In Ground Gravity System

Stone & Pipe Systems

There are two primary groups of in-ground Gravity Private Onsite Wastewater Treatment Systems (POWTS). One group is a POWTS using washed stone to support and raise the perforated piping network within the POWTS cell. This type of POWTS installation is seldom being used today in this county.

The reason why stone and pipe systems are not being installed is due to the limited availability and reliability of clean washed stone. The stone, if not properly washed, will retain excess amounts of clay, silt and very fine sand that can clog existing available soil pore space. The in-ground gravity system will be installed where soils have been determined by a State of Wisconsin certified soil tester that the existing soils can meet the standards set forth for this system type.

Stone-Free Systems

The second type of in-ground gravity POWTS is a stone-free system. There are a number of these approved products being used in Kenosha County.

Leaching Chamber

The most common type of stone-free system is the leaching chamber, which consists of lengths of half-pipe, connected end-to-end setting on native soil in a trench excavation. The top of these units are solid synthetic material and the sides are louvered to allow the flow of wastewater out of the chamber. Although systems with this product are slightly more expensive than the stone and pipe systems, they are highly efficient and eliminate the trucking and handling of washed stone to a site. Leaching chambers can also be used in mounds and other pressurized systems. See a leaching chamber diagram (PDF).

Gravel-less Pipe System

The other type of stone-free system commonly being used in Kenosha County is the gravel-less system that consists of a perforated pipe within a synthetic net bag, filled with poly-styrene pellets. This is then bundled with two (2) more of these net bags filled with the pellets but no pipe thus creating additional area for dispersal of wastewater in a trench excavation. This dispersal unit comes in ten foot (10 ft.) lengths and is somewhat flexible thus allowing installations around trees or on convex contours of a sloping site. Gravel-less pipe can also be used in pressure distribution systems such as mounds and also eliminates the trucking and handling of washed stone aggregate.


Installation times by the excavating contractor are faster using either one of these units. Disturbance to a client’s property is minimized because the contractor does not have dump trucks place several yards of washed stone on the construction site, thus eliminating the use of a backhoe or skid-steer making multiple trips across the property moving stone material to the excavated trenches.