Septic System Design Basics

Septic System Design Basics

July 14, 2021

Not every household is hooked up to a network of public sewage pipes. Farms and rural homes are often tasked with installing their own private septic systems. While they’re better for the environment, the septic system planning process can be a daunting task for homeowners. Here’s everything you need to know about a basic septic system design.

Septic tank size

A standard septic system design consists of two main components: the septic tank and the drain field. A septic tank temporarily holds wastewater and organic matter until it’s ready to filter back into the underground water table. Septic tanks are usually made with heavy materials like concrete, but you can construct a more lightweight one as long as the tank gets anchored to prevent it from jostling around.

The size of your septic tank will depend on how many people will be using it and their combined daily water usage. Generally speaking, higher volumes of water usage require you to install a larger septic tank. The average septic tank size for a single family home is about 1,500 gallons.

Types of soil

Certain types of soil are better suited for septic systems than others. The bacteria in soil is what breaks down human waste and serves as a natural purification system. Soil with a high absorption rate most efficiently purifies wastewater and returns it to the water table. Soil that primarily consists of flat grain particles is highly compact and results in a lower absorption rate.

The soil on every piece of property is different. As you start the septic system planning process, ask your local civil engineer to conduct a percolation test. This test will determine your soil’s absorption rate, which influences design features like which type of septic tank you’re allowed to install and the drain field’s dimensions.

Drain field dimensions

The drain field is a section of land that’s responsible for filtering wastewater back into the water table. It’s located underground and consists of building materials like perforated PVC pipes and gravel. Wastewater flows through the pipes, then exits into the gravel or some other form of aggregate rock. The remaining liquid is absorbed into the soil, where bacteria neutralize any leftover contaminants. If your property’s soil has a low absorption rate, the drain field will need a larger surface area.

Bury the wastewater pipes 30 inches below the ground level, and make sure they slope downhill and away from your house. When you dig the trenches, leave enough room for aggregate rock to completely surround each pipe. Your septic system design should also take into consideration your local municipality’s regulations regarding the distance between your drain field and natural bodies of water. Compliance with local regulations saves you from paying hefty fines and protects the water quality of your community.

Septic systems are difficult to design on your own. The smallest mistake will cause a safety hazard, costly damage to your property and a fair chunk of change for violating local regulations. Save yourself the hassle and leave septic system planning to the environmental engineers at High Plains Engineering & Design, LLC. Our team of seasoned professionals will take care of all the work so you don’t have to!

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