When it comes to a septic system, the tank is usually the one thing that comes to mind. Yet, the leaching field, which is out of sight, out of mind… is nonetheless a vital component of this installation. Its proper functioning is primordial, with regard to you and your family and the surrounding community and environment. 

A leaching bed, or drainage field, is where bacteria and microorganisms found in your septic system will systematically break down waste matter. Should it fail, the entire wastewater treatment system will be affected. 

We’ll explain the functioning of a leaching bed, as well as what your role is in ensuring its proper working order. 

The Functionality of a Septic Drain Field

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On average, Canadians use 329 litres of water a day. Yet residents of the province of Quebec use, on average, 400. There’s no need for great mathematical solving to understand that, if a household has several occupants, the septic system will have to treat a significant amount of wastewater daily.

Wastewater will ideally be channelled due to gravity between the septic tank and the pipes. When necessary, it will be directed toward the leaching bed with the use of a pump. Since bacteria require oxygen to treat wastewater, the leaching bed is built in non-water-saturated soil (surface water or phreatic zone), and free of all porous elements (asphalt, concrete, shed, etc.). 

Wastewater Treatment

A leaching bed is an underground network that treats and redirects septic tank wastewater. Wastewater, which is partially treated by the septic tank, is channelled to perforated pipes that are part of the leaching bed with the help of a pump or gravity. The wastewater will then percolate through a bed of gravel, which is a process that’s designed to eliminate pollutants before the water is released into the ground. 

Decomposition of Contaminants

During this last step of the treatment process, microorganisms found in the soil digest and eliminate residual filth (suspended solids, organic chemical products, viruses, bacteria). Their role consists of breaking down the contaminants found so that the wastewater seeping into the soil, mixing with groundwater, is rendered clean. The whole process prevents contaminating the phreatic zone.

What’s the standard size of a leaching bed?

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The size of a leaching bed depends on both the choice of equipment and the property’s requirements (number of persons in the household or number of bedrooms).

For big installations, 10-cm wide pipes (4 inches) can be 30 metres long (100 feet), each positioned within 4 inches of each other. The pipes are typically sitting 90 to 120 cm deep (36 to 48 inches), and are laid on a 30-cm thick bed of gravel (12 inches), protected by a layer of backfill.  

Therefore, a standard leaching bed will require 1,938 square feet of grass-covered land to suit a 3-bedroom residence. While this may seem rather big, and such an amount of space isn’t always readily available, there are options tailored for smaller pieces of land. A modified leaching bed is one of the most commonly employed solutions. Not only is it cheaper, but it’ll make do with 646 square feet of space.

Difference Between a Conventional and Modified Leaching Bed

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As you’ve probably gathered, a leaching bed solely relies on bacteria and microorganisms found in the septic tank, as well as the soil’s filtration capabilities, to treat wastewater. 

While bacterial colonies are often subjected to unfavourable conditions caused by chemical products and detergents discharged into the system, the soil’s filtration abilities depend on several factors: soil composition, slope, surface area, depth of phreatic zone, permeability, etc. 

As such, the water, which is more or less treated, is eventually channelled into groundwater and water streams. 

Conventional Leaching Bed

The design, layout, and size of a leaching bed are contingent on the amount of wastewater to be treated (number of bedrooms in a household), the soil’s capacity to absorb water, and the depth of the phreatic zone.

PROS

• 20- to 35-year service life (35 years in low-sloped, porous soil, and regularly maintained);

• Roughly $6,000; it’s the cheapest system;

• No energy use;

• Aesthetic, solely requires a slight slope;

• No annual maintenance fees.

CONS

• High risk of clogging;

• Risk of poor wastewater drainage;

• Higher risk of soil pollution given the size of the field;

• The specific land area shouldn’t have a slope exceeding 10 to 30% (based on the chosen treatment system).

Modified Leaching Bed

Especially sought-after between 1980 and 1990, a septic system with a modified leaching bed is still the most commonly used conventional installation to date. It’s definitely preferred, not only for reasons related to cost and simplified functioning but also because it’s suited to smaller pieces of land. 

While a conventional leaching bed requires an empty 1,938 square feet of grass-covered land for a 3-bedroom household, the modified leaching bed will provide the same advantages while solely requiring a 646-square-foot plot. 

Not unlike a conventional septic system, a modified leaching bed also consists of side-by-side absorption trenches and an absorption bed designed to filter pre-treated wastewater. This more compact system has a secondary treatment system—a modified filter—on top of a primary system.  

PROS

• More compact than a standard leaching bed;

• Worthwhile price;

• No maintenance fees, except to empty the septic tank;

• Simplified functioning.

CONS

• Has an effective service life of about 15 years, but can see 25 years;

• The entire absorption surface area has to be excavated and then filled with crushed stone, which means much more significant earthworks. 

• The surface area in question must have a slope of 10% or less.

• The rock, groundwater, or porous or not soil layer must be at least 1.2 m (48 inches) below ground.

Absorption Wells

Absorption wells are the recommended solution when the land’s surface area can’t accommodate a leaching bed. Absorption wells, or infiltration wells, don’t require drains or trenches, they can be installed in confined spaces, meaning land with a limited surface area (323 square feet for three bedrooms). The filtration process is done via the wells’ walls.  

PRO 

• Suitable for small surface area plots (323 square feet for three bedrooms).

CONS

• The ground in question must be twice as porous as what’s needed for the other wastewater treatment systems;

• Solely three-bedroom or less households can benefit from this option.

Regulation 

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Wastewater overflows are hazardous to both human beings and the environment. For that reason, laws have been introduced to ensure that the installations aren’t only adequately built (solely authorized contractors can proceed with a septic system installation) but also properly maintained.

As such, septic systems will be deemed viable as long as there’s no evidence of direct environmental pollution or health hazards, as stipulated in Section 20 of the Environment Quality Act: 

No one may emit, deposit, issue or discharge or allow the emission, deposit, issuance or discharge into the environment of a contaminant in a greater quantity or concentration than that provided for by regulation of the Government.

The same prohibition applies to the emission, deposit, issuance or discharge of any contaminant the presence of which in the environment is prohibited by regulation of the Government or is likely to affect the life, health, safety, welfare or comfort of human beings, or to cause damage to or otherwise impair the quality of the soil, vegetation, wildlife or property.

Therefore, if a septic system is deemed ineffective, the government may force the homeowner to replace it. Lastly, note that it’s illegal to alter your septic system yourself, or replace it yourself. 

How much does a septic system cost?

Installing a septic system (septic tank, leaching bed, and artisan well) costs between $15,000 and $45,000. To that amount, one can add soil percolation test fees. 

The overall cost is influenced by several factors, which explains the considerable discrepancies:

• number of residents in a home;

• the chosen system, the complexity of installation;

• the chosen contractor;

• region where the system will be installed, etc.

Maintenance and Compliance

When it comes to a septic tank or leaching bed maintenance (emptying the tank), one must budget between $150 and $250. For an inspection meant to confirm the system’s overall compliance, one will spend between $300 and $500.