What are the main factors to consider when designing a septic tank?

Key factors include size and capacity based on household occupants (typically 1,000-1,250 gallons for four people), type of wastewater being treated, soil and site conditions for proper drainage, compliance with local regulations and permits, and construction materials like concrete or plastic that affect durability and cost.

How does a septic system work?

Wastewater flows from the home into the septic tank where solids settle as sludge, oils float as scum, and liquid effluent remains in the middle. The effluent then moves to a distribution box and spreads uniformly into the drainfield. In the drainfield, liquid percolates through soil where microbes break down contaminants, and purified water returns to the groundwater supply.

What size septic tank do I need for my home?

A family of four typically requires a minimum septic tank size of 1,000 to 1,250 gallons. Larger homes with more occupants or water fixtures need bigger tanks. The required capacity depends on the number of occupants, water usage patterns, and the number of plumbing fixtures in your home.

What are the different types of septic system designs?

Beyond basic systems, alternatives include chamber systems using modular chambers instead of gravel, mound systems for shallow soil conditions, aerobic treatment units (ATUs) that add oxygen for enhanced biological treatment, and constructed wetlands or sand filters for challenging sites requiring additional treatment levels.

What soil conditions are needed for a septic system?

Soil tests determine if land can safely absorb effluent and influence system type selection. The soil's percolation rate affects drainfield size and design. Flat terrain aids proper drainage, while areas with high water tables may require specialized systems like mound systems to ensure effective wastewater treatment.

What are Factors to be Considered in the Design of a Septic Tank?

Dec 17

Written By William Dainty

Designing a septic tank involves considering various factors to ensure effective wastewater management. Size and Capacity is crucial, as the tank must accommodate the number of occupants, water fixtures, and flow rates in your home. For instance, a family of four typically requires a minimum tank size of around 1,000 - 1,250 gallons, while larger homes need bigger tanks.

Type of Wastewater and Site Conditions

Effluent Nature is another consideration. Septic systems handle both blackwater from toilets and gray water from other sources, each needing different levels of treatment.

Soil and Site Conditions are pivotal too. Soil tests determine if land can absorb effluent safely, influencing system type choices. Flat terrain aids in proper drainage, while areas with high water tables might need specialized systems.

Local Regulations and Materials

Compliance with Local Codes and Permits ensures adherence to legal and environmental standards, preventing issues. The Materials used for the tank, such as concrete or plastic, affect durability and cost; concrete is robust and cheaper, while plastic is lighter and more expensive.

What is the basic design of a septic system?

A basic septic system design is an onsite wastewater treatment system widely used where municipal sewers are not available. It consists of several essential components that work harmoniously to ensure household wastewater is treated and safely dispersed.

Main Components of a Septic System

1. Septic Tank

The septic tank is a watertight underground container commonly made of concrete or plastic, typically holding at least 1,000 gallons for a standard residential setup.
Function: It receives all wastewater from the house, separating it into three layers.

Solids settle at the bottom (sludge).
Oils and grease float to the top (scum).
Liquid effluent remains in the middle.

Treatment: Anaerobic bacteria partially digest the solids, reducing their volume as gases vent through the home's plumbing.

2. Distribution Box (or Header Pipe)

The distribution box channels the partially treated effluent from the tank evenly into the drainfield via a network of pipes.

3. Drainfield (Leachfield)

A network of perforated pipes or chambers laid in trenches lined with gravel.
Function: Effluent is spread across this area, percolating through the soil where it gets further purified by soil microbes.

How the Basic Septic System Works

Wastewater exits the home and enters the septic tank.
Solids settle, while scum forms a top layer, and the effluent is left in the middle.
Effluent flows into a distribution box, then uniformly into the drainfield.
In the drainfield, the liquid infiltrates the soil slowly, allowing further microbial breakdown.
Purified water returns to the groundwater supply, completing the cycle.

Variations and Alternative Designs

Different conditions may require variations of the basic system:

Chamber systems: Utilize modular chambers instead of gravel.
Mound systems: Suitable for shallow soil conditions, creating raised mounds for effluent treatment.
Aerobic treatment units (ATUs): Enhance biological treatment by adding oxygen.
Constructed wetlands or sand filters: Offer solutions for challenging sites or when enhanced treatment is needed.

Key Considerations for Proper Design

Soil type and percolation rate: Determine the appropriate size/type of drainfield.
Household size and water use: Influence the septic tank's required capacity.
Regulatory codes: Local codes guide system design and placement.
Maintenance needs: Regular pumping and inspection prolongs system life.

Takeaways

For areas without access to municipal sewers, a basic septic system, with its septic tank, distribution box, and drainfield, is a reliable solution for managing household wastewater. It's crucial to consider site-specific factors like soil type and water usage to ensure system effectiveness and longevity.

Considering the investment into a septic system in Southern Ontario, you want the best septic designers with the most experience. Contact Bill at Headwaters Construction

William Dainty