Div. B › Part 8 › 8.7 › 8.7.8 — Type B Dispersal Beds

8.7.8.2 — Construction Requirements

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(1) The treatment unit used in conjunction with a leaching bed constructed as a Type B dispersal bed shall provide an effluent quality that does not exceed the maximum concentrations set out opposite a Level IV treatment unit in Columns 2 and 3 of Table 8.6.2.2.

(2) A Type B dispersal bed shall be,

(a) rectangular in shape with the long dimension parallel to the site contours,

(b) not more than 1 000 mm in depth measured from the bottom of the stone layer to the finished grade when installed in soil with a percolation time that exceeds 15 min, and

(c) backfilled with leaching bed fill so as to ensure that, after the leaching bed fill settles, the surface of the leaching bed will not form any depressions.

(3) The bottom of the stone layer shall be at least 600 mm above the high ground water table, rock or soil with a percolation time greater than 50 min.

(4) The effluent shall be distributed over the Type B dispersal bed through a pressurized distribution system having a pressure head of not less than 600 mm when measured to the most distant point from the pump.

(5) The distribution pipes shall,

(a) be self-draining so as to prevent freezing of their contents, and

(b) have orifices of at least 3 mm in diameter, spaced equally along the length of the pipes.

(6) The stone layer containing the distribution pipes shall,

(a) be comprised of washed septic stone, free of fine material, with gradation conforming to Table 8.7.3.3.,

(b) extend not less than 250 mm below the distribution pipe, and

(7) The distribution pipes shall be spaced not more than 1.2 m apart with the outermost pipe spaced not more than 600 mm from the edge of the bed.

(8) The pump chamber shall be sized to provide sufficient storage volume so that the effluent is evenly dosed on an hourly basis over a 24-hour period.

(9) When there is more than one Type B dispersal bed in a leaching bed, the Type B dispersal beds shall be separated by at least 5 m measured from the edge of the stone layers.

(10) A Type B dispersal bed 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).

Tables & Figures referenced

Table 8.2.1.6.B : Minimum Clearances for Distribution Piping and Leaching Chambers : Forming Part of Sentence 8.2.1.6.(2)

Loading Table 8.2.1.6.B…

Table 8.6.2.2 : Other Treatment Unit Effluent Quality Criteria : Forming Part of Sentences 8.6.2.2.(1) and (2)

Loading Table 8.6.2.2…

Table 8.7.3.3 : Gradation of Septic Stone : Forming Part of Sentences 8.7.3.3.(5) and 8.7.8.2.(6)

Loading Table 8.7.3.3…

OBC Definitions

Defined terms on this page

chamber

means a structure in a shallow buried trench that is constructed with an open bottom and that contains a pressurized distribution pipe.

distribution pipe

means a line or lines of perforated or open jointed pipe or tile installed in a leaching bed for the purpose of distributing effluent from a treatment unit to the soil, as defined in Part 8 of Division B, or leaching bed fill in the leaching bed.

effluent

means sanitary sewage that has passed through a treatment unit.

fill

means soil, rock, rubble, industrial waste such as slag, organic material or a combination of these that is transported and placed on the natural surface of a soil or rock or organic terrain; it may or may not be compacted.

grade

means the average level of proposed or finished ground adjoining a building at all exterior walls.

ground water

means , when applied to a sewage system, water below the surface of the ground that occupies a zone of the earth’s mantle that is saturated with water.

ground water table

means , when applied to a sewage system, the elevation of the upper surface of the ground water existing in the area of the sewage system.

high ground water table

means the highest elevation at which there is physical evidence that the soil, as defined in Part 8 of Division B, or the leaching bed fill has been saturated with water.

leaching

means dispersal of liquid by downward or lateral drainage or both into permeable soil, as defined in Part 8 of Division B, or leaching bed fill.

leaching bed

means an absorption system constructed as absorption trenches or as a filter bed, located wholly in ground or raised or partly raised above ground, as required by local conditions, to which effluent from a treatment unit is applied for treatment and disposal and that is composed of, (a)the soil, as defined in Part 8 of Division B, leaching bed fill or other filter media that is contained between the surface on which the sanitary sewage is applied and the bottom of the bed, (b)the leaching chamber or the distribution pipe and the stone or gravel layer in which the distribution pipe is located, and (c)the backfill above the distribution pipe or the leaching chamber, including the topsoil and sodding or other anti-erosion measure, and the side slopes of any portion elevated above the natural ground elevation.

leaching 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.

leaching chamber

means a formed structure with an open bottom and permeable sidewalls installed in a leaching bed for the purpose of distributing effluent from a treatment unit to the soil, as defined in Part 8 of Division B, or leaching bed fill in the leaching bed.

percolation time

means the average time in minutes that is required for water to drop one centimetre during a percolation test or as determined by a soil evaluation or analysis.

potable

means fit for human consumption.

pressurized distribution system

means a leaching bed in which the effluent is distributed through the use of pressurized distribution pipes.

rock

means a portion of the earth’s crust that is consolidated, coherent and relatively hard and that is a naturally formed, solidly bonded, mass of mineral matter that cannot readily be broken by hand.

soil

means , except for the purposes of Part 8 of Division B, a portion of the earth’s crust that is fragmentary or such that individual particles of a dried sample may be readily separated by agitation in water, and includes boulders, cobbles, gravel, sand, silt, clay and organic matter.

treatment unit

means a device that, when designed, installed and operated in accordance with its design specifications, provides a specific degree of sanitary sewage treatment to reduce the contaminant load from that of sanitary sewage to a given effluent quality.

type b dispersal bed

means a leaching bed comprised of a pressurized distribution system that uniformly distributes effluent from a Level IV treatment unit as described in Table 8.6.2.2. of Division B to the underlying soil, as defined in Part 8 of Division B, through a set of distribution pipes installed in a bed comprised of septic stone.

construct

to do anything in the erection, installation, extension or material alteration or repair of a building and includes the installation of a building unit fabricated or moved from elsewhere; Act

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