Treatment Mounds

8. Treatment Mounds

 

See Pg. 197, Fig. Typical M 1 in Appendix "B"

8.1 Design Standard

1. the soil percolation rate to a depth of at least 600 mm (2 ft.) below the sand layer is faster than 120 minutes per 25 mm (1 in.), and
2. below the sand layer there is a layer of soil at least 300 mm (1 ft.) thick that has a percolation rate slower than 5 minutes per 25 mm (1 in.).

   Intent: Fill soil may be placed under the mound to provide the depth of suitable soil. The fill soil used should be a loamy sand to a sandy loam. Soil with a high percentage of clay content should not be used.

See Pg. 38, Article 7.1.6. for Vertical Separation Requirements.
See Pg. 178, Fig. Vertical Separation in Appendix "B"
See Pg. 182, Fig. DF 1B in Appendix "B"

1. have a surface area designed on the basis of not more than 50 L of effluent per square metre (1 gal per sq. ft.) per day loading rate,
2. have a surface area of not less than 37 square metres (400 sq. ft.),
3. be 3 m (10 ft.) wide or less, measured at the top of the sand layer,
4. be not less than 300 mm (1 ft.) thick, and
5. be on or above the existing soil.

Intent: Clause 8.1.2.(e) requires the mound to be built on the existing grade of the soil. Soil should not be stripped away creating a depression in the ground or be stripped away and replaced by fill material.

Making the sand layer narrower than 10 feet and longer can provide a better working and more effective mound.

See Pg. 198, Fig. M1 in Appendix "B"
See Pg. 199, Fig. M1b in Appendix "B"
See Pg. 200, Fig. M1c in Appendix "B"
See Pg. 51, Construction of Treatment Mounds in Appendix "B"
See Pg. 56, Article 8.3.2. for Sand quality requirements.
See Pg. 182, Fig. DF 1B in Appendix "B"

1. be at least equal to 70 percent of the trench bottom area determined by Article 7A.1.4. or Article 7A.1.5.,
2. when on a slope exceeding 1 percent, be measured downslope from the upslope side of the sand layer area receiving the effluent, and
3. be constructed of a loamy sand or sandy loam fill material.

Intent: The intent of this Article is to assure that an adequate area of soil is available for the effluent to infiltrate, that this area is fully covered by the berm, and that the permeability of the berm fill material is suitable to distribute the effluent over the infiltration area.

The infiltration area required under the treatment mound is 70 % of the area required for a disposal field because of the additional treatment of the effluent provided in the sand layer prior to the effluent entering the soil.

See Pg. 198, Fig. M1 in Appendix "B"
See Pg. 199, Fig. M1b in Appendix "B"
See Pg. 200, Fig. M1c in Appendix "B"
See Pg. 149, Sizing the Infiltration Area in Appendix "B"

1. a layer of gravel over the sand layer, or
2. chambers that provide an infiltrative area that is not less than 80% the designed area of the sand layer receiving the effluent.

See Pg. 198, Fig. M1 in Appendix "B"
See Pg. 199, Fig. M1b in Appendix "B"
See Pg. 200, Fig. M1c in Appendix "B"
See Pg. 202, Fig. M3 in Appendix "B"

1. the sand layer shall be covered with a minimum of 50mm (2 in.) of gravel, and
2. a pressure effluent distribution lateral on top of the gravel shall be provided for each row of chambers.

See Pg. 202, Fig. M3 in Appendix "B"
See Pg. 147, Treatment Mound Design in Appendix "B"

Intent: Smaller doses provide better treatment conditions. Doses may be smaller than 25%.

Note: Gravity distribution of effluent in a treatment mound is not permitted.

A treatment mound is a closed system that is sensitive to internal hydraulic pressures which can cause a breakout at the sides of the mound if hydraulically overloaded.

See Pg. 182, Fig. DF 1B in Appendix "B"

Note: Gravity distribution of effluent in a treatment mound is not permitted.

See Pg. 21, Article 3.1.8.

The minimum head pressure as specified in Pg. 73, Table A.1.B. in Appendix "A" is at the farthest point of the distribution laterals from the manifold.

Remember to consider pressure loss in effluent line to the treatment mound.

See Pg. 75, Table A.1.C.1 in Appendix "A" for friction loss in the effluent line between the septic tank and the treatment mound.

See Pg. 194, Fig. PDL 3 Squirt Test in Appendix "B"

See Pg. 138, Pressure Distribution Lateral Design in Appendix "B"

1. to direct the spray in a direction that will not cause erosion of the soil or sand layer, and
2. be provided with a device that will deflect the spray to prevent erosion of the soil above and the entry of foreign material into the orifice if the orifice is pointed upwards.

Intent: Orifices may be placed at the bottom of the piping to help drain the pipe and protect from freezing. Locating the orifice on the upper half of the pipe can help prevent clogging of the orifice. Wherever the orifices are located, there must be room for the water to escape and the spraying water must not cause any erosion of the soil or sand around it.

When the distribution laterals are installed in gravel, pointing the orifices down will not erode the sand layer. However, there is a greater possibility of orifice clogging and slightly uneven distribution of effluent.

If the orifices are pointed up, orifice shields must be provided to prevent gravel from laying on the orifice and restricting the flow or erosion of the soil above. Also, greater care must be taken to ensure the distribution lateral is graded to allow drainage. A few orifices can be drilled to point down to allow for drainage of the pipe.

If the distribution laterals are installed inside a chamber, the orifices must be pointed up to prevent erosion of the surface of the sand layer under the chamber.

See Pg. 201, Fig. M2 in Appendix "B"
See Pg. 193, Fig. PDL 2 in Appendix "B"
See Pg. 194, Fig. PDL 3 Squirt Test in Appendix "B"
See Pg. 140, Squirt Test in Appendix "B"
See Pg. 138, Pressure Distribution Lateral Design in Appendix "B"

8.2. Installation Standards

1. 1. 3 m (10 ft.) of a property line,
   2. 15 m (50 ft.) of a water source,
   3. 15 m (50 ft.) of a water course,
   4. 3 m (10 ft.) of a septic tank,
   5. 9 m (30 ft.) of a basement, cellar, or crawl space, and
   6. 3 m (10 ft.) of a building that does not have a basement, cellar, or crawl space.

2. For the purposes of Sentence 8.2.1.(1), all measurements are to be taken from the point where the side slope of the mound intersects with the natural soil contour.

See Pg. 38, Article 7.1.6. for Vertical Separation Requirements.
See Pg. 178, Fig. Vertical Separation in Appendix "B".

See Pg. 198, Fig. M1 in Appendix "B"
See Pg. 199, Fig. M1b in Appendix "B"
See Pg. 200, Fig. M1c in Appendix "B"
See Pg. 147, Treatment Mound Design in Appendix "B"

1. not less than 225 mm (9 in.) of gravel shall be placed over the contact area below the distribution laterals,
2. not less than 50 mm (2 in.) of gravel shall be placed over the distribution laterals, and
3. straw or equivalent fibrous material shall be placed over the gravel to an uncompacted depth of 75 mm to 100 mm (3 in. to 4 in.) to prevent the migration of soil into the gravel.

See Pg. 198, Fig. M1 in Appendix "B"
See Pg. 199, Fig. M1b in Appendix "B"
See Pg. 200, Fig. M1c in Appendix "B"
See Pg. 147, Treatment Mound Design in Appendix "B"

1. connected to a manifold pipe with all ends capped,
2. spaced not less than 900 mm (36 in.) and not more than 1000 mm ( 40 in.) on center,
3. located not less than 400 mm (16 in.) or more than 500 mm ( 20 in.) from the edge of the gravel layer, and
4. sized in accordance with Table A.1.A.

Treatment mounds may be constructed with the contact area between the gravel or chambers and the sand layer less than 3 m (10 feet) wide. When a longer, narrower treatment mound is desired, the number of distribution laterals can be reduced from 3 to 2. A treatment mound with only 2 distribution laterals would have a maximum width of the contact area between the gravel, or chambers, and the sand layer of 2 m (6.5 feet).

See Pg. 198, Fig. M1 in Appendix "B"
See Pg. 201, Fig M2 in Appendix "B"
See Pg. 202, Fig. M3 in Appendix "B"
See Pg. 193, Fig PDL 2 in Appendix "B"
See Pg. 138, Pressure Distribution Lateral Design in Appendix "B"

See Pg. 138, Pressure Distribution Lateral Design in Appendix "B"

Intent: To provide an adequate slope on the top of the treatment mound to prevent storm water from standing on the top of the mound.

See Pg. 198, Fig. M1 in Appendix "B"
See Pg. 199, Fig. M1b in Appendix "B"
See Pg. 200, Fig. M1c in Appendix "B"
See Pg. 147, Treatment Mound Design in Appendix "B"

Intent: A contractor meets the requirement of this Article by seeding the mound to grass, leaving the responsibility to water and maintain the grass cover to the owner. The grass cover is needed to prevent erosion of the mound and to assist in evaporating the effluent.

See Pg. 198, Fig. M1 in Appendix "B"
See Pg. 199, Fig. M1b in Appendix "B"
See Pg. 200, Fig. M1c in Appendix "B"
See Pg. 147, Treatment Mound Design in Appendix "B"

See Pg. 198, Fig. M1 in Appendix "B"
See Pg. 199, Fig. M1b in Appendix "B"
See Pg. 200, Fig. M1c in Appendix "B"
See Pg. 147, Treatment Mound Design in Appendix "B"

8.3 Requirements for Materials

1. be smooth, rigid plastic piping, and
2. be certified for a pressure application by a testing agency recognized by the Standards Council of Canada, or acceptable to an Administrator.

See Pg. 201, Fig. M2 in Appendix "B"
See Pg. 193, Fig. PDL 2 in Appendix "B"
See Pg. 138, Pressure Distribution Lateral Design in Appendix "B"

See Pg. 51, Article 8.1.2.

See Pg. 147, Treatment Mound Design in Appendix "B"