service chair | 650 Bowling Alleys (Food Service not included) Establishments[1] | Volume, litres per lane | 400 Churches and Similar Places of Worship — per seat Establishments[1] | Volume, litres (a) No kitchen facilities, or | 8 (b) Kitchen facilities provided | 36 Country Club (excluding Food Service) Establishments[1] | Volume, litres (a) Per resident, | 375 (b) Per employee per 8 hour shift, and | 50 (c) Per member or patron | 40 Day Care Facility Establishments[1] | Volume, litres per person (staff and children) | 75 Dentist Office Establishments[1] | Volume, litres (a) Per wet service chair, and | 275 (b) Per dry service chair | 190 Doctors Office Establishments[1] | Volume, litres (a) Per practitioner, and | 275 (b) Per employee per 8 hour shift | 75 Factory (excluding process or cleaning waters) — per employee per 8 hour shift Establishments[1] | Volume, litres (a) No showers, or | 75 (b) Including showers | 125 Flea Markets[2] (open not more than 3 days per week) Establishments[1] | Volume, litres (a) Per non-food service vendor space, | 60 (b) Per food service establishment / 9.25 m² of floor space, and | 190 (c) Per limited food service outlet | 95 Food Service Operations Establishments[1] | Volume, litres (a) Restaurant (not 24 hour), per seat | 125 (b) Restaurant (24 hour), per seat | 200 (c) Restaurant on controlled-access highway, per seat | 400 (d) Paper service restaurant, per seat | 60 (e) Donut shop, per seat | 400 (f) Bar and cocktail lounge, per seat | 125 (g) Drive-in restaurant per parking space | 60 (i) Cafeteria — per meal | 12 Take-out restaurant (no seating area) Establishments[1] | Volume, litres (h) (i) per 9.25 m² of floor area, and | 190 (h) (ii) per employee per 8 hour shift | 75 Food outlet Establishments[1] | Volume, litres (j) (i) excluding delicatessen, bakery and meat department, per 9.25 m² of floor space, | 40 (j) (ii) per 9.25 m² of delicatessen floor space, | 190 (j) (iii) per 9.25 m² of bakery floor space, | 190 (j) (iv) per 9.25 m² of meat department floor space, and | 380 (j) (v) per water closet | 950 Hospitals — per bed Establishments[1] | Volume, litres (a) Including laundry facilities, or | 750 (b) Excluding laundry facilities | 550 Long-Term Care Homes, etc. Establishments[1] | Volume, litres per bed | 450 Office Building[3] Establishments[1] | Volume, litres (a) Per employee per 8 hour shift, or | 75 (b) Per each 9.3 m² of floor space | 75 Public Parks Establishments[1] | Volume, litres (a) With toilets only per person, or | 20 (b) With bathhouse, showers, and toilets per person | 50 Recreational Vehicle or Campground Park Establishments[1] | Volume, litres (a) Per site without water or sewer hook-up, or | 275 (b) Per site with water and sewer hook-up | 425 Schools — per student Establishments[1] | Volume, litres (a) Day school, | 30 (b) With showers, | 30 (c) With cafeteria, and | 30 (d) Per non-teaching employee per 8 hour shift | 50 Service Stations (no vehicle washing)[3] Establishments[1] | Volume, litres (a) Per water closet, and | 950 (a) Per water closet, and (i) per fuel outlet[4], or | 560 (a) Per water closet, and (ii) per vehicle served | 20 Shopping Centre (excluding food and laundry) Establishments[1] | Volume, litres per 1.0 m² of floor space | 5 Stadiums, Race Tracks, Ball Parks Establishments[1] | Volume, litres per seat | 20 Stores[3] Establishments[1] | Volume, litres (a) Per 1.0 m² of floor area, or | 5 (b) Per water closet | 1,230 Swimming and Bathing Facilities (Public) Establishments[1] | Volume, litres per person | 40 Theatres Establishments[1] | Volume, litres (a) Indoor, auditoriums per seat, | 20 (b) Outdoor, drive-ins per space, or | 40 (c) Movie theatres per seat | 15 Veterinary Clinics Establishments[1] | Volume, litres (a) Per practitioner, | 275 (b) Per employee per 8 hour shift, and | 75 (c) Per stall, kennel or cage if floor drain connected | 75 Warehouse Establishments[1] | Volume, litres (a) Per water closet, and | 950 (b) Per loading bay | 150 Notes to Table 8.2.1.3.-B: (1) The occupant load shall be calculated using Subsection 3.1.17. (2) Flea markets open more than 3 days per week shall be assessed using the volumes stated under the heading "Stores". (3) Where multiple calculations of sanitary sewage volume is permitted, the calculation resulting in the highest flow shall be used in determining the design daily sanitary sewage flow. (4) The number of fuel outlets is considered the maximum number of fuel nozzles that could be in use at the same time
Open OBC Div. B Table 8.2.1.3-B. in the code viewer
OBC Div. B 8.2.1.4. Clearances
(1)Unless it can be shown to be unnecessary, where the percolation time is 10 min or greater, the location of all components within a sewage system shall be in conformance with the clearances listed in Article 8.2.1.5. or 8.2.1.6.
(2)Unless it can be shown to be unnecessary, where the percolation time is less than 10 min, the clearances listed in Articles 8.2.1.5. and 8.2.1.6. for wells, lakes, ponds, reservoirs, rivers, springs or streams shall be increased to compensate for the lower percolation time.
(3)No building shall be constructed closer to any part of a sewage system than the clearances listed in Article 8.2.1.5. or 8.2.1.6.
(4)If more than one sewage system is located on a lot or parcel of land, there shall be no overlap of any part of the systems.
Open OBC Div. B 8.2.1.4. in the code viewer
OBC Div. B Table 8.2.1.5. Clearance Distances for Class 1, 2 and 3 Sewage Systems — Forming Part of Sentence 8.2.1.5.(1)
Table 8.2.1.5. Clearance Distances for Class 1, 2 and 3 Sewage Systems — Forming Part of Sentence 8.2.1.5.(1) Sewage System | Minimum horizontal distance in metres from a well with watertight casing to a depth of at least 6 m | Minimum horizontal distance in metres from a spring used as a source of potable water or well other than a well with a watertight casing to a depth of at least 6 m | Minimum horizontal distance in metres from a lake, river, pond, stream, reservoir, or a spring not used as a source of potable water | Minimum horizontal distance in metres from a property line Earth Pit Privy | 15 | 30 | 15 | 3 Privy Vault | 10 | 15 | 10 | 3 Pail Privy | 10 | 15 | 10 | 3 Greywater System | 10 | 15 | 15 | 3 Cesspool | 30 | 60 | 15 | 3
Open OBC Div. B Table 8.2.1.5. in the code viewer
OBC Div. B Table 8.2.1.6-A. Minimum Clearances for Treatment Units Forming Part of Sentence 8.2.1.6.(1)
Table 8.2.1.6.-A — Minimum Clearances for Treatment Units Forming Part of Sentence 8.2.1.6.(1) Object | Minimum Clearance, m Structure | 1.5 Well | 15 Lake | 15 Pond | 15 Reservoir | 15 River | 15 Spring | 15 Stream | 15 Property Line | 3
Open OBC Div. B Table 8.2.1.6-A. in the code viewer
OBC Div. B Table 8.2.1.6-B. Minimum Clearances for Distribution Piping and Leaching Chambers Forming Part of Sentence 8.2.1.6.(2)
Table 8.2.1.6.-B — Minimum Clearances for Distribution Piping and Leaching Chambers Forming Part of Sentence 8.2.1.6.(2) Object | Minimum Clearance, m Structure | 5 Well with a watertight casing to a depth of at least 6 m | 15 Any other well | 30 Lake | 15 Pond | 15 Reservoir | 15 River | 15 Spring not used as a source of potable water | 15 Stream | 15 Property Line | 3
Open OBC Div. B Table 8.2.1.6-B. in the code viewer

Show all 15 articles

OBC Div. B Table 8.2.1.6-C. Minimum Clearances for Holding Tanks Forming Part of Sentence 8.2.1.6.(3)
Table 8.2.1.6.-C — Minimum Clearances for Holding Tanks Forming Part of Sentence 8.2.1.6.(3) Object | Minimum Clearance, m Structure | 1.5 Well with a watertight casing to a depth of at least 6 m | 15 Any other well | 15 Spring | 15 Property Line | 3
Open OBC Div. B Table 8.2.1.6-C. in the code viewer
OBC Div. B 8.7.4.2. Construction Requirements
(1)Except for a shallow buried trench, a leaching bed comprised of absorption trenches may be constructed in leaching bed fill, if unsaturated soil or leaching bed fill complying with Subclause 8.7.2.1.(1)(b)(ii) extends
(a)to a depth of at least 250 mm over the area covered by the leaching bed fill, and
(b)for at least 15 m beyond the centre lines of the outer distribution pipes or leaching chambers in any direction in which the effluent entering the soil or leaching bed fill will move horizontally.
(2)If the unsaturated soil or leaching bed fill described in Sentence (1) has a percolation time greater than 15 min, any additional leaching bed fill added to it to form the leaching bed shall have a percolation time not less than 75% of the percolation time of the unsaturated soil or leaching bed fill to which it is added.
(3)Leaching bed fill that does not meet the requirements of Sentence (2) may be used to form the leaching bed if
(a)the distance from the bottom of the absorption trench to the underlying soil is not less than 900 mm, or
(b)where the distance from the bottom of the absorption trench to the underlying soil is less than 900 mm, the percolation time of the least permeable soil or leaching bed fill within 900 mm from the bottom of the absorption trench is used to calculate the length of the distribution pipe under Article 8.7.3.1. or the length of the leaching chamber under Article 8.7.3.2.
(4)Sentence (2) does not apply to any leaching bed fill added as backfill above the stone layer in which the distribution pipe is located.
(5)All leaching bed fill added shall be stabilized against erosion.
(6)The site to which the leaching bed fill is added shall be generally clear of vegetation.
(7)The leaching bed fill that is added shall be compacted in layers in such a manner as to avoid uneven settlement of the distribution pipes or leaching chambers.
(8)Any distribution boxes, header lines, absorption trenches, distribution pipes or leaching chambers shall be installed only after the leaching bed fill has been compacted in accordance with Sentence (7).
(9)Except as provided in Sentence (10), the sides of the added leaching bed fill shall be sloped to ensure stability, but shall not be steeper than one unit vertically to four units horizontally.
(10)The side slope of the leaching bed fill may be increased up to one unit vertically to three units horizontally if measures are taken to prevent erosion and ensure stability of the leaching bed fill.
(11)The distances set out in Column 2 of Table 8.2.1.6.B. shall be increased by twice the height that the leaching bed is raised above the original grade.
Open OBC Div. B 8.7.4.2. in the code viewer
OBC Div. B 8.2.1.6. Clearances for a Class 4 or 5 Sewage System
(1)Except as provided in Sentences 8.2.1.4.(1) and (2), a treatment unit shall not be located closer than the minimum horizontal distances set out in Table 8.2.1.6.-A.
(2)Except as provided in Sentences 8.2.1.4.(1) and (2), the centre line of a distribution pipe or leaching chamber shall not be located closer than the minimum horizontal distances set out in Table 8.2.1.6.-B and these distances shall be increased when required by Sentence 8.7.4.2.(11).
(3)Except as provided in Sentences 8.2.1.4.(1) and (2), a holding tank shall not be located closer than the minimum horizontal distances set out in Table 8.2.1.6.-C.
Open OBC Div. B 8.2.1.6. in the code viewer
OBC Div. B 8.2.2.1. Application
(1)This Subsection applies to any tank used in a sewage system for collecting, treating, holding or storing sanitary sewage.
Open OBC Div. B 8.2.2.1. in the code viewer
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 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.
Open OBC Div. B 8.2.2.2. in the code viewer
OBC Div. B 8.2.2.3. Septic Tanks
(1)The minimum working capacity of a septic tank shall be the greater of 3,600 L and
(a)in residential occupancies, twice the daily design sanitary sewage flow, or
(b)in non-residential occupancies, three times the daily design sanitary sewage flow.
(2)Every septic tank shall be constructed in such a manner that any sanitary sewage flowing through the tank will pass through at least 2 compartments.
(3)The working capacity of the compartments required in Sentence (2) shall be sized such that
(a)the first compartment is at least 1.3 times the daily design sanitary sewage flow but in no case less than 2,400 L, and
(b)each subsequent compartment shall be at least 50% of the first compartment.
(4)Where multiple tanks are to be used to meet the requirements of Sentences (2) and (3), the tanks shall be connected in series such that
(a)the first tank in the series shall have at least a capacity as calculated in Clause (3)(a), however at no time shall a tank having a working capacity of less than 3,600 L be used,
(b)all additional tanks after the first tank, excluding pump or dosing tanks shall have at least a working capacity equal to the volume required by Clause (3)(b),
(c)the pipe between the outlet of one tank and the inlet of the next tank in the series shall have a minimum slope of 2 percent,
(d)there shall be no partitions in the tank except where a partition is required to maintain the structural integrity of the tank, in which case openings within the partition shall be provided to allow the free movement of sanitary sewage throughout the tank, and
(e)all piping between tanks shall be continuous and shall be connected to the tank through the use of flexible watertight seals that will permit differential movement between the tanks.
(5)Partitions separating the septic tank into compartments shall extend at least 150 mm above the liquid level at the outlet, and there shall be one or more openings through or above the partition.
(6)The openings required between compartments referred to in Sentence (2) shall have a total cross-sectional area of at least three times the area of the inlet pipe and be located between the top and a level 150 mm above the liquid level at the outlet to provide for the free flow of air between compartments.
(7)Sanitary sewage shall pass from one compartment to another of the septic tank as follows:
(a)by means of a device similar to that described in CSA B66, "Design, Material, and Manufacturing Requirements for Prefabricated Septic Tanks and Sewage Holding Tanks" for outlet devices, or
(b)through two or more openings through the partition located in a horizontal line, and evenly spaced across the width of the partition, centred at approximately 40% of the liquid depth below the surface of the liquid, and having a total area of between three and five times that of the cross-sectional area of the inlet pipe.
(8)A septic tank shall be of such design and construction as will permit the collection and holding of sanitary sewage in it to a depth of not less than 1,000 mm, except that a depth of not less than 900 mm is permitted where the excavation is in rock, or to avoid rupture or displacement of the tank due to ground water pressure.
(9)Except as provided in Sentences (10) and (11), every septic tank shall be installed in such a manner that the access openings are located not more than 300 mm below the ground surface.
(10)Where the top of the septic tank is located more than 300 mm below the ground surface, it shall be equipped with risers that extend from the access opening of the septic tank to within 300 mm of the ground surface.
(11)Where risers are used they shall conform to the requirements of CSA B66, "Design, material, and manufacturing requirements for prefabricated septic tanks and sewage holding tanks," and shall have adequate access openings to allow for regular maintenance of the septic tank.
Open OBC Div. B 8.2.2.3. in the code viewer
OBC Div. B 8.2.2.4. Holding Tanks
(1)All holding tanks shall be of such design and construction as will allow the complete removal of solid matter that can be expected to settle in the holding tank through an apparatus or device suitable for allowing the contents of the holding tank to be removed from the holding tank.
(2)A holding tank shall have a working capacity of not less than 9,000 L.
(3)Where two or more tanks are used to meet the requirement of Sentence (2), they shall be deemed to be one holding tank provided they are connected in such a manner as will allow the sanitary sewage contained in them to flow between the tanks.
(4)The working capacity of the tanks described in Sentence (3) shall not include any portion of any tank that cannot be completely drained due to the manner in which the connections are made.
Open OBC Div. B 8.2.2.4. in the code viewer