5 Things To Consider When Designing A Septic System

A septic tank is a type of wastewater treatment system that is installed on-site for sewage collection. Septic refers to an anaerobic bacterial environment that breaks down or neutralizes the sewage that is released into a tank. While there are multiple types of tanks, septic tanks are expected to be used by roughly 20% of the population in North America. Many homeowners are installing this type of system in their homes because septic tanks are believed to be a superior alternative to public sewer systems.

When installing a septic system for a site, you must first analyze and design the system—it is a precise operation since your dimensions must be perfect to ensure that the tank is the correct size for your water usage.

5 things to consider when deciding on a septic system design:

1. Local Codes and Rules

Any big project, such as a septic system setup, necessitates ensuring that your project complies with your area’s laws and rules. You could find yourself midway through the design process and having to restart the wastewater treatment system plan because you were unaware of a regulation that you must follow. Therefore, you should always check with the authorities for the rules and codes to follow. Hiring an experienced consultant is advisable since they are aware of the local regulations.

2. Testing the soil

The septic system’s ability to function relies heavily on the soil’s condition. Your septic system’s performance is influenced by the kind of soil, even depending on the type of soil particle. There are tens of thousands of different soil kinds, with each type affecting your septic system differently. When the soil is too coarse, wastewater flows through too rapidly to be treated properly. Clay-rich soil is also unfavorable because it retains water for too long, leading it to drain slowly.

3. Types of septic systems

Once you know your soil composition and placement structure for the tank, you may look up your local laws to see what type of septic system you’ll need. Most typical septic systems consist of a septic tank and a drainage system that collects wastewater from the residence and treats it in the soil.

Few other types of septic systems include:

  • Conventional system
  • Pump chamber system
  • Mound systems
  • Cluster systems

4. Size of the septic area

You may start mapping out your septic area after you know which type of septic system you have. You’ll have to check the local codes once more to ensure your area is within legal restrictions and understand how close your septic area must be to your house, land borders, and waterways. The next step is deciding the capacity of the septic system based on the house’s size and water usage.

5. Calculate the septic tank capacity

Wastewater flows back into the residence if a septic tank’s volume is insufficient. Therefore, you need to choose the right tank size. Let’s understand it better with an example of a house with five members with an average consumption of 137 gallons/day on average. Let us calculate in a step-by-step process:

  1. We use a three-day retention duration in septic system design. As a result, the constructed tank should be able to contain residential wastewater for at least three days. Total wastewater in three days = 412 gallons; as a result, we choose a tank with a total capacity of 528 gallons, with a height between 1.8 meters to 2.4 meters. Short-circuiting of input and exit flow can occur when a tank is too deep or too shallow.
  1. Take the amount of dirt that has settled down for each individual as 7.9 gallons per year. So, we’re going to do sludge removal for two years. 7.9 gallons × 5 people x 2 years = 79 gallons average total muck. Therefore, the required Overall Septic Tank Capacity = 607 gallons (258+79).
  1. We use a 4:1 or 2:1 length-to-width ratio for septic tanks. The ratio of length (L) to breath (B) is 4 to 1. As a result, 4 B x B = 1.2 Sq. m, with B=0.54m. (Note: The tank’s total breadth must not be below 750mm.)
  1. Thus, the septic tank capacity would be, 3 × 2.1 x 0.75 = 4.725 Cum = 4.725x 1000 = 1248 gallons.

Depending on the available area for the septic system, one can increase or decrease the tank height and calculate suitable length and breadth dimensions for the tank to meet the capacity requirements.


Septic system design isn’t complicated, but the need for accuracy in your calculations makes the procedure difficult. An essential element to consider is local restrictions, which may have an influence on the design. Instead of creating your septic system, employ a civil engineer with septic system design knowledge who can construct the ideal system for your house or enterprise. With the right design, you can eliminate drainage problems on your property.

Looking for a professional engineer to guide you in your designing process? Design Everest has a pool of experienced engineers and architects who can help you with your septic system design.

Contact us for affordable, top-quality services for commercial, residential, and industrial projects.

If you are constructing a new building, having the correct site preparation is crucial to the success of your project. From surveying the property and
The City of San Jose requires a grading permit for all property improvements that alter the natural surface of the ground. These include building a new
Stormwater runoff is the rainwater or melted snow rolling off of surfaces in your community, such as streets and rooftops, into storm drains, and then
As the owner of real estate property, you may know where your property begins and ends. In the United States, many owners build a fence between their


Email Subscription

Opt In
This field is for validation purposes and should be left unchanged.

Get a Quote (Simplified)

"*" indicates required fields

Opt In
This field is for validation purposes and should be left unchanged.