consists of long underground perforated pipes or tiles connected to a septic tank. The network of pipes is laid in gravel-filled trenches (2-3 feet wide), or beds (over 3 feet wide) in the soil. Liquid waste or effluent flows out of the tank and is evenly distributed into the soil through the piping system. The soil below the drainfield provides the final treatment and disposal of a septic tank effluent. After the effluent has passed into the soil, most of it percolates downward and outward, eventually entering the groundwater. A small percentage is taken up by plants through their roots, or evaporates from the soil.