No Snowmobiling Over the Drainfield!

Homeowner with winter septic tank woes should opt for a little bad-weather preventive maintenance

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QUESTION:

I live in Northern Minnesota, and if I knew then what I know now, I would have insulated my septic tank when it was installed. For most of the winter, there is no snow on the ground over the tank because of the heat escaping. Everywhere else there’s three or four feet of snow on the ground. We obviously put a lot of hot water in the tank.

Would it be any advantage to lay a 4- by 8-foot sheet of 2-inch expanded polystyrene on the ground over the tank (before snowfall) to help keep the heat in for better bacterial action? I would really hate to have to dig up the entire septic tank to insulate the top, but I am tired of having to drive around this sinkhole all winter with my snowmobile.

 

ANSWER:

You won’t like the first thing I am going to tell you: Change the location of your snowmobile trail! It is good you are not driving over your leachfield, and you should not drive over the septic tank either. If you place insulation on the ground and then run over that area and pack down the snow cover, you have lost much of the insulation value. Loose, fluffy snow is a good insulator, but packed snow is not.

The amount of heat loss depends on the material and the temperature difference between the two points under consideration. Heat loss from the cement cover of the septic tank to the soil surface depends on the temperature of the septic tank cover and the temperature of the soil surface. The colder the soil surface, the more the heat loss. It seems this is just common sense.

 

SOIL MOISTURE

The resistance to losing heat through the soil depends on how wet the soil is. Kansas State University studied the resistance to heat transfer of fine-grained soil with 20 percent moisture content and found it to have an R-value of 1. By comparison, high-density polyurethane has an R-value between 5 and 5.4, so one can see how much better the polyurethane insulates to prevent heat loss. The higher the R-value, the greater the resistance to transferring heat.

When the heat from the septic tank moves through the soil and heats the soil surface above 32 degrees, snow cover will begin to melt. The water soaks into the soil, making the soil an even better conductor of heat.

While a soil with 20-percent moisture has an R-value of 1, a soil saturated with water from snowmelt would have an R-value approaching zero. So we definitely don’t want to melt the snow. Heat should be prevented from moving through the soil. This means the proper place for the insulation is on the tank cover and along the upper sidewalls.

To properly insulate a septic tank, use expanded polystyrene over the cover and down along the sides at least two and preferably four feet. An opening should be made where the manhole is located to provide for future cleaning of the septic tank. Backfill the soil and establish a good grass cover over the septic tank area.

I suspect from your inquiry you are a sewage system installer and have read my column in Pumper. I advise you and your fellow installers in the cold North Country to insulate every septic tank you install. Adding insulation at the time the tank is being installed is easy and inexpensive. That insulation will pay big dividends in the future.

And in answer to one of your questions, if more of the heat stays in the septic tank, the contents of the tank will be warmer. This increase in temperature will be beneficial to bacterial action in the tank. According to my colleagues who know bacteriology, the optimum temperature for bacteria is the temperature of the human body.

 

FROZEN DRAINFIELD

There also can be a freezing problem over the drainfield, and an installer should advise his customers about this. I suggest leaving the grass cover over the drainfield as long as possible as it goes into the winter. If one is in an area with adequate snow cover, the longer grass will hold the snow over the drainfield. Even if there is little snow cover, the long grass will catch some snow and help insulate the area.

In areas where there is normally not a lot of snow, but extremely cold winter weather, drainfield freezing can be more of a problem than farther north where snow is common. Tree leaves, hay or straw can be good insulating material.

A frozen drainfield is a real problem, and the homeowner will either pay the expense of thawing it out and then covering it, or reduce water usage and have the septic tank pumped whenever it gets full. Either way, the solution will be expensive. The few dollars needed to cover the drainfield area against freezing would certainly be money well spent.

Before the days of snowmobiles, one did not have to worry about them packing down the snow on a drainfield. It is a good idea to set stakes around the drainfield area, connected with a light rope and blaze orange ribbons tied on the ropes. This should keep the snowmobiles off the drainfield area.

It is an excellent idea for installers to send a note to customers with suggestions about preventing drainfield freezing. Such contact with previous customers is sure to build a base for some new customers.

Good luck and happy snowmobile trails, but not over the septic tank and drainfield!



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