During winter months, water freezes on ponds, rivers, puddles, and in the ground. Where you live determines how deep the water will freeze in the ground—this is the frost line. According to data from the National Oceanic and Atmospheric Administration (NOAA), the frost line can range from 100 inches deep in northern Minnesota (or permafrost in Alaska) to none in sunny southern Florida. The majority of the country’s frost line ranges between 20 and 50 inches deep.
Local building codes use this data to determine the depth of concrete footings to prevent frost heave (when water freezes, it expands, often pushing solid objects like rocks or deck footings towards the soil surface). The data is used to determine the depth of water and sewer lines to prevent them from freezing.
Occasionally, a prolonged cold snap will drive the frost line down, and those water or sewer lines—and sometimes the septic system itself—can freeze. Septic lines installed too close to the surface are at risk; the absence of snow, which acts as an insulator, can lower the temperature of the soil; and infrequent use and scant water flowing through the pipes can cause them to freeze more easily. Even septic pipes in an uninsulated basement or the pipes that connect the tank to the drain field can freeze, which also can cause a backup.
How to Know if Your Septic System is Frozen
It’s not something that happens all the time, but there are symptoms of a frozen septic system that should set off the alarm bells. The first symptom is that the drains stop working. Toilets won’t flush, sinks, bathtubs, and washing machines won’t drain. In extreme cases, you may have sewage backing up into your home.
What to Do When Your Septic System is Frozen
When confronted with a frozen septic system, many folks will call a plumber. If you live in an area that has arctic winters, chances are good that most of the local plumbers will have experience in thawing out drain and septic lines.
Thaw via the drain
If you’re so inclined, you can also try to thaw them out yourself. Pouring hot water into drains may help to melt a partially ice-bound drain.
There are commercial products advertised to clear frozen drains and pipe. Still, they often contain caustic substances such as sulfuric acid that can damage the plumbing itself and enter and potentially contaminate the groundwater. Hence, it’s probably a good idea to stay away from them. And though it may be tempting, you shouldn’t add antifreeze (propylene glycol) to your system, either—not only will it eventually enter the water table, it will also interfere with the biological process of the septic system.
If the frozen lines are accessible—in the basement, for instance—you can try pouring hot water over the frozen sections of pipe. If the pipe is PVC, be careful not to use boiling water that may cause the pipe to crack.
You can also use an electric space heater to raise the ambient temperature. It’s a slower process, but it will do the job. If you have cast iron sewer lines, you can also try thawing them with a heat gun, a method that’s not recommended for PVC pipes, however. Heat tape is another viable option but it poses a potential electrical hazard and shouldn’t be used if there’s standing water in the basement.
Use a hot water bib
If you have access to a hot water hose bib, you can hook up a hose fitted with a spray nozzle, uncover the septic tank access, and insert the hose and nozzle into the feeder or outlet pipe (whichever is blocked) until it hits the ice. Then turn the hot water on, which will melt the ice.
Use a steam machine
There are also steam machines that professionals sometimes use to thaw pipes. One, called the Arctic Blaster, consists of a steel water tank connected to a heavy-duty hose. Using a propane torch, you heat the tank until the water boils, then insert the hose into the frozen pipe, gradually melting the ice with steam. They are not cheap, but the good news is that your local rental center may have one in stock that you can rent for the day. Don’t forget that you’ll need a propane tank and torch as well.
How to Prevent a Septic System from Freezing
There are preventative measures you can take to keep your septic system flowing.
Inspect the septic lines
If you happen to be building a new house or installing a new septic tank, make sure that the tank is buried well below the frost line, along with the septic lines from the house to the tank and from the tank to the leach field. The piping and tank should be covered with some type of insulation, usually two to four inches of rigid foam, before being buried. Try not to compact the soil above the lines and tank, as compacted soil freezes more readily.
If your system is already in place, you can add insulation to the soil above the system. In September, stop mowing in the tank area and allow the grass to grow longer, which will help insulate the soil.
Layers of mulch, hay, or leaves piled over the septic area at least 8 inches deep will also keep the soil warmer during the winter. A tarp laid over the insulating vegetation will keep it drier and less apt to freeze. Pay special attention to the foundation above where the septic line exits the house—this is a common spot where freezing occurs.
Check for plumbing leaks
An active system is continually adding warm water to the tank, reducing the chance that it will freeze. But small amounts of water that trickle into the pipes are more likely to freeze, so check all plumbing fixtures and have any leaky faucets fixed.
If the system is part of a seasonal house or cabin, be sure to turn the water off and drain all toilets, faucets, and other fixtures. It’s also recommended that you have the septic tank pumped to remove liquid that can freeze in your absence.