Did you know that a septic tank can sometimes float right up out of the ground? As you can imagine, this tends to damage the septic tank's connecting pipes and sometimes the tank itself and leads to expensive septic tank repair. Here are some of the contributing factors that can make a septic tank more likely to float.
1. Excessive water or flooding
Flooding events or excessive rainfall that saturates the ground around your tank are the types of situations that typically trigger a tank floating event.
This doesn't just mean during a hurricane storm surge type of flood, either. If your backyard frequently has a lot of puddles after rainstorms, your septic system sits in a low spot, or you drain all your wastewater from your roof and driveway into the septic area, the ground may become overly saturated with water without a huge storm event.
2. An unused or leaking tank
If your tank hasn't been used recently, it may not have very much wastewater in it. The system may already have pumped all or most of the liquid wastewater out to the leach field, leaving only a small layer of solids at the bottom of the tank. This can leave the tank mostly full of air, which is quite buoyant compared to water.
Another factor could be if your tank had a bad leak that let most of the liquids out of the tank just before the flooding event. Like an unused tank, this leaking tank could then be mostly filled with air as the surrounding soil suddenly becomes waterlogged. A rusted-out steel tank or a missing plug in the bottom of a fiberglass tank could be the cause of the leak.
3. A lightweight tank that's not anchored
Although concrete tanks are so heavy that they're highly resistant to floating, newer plastic and fiberglass tanks are much lighter in weight. They're desirable for other reasons (such as ease of transport and resistance to hydrogen sulfide gas corrosion). However, if one of these tanks is installed without correct anchoring, it could be susceptible to floating during a flood.
As you can see, the events leading up to a floating event, the situation where your tank is buried, and even the tank's characteristics and installation can all be important. Typically, multiple factors have to work together to cause a floating problem. If you have a flooding situation without a lightweight tank, you're not likely to have a floating problem, for instance.
The good news is that this means a well-anchored, well-maintained tank that's currently in use is less likely to float, even if your yard is completely flooded. However, a flooded septic system may have other problems as well, so be sure to call a professional who can assess your septic tank and leach field and provide any needed septic repair services.