Alternative or enhanced treatment systems are used when the soil is not adequate to treat the effluent, or when there is not enough soil to install a conventional system due to seasonal water tables and /or imper-vious soil. In King County, the most commonly used alternative system are Mound, Sand Filters, and Pressure Distribution systems.
These systems consist of a septic tank, pump tank, and drainfield. The drainfield consists of small pres-sure lines which distribute the effluent from the septic tank evenly throughout the drainfield 1 – 4 times per day. The openings in these pressure lines are very small tend to clog easily, so you should avoid the use of a garbage disposal.