The system discussed above is a conventional system installed in the soil that exists on the site. Where the site conditions do not lend themselves to installing this type of system, there are alternatives.
For example, if ground water or percolation rates are unsuitable, it may be possible to install what is called a “mound” system. In a mound system, a suitable soil is placed above the unsuitable soil. A conventional system is then installed in the mound. There are some additional requirements for this type of design.
If there is not enough room for a conventional leach field, it may be possible to install one or more cesspools, or seepage pits. These units are usually round, require less open ground, and are deeper than a conventional leach field. Again, there are specific requirements for these systems.
Conventional, mound, and seepage pit systems all work by what is called anerobic bacterial action. This means the bacteria work without oxygen. Some systems are designed to be aerobic – meaning the bacteria need oxygen (air); There are also hybrid systems that use a combination of anerobic and aerobic sections. Your design professional will advise you if one of the non-conventional systems is best for your needs.