Appendix B

Table of Contents

1.	Scope	6.	Packaged Sewage Treatment Plants		Appendix A
2.	Definitions	7.	Effluent Treatment and Disposal		Appendix B
3.	General	8.	Treatment Mounds		List of Figures
4.	Piping	9.	Sand Filters
5.	Septic, Holding, and Effluent Tanks	10.	Open Discharge System
		11.	Sewage or Effluent Lagoons

Appendix "B"

Connection to Municipal Sewer or Private Sewage System

The Alberta Building Code 1997 states:

7.2.1.15. Sewer Hookup
1) Building Sewers shall discharge into a public sewage system where such a system is available at the time of construction.

7.2.1.16. Private Disposal
1) Where a public sewage system is not available, the building sewer shall discharge into a private sewage disposal system.

This article in the building Code requires that where available the building shall be connected to a municipal or public sewer. The determination that the public sewer is available, is made by the municipality or owner of the public sewer.

See Pg. 19, Article 3.1.2

Piping

Whenever possible, all piping must be CSA "Certified", or certified by a recognized testing agency accepted by the Standards Council of Canada, to meet or exceed the requirements of the appropriate CSA standard for its intended use. See Pg. 30, Article 4.3.2.

However, there are applications within Private Sewage Systems where there is no existing certification standard for the intended use of the piping. In these applications, acceptance must be given to materials that have been used and proven to be suitable for their intended use in the past. See Pg. 27, Article 3.3.1 Pg. 29, Article 4.3.1 and Pg. 30, Article 4.3.3. See Pg. 93, Table A.5.A. in Appendix "A" for a listing of acceptable piping materials.

For pressure applications, a piping certified for a pressure application must be used.

Building Drain

The building drain is the piping which conducts the sewage from within the building to a point 1 m (3.25 ft.) outside the building. In many cases, the building drain connects directly to the septic tank, sewage holding tank or packaged sewage treatment plant.

Piping requirements for the Building Drain are provided in the National Plumbing Code and not addressed in the Private Sewage Systems Standard of Practice.

In general terms, if the plumbing system serves no more than three bathrooms (along with the kitchen and laundry fixtures), it is possible that the building drain may be 75 mm (3 inch) piping to the septic tank, holding tank or packaged sewage treatment plant. A 75 mm (3 inch) building drain should be graded at not less than 2% (1/4 inch per foot). A 100 mm (4 inch) building drain should be graded at not less than 1% (1/8 inch per foot).

Building Sewer

The building sewer connects to the building drain at a point 1 m (3.25 ft.) outside the building and may extend to the property line, a sewage lagoon or connect to a septic tank, packaged sewage treatment plant or sewage holding tank. Only the first 1800 mm (6.0 ft.) of the building sewer up stream of a septic tank, holding tank, packaged sewage treatment plant or sewage lagoon are addressed in the Private Sewage Systems Standard of Practice regarding wall thickness and frost protection. Piping requirements for the Building Sewer are provided in the National Plumbing Code and are not addressed in the Private Sewage Systems Standard of Practice. Extended "Y" cleanouts must be installed at intervals to accommodate cleaning. Intervals between cleanouts of not more than 26 m (85 feet) is recommended for a 100 mm (4 inch) building sewer.

Effluent Sewer

The gravity effluent sewer may connect to the outlet of a siphon type septic tank, packaged sewage treatment plant or sand filter and conveys effluent to an effluent disposal component. An effluent sewer may also extend from inside an access opening extension, for ease of access and connection to the pump discharge line. See Pg. 174, Fig. Pumps 4 and Pg. 175, Fig. Pumps 5 in Appendix "B". A gravity effluent sewer may be 75 mm (3 inch) or 100 mm (4 inch) pipe, and should be laid on an even continuous grade of not less than 2% (1/4 inch per foot) if 75 mm(3 inch), and 1% (1/8 inch per foot) if 100 mm (4 inch).

If plastic pipe is used, it must be not lighter than D.W.V. (1/4" wall thickness) within 1.8 m (6 feet) of the tank or access opening extension and preferably until it rests on solid, undisturbed ground. See Pg. 29, Article 4.2.6. . If the effluent sewer must cross under such a bare spot, provide frost protection. See Pg. 165, Fig. Frost 1. in Appendix "B".

Effluent Line

An effluent line is a pump discharge line. This line carries effluent from a pump chamber to an effluent disposal system component and may be polyethylene pipe or rigid plastic piping certified for a pressure application. Pipe size may vary in diameter from 18 mm (3/4 inch) to 50 mm (2 inch) depending on it's application. Piping used for this application must be certified for the pressure it carries and usually has at least a 500 kpa (75 psi) rating. All fittings used with polyethylene pipe should be durable and rated for the operating pressure of the line. Fittings most often used are nylon or stainless steel and clamps should be of all stainless steel construction.

Weeping Lateral Piping

Gravity Lateral

Gravity weeping lateral piping is lengths of perforated piping in a disposal field. The manufacturers of certified perforated piping provide a label or identification on the pipe at the top centre when the pipe is in it's proper installed position. Plastic piping may be smooth as in the case of ABS or PVC piping certified as complying with the CAN/CSA B182.1 standard or, it may be corrugated polyethylene complying with CGSB-41-GP-31. Gravity perforated piping is always installed level, and always installed in gravel or other equivalent weeping lateral trench media. See Pg. 48, Article 7.A.3.1, Pg. 48, Article 7.A.3.2, Pg. 49, Article 7.A.3.3. and Pg. 180, Fig. DF 1 in Appendix "B"

Pressure Distribution Lateral

Pressure distribution laterals are usually constructed of PVC schedule 40 plastic piping not smaller than 19 mm (3/4 inch) or larger than 50 mm (2 inch). The orifices in the laterals are drilled as required for the particular installation and are not smaller than 3.2 mm ( in.). The size and spacing of the perforations is dependant upon the length of the lateral See Pg. 69, Table A.1.A. in Appendix "A", and the amount of effluent to be discharged in a specific period of time, depending on pump head pressure. See Pg. 73, Table A.1.B. in Appendix "A".

To test the design of the pressure distribution lateral a squirt test can be used. See Pg. 194, Fig. PDL 3 Squirt test.

When using pressure distribution laterals there are additional requirements for septic tank sizing and pump screen requirements. See Pg. 31, Article 5.1.1 and Pg. 44, Article 7A.1.9 (f) .

Extreme care and caution must be exercised in the design of a pressure distribution lateral pipe system to assure adequate volumes and avoid excessive pressure loss. This will ensure the objective of even distribution of effluent throughout the entire length of individual weeping lateral trenches. See Pg. 44, Article 7.A.1.9. and Pg. 69, Table A.1.A. in Appendix "A". See Pg. 138, Pressure Distribution Lateral System Design in Appendix "B"

In all cases use straight lengths of piping approved for pressure applications. Piping that comes in a coil is not acceptable.

Distribution Laterals in a Treatment Mound

Pressure distribution laterals for a treatment mound are usually constructed of PVC plastic piping not smaller than 19 mm (3/4 inch) or larger than 50 mm (2 inch). The orifices in the laterals are drilled as required for each installation and are not smaller than 3.2 mm ( in.). The size and spacing of the perforations is dependant upon the length of the lateral See Pg. 69, Table A.1.A. in Appendix "A", and the amount of effluent to be discharged in a specific period of time, depending on pump head pressure. See Pg. 73, Table A.1.B. in Appendix "A". Extreme care and caution must be exercised in the design and manufacture of laterals to obtain even distribution of effluent throughout the treatment mound. The effluent pump must be provided with a suitable screen to prevent smaller particles from being discharged into the system and cause plugging of the orifices. See Pg. 21, Article 3.1.8.. See Pg. 138, Pressure Distribution Lateral System Design in Appendix "B".

Pressure Distribution Laterals Within a Sand Filter

Piping for an effluent distribution system in a sand filter is required to be smooth, rigid plastic piping that is certified for a pressure application. The piping may be as small as 19 mm (¾ in.) and is drilled to provide orifices which may not be smaller than 3 mm ( in.). The design of the system should provide adequate pressure and volumes for equal distribution of the effluent over the complete sand filter surface area and maintain a specified minimum pressure at the end(s) of the distribution system piping. See Pg. 69, Table A.1.A. in Appendix "A".

Because of the small diameter of the orifices, the effluent pump must be provided with a suitable screen to prevent smaller particles from being discharged into the system and cause plugging of the orifices.  See Pg. 21, Article 3.1.8.. See Pg. 138, Pressure Distribution Lateral System Design in Appendix "B".

Laying Sewer Pipe

All gravity sewer piping must be graded and water-tight. Lay pipe on a firm trench bottom, and carefully compact the backfill on the sides of the piping to prevent the piping from becoming oval shaped or breaking under the weight of the backfill above it. Maintain an even and constant rate of fall. Sags cause blockages in the pipe. See Pg. 28, Article 4.1.2, Pg. 28, Article 4.1.3, Pg. 28, Article 4.1.4, Pg. 29, Article 4.2.5, Pg. 29, Article 4.2.6

See Pg. 164, Fig. Pipe 1, Pg. 168, Fig. Tanks 2, Pg. 170, Fig. Tanks 4 in Appendix "B"

Frost Protection

Freezing of Systems

A properly installed treatment and disposal system has an excellent chance of surviving even the most extreme winters if a few simple precautions are taken.

Do not allow any household sewage to bypass the septic tank. Systems which do not receive bathroom sewage or hot water are more likely to freeze. See Pg. 21, Article 3.1.7. and Pg. 22, Article 3.1.10.

Insufficient earth cover on the septic tank may admit air and frost to the contents. The result will be a decrease in bacterial activity and a colder effluent that may freeze in the effluent treatment and disposal system. The admission of chemicals or antiseptics may have a similar effect.

Where the septic tank is installed at or above the normal ground level (as may be the case with a siphon type of septic tank), and is located within 1 m (3.25 ft.) from the building, frost protection may be provided by 450 mm to 600 mm (1 ½ to 2 feet) of mounded earth cover.

Note: In cases where it is necessary to locate the septic tank or packaged sewage treatment plant some distance from the house, and the building sewer requires protection, the frost box should terminate 1 m (3.25 ft.) from the building wall. If carried to the wall, it may conduct odours to the building. Tamp clay tightly around the building drain for this 1 m (3.25 foot) space to the wall.

Siphon or pump chambers assist with frost prevention by saving up the effluent and then flushing it rapidly past cold sections whereas, a trickle system has proven to be far more likely to freeze.

The liberal use of clean course gravel or similar media in weeping lateral trenches provides a dead air space and some insulating qualities. It allows the effluent to leave the weeping lateral piping quickly which greatly assists in the prevention of frozen disposal fields.

Chamber type disposal fields are also installed in Alberta. Temperatures inside the chamber trenches were monitored and indicate there is little chance of a freezing hazard.

Protecting Sewers From Frost And Traffic

All gravity sewer piping located under a driveway, road, path, or bare yard, with less than 1.2 m (4 feet) of earth cover, should be protected by a "frost box." See Pg. 28, Article 4.2.1. See Pg. 165, Fig. Frost 1. in Appendix "B".

Pressure effluent lines may require more protection against frost because of their small diameter and the possibility of containing effluent at all times. If they are not installed well below frost level, extreme care must be taken during their installation to prevent sagging and trapping of effluent. This will allow for complete drainage of the piping between pump cycles. Frost protection suitable for water service piping must be considered if the pipe does not drain.

Septic Tanks And Sewage Holding Tanks

Septic Tank

A septic tank or sewage holding tank must be CSA certified and/or constructed and tested in accordance with the CAN/CSA-B66-M90 Standard by a recognized testing agency. The term "septic tank" is a generic term that is commonly misused. Modern "septic tanks" may be manufactured in a number of different configurations. All "septic tanks" must have one or more septic chambers and may have an integral or external effluent chamber to accommodate a syphon or pump included in their design. See Pg. 166, Fig. Tanks 1 and Pg. 167, Fig. Tanks 1a in Appendix "B"

Purpose

The septic chamber is essentially a water-tight storage container into which raw sewage is discharged and retained for 24 hours or more. It's purpose is primarily to allow solids in the sewage to settle out (sludge) or to float (scum) thereby permitting the liquid portion of the sewage to leave the chamber comparatively free of settleable and floating solids.

Sewage which has emerged from a septic chamber is termed " Effluent." The subject of sewage treatment and disposal falls into two distinct stages:

• (a) the retention and digestion of floating and settleable solids in the septic chamber; and
• (b) the safe treatment and disposal of the effluent.

How The Septic Chamber Works

It is imperative that the septic tank owner thoroughly understands the dangers related to sewage.

The septic chamber largely accomplishes it's purpose through the digestion of the sewage by anaerobic bacteria. These anaerobes are present in body wastes. They thrive in an environment which is warm, wet, dark and devoid of fresh air. The septic chamber simply allows the sewage to rest for a 24 hr. period under these conditions, so that rapid multiplication of bacteria takes place.

This digestion will establish itself spontaneously in a tank receiving normal household sewage providing temperatures are not extreme and the proper environmental conditions exist. Tanks started in cold weather should be partially or totally filled with hot water to assist the growth of anaerobic bacteria.

Use of The Septic Tank

All normal household wastes including the bath, water closet, basin, kitchen sink, and laundry must discharge to the septic tank. Appreciable amounts of lye, strong caustics, acids, disinfectants and other materials which are likely to adversely affect the development of bacteria, should not be admitted to the septic tank. Small amounts of hypochlorite or household bleaches such as those used to disinfect water supplies or to sterilize dishes will not reduce the septic action, but the continual admission of small amounts or single large amounts may be detrimental.

Rain water, and seepage water should not be admitted to the system. Any excessive volume of cold water from any source may wash away and seriously deplete the bacteria population in the tank as well as lowering the operating temperature. See Pg. 32, Articles 5.1.4, , Pg. 33, Article 5.2.4 , Pg. 36, Article 6.2.4

Laundries, hospitals, large public kitchens, etc., may be expected to contribute volumes of wastes which would be better handled by a separate system and may also require specialized treatment due to increased sewage strength. An engineer should be consulted in these or any other unusual cases. See Pg. 19, Article 3.1.2, and Pg. 21, Article 3.1.7

Location of The Septic Tank

See Pg. 32, Article 5.2.1.,Pg. 32, Article 5.2.2

The prime considerations in locating a septic tank are:

1. Protection of the potable water supply. The septic tank is considered to be a water-tight component of the disposal system, however piping connections, access cover extensions, etc. may be subject to leakage after installation due to settling or other reasons. See Pg. 32, Articles 5.1.4, and Pg. 33, Article 5.2.4.
2. The type of septic tank being used (pump or siphon). See Pg. 166, Fig. Tanks 1, Pg. 168, Fig. Tanks 2, Pg. 169, Fig. Tanks 3, Pg. 171, Fig. Pumps 1, Pg. 172, Fig. Pumps 2 and Pg. 173, Fig. Pumps 3. in Appendix "B".
3. The depth of bury over the septic tank. The maximum depth of bury over a septic tank is specified by the tank manufacturer. You may wish to consider locating the septic tank a remote distance from the house to avoid excessive depth of bury or additional costs of access cover extensions versus frost protection. See Pg. 169, Fig. Tanks 3, See Pg. 170, Fig. Tanks 4, and Pg. 165, Fig Frost 1 in Appendix "B".
4. Access for cleaning. The general planning should be to locate the septic tank adjacent to the bathroom, on the opposite side of the house from the water supply, and where it is readily accessible for cleaning. Keep in mind that the septic tank must be cleaned periodically and must be accessible to a vacuum truck.
   

To Select The Size of The Septic Tank

The minimum "working capacity" of a septic tank shall not be less than 1800 litres (400 Imperial gallons).

For single family dwellings and duplexes see Pg. 31, Article 5.1.1..

Note: Manufacturer's model number designation of their septic tanks do not necessarily indicate the "Working Capacity" of their products, therefore, caution must be exercised when sizing a septic tank.

For other than single family dwellings or duplexes refer to the Pg. 22, Article 3.1.14. to determine the expected volume of sewage per day. The total expected volume of sewage per day shall determine the minimum "working capacity" of the septic tank.

The "working capacity" of the septic tank means the liquid volume of sewage that will remain in the septic chamber(s) when the tank is in normal use, but does not include the air space, siphon, pumping, or effluent chamber. It is important to note that when reference is made to sizes and capacities of tanks, one should not consider the volume of the siphon or pump chamber in these figures.

 Click to see larger Image

There are septic tanks that have the septic chamber divided into two compartments. The total volume of these two compartments are combined to become the "working capacity" of the septic chamber. The use of these tanks would also require either an integral effluent chamber or a separate, external effluent chamber.

Effluent disposal systems such as - sand filters; treatment mounds; or disposal fields that are designed to distribute effluent throughout the entire length of the weeping lateral trench; utilize a smaller diameter pressure distribution piping system having orifices spaced along the distribution lateral pipe.( See Pg. 11, definition distribution lateral pipe). To reduce the risk of these small orifices becoming clogged, a septic tank serving one of these systems must have a minimum "working capacity" of 2700 L (600 Gal.) and be a minimum of 1.5 times the expected volume of sewage per day.

To accommodate waste from garbage grinders, septic tanks should have their "working capacity" increased by 50% or the tank should be cleaned more often to remove the sludge that accumulates at a faster rate.

Types of Septic Tanks

Numerous prefabricated septic tanks are available in various types and sizes suitable for domestic use:

1. Single chamber trickle tanks, Note: Single chamber trickle tanks may not be used alone, but may be used in conjunction with other septic tanks.
2. Double chamber, pump (a septic chamber and an effluent chamber that accommodates a pump),
3. Double chamber, syphon (a septic chamber and an effluent chamber that contains a syphon)

The shapes are often a rectangular box however, they may be a horizontal or vertical cylinder, or a sphere. They are manufactured from durable materials such as concrete, fibreglass, polyethylene and steel.

Septic tanks must be sized to accommodate the estimated sewage flow. Where a large tank is not available, several smaller tanks may be installed in series to provide the working capacity required. See Pg. 191, Fig. DF 13 in Appendix "B".

Single Chamber (Trickle Type) Septic Tanks

A single chamber septic tank may not be used to trickle effluent directly into an effluent disposal system. The distribution of effluent is very difficult and the system will be subject to freezing with trickle tanks. See Pg. 20, Article 3.1.3. Trickle type septic tanks are generally limited to the uses shown in Pg. 191, Fig. DF 13 in Appendix "B".

Double Chamber (Pump or Siphon) Septic Tanks

The septic chamber or settling chamber must hold not less than 1800 litres (400 Imperial gallons) of sewage. This is referred to as the "working capacity" of the septic tank. The second chamber in a septic tank is referred to as the "effluent chamber."

Effluent Chamber - (Siphon or Pump) - Purpose

An effluent chamber may be constructed as an integral part of the septic tank, or as a separate external chamber which receives effluent from a septic chamber of a septic tank or packaged sewage treatment plant. An effluent chamber is a desirable component of a private sewage system and depending on the other private sewage system components, may be expected to perform a number of functions.

In conjunction with a standard septic tank and disposal field, the effluent chamber by storing the effluent and then discharging it rapidly and intermittently provides:

1. a more even distribution of effluent throughout the disposal field,
2. the important rest period for aeration of the disposal field, and
3. some protection against freezing. See Pg. 20, Article 3.1.3.
   

Capacity of Effluent Chambers

The volume of discharge from the effluent chamber varies in size with the capacity of the effluent chamber, and whether the effluent chamber is provided with a syphon or a pump.

It is not always possible to obtain a septic tank with the ideal size of effluent chamber or volume per flush. The volume per flush from the effluent chamber should be adequate to flush between 6 L and 12 L per square metre (0.07 to 0.25 gal. per square foot) of weeping lateral trench in a disposal field served with a septic tank with no other pretreatment. See Pg. 43, Article 7A.1.6

It is however possible to adjust the location of the pump controls to set the pump to turn on and off at specific levels to discharge a measured amount of effluent as required. In siphon type septic tanks or pump type septic tanks having small effluent chambers, it may be advisable to consider the installation of a Split field to better match the volume per flush with the square metres (square feet) of weeping lateral trench. Please refer to the Disposal Field section for information regarding Split Fields.

For larger installations, it may be necessary to install another tank after the septic tank(s) to act as a separate effluent chamber and provide a sufficient volume of effluent per flush into the effluent disposal system. Here again the split field or sequential pressure distribution lateral dosing may be considered. See Pg. 196, Fig. PDL 5 and Pg. 191, Fig. DF 13 in Appendix "B".

In a system that uses a treatment mound, the volume per flush should not exceed 25% of the expected volume of sewage per day into the treatment mound.

In more advanced and large treatment systems, the effluent chamber may be required to be of a size capable of storing the equivalent of the expected volume of sewage per day. A timer may be required to control a pump which may discharge smaller volumes of effluent to an effluent treatment component in equal timed doses, many times a day.

Elevations

One disadvantage of a siphon tank is the loss of elevation between the inlet and the outlet. See Pg. 168, Fig. Tanks 2 in Appendix "B". The loss in elevation in a septic tank with siphon varies widely from about 20 inches to 32 inches depending upon the size and design of the siphon.

Pg. 168, Fig. Tanks 2 in Appendix "B", illustrates why, in a level area, the building drain must be located at, or above, ground level if the discharge pipe from the siphon chamber is to be at a level which will provide a shallow installation depth not exceeding 600 mm (24 inches) from the top of the weeping lateral piping to the ground surface. To provide cover for septic tank, it is necessary to mound the earth over the top of the septic tank which may be higher than the original ground level.

Excavations For Sewage Tanks and Effluent Tanks

Care must be taken in the excavation for the septic tank, sewage holding tank, or other tanks to ensure the excavation has a flat, undisturbed base to support the weight of the tank and it's contents. If the excavation is dug too deep and the tank is installed on uncompacted fill, the tank will settle and damage to the connecting piping may result as shown in Pg. 170, Fig. Tanks 4 in Appendix "B". If a siphon type septic tank is used, the operation of the siphon may also be severely impaired because of the outlet piping being graded the wrong way. See Pg. 33, Article 5.2.5.

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Alberta Occupational Health and Safety, General Regulations Extract

The following is an extract from Alberta Occupational Health and Safety Act, General Safety Regulations regarding excavations and trenches. These procedures must be followed to assure safe excavation and trenching practices

Part 10, Trenching and Excavations

EXCAVATIONS, TRENCHES, TUNNELS AND UNDERGROUND SHAFTS

169 In this Part,

1. excavation means any dug out area of ground other than a trench, tunnel, underground shaft or an open pit mine;
2. "hard and compact", in relation to soil, refers to soil that can only be excavated by machinery and shows no sign of cracks after excavation;
3. spoil pile means material excavated from an excavation, trench, tunnel or underground shaft;
4. temporary protective structure means a structure or device designed to provide protection in an excavation, trench, tunnel or underground shaft from cave-ins, collapses or sliding or rolling materials, and includes shoring, bracing, piles, planking or cages;
5. trench means an elongated dug out area of ground whose depth exceeds its width at the bottom. AR 448/83 s169

170 This Part does not apply where a professional engineer has certified that the ground formation is and will remain throughout the use of the excavation, trench, tunnel or underground shaft stable, free from cave-ins and sliding or rolling materials and other hazards associated with the workings and which may compromise the safety of workers. AR~. 448/83 s170

171 A worker shall not enter an excavation, trench, tunnel or underground shaft that does not comply with this Part. AR 448/83 s171

172(1) Where the freezing of soil by artificial means, grouting or any other process intended to stabilize the soil is

1. designed by a professional engineer to control soil conditions, and
2. performed in accordance with the professional engineer s specifications, the freezing, grouting or other process is acceptable as an alternative to the shoring of an excavation, trench, tunnel or underground shaft or to the cutback of an excavation or trench.

(2) An employer shall ensure that the specifications required by this Part for a temporary protective structure that is to be used in an excavation, trench, tunnel or underground shaft

1. show the size and specifications of the structure, including the type and grade of materials for its construction,
2. show the loads for which the structure is designed, and
3. are certified by the professional engineer.

(3) An employer shall ensure that temporary protective structures referred to in subsection (2) are installed, maintained and dismantled in accordance with the specifications of a professional engineer and remain in place as long as workers are in the excavation, trench, tunnel or underground shaft.

(4) Before the commencement of work on an excavation, trench, tunnel or underground shaft, an employer shall establish the location of all underground pipelines, cables and conduits in the area where the work is to be done and shall have their location adequately marked.

(5) Where an operation that includes the disturbance of soil within 600 millimetres of an existing pipeline or 300 millimetres of an existing cable or conduit is to be undertaken, the employer shall ensure that the pipeline, cable or conduit is exposed by hand digging by a competent worker before work is allowed to progress within those distances.

(6) Notwithstanding subsection (5), if a cable or conduit has been de-energized and grounded, other excavating methods may be used if the power authority operating the cable has previously been notified of the operation AR 448/83 s172

173(1) Before a worker begins working in an excavation more than 1.5 metres in depth and closer to the wall or bank than the depth of the excavation, his employer shall ensure that the worker will be protected from cave-ins or sliding materials by

1. the cutting back of the walls of the excavation to reduce the height of the remaining vertical walls, if any, to not more than 1.5 metres,
2. the installation of temporary protective structures, or
3. a combination of cutting back of the walls and the installation of temporary protective structures

(2) Where the cutback method is used, the walls must be cut back

1. in hard and compact soil, to not less than 30 degrees from the vertical, and
2. in other soils to not less than 45 degrees from the vertical,

(3) An employer shall ensure that

1. temporary protective structures in an excavation 3 metres or less in depth are constructed of materials of sufficient strength to prevent the walls of the excavation from caving in or otherwise moving into the excavation;
2. temporary protective structures in an excavation over 3 metres in depth are designed and certified by a professional engineer;
3. where a foundation may be affected by an excavation, the foundation is supported before proceeding with the work by a temporary protective structure designed, constructed and installed in accordance with the specifications of a professional engineer;
4. loose materials are scaled or trimmed from the sides of an excavation where workers are or will be present;
5. the spoil pile is piled so that
   1. it is kept at a distance of at least 1 metre from the edge of the excavation, and
   2. the slope of the spoil pile adjacent to the excavation is at an angle of not less than 45 degrees from the vertical.

(4) When workers are carrying out an excavation in the vicinity of an overhead power line, their employer shall ensure that the work is carried out in a manner that will not reduce the original support provided for the power line poles.
AR 448/83 s173;348/84

Trenching

174(1) Before a worker enters a trench more than 1.5 metres in depth, his employer shall ensure that the worker is protected from cave-ins or sliding materials by

1. the cutting back of the walls of the trench to reduce the height of the remaining vertical walls, if any, to not more than 1.5 metres,
2. the installation of temporary protective structures, or
3. combination of cutting back of the walls and the installation of temporary protective structures.

(2) Section 173(2), (3)(c) to (e) and (4) apply to a trench as they apply to an excavation.

(3) An employer shall ensure that

1. shoring, stringers and bracing used in a trench between 1.5 and 6 metres deep are constructed of lumber and comply with Schedule 1 to this Part;
2. temporary protective structures used in trenches are designed and certified by a professional engineer, except where shoring, stringers and bracing have been installed in accordance with clause (a);
3. where a cage is used in a trench, it is designed by a professional engineer to provide adequate protection against sliding, caving or rolling materials;
4. where machinery or a heavy object is placed or is working within a distance from a vertical line drawn from the near edge of the bottom of the trench equal to the depth of the trench, or if the trench is adjacent to or abutting a building or other structure, additional protection certified by a professional engineer is used in the trench to compensate for the stress or weight of the machinery, object, building or structure;
5. where the vertical walls of the square-cut portion of a trench are 1.5 metres or more in height, the vertical walls are shored or braced or a cage used.

(4) Notwithstanding subsection (3)(a),

1. screw jacks, hydraulic equipment or other apparatus may be used as shoring, stringers or bracing, if it is at least equivalent in strength and reliability to the shoring, stringers or bracing described in Schedule 1 to this Part, and
2. for trenches less than 2.4 metres deep in hard and compact soil, stringers need not be used.

(5) When installing shoring, stringers or bracing, a worker shall use a ladder and work downward from the top of the trench, installing each brace in descending order.

(6) When removing shoring, stringers or bracing, a worker shall use a ladder and work upward from the bottom of the trench, removing each brace in ascending order.

(7) An employer shall ensure that a worker complies with subsections (5) and (6).

(8) Where the quality of the ground in which a trench has been dug has deteriorated during operations to the extent that it would be unsafe to use the method of removal required by subsection (6), the employer shall ensure that the shoring, stringers or bracing is removed by a method which does not require the worker to enter into any portion of the trench.

(9) Subsection (1) does not apply where a trench is constructed in solid rock throughout the entire trench.
AR 448/83 s174;348/84

The drawing on the following page will assist in interpreting the safe trenching requirements:

Click on

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Maintenance And Cleaning The Septic Tank

Every person using a septic tank will contribute a volume of solids to the septic chamber that digests at a very low rate in the anaerobic environment of the tank. These solids accumulate over a period of time and reduce the storage capacity of the septic chamber. Also, there is a volume of greases, soap curds and other material that float on the surface of the liquid. These settleable and floating solids must be removed from the septic chamber periodically and disposed of in another manner.

If the septic tank is not cleaned soon enough, the detention period which it will provide for the sewage, will continue to decrease. As a result, more and more suspended solids and organic material will be carried from the septic chamber into the effluent chamber and discharged into the effluent disposal system. Once in the effluent disposal system, the additional suspended solids and organic material will clog the infiltrative surface of the soil eventually causing failure of the system. The septic tank can be cleaned many times for the price of installing a new effluent disposal system:

The size of the septic chamber determines the intervals between cleaning. The larger the septic chamber, the better the separation of solids from the effluent especially during peak flows. The septic chamber should be checked each spring or early summer for the amount of accumulated sludge and scum in it. A septic chamber with .45 m (18 inches) of sludge is ready to be cleaned. Cleaning the tank in the spring will allows the bacterial action re-establish quicker through the warm summer. It is not necessary to thoroughly scrub and flush the septic chamber until it is visibly clean. The small amount of sludge that remains on the floor and walls will re-seed the septic tank and contribute to the re-establishment of its normal operation. Vacuum-pumped sewage hauling trucks are available commercially to clean septic tanks. This equipment is capable of doing an excellent cleaning job without spillage.

See Pg. 32, Article 5.2.2

Sludge And Scum

Not all suspended matter in raw sewage is digestible in the septic tank. Some of the solids settle out and become sludge in the bottom of the tank. Grease and oily substances, rise to the surface and along with minute particles of suspended solids eventually form a thick scum. The scum, being buoyant, floats partly above the water line (27%), and for this reason a minimum volume of air space is required in each septic tank. The accumulated scum may roughly average half the volume of the accumulated sludge, however, it is not unusual to find septic tanks that do not have any volume of scum and may appear to have only a slight oil slick over the surface.

The Disposal of Sludge

Many of the pathogenic or disease producing bacteria found in sewage are capable of becoming spores, in which state they can withstand extreme cold or heat and extended drying conditions. For this reason, effluent or sludge from the septic tank should not be used to water or fertilize gardens.

If the contents of a septic tank, or sewage holding tank are spread on a field of summer fallow, where it will be well away from buildings or animals, it will rapidly become inoffensive and is a good nitrate fertilizer.

Burial and covering is always an excellent method. Never permit sludge to contaminate any surface waters.

Sewage Holding Tanks

In areas where the minimum distances cannot be provided or the soil conditions are limiting for other forms of disposal, it may be necessary to install a water tight sewage holding tank and haul all sewage away for disposal in a suitable location. See Pg. 25, Article 3.2.1., Pg. 31, Article 5.1.2 and Pg. 32, Article 5.1.3

The high cost of operation dictates that this method be used only where absolutely necessary.

Danger

Deadly gases are present in a septic or sewage holding tank. Never enter septic or sewage holding tanks without knowing and following Occupational Health and Safety requirements .

Pumps

Pumping of Sewage

- See Pg. 25, Article 3.1.15

It is often desirable to have plumbing fixtures located in the basement. If the building is located near a hill side, the building drain may be located below the basement floor, and a comparatively simple system of sewage disposal may be installed that may not require a pump, if flow can be obtained by gravity.

If there is not sufficient slope on the ground surface to permit the use of this method, sewage or effluent may be raised to an elevation suitable for the disposal of effluent by the installation of a "Raw Sewage Lift Pump" or an "Effluent Pump." See Pg. 171, Fig. Pumps 1, Pg. 172, Fig. Pumps 2, and Pg. 173, Fig. Pumps 3 in Appendix "B".

Raw Sewage Lift Pumps

See Pg. 171, Fig. Pumps 1 in Appendix "B"

Systems can be installed where raw sewage is pumped to a higher elevation where it can then run by gravity to the septic tank, sewage holding tank or packaged sewage treatment plant.

It is generally preferred to have all main and upper floors of a building drain to a septic tank, sewage holding tank or packaged sewage treatment plant by gravity and only the basement plumbing fixtures drain to the raw sewage lift pump. The raw sewage lift pump discharges the sewage from the basement fixtures into the building drain where it too can flow by gravity to the septic tank sewage holding tank or packaged sewage treatment plant. This system requires the installation of a container, control system and a pump capable of handling solids. There are many pump manufacturers that provide a complete packaged unit suitable for domestic applications. There are some advantages to this type of installation:

1. only a small percentage of the total sewage is required to be pumped,
2. in the event of a pump or power failure, only the plumbing fixtures in the basement are affected,
3. If the effluent disposal system fails, there is little chance of flooding the basement with sewage.

Effluent Pumps

See Pg. 25, Article 3.1.15 regarding high level alarms.

It is sometimes necessary to install the septic tank deep enough to receive all sewage from the building by gravity, and to raise only the effluent to a suitable disposal level. An effluent pump must be specified by the manufacturer to be suitable for handling "effluent."

The most popular method of pumping effluent uses a submersible effluent pump installed in the effluent chamber of the septic tank. See Pg. 172, Fig. Pumps 2. in Appendix "B". Due to the presence of dangerous gases in septic tanks, it is imperative that special provisions are made for the installation, removal and servicing of the pump and controls so that entering of the tank is not required.

Another method of effluent pumping is to install a non-submersible effluent pump in the basement. This requires the installation of a suction line from the septic tank to the pump and a discharge line to the point of disposal. See Pg. 173, Fig. Pumps 3. in Appendix "B".

Although surface water and runoff water is to be directed away from the disposal area (See Pg. 21, Article 3.1.6), under extreme and unusual conditions there have been situations where surface or runoff water was allowed to pool over the disposal field for a short period of time. Under this condition, water has been known to seep down through the soil into the disposal field and flow back through the effluent sewer, into the septic tank and eventually flood the basement. This may be avoided if the pump discharge into the effluent sewer is at an elevation that is well above the ground surface over the disposal field. Pg. 174, Fig. Pumps 4 and Pg. 175, Fig. Pumps 5 indicate possible methods of connection that may be suitable under most conditions.

See Pg. 25, Article 3.1.15 regarding high level alarms.

Submersible Effluent Pump Controls

It is essential that no electric motors, wiring, switches, or working parts of the effluent pumping system be subjected to the highly corrosive and deteriorating effects of the atmospheric conditions which exist in the effluent chamber. There are many types of pump controls available which are suitable for this application. In selection of controls, it is imperative to select controls which are capable of carrying the electrical current demanded by the pump.

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Packaged Sewage Treatment Plants

There are many different makes and models of packaged sewage treatment plants. To be acceptable for installation in the Province of Alberta, they must be certified to the National Sanitation Foundation (NSF) International Standard NSF 40 - 1996, the NSF Standard for Wastewater Treatment Systems. As this is a U.S. standard, all units are rated in U.S. gallons and this must be taken in to consideration when sizing a packaged treatment plant for use in Alberta. See Pg. 35, Article 6.1.2. and Pg. 36, Article 6.3.1.

Packaged sewage treatment plants are aerobic treatment plants that use various methods, depending on their design, to expose the sewage to oxygen. Increased levels of oxygen in the sewage provides for the establishment of large aerobic bacteria populations. These aerobic bacteria populations accelerate the decomposition of the suspended solids in sewage.

Packaged sewage treatment plants perform best when they are subjected to a constant and consistent volume and quality of sewage. It takes some time to initially establish a bacteria population as there is a balance between the size of the bacteria population, the amount of solids discharged to the packaged sewage treatment plant that the bacteria can use as food, and the amount of oxygen available to the bacteria. If there is a sudden increase in the amount of solids, there may be a decrease in the quality of effluent discharged from the packaged sewage treatment plant until the bacteria population increases in size to accommodate the new volume of solids. See Pg. 35, Article 6.1.1. Some treatment plants include within their design methods that equalize small fluctuations in flow through the day. In any installation, methods to equalize flow should be considered and included in the design.

During an extended holiday, a reduction in the bacteria population due to the lack of sewage that the bacteria use as food will occur. This may result in a decreased effluent quality when use resumes until the bacteria population increases again to match the volume and strength of the sewage discharged to the unit. Bacterial populations can be maintained by providing alternative organic matter to the system, thereby providing an alternative food supply for the bacteria until normal sewage flow is again established.

A packaged sewage treatment plant requires maintenance. As a certification requirement of the NSF 40 Standard, a 2-year initial service policy shall be furnished to the owner by the manufacturer or the authorized representative and the cost of the initial service policy shall be included in the original purchase price. The initial policy shall contain provisions for four inspection/service visits (scheduled once every 6 months over the 2-year period) during which electrical, mechanical, and other applicable components are inspected, adjusted, and serviced. See Pg. 19, Article 3.1.2. Every system requires maintenance which is specifically determined by the manufacturer. Be sure to advise the owner of maintenance requirements.

See Pg. 21, Article 3.1.7 and Pg. 22, Article 3.1.14 .

Excavation For Packaged Sewage Treatment Plant

Care must be taken in the excavation for the packaged sewage treatment plant to ensure the excavation has a flat, undisturbed base to support the weight of the tank and it's contents. See Pg. 36, Article 6.2.5 .

With many of the packaged sewage treatment plants, it is of extreme importance that the plant be installed level and remain level for proper operation. If the excavation is dug too deep or the tank is installed on uncompacted fill, the plant will settle and damage to the connecting piping or a reduction in the efficiency of the packaged sewage treatment plant will result in low quality effluent. See Pg. 170, Fig. Tanks 4 in Appendix "B".

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Soils Tests

Critical Design Information

The most important criteria in the design of an effluent treatment and disposal system is the soil. To design the system for a given amount of effluent, the ability of the soil to absorb and treat the effluent must be determined. A system that is undersized may operate for a short time, in so far as absorbing the effluent, but it will soon become clogged with the organic material and suspended solids in the effluent. The soil will no longer be able to absorb the effluent and a failure of the system will occur.

A close examination of the soil and proper testing of the soil is required for the sound design of a system and to assure the long term acceptance of effluent. There are two tests or methods used to determine the effluent acceptance rate of the soil. These are the Percolation Test and Soil Texture Classification.

Percolation Test

The purpose of the percolation test is to obtain data that can be used to determine the soil infiltration area required to accept the expected volume of sewage per day.

Soil with a rate of 40 to 50 min per 25 mm ( per inch) indicates a clay loam which is a fine texture and has small pore spaces. A percolation test resulting in a rate of 5 to 10 min per 25 mm ( per inch) indicates a course or porous soil texture such as loamy sand. The clay loam accepts and transmits water much slower than a soil such as loamy sand.

The rate at which a soil will accept water or effluent is dependent (to a great extent but not exclusively) upon the size of the pore spaces between the individual soil particles. Sand particles are large and leave large pore spaces between particles causing little restriction to the movement of air and water or effluent through the soil. Clay particles are extremely small particles and accordingly, leave extremely small pore spaces between the particles, providing a greater restriction to the movement of air and water or effluent.

A percolation test is subject to many factors that may influence the results obtained and thus the relevance of the results obtained. Some of these factors include:

1. Improper soaking or failure to properly pre-soak the test hole,
2. a large pore in the soil created by a dead plant root,
3. animal burrows,
4. cracks in dry clayey soil,
5. changes in the soil texture and structure of the underlying soil layers (soil horizons),
6. locating the test hole in areas of previous excavations,
7. frozen soil,
8. location of test holes not representative of disposal site conditions.

A percolation test gives an indication of the rate the soil will accept and move clean water.

Percolation Test Procedure

Test hole:

The test hole for the percolation test is 8" in diameter and augured to a depth of 3 feet. Any glazing on the side walls from the auger should be removed as this can slow the movement of the water into the soil. The test hole will be filled with water to an 18" depth for the test.

Comments: The location of the test holes (2 are required at the proposed site) are selected to provide an accurate representation of the overall conditions found at the site. If someone were to ask why the specific locations of the test holes were chosen the person conducting the test should be able to give sound reasons. The required depth of the hole is 36" which is the maximum depth of a disposal field and will provide a good representation of the soil surrounding and immediately below the system. The system may be intended to be installed at a depth of between 1 and 2 ft. or on the surface as is the case with a treatment mound. However, it is important to know the capability of the soil below the system as most of the effluent will be traveling downward. A restrictive layer immediately below the system can cause the water to mound up and cause saturated conditions in and around the system. The soil below the system can be determined in an examination of the soil layers in a test pit or core sample obtained using a soil bore.

Additionally, care must be taken that when making the hole to a depth of 3 ft. the bottom portion of the hole has not penetrated through a restrictive layer and into a courser soil that has a fast percolation rate. This will result in an inaccurate percolation rate. Examine the soil texture and structure as the hole is made to be sure the soil is consistent and the test will provide an accurate representation of the soil's capability. In the case where the bottom of the test hole has extended into a faster layer of soil a new test hole augured to less than a 3 ft. depth can be used to accurately measure the soil the system is set in. The depth of water at the start of the measurement is set at 18 inches. Always start with a water depth of 18 inches as changing the depth of the water from 18 inches can significantly change the result. Further examination of the soil should be conducted to ensure the underlying soil does not have too fast a percolation rate (in excess of 5 minutes per inch).

Pre-soaking the Test Hole:

The soil must be soaked prior to taking a measurement to assure accurate results.

Comments: The soil surrounding the test hole must be adequately pre-soaked to provide an accurate representation of the soil's capability. Soaking of the hole is required to wet the soil particles and cause them to expand in the case of clays, and to fill the soil pores and any other voids or passage ways with water. Prior to being adequately soaked, percolation rates will vary significantly.

Properly soaking the hole requires keeping water in the hole to at least the 18" level for at least 15 hours. A device that will supply water to the test hole is shown at Pg. 215, Fig Perc 2 . Providing at least a 20 gallon capacity container will supply a percolation test hole in approximately 8 minute per inch soil for the 15 hours. If the 20 gallons is exhausted before the 15 hours the soil has a fast percolation rate indicating a course textured soil and there is little possibility the test will not be accurate due to inadequate soaking. Further soaking would not be required in this case. If an examination of the soil texture indicates there is clay in the soil, continue soaking and or determine why the water was used up so fast.

Measurement:

After the soaking period and establishing the water level at an 18" depth, measurements from a fixed point at the top of the hole are taken at 30 minute intervals to measure the fall of the water which is used to determine the time required for the water to drop 1 inch.

Comments: Establish a solid fixed point above the ground surface to ensure that each measurement is taken from the same point or set up a device as shown on Pg. 214, Fig Perc 1 (Wrong measurements will be obtained if measuring from the bottom of the hole to the surface of the water. This is because the measuring device is being placed at different locations on the bottom of the hole and the measurement cannot be easily seen down in the hole).

The water level is set to 18" depth at the start of each measurement. Measurements are made until two successive water level drops do not vary by more than 1/8 of an inch over the 30 minute measuring period. This indicates stabilized percolation. Proper pre-soaking of the test hole should result in the first two measurements being very close. In sandy soils where the first 6 inches of water soaks away in less than 30 minutes measurements are taken at 10 minute intervals for one hour.

Warning - Varying rates:

If the percolation rates measured in the two test holes varies significantly a problem has been detected.

Varying rates show:

1. a mistake was made in one of the test holes,
2. the test was affected by one of the conditions discussed above, or
3. the site has variable and complex soil conditions that require further investigation and must be determined for proper design.

Further testing is required to determine the cause of the variation and/or actual soil conditions that must be considered in the design.

Warning - Relate to soil texture:

Percolation tests should result in a loading rate similar to the loading rate that would be determined by the soil texture. When conducting the percolation test estimate the soil texture, determine the appropriate loading rate and find a corresponding percolation rate resulting in the same loading rate. While a difference is not unexpected the loading rates should be similar assuming the soil texture estimate is close and the percolation test was conducted successful. For example if the soil texture estimate is clay loam, the percolation rate will not be 10 to 20 minutes per inch. If that was the result of the percolation test the test was flawed and further investigation should be carried out.

Warning - Subdivision perc tests:

Percolation tests are often conducted as part of the exercise in obtaining subdivision approval. The results of these tests are not to be used in the sizing of individual onsite systems. These tests are taken in widely spaced locations and do not accurately reflect, often not even closely, the actual conditions at the selected disposal system site. Many things, such as site grading after the percolation testing occurred or a small difference in location from the original test site, can change the actual results.

See Pg. 38, Article 7.1.5, Pg. 39, Article 7.2.2 . See Pg. 94, A.6. Percolation test Procedure in Appendix "A" for the method of conducting a percolation test set out in the Standard of Practice. See Pg. 214, Fig. Perc 1, Pg. 215, Fig. Perc 2, and Pg. 216, Fig. Perc 3 in Appendix "B"

Soil Texture

Soil texture affects the movement of water in the soil.

The soil texture classification type may be used in calculating the effluent loading rate in litres per square metre (gallons per square foot) for that soil texture classification. See Pg. 37, Article 7.1.4, Pg. 42, article 7A.1.5 and Pg. 179, Fig. 7A.1.5.A. The soil texture is a classification determined by the relative amounts of sand, silt and clay in a soil (the mineral portions of the soil). How coarse (sandy) or fine (clayey) the soil is, affects the ability of the soil to transmit air and water or effluent.

The mineral portion of the soil (excluding fragments with a mean diameter larger than 2 mm) is divided into three size fractions: Sand (S) with particle sizes between 2.00 and 0.05 mm, Silt (Si) with particle sizes between 0.05 and 0.002 mm, and Clay (C) with particle sizes less than 0.002 mm.

Soil texture refers to the relative percentage of sand, silt, and clay in a soil, i.e., particle size distribution. The texture of a soil is expressed as a class name formed by combining the terms of sand, silt, clay and loam. For example, if the clay fraction dominates the properties of the soil, the soil class name would simply be "clay." However, if this soil contains enough sand to appreciably modify the properties imparted by the clay, then the class name would be "sandy clay." When the percentage of sand and clay are known, the class name can be determined from the textural triangle shown in Table 7A.1.5.A. There are ways of accurately determining soil texture in the laboratory such as the pipet and hydrometer methods. Where the soil texture is to be used as the only sizing criteria the soil must be analyzed by a soils laboratory using recognized methods.

A less precise method, manual texturing, can be employed in the field to make estimates of soil texture and is based on the "feel" of a moist soil sample.

Hand Texturing of Soil

To hand texture, you may wish to try the steps below or those in the following graphic illustration.

1. Place about a teaspoon of soil in the palm of your hand and moisten the soil by slowly adding water. Knead the soil and add water until it has the consistency of moist putty (not soup).

2. To estimate the textural class, use the following guidelines:

1. pure clay will feel very slippery and very sticky
2. pure silt will feel smooth and slippery but not sticky
3. pure sand will feel very gritty.

3. Press and rub the moistened soil between your thumb and forefinger to estimate the gritty and slippery feel, then pull the two fingers apart to estimate stickiness.

This is an example procedure for hand texturing of a soil sample. Be advised that this is presented as an additional example of a qualitative field technique and that accuracy improves with experience (often many years are required). By obtaining a number of known soil texture samples you can practice with these to help you calibrate your fingers to do the manual texturing of soils.

Hand Texturing of Soil (Graphic Illustration)

 Click on Image for Larger View

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Textural Properties of Dry and Wet Mineral Soils
Soil	Feeling and Appearance
Class	Dry Soil	Moist Soil
Sand	Loose, single grains which feel gritty. Squeezed in the hand, the soil mass falls apart when the pressure is released.	Squeezed in the hand, it forms a cast which crumbles when touched. Does not form a ribbon between thumb and forefinger.
Sandy Loam	Aggregates easily crushed; very faint velvety feeling initially but with continued rubbing the gritty feeling of sand soon dominates.	Forms a cast which bears careful handling without breaking. Does not form a ribbon between thumb and forefinger.
Loam	Aggregates are crushed under moderate pressure; clods can be quite firm. When pulverized, loam has velvety feel that becomes gritty with continued rubbing. Casts bear careful handling	Cast can be handled quite freely without breaking. Very slight tendency to ribbon between thumb and forefinger. Rubbed surface is rough.
Silt Loam	Aggregates are firm but may be crushed under moderate pressure. Clods are firm to hard. Smooth, flour-like feel dominates when soil is pulverized.	Cast can be freely handled without breaking. Slight tendency to ribbon between thumb and forefinger. Rubbed surface has a broken or rippled appearance.
Clay Loam	Very firm aggregates and hard clods that strongly resist crushing by hand. When pulverized, the soil takes on a somewhat gritty feeling due to the harshness of the very small aggregates which persist.	Cast can bear much handling without breaking. Pinched between the thumb and forefinger, it forms a ribbon whose surface tends to feel slightly gritty when dampened and rubbed. Soil is plastic, sticky and puddles easily.
Clay	Aggregates are hard; clods are extremely hard and strongly resist crushing by hand. When pulverized, it has a grit-like texture due to the harshness of numerous very small aggregates which persist.	Casts can bear considerable handling without breaking. Forms a flexible ribbon between thumb and forefinger and retains its plasticity when elongated. Rubbed surface has a very smooth, satin feeling. Sticky when wet and easily puddled.

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Dry and wet feel of various soil textures

 

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Particle Or Grain Size Analysis Test

A Particle or Grain Size analysis test is a laboratory procedure performed on a soil sample to establish the amounts of sand, silt and clay in the sample. The procedures may include sieving, pipette sampling or hydrometer methods. Once the amounts of sand, silt and clay have been established, the results may be applied to the soil classification chart in article 7A.1.5A, (see Pg. 43, Fig 7A.1.5.A ) to obtain a soil classification type.

Saturation Percentage Test

A very simple soils test called a "Saturation Percentage," may provide valuable information as to the pore sizes and particle sizes in relationship to the combination of sand, silt and clay in a soil sample taken from your proposed disposal site. Although the saturation percentage test may not be used for initial sizing, it may provide information relating to the long term operation of your disposal system.

The procedure for a Saturation Percentage test is:

1. obtain a soil sample, preferably from the depth of the bottom of the disposal system,
2. dry the sample completely. This can be done in an oven or can be left to dry naturally, time permitting.
3. remove all rocks from the sample and grind the sample to break up as many large particles as possible into a fine, uniform sized mixture.
4. accurately measure an amount (100 grams is adequate) of the dry sample. Be sure not to include the weight of the container in your 100 gram measure.
5. add water slowly and carefully over a period of time, giving the sample time to absorb the water completely. Continue to add water until the sample is completely saturated and can absorb no more water.
6. weigh the wet sample and subtract the weight of the dry sample from the weight of the wet sample. The difference in the weight, in relationship to the weight of the dry sample is the saturation percentage.

For example: the difference between a wet sample weighing 150 grams and a dry sample weighing 100 grams is 50 grams which is the weight of the water evaporated. Therefore the saturation percentage is 50% of the weight of the dry sample.

The higher the saturation percentage, the higher the percentage of smaller soil particles (silts and clays) and the greater the risk of disposal system failure.

Many types of clay shrink when dry and swell when wet which reduces pore size between particles. The swelling and shrinking of soils that leave large cracks on the surface is particularly noticeable in soils containing large amounts of Montmorillonite clay which is a very fine clay. As a consequence, much larger absorption areas must be utilized for the same given amounts of effluent and time.

Montmorillonite clay is found throughout Alberta in varying amounts. See Soil Montmorillonite Map Pg. 88, A.3.C.. Montmorillonite, being the finest textured of all clays, is also affected by chemical elements in the water supply and consequently the effluent.

A chemical water analysis of the proposed water supply may be the first indicator of probable sewage disposal problems, even before the installation of the sewage disposal system.

Soil Structure

Structure, Porosity and Water Movement

Structure, which is the formation of larger soil particles (clumps of soil) by cementing together individual sand, silt, and clay particles, affects the pore size and the rate at which water will move through soil. It is not only the size of soil particles that determines how fast water moves through soil, but the size of the spaces or pores between the particles or aggregates. Loamy soils have a mixture of pore sizes, some large and some small, depending upon the arrangement of the different particles. A field soil with a high percentage of clay particles has more pores than a sandy soil but will drain much more slowly because the pores are very small. A soil which has a well-defined structure will transmit water much more rapidly than a soil where the structure has been destroyed by compaction or smearing.

The type of structure determines the dominant direction of the pores and hence, water movement in the soil. Well-structured soils with large voids between peds (clumps of soil) will transit water more rapidly than structure-less soils of the same texture, particularly if the soil has become dry before the water is added. Fine-textured, massive soils (soils with little structure) have very slow percolation rates.

Platy structures resist vertical percolation of water because cleavage faces are horizontally oriented. Often vertical flow is so restricted that the upper soil horizons saturate, creating a perched water table. Soils with granular, blocky, prismatic, or columnar structures enhance flow both horizontally and vertically.

Structure is one soil characteristic that is easily altered or destroyed. Structure is very dynamic, changing in response to moisture content, chemical composition of soil solution, biological activity, and management practices. Soils containing materials that shrink and swell appreciably, such as montmorillonite clays, show particularly dramatic changes. Mechanical equipment used during construction can also alter soil structure by causing compaction or smearing of the soil at the infiltrative surface, either in a trench or on the absorption area of a treatment mound.

When the soil peds swell upon wetting, the large pores become smaller and water movement through the soil is reduced. Therefore, when determining the hydraulic properties of a soil for wastewater disposal, soil moisture contents should be similar to that expected in the soil surrounding a soil disposal system. This is one of the reasons for requiring a soaking period when performing a percolation test.

Experience and research shows that strong soil structure can compensate for high clay content in the soil and result in a soil with suitable permeability.

Drainage Classes

Drainage classes can be estimate by examining root depth (remember not all plants will grow deep roots even in well drained soil). Drainage is an important consideration in the selection of a site for a sewage treatment and disposal system. In all, there are five drainage classes, as follows:

1. Well-drained soils are those in which plant roots can grow to a depth of 90 cm without restriction due to excess water.
2. On moderately well-drained soils, plant roots can grow to a depth of 50 cm without restriction.
3. Somewhat poorly-drained soils restrict the growth of plant roots beyond a depth of 36 cm.
4. Poorly-drained soils are wet most of the time, and are usually characterized by alders, willows, cat tails, or slough grass. (Examine the edges of sloughs or known wet spots in the area and identify common vegatation expected in these areas).
5. On very poorly-drained soils, water stands on or near the surface most of the year.

Seasonally saturated soils and high water tables

When digging into the soil standing water may not be evident at that particular time of year. The depth to saturated soil will change at different times of the year. Evidence other than standing water must be looked for to determine the absence of saturated soil zones. Adequate vertical separation must be provided between saturated soil and the point of entry of effluent into the soil to assure proper treatment of the effluent (see Pg. 38, Article 7.1.6 ). If a soil is consistently saturated for a substantial period of the year, year after year, mottling of the soil will occur. Mottled soil will not have a bright consistent color that indicates a well drained soil. The color will be washed out and/or will have blotches of rust and grey colors.

Mottled soil is the result of periodic, recurring water logged soil conditions; an anaerobic environment, over a long period of time. It encourages the reduction of iron compounds by anaerobic microorganisms and often causes mottling of soil into a patchwork of gray and rust colors. The process is known as gleying.

Sodium Affecting Soils

Sodium Adsorption Ratio (SAR)

This measurement is one indicator that a problem could be caused by the sodium in the water. Excess sodium, in relation to calcium and magnesium concentration, in soils destroys the structure of montmorillonite clay particles reducing permeability of the soil to water and air.

Both Alberta Environment and Environment Canada publish guidelines for irrigation with municipal wastewater. Alberta Environment's publication "A Practical Guide to Municipal Wastewater Irrigation" states:

Water Quality for Irrigation Suitability

Because an equilibrium exists between the soil and the soil water, irrigation with a wastewater with unsatisfactory chemistry will result in an unacceptable change in soil chemistry. An effluent with an SAR over eight is considered unsatisfactory while an EC of 250 millisiemens per metre (mS/M) or greater should be considered unsatisfactory unless the soil is well drained.

Environment Canada's "Manual for Land Application of Treated Municipal Wastewater and Sludge" provides Table B-3 for standard rate irrigation and Table B-4 for high rate irrigation.

Table B-3 Recommended Wastewater Quality Criteria for Standard Irrigation Rate
	Degree of Problem
Irrigation Problem	No Problem	Increasing Problem	Severe Problem
Salinity EC (mS/cm)*	< 1.3	1.3 - 3.0	> 3.0
Permeability SAR **	< 6	6 - 9	> 9
Boron (mg/L)	< 0.7	0.7 - 2.0	> 2.0
pH	Normal Range 5.5 - 9.0
* Assume a well drained soil and leaching fraction of 0.15 ** Suggested for fine and medium textured soils, SAR limits can be relaxed if soils are course textured (LS and S). Important: The above guidelines are superseded by provincial regulations or guidelines

Table B-4 Recommended Wastewater Quality Criteria for High Rate Irrigation
	Degree of Problem
Irrigation Problem	No Problem	Increasing Problem
Salinity (dS/cm)	< 4	4+
Permeability SAR **	< 6	6+
Boron (mg/L)	< 1	1 +
pH	Normal Range 5.5 - 9.0
* Assume a very well drained soil and a leaching Fraction of 1.0.

If certain qualities of municipal waste water (from a sewage lagoon) are not considered suitable to use as irrigation water during the summer months of the year only, because of the potential of changing the permeability of the soil, it is not reasonable to think effluent from a private sewage system can be discharged in the soil every day of the year, every year, without affecting the permeability of the soil.

Water with a high SAR (Sodium Adsorption Ratio), may be natural soft water, from a deep well, soft water produced by a water softener and waste water used in regenerating a water softener. These waters may be detrimental to a sub-soil effluent disposal system under certain circumstances. Generally, the higher the SAR of the potable water, the greater the salinity or EC of the water and the higher the saturation percentage of the soil, the greater the probability of sewage disposal failure.

SAR of the Potable water supply may be obtained from a chemical water analysis report. Some labs provide it as a routine item, others do not. If the SAR is not provided it may be calculated. It is important to realize that chemical water analysis reports usually provide information in ppm or mg/l, and neither of these units of measurement may be used. As there are three different elements used in the calculation, they must be converted into a common denominator in accordance with their atomic weights. This common denominator is referred to as me/l, and may be obtained by dividing sodium by 23, calcium by 20 and magnesium by 12. The numbers obtained from these three calculations may then be applied to the formula:

If the SAR of the potable water supply is greater than 6, and the salinity of EC of the potable water is greater than 250, it is highly recommended that a saturation percentage test of the soil be done.

There are many variables in water quality and chemistry, soils and soil chemistry, vegetation and use of the private sewage system that may have an effect on the life and operation of a system. There has been a great deal of research done regarding water and soil chemistry for irrigation purposes, but very little research has been done regarding private sewage systems.

Note: These tests at this time have no direct relationship in regards to sizing of a disposal system. A percolation test and/or Soil Texture classification is required to establish a loading rate in litres per square metre or gallons per square foot to size the effluent disposal system.

Water Softeners

The use of a water softener which uses Sodium Chloride as a regeneration agent may cause problems for a treatment and disposal system as it will increase the SAR of the potable water used in the building and thus the waste water entering the treatment and disposal system. If a water softener must be used, a softener that uses Potassium Chloride can avoid the problems of a sodium based softener. Also, avoid the installation of water softeners that automatically backwash at preset intervals of time rather than by water volume used. This type of unit may discharge unneeded volumes of water and concentrations of salt into the disposal system.

Problems with the soil caused by a water softener using sodium are not created so much from the backwash from the softener. The problem occurs with the increased levels of sodium that are found in the water that is used in the house, the softened water. The sodium is in the water used at the fixtures, the hardness minerals are washed out in the backwash water.

If a water softener must be used, "Sensing" or Metering" type water softeners are preferred. These water softeners only backwash or regenerate when hardness of the water is sensed or after a preset volume of water has been used, thereby reducing the total volume of salts discharged into the disposal system. There are some private sewage system installers that will not provide any warranty on their systems if a water softener discharges into a piping system that connects to the septic tank.

Under no circumstances should any water softener be used for Iron removal. If iron removal is required, the use of a proper iron filter should be employed. Note: the wastes from an iron filter may not be discharged into a private sewage system. Iron filters often discharge large amounts of water in the backwash and the chemical make up of the backwash water can be harmful to the soil disposal system. See Pg. 20, Article. 3.1.4.. Backwash water from water treatment devices is not contaminated with pathogens and does not need treatment in the sewage treatment and disposal system. Direct this excess water elsewhere and save on the design and cost of the treatment and disposal system.

The Disposal of Effluent

Clearances

Boundaries and property lines, buildings, wells and other water sources, are a major consideration in laying out a disposal system. Refer to the Standard of Practice for acceptable minimum clearance requirements for each component of your proposed system.

Effluent - Methods of Disposal

The liquid portion of the sewage which passes through the septic tank is known as effluent. The treatment and disposal of effluent may be accomplished by one of the following methods outlined in Sections 7, 8, 9, 10 and 11 of the Standard of Practice, depending on the percolation rates, soil conditions and water table.

Disposal Fields

Disposal Fields - General (Subsurface and Raised disposal fields)

Septic tank effluent contains minute particles of sewage, or suspended solids, and bacteria. When the effluent is discharged into the ground, these impurities are attacked by myriad biological organisms naturally present in the soil. These organisms utilize the organic materials as food and thus oxidize them into safe and stable compounds.

The biological microorganisms which perform this function are "aerobic," meaning they require the presence of available oxygen for life. Their natural habitat is the surface and upper layers of the soil. This is why lighter soils and comparatively shallow disposal fields are the most efficient for effluent disposal. To take advantage of the treatment provided by these microbes weeping lateral trench bottoms are not to be excavated in excess of 900 mm (3 feet) below the ground surface. Shallower trenches can provide better treatment and longer life. See Pg. 47, Article 7A.2.4, and Pg. 46, Article 7A.2.3 .

The intermittent flushing of disposal fields, even distribution of effluent, the rest period required between flushes, the air space provided by the media in disposal field trenches, and the use of enough weeping lateral trench area in a disposal field to allow a thin application of the effluent, all help in keeping the disposal system "Aerobic."

If an effluent disposal system is too small causing it to be constantly saturated, the oxygen is driven out of the soil and the aerobic organisms die. The system then becomes anaerobic, inefficient, a danger to health and may ultimately fail. For this reason, disposal fields installed in heavier soils are larger to enable the effluent to soak in and provide a period of dry time to help maintain aerobic conditions.

There are different methods and requirements for sizing disposal fields depending of the method of treatment which effects the quality of the effluent being discharged into the soil. The higher the quality of the effluent and the fewer suspended solids, the lower the biological oxygen demand requirements to complete the treatment. The higher the quality of the effluent, the smaller the disposal field requirements are.

In general, a disposal field requires a soil absorption area dependant on the expected volume and strength of sewage per day and the percolation rate of the soil obtained from percolation tests or the loading rates specified for soil classifications obtained from Particle or grain size analysis tests.

Different private system components provide different levels of treatment therefore, reductions in the amount of absorption area may be allowed. See Pg. 40, Article 7A.1.2, Pg. 40, Article 7.A.1.3 .

A septic tank provides a minimum level of treatment, therefore a full sized disposal field is required.

If the effluent from a septic tank is treated by a closed bottomed sand filter, which provides a higher level of treatment, prior to discharge to a disposal field, the disposal field supplied with effluent from the sand filter may be reduced by 30%.

A packaged sewage treatment plant also provides a higher level of treatment than a septic tank, therefore, the disposal field area may be also be reduced by 30% of what would be required by a disposal field supplied with effluent from a septic tank with no other treatment devices.

Additional reductions in disposal field area may also be allowed by using a pressurized effluent distribution lateral system which is designed to distribute effluent evenly throughout the entire length of the weeping lateral trenches. This system effectively delivers effluent to all parts of the disposal field preventing any one part from being saturated and anaerobic. Effluent can be delivered in small even doses making a more efficient system. Even distribution makes the organic matter in the sewage available as food to all the microbes in the entire disposal field See Pg. 44, Article 7.A.1.9. .

Weeping Lateral Trenches

Although the Standard of Practice requires a minimum of 900 mm ( 36 inches) of earth between weeping lateral trenches, a distance of 3 m (10 feet) is recommended for ease of installation. See Pg. 46, Article 7.A.2.3 .

Trenches for weeping laterals must be .45 m (18 in.) minimum width and 0.9m (36 ") maximum width. The maximum depth of the trench is 0.9m (36 "). There is no minimum depth but a soil cover of 300mm (12") has shown, over time, to be adequate protection from frost for the weeping lateral trench. The required depth to prevent freezing may be less depending on the type of soil and protection from surrounding trees and winter snow cover which will vary from site to site. The gravity weeping lateral perforated piping is installed with the top of the pipe even with the top of the gravel in the trench. See Pg. 47, Article 7.A.2.4. .

Pressure distribution laterals may also be used in gravel weeping lateral trenches which will allow the trench area to be reduced by 20%. See Pg. 138, Pressure distribution.

Obtain the total area required for disposal fields from:

1. Pg. 89, Table A.4.A. for single family dwellings or duplexes, or;
2. By using a Percolation test and formula found in Pg. 41, Article 7.A.1.4. , or,
3. By using a Soil Texture Classification and Loading Rate as specified in Pg. 42, Article 7.A.1.5. .

Refer to Pg. 22, Article 3.1.14. to determine the expected volume of sewage per day.

Use the full area of trench bottom indicated. An under sized disposal field may soon become overloaded, effluent may seep to the surface, and it is more likely to freeze.

Each weeping lateral pipe, and the trench bottom throughout their entire length, should be nominally level. The top of the trench (ground surface) can vary as long as the cover over the weeping lateral pipe does not exceed the 600 mm (24 in.) maximum depth.

The weeping lateral piping shall be bedded in gravel, or other acceptable media. When gravel or alternate acceptable media is used, the top of the media should be even with the top of the weeping lateral piping. This provides support for the piping and prevents it from becoming oval shaped or broken due to the weight of the soil above or, in the event that vehicles are driven over the trenches. The installation of media higher than this is not recommended. See Pg. 48, Article 7.A.3.1..

If gravel is used in the weeping lateral trench a 12 inch depth of clean, coarse gravel of a particle size 15 mm to 40 mm (½ in. to 1 ½ in.) Is used in the bottom of the trench. The lower 150 mm ( 6 inches ) of gravel may be substituted with clean sand. The sand should not contain any silt or clay. See Pg. 48, Article 7.A.3.2. .

Gravel is necessary for these reasons:

1. It allows effluent to escape freely from the weeping lateral so it cannot freeze.
2. It provides air space in the trenches for the aerobic bacteria which are necessary to treat the effluent and prevent the suspended solids in the effluent from plugging the pore spaces of the soil.
3. If weeping laterals (perforated pipe) are laid directly in soil, the perforations soon plug and the effluent cannot escape. Gravel keeps the escape holes open, .3 m (12 in) of gravel is preferred.

Cover the clean gravel with any kind of straw (except Flax straw) or a filter fabric to prevent the backfill soil from falling into the gravel and filling the air spaces in the gravel.

If tire shreds are used as a gravel replacement, the tire shreds must be compacted in the trench prior to the installation of the weeping lateral piping. Also, a filter fabric is required over the tire shreds instead of the straw. See Pg. 49, Article 7.A.3.3. .

Backfill in the weeping lateral trenches must not be compacted. Do not pack the backfill or run vehicles over it. Allow 50 mm to 75 mm (2 or 3 in.) of excess backfill to make up for settling, and allow the backfill to settle naturally.

Chamber Type Disposal Fields

Chamber type disposal fields are an alternative to gravel filled disposal fields. Chambers are manufactured structures that replace both the gravel and the weeping lateral piping. The chambers are installed in the excavated trenches beginning with a starter section and each chamber interlocks with the next chamber. The manufacturer provides ends, splash pads and other accessories for their chambers.

There are several manufacturers of chambers and each manufacturer has different installation requirements. Some manufacturers require the chambers to be covered with a filter fabric, others do not. The method of connecting piping to the chambers may be different from manufacturer to manufacturer as well as the method of installation of small diameter piping for pressurized distribution laterals for the distribution of effluent throughout the entire length of the weeping lateral trench. See Pg. 50, Article 7.B.2.1..

Chamber type disposal fields are subject to all normal installation requirements for disposal fields (See Pg. 46, Article 7A.2.3 and Pg. 47, Article 7A.2.4). However, there are some additional requirements for the installation of chambers. Chamber system installations must include splash pans supplied by the manufacturer or the most upstream 3 m (10 ft.) of all weeping lateral trenches or other area that receives effluent, shall be filled with a minimum of 100 mm (4 in.) of gravel, or use some other suitable means to dissipate the hydraulic energy of the effluent it is receiving to prevent erosion or disturbance of the trench bottom. See Pg. 50, Article 7.B.2.2. .

Although the there may be some advantages to the use of chambers such as they are light weight, easy and quick to install, and less site cleanup (removal of excess or spilled gravel and straw) is required, chambers are subject to same problems in the soil as gravel filled trenches. The same site variables that effect the operation of gravel filled trenches, also effect the operation of chamber systems. See Pg. 184, Fig. DF 5 and Pg. 185, Fig. DF 6 in Appendix "B"

Chamber systems must provide the same equivalent square footage of trench bottom as required for a gravel filled trench system. A chamber is credited with an equivalent width 1.6 times its actual width. A 15" wide chamber times the 1.6 factor gives an equivalent width of 24 inches. A disposal field requiring a total of 1000 sq. ft. would require 500 ft. of 2 foot wide gravel trenches or 500 ft. of 15 inch wide chambers. The length of the trench is not reduced in comparison to an equivalent width of gravel filled trench. See Pg. 50, Article 7.B.2.2. .

Sizing of Disposal Field Trench Bottom Area

Disposal fields are sized using two basic criteria:

1. The volume of sewage expected per day (with consideration to the strength of the sewage effluent) See Pg. 22, article 3.1.14
2. The soil capacity for receiving effluent (determined by a perc test or soil classification) See Pg. 41, Article 7A.1.4 and Pg. 42, 7A.1.5

Although there may be other site specific consideration that must be made, by using the soil capacity and volume of sewage expected the trench bottom are can be determined.

Disposal Field Worksheet

The following worksheet provides a process for calculating the required trench bottom area in a disposal field.

Location of Disposal Fields

Avoid hard packed yards, driveways, paths, etc. See Pg. 45, Article 7.A.2.1. and Pg. 38, Article 7.1.5. .

The disposal field should be constructed on elevated, well drained ground. The disposal field must not be constructed in low areas which may be subject to flooding ( See Pg. 21, Article 3.1.6. ), or where a seasonally saturated layer is evident below the trench bottom, or within a vertical distance of 1.5m (5 feet) from an impervious layer of rock or water table. See Pg. 38, Article 7.1.6 .

A sloping, sheltered, well drained, sunny location where the snow piles deep in winter and the grass is well kept in summer is ideal. Do not allow growth to shade the ground surface. See Pg. 48, Article 7A.2.9

Level Ground Systems

In level areas, using a siphon type septic tank, there is often a problem in keeping the disposal field at a shallow 300 mm to 600 mm (12 to 24 in.) depth. The loss in elevation within a septic tank with siphon requires the building drain and inlet to the septic tank to be above ground. See Pg. 183, Fig. DF 2, Pg. 183, Fig. DF 3, Pg. 183, Fig. DF 4, Pg. 185, Fig. DF 6, Pg. 190, Fig. DF 11 in Appendix "B" and Pg. 47, Article 7.A.2.5 .

A level ground disposal field differs from a sloping ground disposal field in that:

1. fittings such as (Y's), (T's), (TY's), or "crosses" may be used to inter-connect all field headers and weeping laterals, and;
2. all perforated piping must be at the same level, and; See Pg. 47, Article 7.A.2.5. .
3. all weeping lateral trench bottoms must be at the same level.

Sloping Ground Systems

Where it is necessary to locate a disposal field on a sloping area, special precautions must be taken to see that all laterals are equally supplied with effluent and installed at the proper depth. This can be accomplished by the methods shown in Pg. 184, Fig. DF 5, Pg. 186, Fig. DF 7 and Pg. 187, Fig. DF 9 in Appendix "B".

It is of great importance to note that in all sloping ground systems that each weeping lateral is installed level, but at a different elevation. Pg. 184, Fig. DF 5, Pg. 186, Fig. DF 7 and Pg. 187, Fig. DF 9 in Appendix "B" shows each installation has three laterals, each connected to the other by means of a solid pipe. Each weeping lateral trench is deeper than the trench for the solid pipe.

Use gravel only under the weeping laterals. If gravel is used under the solid piping, the effluent may follow the gravel down the hill side.

Sloping Ground Systems Using Distribution Boxes

The distribution box is possibly one of the oldest methods of attempting to distribute relatively even volumes of effluent to weeping laterals with gravity flow. There have been elaborate distribution box designs that have included such things as adjustable weirs, baffles, adjustable orifices etc., and at the time of installation, did distribute effluent to all weeping laterals. Unfortunately, over the long term of operation, distribution boxes have failed to provide relatively even distribution of effluent to weeping lateral trenches using gravity flow.

Distribution boxes have traditionally been rectangular in shape, having the inlet on one side and many outlets along the other side and in some cases, the ends. This form of distribution box covers a large surface area and provides great horizontal distances between the outlets that are farthest apart. With the great surface area of this design, the distribution box is very subject to movement caused by frost heave. After use over one winter, it is normal to find the distribution box off level and distributing a large amount of effluent to the lower end and little or no effluent to weeping laterals connected to the higher end of the now sloping distribution box.

To minimize this problem, it is important to:

1. keep the distribution box as small as possible, See Pg. 47, Article 7.A.2.7. ,
2. keep the number of outlets to a minimum,
3. keep the outlets as close together as possible,
4. provide a volume flush to the distribution box and field, and
5. prevent the momentum of the incoming effluent from washing directly onto an outlet.

Pg. 184, Fig. DF 5 in Appendix "B" shows distribution box design and a method of distribution to a chamber type disposal field on sloping ground with weeping laterals at different elevations. It is also important to minimize the length of pipe(s) between the distribution box and the weeping laterals to avoid freezing problems in the piping. See Pg. 134, Article 7A.1.8 .

Sloping Ground Systems Using Drop Boxes

See Pg. 186, Fig. DF 7 and Pg. 186, Fig. DF 8 in Appendix "B"

Pg. 186, Fig. DF 7 in Appendix "B" uses a drop box instead of fittings to supply the weeping laterals with effluent from the gravity distribution header. Drop boxes are simply a container with holes cut in it for the inlet, outlet, and the weeping lateral(s). A 20 litre ( 5 gal.) plastic pail, complete with lid, may be utilized as a suitable drop box. The holes cut in the drop box should fit the piping tightly and should be sealed water-tight around the piping. The ends of the weeping laterals must also extend into the drop box far enough to be capped off. Periodic capping allows the weeping lateral(s) to be given a rest period by forcing the effluent to overflow to the next drop box and lateral(s). The lid of the plastic container provides access for capping the weeping lateral(s), and a method of monitoring the condition of the disposal field. Proper marking of the location and protection of the drop box lid is required.

Drop boxes load each trench progressively down the hill. As one trench is filled and reaches capacity the excess effluent will then flow to the next trench. This results in each trench being filled and saturated as they are used. This causes anaerobic conditions in the trench and removes any advantage of increased digestion of the sewage by aerobic microorganisms in. While drop boxes are an acceptable method of distribution it is not a preferred method.

See Pg. 47, Article 7.A.2.8.

Sloping Ground Systems Using Bi-level Crosses

See Pg. 187, Figs. DF 9 and Pg. 188, Fig. DF 10 in Appendix "B".

Note: This method is not recommended for installation on slopes exceeding 10% (10 vertical to 100 horizontal) grade .

Disposal fields using Bi-level crosses should have the effluent sewer and distribution header running straight down the hill. The distribution header is located higher than the weeping laterals and each lateral is distributed with effluent in succession. The weeping laterals which connect under it, are at right angles and are level. Holes should be carefully measured and cut in the bottom of the distribution header, according to the number of weeping laterals which cross under it and are fed by it. The trenches for the weeping laterals may bend around a hill like a level irrigation ditch.

On Bi-level cross systems, no gravel should be used under the main distribution header as it may cause the system to fail. Gravel should only be under the weeping laterals. In this way the effluent is held on the hill side for treatment, and evaporation.

When using bi-level crosses in a field, it is essential that the holes in the distribution header are sized carefully. If the holes are too small, too much effluent may pass the first weeping laterals and overload the bottom laterals. If the holes are too large, only the first weeping laterals will be supplied with effluent.

A holding tank for overloads and emergency pumping may be recommended for the end of the distribution header in some applications. In the event the weeping laterals become loaded or frozen, the excess effluent has clear passage through the elevated header to the holding tank. This system has proven very successful in systems which may be subject to occasional short term overloads, or to supplement a disposal field where there is not enough room to install the sufficient area of weeping lateral trench.

See Pg. 135, Article 7A.1.8, Pg. 47, Article 7A.2.6.

Split Disposal Fields

Split fields are advantageous in areas with soils that have a high saturation percentage (high percentages of clay or expansive clays), as these soils may be expected to have reduced percolation rates after being in use for a period of time. These expansive clays will shrink as they dry causing considerable cracks in the soil which will accept effluent when the laterals are put back into use. The cracks will provide a greater surface area for the effluent to enter the soil.

Another advantage of the split field system is that two smaller disposal fields may be installed in two smaller areas separated from each other. See Pg. 183, Fig. DF 4., or Pg. 189, Fig. DF 11 in Appendix "B". For example, one disposal field in the front of the house and the other in the back yard. This can be a viable alternative in situations where there is not sufficient room in one area to install the total area of weeping lateral trench required, or a way to add on to an existing disposal field which has failed. In this case, the new disposal field would be half the size of the total trench bottom area of weeping lateral trench required. The old disposal field could then be rested and may work again as an alternative field.

This system takes the total required trench bottom area of weeping laterals required and splits it into two (or more) separate disposal fields. The minimum size of each disposal field when using the split field method should not be less than 37 m2 (400 square feet) of weeping lateral trench. See Pg. 40, Article 7.A.1.2., Pg. 43, Article 7A.1.6

The use of a diverter (a small manhole in which the unused outlet is plugged), allows the owner to switch the flow of effluent from one field to the other. This provides a rest period where a saturated or inefficient field may dry out and regenerate it's self. See Pg. 190, Fig. DF 12 in Appendix "B".

The resting period when possible should be one year. Such a rest will change an anaerobic, saturated, clogged soil back to it's original aerobic, pervious condition. The same surface area, using a split field system, will be several times more efficient than a single field which never has the opportunity to become refreshed.

As a field is halved, so also is the volume per flush halved. See Pg. 43, Article 7.A.1.6.. This may avoid the need for larger and/or separate effluent chambers and result in a considerable saving in cost.

Example

1. 340 litres (75 gallons) per flush is adequate for 37 m2 to 55 m2 (400 to 600 square feet) of weeping lateral trench.
2. a minimum of 454 litres (100 gallons) flush is required for 75 m2 (800 square feet) of weeping lateral trench.

A minimum size septic tank for a three bedroom house would have a working capacity in the first chamber of 1800 litres (400 gallons) and an effluent chamber capable of discharging 340 litres (75 gallons). This could not be used if the standard of practice required more than 56 m2 (600 square feet) of weeping lateral trench. However, using the split field system, a minimum sized septic tank and effluent chamber could serve two 56 m2 (600 square feet) disposal fields, or a total of 112 m2 (1200 square feet) of weeping lateral trench.

Larger split fields may be installed as shown in Pg. 196, Pg. 178, Fig. PDL 5 and Pg. 191, Fig. DF 13 in Appendix "B". In this case several trickle septic tanks have been installed in series to provide the working capacity required for the expected volume of sewage per day. The last tank in the series is used as an effluent chamber in which a pump must be installed. See Pg. 20, Article 3.1.3.

When designing these large systems consideration should be given to rotating the area of the disposal field the effluent is delivered to so that the required volume per flush is minimized. The effluent tank can be kept smaller and the pump capacity required is minimal when rotating loading areas.

The advantages of a split field system should always be considered when selecting a system design.

Raised Disposal Fields

Raised disposal fields may be installed where a seasonally saturated layer or water table is too close to the ground surface to permit the installation of a normal system. This system is installed by hauling sufficient fill material to provide the minimum vertical separation distance from the bottom of the trench to the water table. When considering this method, it is a good practice to haul in the fill material and let it settle naturally over winter before proceeding with the installation of the system. This will help to avoid settling and landscaping problems after the installation is made. Grass cover should be established as soon as possible after the installation is completed. All normal installation requirements for disposal fields apply. See Pg. 38, Article 7.1.6 . See Pg. 178, Fig. Vertical Separation in Appendix "B"

Lined Trenches For Porous Soils

In the soil, microorganisms break down the organic matter ( measured by the Biochemical Oxygen Demand and Total Suspended Solids) carried into the effluent disposal system. Pathogens become trapped in the soil, either by being adsorbed onto the soil particles or stuck to the microbial slimes deposited by the soil bacteria. Once trapped, many pathogens are destroyed by differences in temperature, lack of moisture or food, or preyed upon by larger soil bacteria. Others may also be inhibited or destroyed by natural antibiotics that are created by soil fungi and other organisms.

In order for treatment of effluent to become effective, the soil bacteria must have both oxygen and sufficient time to treat the effluent. These conditions will exist if the soil under the effluent disposal system remains unsaturated.

In an unsaturated soil, effluent moves through the soil slowly in thin films around the soil particles, the larger soil pores (spaces between the soil particles) contain oxygen.

Under saturated flow conditions, the soil pores may be completely filled with effluent and the effluent may travel through the soil very quickly with little or no exposure to oxygen or the soil bacteria. In soils that contain a high percentage of gravel or sand, the soil pores between the particles would be expected to be very large and the flow of effluent through these soils would be very fast and provide little or no treatment.

In very porous soils or soils that have a percolation rate of less than 5 min. per 25 mm ( 5 min. per inch), an effluent disposal system may be provided with a layer of soil 300 mm (1 foot) thick that has a percolation rate in excess of 5 min. per 25 mm ( 5 min. per inch). This liner provides a restrictive layer of soil that the effluent passes through at a slower rate. When the effluent reaches the excessively porous soil outside the liner, there is not sufficient flow rates to allow saturated flow conditions through the porous soil. This forces the effluent to flow through the porous soils in thin films, from soil particle to soil particle providing both exposure to oxygen and sufficient time to treat the effluent. While sufficient treatment of pathogens is expected using this method it does not remove nitrate from the effluent. Additional treatment considerations should be given to accomplish denitrification in many circumstances.

See Pg. 45, Article 7A.2.2 . See Pg. 181, Fig. DF 1A and Pg. 182, Fig. DF 1B in Appendix "B".

Pressure Distribution Lateral Systems

 

Pressure Distribution Lateral System Uses

The intent of a pressure distribution lateral system is to provide for the even distribution of effluent over the entire surface of the treatment area. This assures the entire design area is used equally and prevents localized overloading.

Pressure distribution lateral systems:

1. may be used in disposal fields, both chamber and gravel type, (Enables a 20% reduction in required trench bottom area)
2. are always used in sand filters, and
3. are always used in treatment mounds

A pressure distribution lateral system substantially increases the efficiency of the treatment and absorption of effluent in a soil based treatment and disposal system. The efficiency is gained by two characteristics the pressure distribution system provides:

1. Even use of the entire design treatment area.
2. The ability to apply the effluent in small thin doses over the treatment area.

Gravity distribution cannot be relied on to distribute the effluent to all areas of the system. This causes localized overloading and a heavier biomat will develop in these areas due to higher organic loading and less aerobic conditions. Localized overloading also causes saturated soil conditions which will slow the rate at which the soil can absorb the water. These concepts holds true in disposal fields, treatment mounds and sand filters.

Use in disposal fields

There are advantages and efficiencies, other than a 20 % reduction in disposal field size, to using a pressure distribution lateral system in a disposal filed.

Large disposal fields

• Pressure distribution laterals should always be used in large disposal fields so that equal distribution can be achieved. The system can be set up to alternately feed each individual distribution lateral in extremely large fields to reduce pumping requirements and pipe sizes. See Pg. 195, Fig. PDL 4 and Pg. 196, PDL 5 in Appendix "B"

Course soils having fast percolation rates

• In soils having a percolation rate faster than 5 minutes per inch, and requiring trenches lined with slower percolating soil, pressure distribution should always be used. Using the pressure distribution in these systems reduces the possibility that channeling will occur in the soil lining the trench and will make the most use of the 1 foot of soil provided to line the trench.

Pressure Distribution Lateral System Design

Pressure distribution laterals are essentially rigid plastic pipe having evenly space holes drilled in the pipe out of which the effluent will spray. Pressure distribution laterals must be custom made for each individual installation. Once the desired size and spacing of orifices in lateral is determined the orifices are drilled in the appropriate size of rigid, pressure rated plastic pipe. The lateral piping is usually Schedule 40 rigid PVC pressure piping.

See Pg. 49, 7A.3.4 , Pg. 55, Article 8.3.1. and Pg. 62, Article 9.3.2 and, Pg. 192, Fig. PDL 1 and Pg. 193, Fig. PDL 2 and Pg. 201, Figs. M 2 in Appendix "B".

Orifice selection and spacing

The size and spacing of the orifices will vary depending on the application. Determining the spacing of the holes begins with the selecting the spacing of the orifices to provide even distribution and utilize the entire treatment area efficiently. The standard of practice sets maximum spacing of orifices depending on the application.

• Maximum orifice spacing for disposal fields and treatment mounds is 5 ft., See Pg. 44, Article 7A.1.9. (a good target for treatment mounds is one orifice for every 6 sq ft.)
• For sand filters, spaced to provide minimum coverage of one orifice for every 2 sq. ft in a coarse sand, sand filters and one orifice for every 6 sq. ft in a medium sand sand filters, see Pg. 61, Article 9.2.7.

Spacing of the holes will have some affect on the total volume of effluent discharged per minute, affecting pump requirements, as spacing will affect the total number of holes.

The diameter and length of the lateral as well as the maximum number, size and spacing of perforations in the pipe must be carefully calculated to maintain even distribution of the effluent. See Pg. 69, Table A.1.A. and Pg. 73, Table A.1.B. in Appendix "A".

Design Pressure Head

Head pressure required in the distribution laterals is set at a minimum of 5 ft. pressure head in disposal fields and sand filters see Pg. 44, Article 7A.1.9 and Pg. 58, Article 9.1.8 and a minimum of 2 foot head for treatment mounds, see Pg. 73, Table A.1.B see note at bottom of table to use minimum 2 foot head pressure. A minimum 5 ft. head pressure is recommended for all systems.

Friction loss in the effluent line and distribution header, and the vertical lift required must be calculated to provide the minimum residual head pressure required at the inlet to the distribution laterals See Pg. 77, Table A.1.C.3. and Pg. 78, Table A.1.C.4. in Appendix "A".

The design head pressure, number and size of orifices will determine the total volume required and must match the rate of discharge from the pump at the calculated head pressure in order to supply each of the orifices throughout the distribution lateral system. See Pg. 73, Table A.1.B. in Appendix "A".

Effluent volume per dosing cycle

The maximum effluent volume per dosing cycle is set out in the standard of practice.

• For disposal fields it is a maximum 20% of the daily volume per dosing cycle, ( Pg. 44, Article 7A.1.9 )
• For treatment mounds it is a maximum 25% of the daily volume per dosing cycle, ( Pg. 52, Article 8.1.6 )
• For sand filters it is a maximum 10% of the daily volume per dosing cycle, ( Pg. 58, Article 9.1.11 )

In all cases smaller doses of effluent with equal resting periods between doses is preferable.

The amount of effluent stored in the effluent tank or dosing chamber will also affect the desired volume per flush. If the effluent tank only holds 60 gallons of effluent the system should not be designed to deliver 60 gallons per minute. If this were the case the pump would only run one minute and be out of effluent and the piping system would barely be full causing unequal distribution of effluent. If insufficient volume is available consider the dosing of individual laterals during each pump cycle using an automatic distribution valve. See Pg. 195, Fig. PDL 4 , and Pg. 196, Fig. PDL 5

Pressure distribution systems on sloping ground.

When using pressure distribution laterals, or simply pressure distribution feeding gravity laterals, in a disposal field on sloping ground additional considerations must be made in the calculation of the system. In particular the selected orifice sizes or providing flow control orifices to each lateral. From one lateral to another, which are at difference elevations, the pressure head in each lateral will change in an amount equal to the change in elevation less the friction loss between laterals. This can significantly affect the volume of effluent discharged from an orifice in one lateral to an orifice in another lateral at a different elevation.

For example assume one lateral is 4 feet lower than another and 5/32" orifices are used in each lateral. The higher orifice at 2 ft head would discharge 0.34 gals/min and the lower orifice at 6 ft head (2ft. + 4ft. the difference in elevation) discharges 0.59 gals/min. A 73% increase in volume discharge. If this increase is not considered the pump will be undersized and the lower laterals will be overloaded. The upper lateral may not receive any effluent because the pump volume is overloaded. This variance must be calculated in the design of the system and the selection of orifice sizes, or flow control devices must be provided to each lateral. The time it takes to fill the piping to the different elevations must also be considered.

A source for methods of calculating these type of systems can be found with some manufactures of on-site sewage treatment equipment and systems.

A squirt test will quickly test the design and should always be performed on any pressure distribution or pressure distribution lateral system when installed.

Squirt Test

The squirt test is a very simple way of checking both the initial design of a pressurized distribution lateral system used in a pressure distribution lateral system in a sand filter, treatment mound or disposal field and for maintenance purposes to see if the orifices are clogged and require service.

Once the pressurized distribution system has been assembled and the orifices drilled, place the assembly in its approximate final location with the orifices pointed upward. Connect the pressurized distribution assembly to the effluent pump and also connect a pressure gauge or clear, vertical site tube to the most downstream end of the distribution lateral that is farthest from the effluent pump.

Turn on the effluent pump and pump some water through the pressurized distribution system. The water being discharged from each orifice should "squirt" approximately 1.5 m (5 feet) high (if that is the selected design pressure head) and there should not be a variation in the height of the squirt over the entire system of more than 20% which will maintain the volume variation between orifices at less than 10%. See Pg. 194, Fig. PDL 3 Squirt Test in Appendix "B".

If the squirt height is proper and even, as mentioned in the previous paragraph, check the pressure on the pressure gauge or record the residual head height in the site tube, and record for future reference. After the system is installed and has been in use for some time, you can reconnect a pressure gauge or site tube to the system and check the pressure. If the pressure has reduced, this is an indication that the pump screen may be plugged or the pump is worn and may need to be serviced. If the pressure has increased, it is an indication that some of the orifices have become clogged and the distribution laterals need to be serviced. See Pg. 194, Fig. PDL 3 Squirt Test.

The Squirt Test can be used to check for proper distribution of effluent in a Sand Filter, Treatment Mound or Disposal Field.

Orifices orientation and orifice shields

When the distribution laterals are installed in gravel, (disposal field trenches, mounds or sand filters) the perforations may be drilled into the top or bottom of the laterals. When drilled into the top of the distribution lateral, the orifices must 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.

See Pg. 53, Article 8.1.12, Pg. 44, Article 7A.1.9, Pg. 61, Article 9.2.7 and Pg. 192, Fig. PDL 1.

There are advantages and disadvantages to locating the orifice in the top or bottom of the pipe. Holes located in the top of the pipe are less prone to plugging as sludge and bacterial growth in the pipe tends to accumulate on the bottom of the pipe. Holes in the bottom of the pipe may clog quicker because of this. Holes in the top of the pipe also quickly allow the air to escape from the pipe. Holes at the bottom of the pipe provide the advantage of allowing the pipe to drain completely. In systems that require, or it is chosen to have, the orifices point up it is acceptable to have a few orifices pointing down to drain the pipe. Provide orifice shields that drain for these orifices to prevent erosion of the sand or soil below.

When the distribution laterals are installed in chambers, the orifices must always be in the top of the distribution lateral but they do not need to be provided with an orifice shield.

See Pg. 44, Article 7A.1.9, Pg. 53, Article 8.1.11, Pg. 54, Article 8.2.6., Pg. 55, Article 8.2.7. Pg. 55, Article 8.3.1, and Pg. 61, Article 9.2.7

Pressure Distribution Lateral System Sizing

(This information can generally be applied to all pressure distribution lateral systems.)

To size the piping and pump requirements for a pressure distribution lateral system, the following information must be determined and available:

1. the spacing, size, total number of orifices and design pressure head proposed for the installation.
2. the vertical head from the elevation of the pump to the distribution system, identify differences in elevation between laterals if any.
3. the length of the effluent line and number of fittings from the pump to the distribution header to determine the friction loss in the piping.
4. the required length of the distribution laterals.
5. the volume of pump discharge at various head pressures (pump curve chart) for the model of pumps available, (a siphon cannot be used). Volumes may have to be converted to imperial measures.
6. Volume of effluent available in effluent chamber and desired duration of pumping or dosing cycle.

Pressure distribution lateral and pump sizing worksheet

The following worksheet provides a method for sizing pressure distribution lateral systems where each lateral is at the same elevation.

Dosing Volume

The amount of effluent to be delivered per dose must be set with the pump on off floats or controls to match the system design.

Example: The maximum dose delivered to a treatment mound is ¼ of the daily volume. (See 8.1.6.) For a 3-bedroom house, the single dose is calculated as 337.5 ÷ 4 = 84 gal.

The amount to be delivered to the mound in each dose is a maximum 84 gallons. More frequent, smaller flushes can provide better treatment but add pump cycles to the pump. In this example we target 4 doses at 84 gallons.

To achieve the maximum dose, the pump controls must be set in the effluent chamber to deliver 84 ÷ 6.25 (gal. per cubic foot) = 13.4 cu.ft. of effluent + the amount needed to fill the distribution line and laterals. (See Pg. 146, Table B1- Liquid Volume of Various Sizes of Plastic Pipes)

If the effluent chamber is 2 ft. by 4 ft. = 8 sq. ft. the calculation is 13.4 cubic ft. total ÷ 8 cubic ft. per foot of drop = a draw down of 1.675 ft. to provide the 84 gallons of effluent, not including the amount for the piping.

In large systems where the effluent volume available is not sufficient to does the entire system it may be desirable to split the system into sections and dose these sections sequentially. This also reduces pumping requirements and pipe sizes.

Table B1 - LIQUID VOLUME OF VARIOUS SIZES OF PLASTIC PIPES
Nominal	Inside Diameter		Volume (per 100 feet of pipe)
Pipe Diameter	mm	inches	Litres	Imp. Gallons
1	26.65	1.049	17	3.74
1¼	35.10	1.380	30	6.48
1½	40.89	1.61	40	8.82
2	52.5	2.067	66	14.66
3	77.93	3.068	145	30.0
4	102.26	4.026	250	55.1

Treatment Mounds

Treatment Mounds Description

A treatment mound includes a layer of specifically graded, clean sand that the effluent is spread over then slowly percolates through as more effluent is applied. This provides an excellent aerobic environment for the removal of organic loading in the sewage effluent. It operates similar to a sand filter in removing the organic loading. Once the organic loading has been removed by the sand layer higher long term infiltration rates into the soil can be achieved.

The sand layer is overlain with a gravel layer or chambers to assist in the distribution of the effluent over the entire surface of the sand layer and provide a brief storage area for the effluent as it is pumped onto the mound. This is then covered and a side berm created using a loamy sand. The covering soil (the loamy sand ) must be very porous to assure good aerobic conditions in the sand layer. A clayey soil cover would limit air movement into the mound and cause anaerobic conditions greatly reducing the effectiveness of the sand layer. See Pg. 198, Fig. M1, Pg. 199, Fig. M1b, and Pg. 200, Fig. M1c in Appendix "B". The treatment mound is designed to create an enhanced environment for microbial activity so special care must be taken in the use of materials and construction t provide that environment.

Treatment Mound Uses

Treatment mounds are a possible solution to difficult soil conditions or other site restrictions such as a high water table (saturated soil). Some soils do not have a percolation rate in the range of 5 to 60 minutes per 25 mm (1 inch), which is necessary for the proper operation and long term success of a disposal field. See Pg. 38, Article 7.1.5.. In other soils, there may be seasonal saturation at depths closer than 1500 mm (5 feet) to the ground surface, such that adequate vertical separation for proper treatment of the effluent is not possible under "natural" conditions with effluent from a septic tank and disposal field. See Pg. 38, Article 7.1.6.. Soils with a "hard pan" layer that restricts downward movement of liquid, or with fractured or permeable bedrock, provide problems for adequate treatment and acceptance of septic tank effluent. See Pg. 38, Article 7.1.6..

If the soil percolation rate is either too fast or too slow or a seasonally saturated soil or water table exists closer than 900 mm (3 feet) from the surface, construction of a treatment mound may be a viable method of effluent treatment and disposal.

Treatment Mound Design

Critical characteristic for the success of mounds include: quality sand layer material, correct sizing of the infiltration area, and proper construction practices.

Important factors in the design and successful operation of a treatment mound are:

1. Quality of clean sand fill
2. Size and shape (infiltration area)
3. Soil surface preparation
4. Construction procedures
5. Distribution of effluent
6. Dosing quantity
7. Location

Sand Layer Elevation and Size

Mound construction begins with the excavation of 1.5 m (5 feet) deep test holes to establish the presence of an impermeable layer or soil mottling. Soil mottling would indicate a seasonally saturated layer caused by a fluctuating water table. Soil mottling is a zone of chemical oxidation and reduction activity, appearing as splotchy patches or red, brown, orange and/or grey in the soil.

A vertical separation of at least 1 m (3.25 ft.) is required between the bottom of the sand layer and any restricting layer or seasonally saturated layer in order to maintain aerobic conditions in the natural or fill soil under the gravel bed.

Soils with a "hardpan" layer or bedrock, restrict the downward movement of the liquids. When impermeable bedrock is present, the vertical separation distance of least 900 mm (3 feet) must be provided, however 1.5 m (5 feet) may provide an additional element of safety and increase the probability of long term success. See Pg. 38, Article 7.1.6.

Determining the existence of, and depth to, any impermeable layer or saturated soil determines the required elevation of the sand layer.

The size of the sand layer required is determined by the expected daily volume of sewage. The sand layer that receives effluent (the area the effluent is applied to) is sized at 1 gallon per square foot. For example a 4 bedroom home at 450 gallons per day load requires a sand layer area of 450 square feet.

Mound Infiltration Area

The Infiltration area of a mound is that area of soil covered by the treatment mound and that receives effluent. The area of the soil receiving effluent must have the capability to absorb this effluent; otherwise, seepage from the toe of the berm may occur. The area of the mound within the berms, excluding the end slopes, provide the infiltration area into the original soil where the slope of the ground is 1 percent or less.

As long as sufficient infiltration area is available so that all of the liquid is accepted into the soil and pressure distribution is used, seepage at the toe of the berm should not occur. One of the major reasons for seepage at the toe of the berm may be inadequate infiltration area. See Pg. 198, Fig. M1, Pg. 199, Fig. M1b and Pg. 200, Fig. M1c in Appendix "B".

On original soil with slopes of 1% or less, the infiltration area is equal to the total width between both berms and the length of the sand layer. It does not include the end slopes beyond the length of the sand layer. See Pg. 198, Fig. M1 in Appendix "B".

On ground sloping more than 1%, all of the effluent is assumed to move downslope and the Infiltration area is measured from the up-slope side of the sand layer receiving effluent to the edge of the downslope berm. See Pg. 199, Fig. M1b in Appendix "B".

The berms located at the ends of the mound are necessary for mound construction but the soil area under these berms is not considered part of the total infiltration area. See Pg. 52, Article 8.1.3.

Sizing of the Infiltration Area

The infiltration area is sized at 70% of the size of trench bottom area required for a disposal field as calculated by using percolation tests or soil texture classification to establish a loading rate per square metre or square foot. See Pg. 52, Article 8.1.3.

Pg. 41, Article 7.A.1.4. provides a formula to calculate loading rates according to the percolation tests results. A table of loading rates for percolation rates up to 120 minutes per inch is provided in table A.4. See

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

Mound Infiltration Area Worksheets

Click here for the worksheets for Treatment Mounds.  

Construction of Treatment Mounds

Compaction of the ground surface under the mound area should be avoided as much as possible. The placing of materials during the construction of the mound is best done with the use of a Hi-Hoe from the edge of the mound. This keeps all construction equipment off the mound area during construction and helps avoid uneven compaction of the construction materials. If a Hi-Hoe is not available, the use of track type machinery should be used. See Pg. 54, Article 8.2.4

Once the location of the outer edges of the berm have been established, the installation of the effluent line from the septic tank to the mound may be installed. The trench for the effluent line should extend only under the edge of where the base of the completed mound will be and must be carefully backfilled and compacted to prevent settling of the mound into the trench.

Prior to the actual installation of the effluent line, the installer must know the pump capacity and head pressure, the distance from the septic tank to the mound and the friction loss throughout the piping to enable him to size the effluent line to provide adequate pressure in the laterals for proper distribution of effluent. See Pg. 69, Table A.1.A. and Pg. 73, Table A.1.B. in Appendix "A".

A properly constructed mound should be placed on at least 600 mm (24 inches) of natural soil which is not seasonally saturated. If this is not possible, suitable fill material (loamy sand) must be imported to provide the minimum 900 mm (36 inch) vertical distance between the bottom of the sand layer and the seasonally saturated layer or hard pan layer. See Pg. 199, Fig. M1b in Appendix "B".

Sandy loam fill material (when required to raise the mound to comply with the vertical separation requirements from a water table or impervious layer (See Pg. 38, Article 7.1.6) should now be placed. The surface of the fill material should be leveled to provide a level base on which to install the sand layer.

Note: See Pg. 56, Article 8.3.2. for sand qualities. The sand that is needed for the construction of a treatment mound must be fairly clean sand that does not contain more than 10% fines.

Jar test for fines

A quick test to see if the sand contains too many fines is to place in a glass quart jar, 50 mm (2 inches) of sand and fill the jar with water. Shake the jar to mix the sand and water, then set the jar down and let the contents settle for several hours. If there is a layer of fines that settle on the top of the sand that is thicker than 3.2 mm ( inch), the sand contains too many fines and is not suitable for use in a treatment mound.

The clean sand is then placed on the undisturbed soil at the base of the mound or on the sandy loam fill material when additional fill material is required. The top of the sand layer that provides the contact area for the gravel layer or chambers must be smooth and level. This contact area between the sand and gravel or chambers is the area used for proper sizing of the treatment mound. See Pg. 51, Article 8.1.2. and Pg. 54, Article 8.2.3 . See Pg. 200, Fig, M1c in Appendix "B"

Note: It is not unusual for an installer to provide a small berm of sand around the leveled off contact area to help contain the gravel, during the placement of the gravel and the distribution laterals. The berm is not to be considered in the size calculation of the contact area. See Pg. 198, Fig. M1, and Pg. 199, Fig. M1b in Appendix "B".

The gravel or gravel and chambers are then placed over the sand layer. If chambers are used, the chambers must be installed on a minimum layer of 50 mm (2 inches) of gravel and the inside area of the chambers must provide exposure to a minimum of 80% of the sand surface (contact area). See Pg. 52, Article 8.1.5.

When gravel is used, the manifold and distribution laterals must be installed in the gravel and covered with the gravel, See Pg. 54, Article 8.2.5.. If chambers are used, the distribution laterals must be installed inside the chambers and the orifices must point upward. See Pg. 141, Orifice orientation and orifice shields for more information.

If gravel is used over the sand layer, the gravel must be covered with straw or a filter fabric to prevent the soil covering from infiltrating into the gravel. If chambers are used, any exposed gravel between the rows of chambers or around the perimeter of the chambers must also be covered with straw of filter fabric. Chambers should be installed in accordance with the manufacturer's instructions. Some chamber manufacturers require a filter fabric to be installed over the chambers, others do not.

The entire surface of the mound constructed so far, must now be covered with loamy sand fill material to provide shape to the mound. The centre of the top of the mound must be covered with a minimum of 300 mm (12 inches) and the edges of the gravel bed and side slopes covered with a minimum of 150 mm (6 inches). The side slopes of the mound shall not be steeper than 1:4 (one vertical to four horizontal). See Pg. 55, Article 8.2.8. and Pg. 55, Article 8.2.12.

A final covering of top soil to support grass growth must then be placed over the entire mound surface. See Pg. 55, Article 8.2.9.

A covering of grass must be established immediately over the surface of the completed mound. See

See Pg. 203, Fig. Typical SF 1, Pg. 204, Fig. SF 1, Pg. 205, Fig. SF 2, and Pg. 206, Fig. SF 3. in Appendix "B".

In a system that uses a sand filter, primary treatment of the sewage takes place within the anaerobic environment of the septic tank or an aerobic packaged sewage treatment plant. Here, separation and settling of solids or flotation of greases removes many solids from the sewage and produces an effluent relatively free of floating or settleable solids. The effluent is then pumped to the aerobic environment of the sand filter for further treatment prior to final discharge into the soil.

Within the upper elevation of the sand filter, there is a pressurized distribution lateral piping system containing orifices, which is designed to discharge effluent evenly over the surface of the sand. To ensure the highest level of treatment, the effluent should be discharged to the sand filter in many small doses over a 24 hour day. This is best accomplished with the use of a timer which can be programmed to accommodate both the number of pump cycles per day as well as the length of each cycle. The use of a timer and the small doses of effluent encourage the movement of effluent through the sand filter to travel from sand particle to sand particle in thin films exposing these thin films to both oxygen and microorganisms that treat the effluent. See Pg. 182, Fig. DF 1B in Appendix "B".

As the effluent passes through the sand filter media, solids and other contaminants are mechanically, biologically and chemically reduced. Naturally occurring microorganisms reside on the surfaces of the sand particles and thrive on the regular doses of nutrients contained in the effluent.

At the lower elevation of the sand filter, effluent which has passed through the sand filter media is collected by an underdrain pipe which carries the effluent out of the sand filter to either a pump chamber or by gravity to a disposal field for final disposal. See Pg. 57, Article 9.1.2 and Pg. 60, Article 9.2.5 . Any gravity piping from a sand filter must kept very short and be well protected from frost. Small regular doses of effluent discharged to a sand filter will result in essentially a trickle type discharge from the sand filter which is very subject to freezing during the colder months of the year. If the disposal field is remote from the sand filter, a pump chamber should be used and the effluent pumped to the disposal field in suitable volumes as to prevent freezing. In most cases pump vaults are installed in the interior of the sand filter and used to dose a disposal field.

Sand filters do require maintenance. The pressurized distribution system should be checked annually for plugged orifices and the laterals flushed and cleaned by running a brush through them. Provisions for access to the ends of the laterals for cleaning purposes must be provided at the time of installation. Periodic cleaning of the septic tank as well as making sure the screen required on the effluent pump is in place and functioning properly is good preventative maintenance.

In the event that an excessive amount of solids has been discharged to the sand filter over a period of time, a layer of solids may form over the top of the sand filter media and become a restrictive barrier on the top of the sand filter media. It may be necessary to disturb the surface of the sand filter media, or in extreme cases, even remove and replace the top layer of sand filter media. The use of a larger working capacity septic tank will provide better primary treatment and result in an effluent with less suspended solids being discharged to the sand filter reducing possible clogging of the sand filter.

Sand Filter Design and Construction

Sand filter size

The size of the sand filter is determined by the expected volume of sewage per day and the loading rate for the specific type of sand used in the sand filter. Loading rates for the sand filter is 2.4 gals per sq. ft. per day for course sand sand filters and 1 gal per sq. ft. per day for medium sand sand filters ( see Pg. 57, Article 9.1.6 and Pg. 58, Article 9.1.7). For example when serving a 4 bedroom home at 450 gals. per day the size of a course sand sand filter will be 187.5 sq. ft., approximately 12 ft. x 15 ft.

Sand filter effluent loading rates

Effluent is distributed over the surface of the sand layer with the use of a pressure distribution lateral system that provides a minimum coverage of 1 orifice per every 2 sq. ft. in a course sand sand filter and 1 orifice for every 6 sq. ft. in a medium sand sand filter. Complete and even distribution of the effluent over the sand layer in intermittent doses is critical to the proper long term operation of the sand filter. Each effluent dose delivered to the sand filter can not exceed 10 % of the daily volume of sewage (see Pg. 58, Article 9.1.11). The sand used is very expensive, if it is not wetted during the dosing it is ineffective and wasted.

The type and quality of sand used in the sand layer is also critical to the long term success of the sand filter. The sand used in the design of the system must be very clean and of a particular grade. The use of sand other than that specified will result in poor performance and premature failure of the sand filter.

To achieve effective treatment, attention must be paid to the details of design and construction of the sand filter. Some companies provide design assistance, component parts for the effluent distribution and control components for the sand filter. Designers and installers not familiar with sand filters should make use of these companies.

Open Discharge

Open Discharge

Due care and consideration must be exercised when proposing this type of system. Open discharge systems are simply a means whereby effluent from the septic tank is discharged directly onto the ground surface.

Although an open discharge system may be one of the most economical methods of treatment and disposal of effluent, it is also the least desirable. This type of system is not intended for use in residential subdivisions and should only be considered for use in rural areas where close proximity to neighbors, water supplies and property lines can be avoided. Health, environmental and nuisance concerns often become a major issue with this type of system. It is strongly recommended that the area wetted by the open discharge system be fenced to keep animals and children away.

There are several methods of open discharge, as shown in Pg. 210, Fig. OD 1, Pg. 211, Fig. OD 2 and Pg. 211, Fig. OD 3 in Appendix "B", depending on the slope of the land, size of the effluent chamber and the depth of bury of the septic tank.

Pg. 210, Fig. OD 1 in Appendix "B" indicates a shallow bury septic tank with a small effluent chamber. Care must be taken to ensure the effluent line is installed below frost level as, the effluent line always contains effluent. The riser should be far enough above ground level to have sufficient head to cause the effluent to drain from the riser, to below frost level when the pump shuts off. The mound around the riser provides support for the riser, as well as some frost protection. The mound should be covered with large gravel or field stone to prevent erosion from falling effluent.

Pg. 211, Fig. OD 2 in Appendix "B" indicates a deeper buried septic tank with a larger effluent chamber. In this case, all the effluent is intended to drain from the effluent line back to the septic tank to prevent the effluent line from freezing. It is necessary to install this effluent line without dips or sags which may trap pockets of effluent which may freeze and obstruct the line in cold weather. The outlet end of the effluent line should be extended at least .3 m (1 foot) above ground level to prevent the outlet from being covered with ice in freezing weather and the outlet area should be protected with large gravel or field stone to prevent erosion and possible pooling of effluent in the area.

Pg. 211, Fig. OD 3 in Appendix "B" indicates the use of a siphon type septic tank when sloping ground conditions are favorable. Here again, the outlet should be extended above ground level and the area where the effluent falls must be protected from erosion. A siphon type septic tank is capable of discharging in excess of 90 L (20 gallons) per minute and severe erosion may occur if not prevented. Care must be taken to ensure there is no air circulation through the septic tank in winter months, in order to prevent freezing of the septic tank.

Open discharge should only be considered when all other forms of treatment and disposal are not feasible. See Pg. 38, Article 7.1.6. See Pg. 178, Fig. Vertical Separation in Appendix "B"

Sewage or Effluent Lagoons

Sewage or Effluent Lagoons

Although septic tanks followed by some form of effluent treatment and disposal system are the most commonly used method for disposal of sewage from domestic residences, residences and larger installations may consider the use of a sewage lagoon. Sewage piped to a lagoon may pass through a septic tank or may flow directly to a lagoon with no treatment.

Lagoons can provide a sewage treatment and disposal solution particularly in areas where heavy clay subsoils (especially clay soils containing amounts of montmorillonite clay) and/or high SAR potable water supplies would make the use of a subsurface effluent disposal system unreliable.

A sewage lagoon is not intended to be drained and must be sized with a large enough surface area to effectively evaporate the expected yearly volume of sewage as well as the annual precipitation that may fall into the lagoon. See Pg. 67, Article 11.1.3.

The detention of the sewage for permits disease producing bacteria to die off. The combined actions of oxygen from the atmosphere, sunlight, bacteria, and algae accomplish the treatment in sewage in lagoons.

The design of a sewage lagoon is such that it has a level, flat bottom and a maximum liquid depth of 1.5 m (5 feet) with 600 mm (2 feet) of freeboard above the maximum liquid depth to the top of the berm.

At the bottom of the lagoon, a small 2 m x 2 m x 2 m (6 x 6 x 6 feet approximately) pit should be installed. See Pg. 67, Article 11.1.4. The sides of this small pit should be lined with rock or a permanent type of cribbing to prevent the sides to slough into the pit. The inlet piping should enter the lagoon approximately 600 mm (2 feet) below the top of the small pit. The purpose of the small pit is to provide frost protection for the inlet pipe. It takes very little sewage to fill the small pit and provide 600 mm (2 feet) of liquid over the inlet pipe. 600 mm (2 feet) of liquid is normally adequate cover to prevent freezing of the inlet piping. The alternative is to fill the lagoon with a minimum of 1.2 m (4 feet approximately) of water before winter to provide 600 mm (2 feet approximately) of liquid over the inlet piping to prevent freezing.

Lagoon berms and bottoms must be constructed of compacted clay or lined so that seepage is minimized. See Pg. 66, Article 11.1.1.

Berms are to have a 1.8 m (6 foot) top width and slopes of three horizontal to one vertical. Pg. 213, Fig. L 1 in Appendix "B", shows details of lagoon construction.

The gradual slope of the inside of the lagoon is very important for operational and safety reasons:

1. The large liquid surface area created by this slope allows for increased absorption of oxygen from the atmosphere for more efficient stabilization of the sewage.
2. The large liquid surface area allows increased evaporation of the sewage, reducing the amount of liquid stored and increasing the efficiency of the lagoon. (a properly sized lagoon is one in which the liquid level rises through the winter months and falls through the summer months).
3. When ice forms in the winter months, the ice expands and floats on the surface of the liquid, rising with the increasing liquid depth. In lagoons which have steep side slopes, the ice has been known to dig into the sides, effectively "capping" the lagoon, preventing any further entry of liquids. This causes the sewage to back up into the house similar to a plugged sewer, and may also result in a frozen building sewer. A hole cut in the ice will allow the liquid to overflow on to the top of the ice and drain the building sewer.
4. In the event that a person or animal should for any reason fall into a lagoon, the gradual side slopes will allow that person or animal to crawl out to safety.

The operation of a lagoon requires regular inspection, and control of grass and weed growth on the berms. Surface run off is to be diverted around the lagoon.

Fencing of lagoons is recommended, and under certain circumstances is required. See Pg. 68, Article 11.1.5.