Septic systems: How big should my drainage field be?

The big puzzle any homeowner installing a septic system deals with is how much yard space should be set aside for the septic field, where the liquid waste is released into the soil.

Yard space is always precious, even out in the country, and you don’t want to give it up to a field that’s too big for your needs.

This is especially so when you consider that once the field is in you can’t really use that space for anything else. You certainly can’t build on it, and you really can’t do much else on it, for fear of damaging the network of drainage pipes beneath.

But build your field too small and you’ve got headaches galore. It will always be at risk of backing up, flooding the yard and emitting a foul odor.  Who needs that?

So here’s some handy guidelines for coming up with a ballpark estimate for how much yard to set aside.

But note, this is just for ballpark purposes.

The exact size, configuration and even the location you’ll want to leave to the company you hire to do the actual installation, and they will depend on a variety of factors.

The two most critical factors are, one, the amount of waste you plan to run through the system and, two, the condition of the soil in the drainage field.

The condition of the soil is a biggie.

If the soil has good percolation conditions—it’s comparatively sandy and waste water seeps down with little resistance—figure a seepage field of 4,500 square feet (say 100 feet long and 45 feet wide) for a three-bedroom house with normal waste output.

But if the soil has poor percolation—it’s full of clay, for example– you can double the size of the field needed for that same three-bedroom house. Figure 9,000 square feet, a big difference.

You also have to take weather into consideration.

Waste water percolates faster in warm climates. If your home is in an area where spring comes late and fall early, you may well need a larger field. How much larger will be up to your contractor to determine.

In any case, your contractor can do a percolation test to determine just how quickly water goes through the soil in your yard, and from that determine just how big your seepage field should be.

A factor to consider when determining where you want your septic system placed in your yard is your local zoning code.  It will dictate how far the tank and field must be from structures, power and water lines, property lines and bodies of water such as ponds. In some cases, it can be 100 feet or more.

Just where a field should go is a subject of much debate.

Some argue it ought to be as close to the house as possible. The shorter the distance, the less chance of blockages and other problems moving the waste from the house to the septic tank.

But others think the system should be as far away as possible, in an open area, making it easier to get to if problems arise.



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