POWTS come in many varieties but they have some common elements or procedures. Generally water runs down gradient from the residence into a septic tank and it is then dispersed into the treatment/disposal area. The septic tank is designed and sized to allow the wastewater to have some retention time in the tank. This is to allow the heavier material to fall to the bottom as sludge and the lighter oils and greases to float to the top as scum. Bacteria inside the septic tank digest some of the solids converting them to gases and water. This process reduces the volume of solid material stored within the tank. This should mean that only the partially treated or clarified liquid (effluent) is discharged to the treatment/disposal area. It is important to clean the tank periodically to allow enough volume for retention of waste and the settling of solids. If the sewage does not have adequate retention time within the tank, some solids, oils, and greases will be discharged to the treatment/disposal area. This will lead to premature plugging of the soil pores and ultimately to the failure of the treatment/disposal area. This can create a very serious public health risk as well as being expensive to correct. As of July 2000, Wisconsin Administrative Code requires effluent filters to be installed in new and replacement septic systems to prevent premature failure of the treatment/disposal component of the system.

All the wastewater created must discharge into the POWTS. Everyone must recognize that the soils ability to accept wastewater from the laundry, kitchen, and bathrooms is not limitless. There is a limit to how much and how rapidly the soil can accept wastewater. If this rate or volume is exceeded, the POWTS will develop problems, potentially leading to failure.

Many older systems were installed prior to the existence of plumbing codes, thereby allowing them to be poorly constructed or installed in poor locations or in unsuitable soils. When systems fail there is often a combination of factors involved. They may be poorly located, improperly constructed, or received abuse and neglect over time by their users.

A Conventional system is the old stand by. It is one of the more simple systems to install and operate because it is a gravity fed, passive system. Water runs down hill from the residence to a septic tank and down hill from the septic tank into the treatment/disposal area. Conventional systems require the greatest amount (deepest) suitable soil. A conventional system requires suitable soils of at least 48 inches deep underneath the system. Suitable soil must be permeable and not have indications of groundwater or seasonal saturation. Colored indicators within the soil called redoximorphic features (mottling) are typical indicators of high ground water or seasonal saturation. Mottling is identified as high or low croma indicators in the soil. During a soil test a Certified Soil Tester (Soil/Site Evaluator) will identify the depth, size, contrast and abundance of any mottling as well as the soil permeability. For new construction, a soil test for a conventional system must identify an area for immediate development and an area for a reserve site for future use. During a typical year in Ozaukee County, less that 10% of the sanitary permits issued qualify for conventional systems due to low soil permeability or seasonal saturation of the soil. Of course, the only way to be certain what system is suitable for any site is to have a soil test conducted by a Certified Soil Tester (Soil/Site Evaluator).

In-Ground Pressure systems require a lesser amount of suitable soil, but do require a second tank (a pump chamber) containing a pump to provide for pressure distribution of the effluent from the septic tank to the treatment/disposal area. In-Ground Pressure systems require at least 46 inches of suitable soil underneath the system. One advantage of this type of system is that it does not need to be down hill from the structure being served because the pump can move the effluent up hill or to a location some distance from the building. This is a tightly designed system because it needs to meet specific pressure and distribution requirements. Once again, few of these systems are installed in Ozaukee County each year because of the suitable soil criteria requirements.

Mound type systems are the most widely utilized system within Ozaukee County. These systems require only 10 inches of suitable soil underneath the system and can be installed on soils with a relatively low permeability. The most permeable soils in this county tend to be the topsoil and the mound systems take advantage of that fact. These systems are very similar to the In-Ground Pressure systems in that they utilize a septic tank and a pump chamber in the same way. The difference is that the mound system is installed above ground rather than below. A mound system is created by: 1) placing one foot or greater of sand on the plowed surface of the soil, 2) the distribution piping is then installed in a bed of aggregate above the top of the sand, and 3) the mound is capped with soil to allow vegetation to grow. This system provides the same level of environmental protection as the previously described systems except it is installed above ground.

At-Grade Systems are simply mound systems without the addition of any sand. These systems require 36 inches of suitable soil underneath the system, rather than the 10 inches required for the standard mound system. A number of these systems have been installed in the county, but the limiting factor is usually the depth of suitable soil.