How large does a septic drain field need to be? 

Drain field, leach field, absorption field, they are all the same thing, but how big should it be?

The size of your drain field is going to be measured in square feet and you want to find an area where it will not be disburbed. Away from buildings, driveways, or trees is going to prevent possible damage down the road. Drain fields for a septic system can vary in size dependingon the soil percolation levels. The percolation test that can be done on a septic system will help us determine how efficiently the soil is taking the water exiting a system or future system. Doing a perc test before you even install your septic system is going to be a good idea. 

If your percolation rate comes back with good results you might get something like one inch of water percolation in three minutes. This would require the drain field to be somewhere around 450 square feet in size. This size is very typical for a three bedroom home. If we took this same size home and put it in a location with a lower rate of percolation in the soil we might see perc results of an hour per inch, which is going to require a larger drain field size. Something closer to 900 square feet or even more might be needed in order to have the septic system function properly with good absorption into the soil. 

Like we said before a septic leach field can also be called a drain field, or a leach bed, or a soakaway bed, an absorption bed or something else. 

Drain fields are designed with perforated effluent distribution pipes spread out through a bed or field of gravel allowing effluent water to percolate into the soil naturally. 

When you look at the leach field structure you are going to seea series of trenches that can range up to a hundred feet long and 1 to 3 feet in with, usually separated by six feet or more in between them. We might see some variations in installations basedon the local requirements. Sometimes thare are some spaces left open between lines just in case a future installation is needed it will make it a lot easier to install instead of having to set up a new distribution box and add new lines in a whole new location. Thinking ahead during install can save some possible work down the road. 

The size of a drain field and where it is going to be placed should also be determined by any local zoning requirements. We often see setback regulations for property borders or if there is a stream on the property, wells, water supply lines, or wetlands, etc. 

Consider this information when determining the size and location of your drain field on your property. Each property is going to be different and you want to make sure the septic system installed is not only going to be right for you, but any other future owner of this property.