A leach line is a long trench filled with washed gravel and a horizontal perforated pipe running through the middle. As waste water leaves the septic tank, it flows out to the leach lines where it can drain back into the ground. Some septic systems utilize drain wells instead of leech lines. Both drain well and leech lines serve the same purpose, they allow the water to percolate back into the soil.
These videos depict the installation of the leach line. After the gravel is installed, the perforated pipe is then laid level on the gravel. The pipe is laid level to allow the water to fill the pipe evenly and distribute equally throughout the length of the trench. After the pipe is laid, another layer of gravel is poured on top of the pipe embedding the pipe in the leach line. The final step before back fill is to cover the rock in geo textile paper to prevent recently excavated loose soil from mingling with the clean gravel.
In Fresno county, the maximum length a leach line can be is 100 feet. A standard leach line will be 2 feet wide with 3 feet of rock below the perforated pipe. However, depending on where you live, you may be required to have an engineer design the leach lines for your septic system. The amount of rock below the pipe in a leach line designed by an engineer can vary greatly. The soil septic factor, also plays a part in determining the amount of square footage your leach field will require. In some cases, test holes are required to be dug to determine the soil septic factor on your property. In other cases, the soil factor is already known.
It is important to know where the leach lines are on your property so that you can avoid planting trees too close to them. Tree roots are a common reason for failed leach lines. Tree roots seek out the water in the leach line and, in many cases, they clog the pipe and stop the water from flowing through to the end of the trench.