Design Characteristics of a Drainfield

The drainfield plays a critical role in your septic's operation and efficiency. The actual waste disposal takes place in the drainfield. You must get the drainfield's design and construction right for it to work properly. Below are some aspects of your drainfield you should get right from the start.

Size

The drainfield's size determines how much waste it can handle. The exact sizing will depend on:

• The household's size
• The expected volume of waste per day
• The percolation characteristics of the soil
• The type of absorption system
• The local zoning requirements

The septic installer will evaluate all these parameters and calculate the size of the field you need. Note that the percolation rate plays a significant role in drainfield sizing. Thus, the installer will have to dig a hole in the designated site and test the soil's percolation rate.

An average home might require as little as 4500 square feet of drainfield or as much as 9,000 square feet of the drainfield, depending on the percolation rate. Many local authorities also require a reserve area in addition to the leach field areas. You may use the reserve area for future expansions or as a substitute leach field in case the first one needs repair.

Trenches 

Septic drainfields come in various designs. A common design features pipes buried within gravel-filled trenches. The pipes have perforations that allow waste to drip out and percolate into the ground. The dripping gives the waste adequate time to soak into the soil.

The specific design parameters of the pipes will depend on your septic system and installation site. However, the following general guidelines apply:

• The trenches should have a gentle slope to allow waste to flow by the action of gravity.
• The trenches should have adequate depth so that the waste doesn't flow back to the surface and the pipes don't freeze during the winter season.
• The trenches should have adequate separation distance so that waste doesn't clog a small area of the field.
• The pipes should be wide enough to handle wastes coming out of the house at any time.

Again, local building codes will determine some of these parameters - such as the trench depth. You must get everything right to ensure your drainfield can handle your home's waste and last a long time.

Materials

The drainpipes should be on suitable materials that will allow the waste to flow ion the house. The base materials can be:

• Gravel
• Crushed stone
• Slag

The base material particles should be roughly equal in size. That way, smaller particles don't fill the spaces between the bigger ones and render the base material infective.

After the base material and the pipe comes the filler material. Newspaper and straw are good examples of good filter materials. A soil layer goes over the filer material as the final layer in the drainfield. The covering layer prevents soil erosion, among other things.

Site

A suitable drainfield site should facilitate waste disposal without the risk of contamination. Thus, a good site should:

• Sit an adequate distance from other facilities, including water sources such as wells
• Should have adequate usable soil above the bedrock
• Should have its usable soil at a safe distance above the underground water table
• Should be downslope of water sources

Lastly, choose a site without any planned developments, such as access roads or parking areas.

The design specifications and requirements may seem complicated for the average person. However, O'Fallon Sewer Service understands what it takes to design and install a septic system, including the drainfield. We have been active in this industry for over 50 years. Contact us for a consultation or quote and enjoy our professional services.