Our first principle for a good sewage treatment system has always been to keep the system as shallow as possible. The reasons? This is usually the best part of the soil for final dispersal and treatment of sewage effluent, and it keeps the system away from potential problems encountered as the installation goes deeper. These problems include bedrock (impermeable or creviced), dense soil layers and water tables (perched or regional).

We have received several emails asking whether having shallow systems results in problems due to freezing. Our answer is always the same: Not if systems are installed properly. Embedded in the most recent emailed freezing questions were statements indicating the writer had done some reading about systems, but clearly had ideas about how they work or don’t work. Some of the ideas were accurate, some not so much. So it’s a good time to review aspects of installation to avoid problems due to freezing.

The reader started off with one of the most common misconceptions about system operation. They recognized that bacteria action in the septic tank generates heat which helps keep systems from freezing. Bacteria in the tank do not generate heat. Rather, the temperatures in the tank are related to the temperature of the sewage delivered to the tank. What is true is the bacteria at higher temperatures are more efficient at breaking down the organic solids in the tank. The same is true in the soil. At about 40 degrees F, bacteria basically shut down.

PART-TIME RESIDENTS

For systems in continuous operation during the cold months, a daily supply of wastewater will be delivered from the house, including hot water from showers, dishwashers and clothes-washing. This helps maintain tank temperatures even if the tank has a shallow 1-foot cover. In far northern areas where temperatures can drop to 30-40 degrees F below zero for extended time, the tops of the tanks are often insulated by laying sheets of foam insulation suitable for earth burial.

One issue we have seen more often in our northern lakes areas are problems with freezing in the tanks and backups. These are vacation homes where owners visit only occasionally during winter months. Our recommendations are to insulate the tank and, where possible, have a neighbor or management personnel visit the residence every week and run dishwashers or washing machines through a cycle or two to add heat to the systems.

Freezing in the piping between system components is often due to improper pipe installation. Remember that sewer piping should be empty between water use events. In PVC piping 3-6 inches in diameter, the minimum slope for the piping is 1/8-inch per foot to move solids and liquid through the pipe. If this is done through proper pipe bedding without any bellies or low spots, there should be no freezing problems even if pipes are only 1-2 feet below the surface. This is just good installation practice; not anything special to prevent freezing.

STOP PESKY LEAKS

For the house sewer line, it is always good practice to install a bidirectional clean-out outside the house that is accessible to a service provider. This way blockages can be jetted without having to go inside the house.

The reader did recognize one very important aspect to avoid, having a trickle of water versus an influx of a larger volume such as from a toilet flush or delivery of water from a dishwasher or washing machine. They were correct in recognizing any dripping faucets or leaky toilets could cause freezing problems in the piping. In addition, furnace condensate should not be delivered directly into the sewer piping, but rather be collected in some type of sump and delivered periodically by a small pump into the piping. If there is a sump to collect wastewater from a basement or lower level, the condensate should be delivered to the sump.

Pipe needs to be insulated if installed under traffic areas such as driveways, walkways or any area where there will traffic of any kind. This thought was brought home to us when we were doing some system research on freezing and we used the same path to take our equipment out over the supply pipe to the dispersal area to measure temperatures. Temperature in the soil treatment area was fine but we caused freezing in the supply pipe. An embarrassing moment for us, and luckily we were working with an understanding homeowner.

Just to reiterate what we have said about insulating pipe in the past, insulated pipe can be purchased. It is basically a pipe within a pipe with foam insulation between the pipes. By sleeving a smaller diameter pipe inside a larger diameter pipe, a level of insulation can be obtained with the air space. Sheet insulation suitable for soil burial can be installed over the piping, or in extreme conditions sheet insulation can also be placed along the walls of the trench when the piping is bedded. 

A final word: With the advent of cameras, if piping is installed with bellies, they are found when the service provider cameras the pipe to determine where and why the pipe is plugged. It is best to install the piping properly the first time!