How to Winterize Onsite Systems

Some systems may need a little extra care this time of year in order to keep working properly through the winter
How to Winterize Onsite Systems

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As winter sets in, savvy homeowners will be wondering how their onsite system will fare in the cold weather. If the system was installed properly and everything is in good working order, there is not a lot that needs to be done to keep the system operating through the winter.

However, here are a few items that you should remind homeowners to consider, and take action as necessary. 

If there is any maintenance of the system that has been put off, now is the time to have it done. If the septic tank needs pumping, it should be pumped. If there is a pump station in the system, now would be the time to have the pump tank checked for any solids and the floats and pump evaluated to make sure they are in good working order. If it’s not working right now, you can assure homeowners that when the temperature drops, it is almost guaranteed not to work. 

Suggest repair or replacement of any damaged riser lids, and recommend lid insulation. Give the drainfield area a once-over inspection for surfacing or ponding so it can be remedied as soon as possible. 

If you recently installed a new onsite system that lacks established vegetative cover, suggest using straw over the area to help insulate the system. Some of the best insulation is provided by the soil itself and the growing vegetation. If vegetation is not established, the surface will cool faster and allow frost to penetrate deeper. Vegetation captures and holds snow over the system. Snow is also a very good insulating material. Assure the homeowner that straw also helps in the spring when snow begins to melt but it is still relatively cold. 

For residences that will be used intermittently, make sure homeowners do something to hold heat in so the system doesn’t freeze. If you’re installing a system at a seasonal home, make sure to insulate the septic tank to prevent freezing. 

In my home state of Minnesota, installers insulate septic tanks and pump stations automatically due to the drastic drop in temperatures. Part of this is because of the length of time we have snow cover, and changing demographics means the population is older and more likely to head to a warmer climate for part of the winter so homes with onsite systems are left unattended for months. 

If a homeowner calls with an established system that has not been insulated, and they are wondering what they can do because they are leaving for the next three months, a temporary solution is to install a tank heater in the septic tank. This is not a substitute for use, so another suggestion would be that the homeowner have a neighbor, family member or friend use the system by running the washing machine or dishwasher once a week while they are away. It is also a good time to suggest that the long-term solution is insulating the tank. 

For some issues, it may be too late to solve the cause of the problems this year, but having a talk with the homeowner will hopefully result in a plan to address the issue as soon as spring comes so the problem can be avoided next year. Here are a couple of the main causes of freezing problems and what to do about them.

Between water use events in the residence, the only thing that should be inside any set of pipes delivering raw sewage or effluent between parts of the system, including pump supply lines, is air. If there is any type of bow or low spot in the pipe or if the piping is not buried below the normal frost line, water can collect and freeze, creating a pipe blockage. In most onsite systems, it is not possible to bury the lines below frost levels since we want them as shallow as possible for acceptance and treatment.

This makes it even more critical that the piping be properly bedded to avoid low spots in the pipe. Jetting the pipes to remove the blockage is the immediate solution. While this is probably good for the jetting business, it is going to happen during the coldest weather and harshest conditions for people and equipment. So, it is important to convince the homeowner that jetting is not the solution and that pipe replacement and proper bedding should be the answer, as soon as weather permits. Fortunately, with the cameras we have at our disposal today, a compelling argument can be made to the homeowner by showing them the bow in the pipe and the blockage.

Something I thought was solved has just recently been brought to my attention again. One of the other causes of freezing in pipes is a slow trickle of water from the residence into the piping. This could be due to leaky fixtures that need to be fixed anyway just due to the hydraulic load on the soil treatment part of the system and also due to condensate from high-efficiency furnaces being routed directly into the house sewer pipe. Over the course of a day, the furnace can deliver several gallons of condensate but not in large enough quantities to flow through the piping unless it is collected in a reservoir or sump and delivered periodically by a pump into the piping.

For systems that have pump tanks and pressure distribution, it is important that the supply line is laid on the proper grade and is properly bedded so the effluent drains back to the pump tank, leaving the pipe empty between uses. Remember also that the drain back into the tank should be through a hole in the supply piping and not back through the pump, which can cause the pump impeller to spin off. While working on the system, be sure this hole is open and not obstructed.

In certain climates, insulation is the only way to prevent frozen lines. Learn more in 3 Ways to Insulate Septic Pipe.

About the Author
Jim Anderson is connected with the University of Minnesota onsite wastewater treatment education program; is an emeritus professor in the university’s Department of Soil, Water and Climate; and is involved with the National Association of Wastewater Technicians. Send him questions about septic system maintenance and operation by emailing


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