The Real Volume of a Septic Tank

Let’s talk about the real volume of your septic system. Most customers don’t know that an entire septic system can hold much more than just the operating capacity of their tank. The stated operating capacity for a tank is the amount septage (liquids and solids) in gallons that a septic tank needs to hold for the waste to reach the baffle leading out of a tank. A common reference to operating capacity is when someone says they have “a 1,000-gallon septic tank”. In this example, it would take 1,000 gallons of septage to reach the baffle leading out of the tank and send septage into the drain field to be purified by the soil and absorbed. However, in the case of a high-level situation, when septage is overfilling the tank or backing up into the home or the area around the system in the yard, there are several hundred more gallons of septage in the system’s pipes and the septic tank that will need to be pumped out.

One place where the system can hold several hundred more gallons is in a riser. A riser is essentially a lid extension from the buried tank to the ground surface so the tank can be easily accessed for pumping. A riser can be 6 inches to 36 inches tall and at least 18 inches across. Besides being an easy access point for pumping and maintenance, this extra room is great to have to keep extra gallons from overwhelming your system and flowing back into your home when your tank is above operating capacity.

A common but forgotten way that your system can be above operating capacity is when there is infiltration of groundwater into the septic tank. This can mean there are holes in the tank or the inlet or outlet pipe is not watertight, allowing ground water to flow into the septic tank. We find holes and over capacity tanks very common with steel tanks that were installed in the 1970’s. We recommend that any homeowner with a steel tank have their tank replaced with a new concrete or plastic tank to keep failures to a minimum and potentially save their whole system from failure.
With a family of 4 using an estimated 400 gallons of water a day, it’s crucial your system be in top working condition. Make sure to pump and inspect your system regularly, every 3-5 years, to keep it working in the best condition possible. If you do find you have questions about your system and it’s volume we recommend you call a local septic professional with high review ratings on Angie’s List.

This article was originally published in May 2016 by Speedy Septic on the Angie’s List Experts Blog.