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BCC Ruling No. 99-23-679

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IN THE MATTER OF Subsection 24 (1) of the Building Code Act, 1992.

AND IN THE MATTER OF Clause of Regulation 403, as amended by O. Reg. 22/98, 102/98 and 122/98 (the "Ontario Building Code").

AND IN THE MATTER OF an application by Mr. Robert Hicks, homeowner, RR #2, Kingsville, Ontario, for the resolution of a dispute with Mr. Kevin Carter, Chief Building Official, , Town of Essex, Ontario to determine whether the proposed leaching bed with absorption trenches having only a vertical separation of 300 mm and soil with a percolation rate of 125 minutes per cm provides sufficiency of compliance with Clause of the Ontario Building Code at Part of Lot 18, Concession 6, Town of Essex, Essex County, Ontario.


Mr. Robert Hicks
Kingsville, Ontario


Mr. Kevin Carter
Chief Building Official
Town of Essex


Mr. Roy Philippe (Chair)
Mr. Doug Robinson
Mr. Bryan Whitehead


Toronto, Ontario


April 15, 1999


April 15, 1999


Mr. Ken Dickson
Dickson Environmental Consulting
Wallaceburg, Ontario
Agent for the Applicant

Mr. Kevin Carter
Chief Building Official
Town of Essex
The Respondent


  1. The Applicant

Mr. Robert Hicks, homeowner, Kingsville, Ontario, has applied for a building permit under the Building Code Act, 1992 to install a new Class 4 sewage system at Part of Lot 18, Concession 6, Town of Essex, Essex County, Ontario.

  1. Description of Construction

The Applicant is proposing to install a new Class 4 sewage system to serve a single, detached Group C - residential dwelling. The proposed dwelling will contain three bedrooms, three bathrooms, have 28 fixture units, and a total finished floor area of 178 m2. The calculated total daily design sewage flow rate will be 2,000 litres per day. The subject dwelling unit is currently under construction.

The proposed new sewage system would consist of a 2,300 litres per day DF60FF Whitewater tertiary treatment unit connected directly to the residence that would transmit effluent to a free access sand filter, which in turn would be connected to a Zabel A300 effluent filter. From there the sewage would flow to a single chamber pump chamber. The effluent would move through these components of the system by means of gravity disposal. From the pump chamber, however, it would be time dosed into the trenches of the disposal bed.

The raised disposal bed and surrounding mantle, set back 5 m from the dwelling, will have a total hydraulic footprint of 762 m2 and will be constructed of imported sand with a percolation rate of approximately 8 minutes per centimetre set on scarified native clay. With a contact area of 762 m2 and a daily flow rate of 2,000 L/d, the application, or loading, rate is calculated at roughly 2.6 litres/m2/day. The proposed raised bed is to have an area of 271 m2 (24.2 m by 11.2 m) and will be 600 mm in height. Using the T-time of 8 min/cm of the imported fill, the length of distribution pipe was calculated to be 30 m and will be laid out in two parallel 15 m trench runs set at depth of 300 mm above the native clay.

The trenches will be located 2 m apart on centre, while the 1:4 slope surrounding the raised bed will commence at distance of 1 m from all sides of the trenches. The chambers set in the trenches would consist of the pressurized distribution pipe resting on 18 mm to 60 mm washed stone. The trench chambers would be covered with a filter cloth. The surrounding mantle will have a one per cent slope from north to south and as a result it will be 3.1 m in width, except to the south of the raised bed where it will be at least 15 m. A driveway encircling the house and sewage system would act as a berm on the north and east side of the mantle.

The site is described as level and covered with trees and low ground cover. The native soil is ranges from 75 to 200 mm in depth. Beneath it is a deep layer of clay with a percolation rate of at least 125 minutes per centimetre, as confirmed by three test holes.

The subject dwelling is served by a well water system.

  1. Dispute

The issue at dispute between the Applicant and Respondent is whether the proposed 600 mm raised leaching bed with absorption trenches having a vertical separation of only 300 mm above soil with a percolation rate of at least 125 minutes per centimetre complies with Clause of the Ontario Building Code. This provision requires that the bottom of the trenches of a shallow buried trench leaching bed system must provide a vertical separation of 900 mm above rock or the high ground water table. It is silent, however, on whether this separation applies also between the bottom of a shallow buried trench and soil with a T-time of more than 125 min/cm. Since the Applicant is proposing only a total of 600 mm of imported fill for the entire raised bed, the subject trenches, at 300 mm above the clay, would not appear to comply if a 900 mm vertical separation is required.

  1. Provisions of the Ontario Building Code

Clause Absorption Trenches

(2) Absorption trenches constructed as shallow buried trenches shall be

(e) at least 900 mm at all points on the bottom of the absorption trench above the high ground water table or rock, and

  1. Applicant's Position

The Applicant submitted the proposed leaching bed with a 300 mm vertical separation complies with the construction requirements for absorption trenches as set out in OBC Sentence Clause, he argued, does not deal with vertical separation from soil, including that with a T-time of greater than 125 min/cm. The result is that this provision of the Code was not applicable to the proposed sewage system. As the Applicant noted, Sentence (1) of the same OBC Article in dispute clearly specifies that the vertical separation from the bottom of absorption trenches in a conventional Class 4 system (i.e. a non-shallow buried trench system) to soil with a particular T-time must be 900 mm. The fact that the Code is silent on the vertical separation from soil in a shallow buried trench system, the Applicant contended, is proof that one is not required.

Regarding the overall design of his system, the Applicant also argued that the length of distribution pipe, calculated by using the 8 min/cm T-time of the imported sand fill, is also appropriate rather than that of the impermeable clay. Again, as he noted, Clause does not refer to a vertical separation to soil, therefore making the requirement to utilize the least permeable soil when calculating the length of distribution pipe also irrelevant. Moreover, as the Applicant indicated, the size of the leaching bed including mantle, allows for a loading rate of approximately 2.6 L/m2 per day, which is well under the maximum rate of 6 L/m2 stipulated in Article At this application rate, there should be no horizontal movement of effluent beyond the bed area.

The Applicant also argued that his proposal made sense when considering the nature of sewage systems equipped with shallow buried trench-type leaching beds. In his view, because such systems are required to provide tertiary treatment units, the nature of filtration in the distribution bed is quite different from conventional Class 4 systems. Whereas the quality of effluent in a conventional, untreated system that reaches the tile bed is poor, in a treated, shallow buried trench system the quality of effluent dosed into the chambers is high. This significant difference means that the beds are required to function much differently. In a conventional Class 4 system, the Applicant argued, the 900 mm vertical separation also includes from soil because that amount of material is required to accomplish much of the actual filtration and treatment. On the other hand, this filtration and treatment is mostly done in the tertiary treatment unit of a shallow buried-type system, making the larger separation unnecessary. As the Applicant indicated, in a shallow buried-type system most of the disposal is done close to the surface and relies upon the plant roots and earthworm channels to move effluent laterally.

  1. Respondent's Position

The Respondent submitted that the vertical separation is required for the proposed sewage system. In his view, while the Code is not specifically clear on the 900 mm separation from soil, nonetheless that is its intent. As he noted, if vertical separations were not necessary for shallow buried trench-type disposal systems, as the Applicant previously argued, then why does Clause contain any such requirements with respect to the high ground water table and rock? The Respondent argued that the type of clay in the area (described as "bullet proof clay") is essentially like rock and would react as rock. He therefore believes it should be treated the same way under the Code, i.e. provided with a 900 mm separation. The Respondent indicated that separation to soil was perhaps inadvertently omitted in the recent drafting of the Code, but it is a consistent requirement throughout Part 8.

  1. Commission Ruling

It is the decision of the Building Code Commission that the proposed leaching bed with absorption trenches having a vertical separation of 300 mm above soil with a percolation rate of greater than 125 minutes per centimetre provides sufficiency of compliance with of the Ontario Building Code provided that:

i) A tertiary treatment unit including a sand filter is provided prior to the discharge to the leaching bed;

ii) Scientific calculations on lateral flow through the imported soil are provided to demonstrate that the water level in the leaching bed will be maintained below the trench bottom; and,

iii) The imported soil meets the minimum design requirements established in Item 2.

  1. Reasons

i) The Building Code is silent on the distance between the bottom of the shallow buried trenches and soil with a percolation rate in excess of 125 minutes.

ii) A tertiary treatment unit is provided and the soil is not considered part of the treatment system.

iii) The use of sufficiently permeable imported sand will ensure proper distribution of the effluent over the entire bed and mantle area, ensuring that the effluent level remains below the trench bottoms.

Dated at Toronto this 15th day in the month of April in the year 1999 for application number 1999-13

Mr. Roy Philippe, Chair

Mr. Doug Robinson

Mr. Bryan Whitehead