How to Install a Septic Tank Drain Field

Putting in a septic drain field is not that difficult. You must follow the local building codes, obtain a permit and have the necessary inspections. Beyond that, it is simply a matter of following a plan. The size of the drain field is dependent on the on the size of the septic tank, the number of people living in the house, the percolation level (ability of water to soak into the ground) and applicable building codes.

Instructions

1. Study local building codes and design the drain field accordingly. Present your plans and obtain approval from local building inspectors. Once approved, obtain your building permit and place it in a prominent location at your site.

2. Measure for the placement of the field lines. Some areas allow you to do the measuring, while others require the use of a surveyor to prevent property line encroachment. Once you complete the placement measurements, an inspector usually has to visit your house to approve the placement.

3. Dig the trenches for the field lines. The size of the septic tank required by the local building codes determines the length of the field lines. The depth of the outlets from the septic tank will determine the depth of the field lines. The drainpipes in the field lines attach to the outlets from the septic tank with a slight downward slope so liquid will drain from the septic tank properly. Have an inspection, if the local building code requires. If you are replacing old field lines to repair an existing septic system, you will need to remove the soil, sand and gravel from the old lines and bring in new soil, sand and gravel.

4. Conduct the percolation (perc) test in the presence of the inspector. Dig a hole in the area where you will place the drain field. Then pour a gallon of water into the hole and time to see how long it takes to percolate into the soil. Based on this test, the inspector will inform you what materials are required for your field. These materials may include sand, gravel, fill dirt and topsoil. For example, the inspector may require six inches of a certain type of gravel in the space beside and on top of the drainpipes, then six inches of a certain type of sand, and eight inches of fill dirt and topsoil over the fill dirt; if the perc test results were good, the inspector may not require any sand.

5. Obtain the materials for the field lines. Lay the drainpipes into the field line trenches and attach them to the outlets from the septic tank. Have another inspection, if the local building code requires you to do so.

6. Fill in the field lines with the required materials (i.e., gravel, sand, fill dirt and topsoil). Have inspections as required during this phase. The inspectors will most likely want to see the gravel and sand layers before you bury them with fill dirt and topsoil. Have a final inspection, if required. Lay sod or plant grass seed on the top soil if desired; the inspector may require this if erosion is a concern.

References

• The Laundry Alternatives, Inc.: How to Install a Drain Field the Right Way
• HomTips.com: The Septic Tank Drainfield

Resources

• InspectaPedia: Building & Environmental Inspection, Testing, Diagnosis, Repair