A septic tank is designed to remove the solids found in wastewater from a Privately Owned Wastewater Treatment System (POWTS). These solids are what cause failure in most cases as they collect in the systems discharge bed and form an impermeable layer, known as a bio-mat. Once the bed is "clogged" with solids, costly renovations must be made. The more solids that can be held in the septic tank, the longer the system will function properly.

The inlet and outlet in these tanks are located near the top of the units. Both the inlet and outlet are covered with a baffle that extends down to the effluent. these baffles help reduce solids output. Most solids will settle on the bottom of the tank. Then solids are then partially consumed by anaerobic bacteria. Remaining solids are removed by pumping.

Fats, Oils,Greases (FOG), and suspended solids (solids held suspended in the waste water) form a scum layer at the top of the tank. This layer is held in the tank by the baffle over the outlet of the tank. In the center of the tank a clear layer of effluent forms. The outlet baffle is placed so that discharge from the tank comes from this clear layer. Most studies indicate that septic tanks will remove about 50% of the solids that flow into it. This varies from system to system based on total flow during the day, and total rest time during the day.

Assuming an average flow system, one tank will remove 50% of the solids, a two tank system will remove 75% of total solids, etc. There are also a number of filters that can be installed in a tank to reduce solid output. See Zabel Filters. Another aid in reducing solid output is multiple chamber tanks. These are septic tanks having more than one chamber. Lake Shore offers several tanks with this configuration. See the models 1,200 2C, 1,750 2C, 2,200 2C two compartment tanks.

Tanks should be pumped every two - three years. Current research indicates that 2 years is optimal. Pumping more often results in reduced bacterial action. Pumping less frequently will result in smaller solid settling distance and higher solids output. Any filters installed in a tank must also be cleaned regularly. See manufacturers recommendation for proper cleaning schedule.

Current Wisconsin regulations require a soil test be performed to determine what type and size of a POWTS is required. Currently the two most predominate types of systems in Wisconsin are Conventional and Mound wastewater disposal systems. This test must be performed by a Certified Soil Tester. These evaluators hold licenses which are issued after passing an exam administered by the State of Wisconsin.

Prior to the institution of soil testing, a percolation or "perc" test was performed. This procedure involved digging a hole in the ground, filling it with water, and timing how long it took to drain or percolate the water into the surrounding soil. As time passed, more and more systems were failing prematurely. It turned out that many "perc" tests were performed on poor soils and were done in late summer and early autumn when ground water was low. This would ensure the property would pass for a conventional system. Well as you may be aware, water levels in the soils of Wisconsin vary greatly during the year. In spring, due to snow and frost thawing, levels are at a yearly high in many areas. These levels recede until winter frost sets in and the cycle starts again. Soils that are dry and capable of absorbing effluent from a septic tank during late summer and early fall may be completely saturated early each year and not suitable for treating wastewater in spring and early summer. This "perc" test also failed to consider a number of other important and neccessary factors in determing whether soils present were capable of treating wastewater effectively year round.

In response to the shortcomings of the "perc" test, the current soil testing regulations were developed. Limiting factors such as high seasonal groundwater (less than three feet from surface ANY TIME DURING THE YEAR), high bedrock, soil being disturbed (land fills, compact soils, etc.) are now considered as part of the evaluation. Other factors must also be weighed. These include the clay, silt and sand content of the soils, soil structure, soil profile, mottling (discoloration due to seasonal changes in ground water levels), etc. are also factored into the evaluation. All of these factors determine what type of POWTS is to be installed. Some parcels of property will not allow for any POWTS to be built and you may have to install a holding tank or not be allowed to build at all. Many local communities will not allow a holding tank to be installed for new construction.

Mound systems, conventional "septic" systems, in-ground pressure systems, at-grade systems, trench systems, etc. are all types of systems used to treat wastewater from structures not served by public sewer. They all do basically the same thing, they are just designed differently to compensate for differing lot constraints and soil conditions.

A MOUND SYSTEM refers to a system in which the soil absorption part of the system must be designed and installed literally on top of the existing grade to assure the wastewater is properly treated on sites that have high groundwater or bedrock.

In all POWTS, including both mound and conventional systems in Wisconsin, the wastewater exits the house and enters a septic tank where the water is partially treated. In a septic tank the inlet and outlet of the tank are both near the top of the tank, allowing the larger solids to settle to the bottom of the tank. A portion of the solids accumulating on the bottom of the tank are eventually "broken down" by anaerobic bacteria, and the balance pumped out when you have your system periodically pumped. Fats, Oils, Greases (FOG), and lighter solids which float on the top of the water in the tank are prevented from exiting ( which leads to clogging of the soil absorption bed), by baffles which cover both the inlet and the outlet of the tank, allowing only relatively cleaner water near the middle of the tank to exit.

Remember: both conventional septic systems and mound systems begin by having the wastewater partially treated in a septic tank and must be periodically pumped for proper maintenance. After the partially treated water exists the septic tank the water may follow gravity into a conventional (below grade) soil absorption bed, or flow into a pump tank to eventually be dosed into a mound system under pressure. A mound system in Wisconsin is a pressurized equal distribution system, which means when water is "dosed" to the mound the wastewater is equally distributed under pressure. This means you use the entire square footage of the mounds soil absorption area to treat the water. The pressurized equal distribution is due to the distribution pipes in the mound being only 1" to 1&1/2" in diameter with small, specifically sized holes drilled at specific spacings. This assures the most equal distribution possible.

A conventional septic system is an in-ground gravity discharge Privately Owned Wastewater Treatment System (POWTS). This system will consist of one or more septic tanks and a gravity discharge feed bed or series of trenches. Characteristics of the soils will be high sand and gravel content along with low levels of clays and silts. Seasonal high ground water and bedrock levels must also be at least three feet below the discharge pipe in the trench. These soil characteristics have to be evaluated by a certified soil tester.

In a conventional system, the wastewater exits the home and enters one or more septic tanks. The inlet and outlet of these tanks are located near the top so to allow solids in the wastewater to settle to the bottom. This is the septic tanks primary function, to keep the solids from leaving the tank. These solids are later partially broken down by anaerobic bacteria. Remaining solids are removed by having the tanks pumped. Pumping should be done every two - three years.

After the effluent leaves the tanks, it is gravity discharged to a "leech" field or series of trenches. A trench system has the best performance characteristics, but requires a much larger area. The "leech" bed is most common. In both systems the effluent passes through the native soil on its way to the ground water. This is why there must be 36" inches of soil between the bottom of the discharge pipe in the bed or trench, and any ground water or bedrock present. After the water passes through this layer of soil it has been purified enough that it may be added back to ground water without posing a health hazzard.

Most of these beds are constructed in the field utilizing clean stone and perforated PVC pipe. There are also performed plastic chamber on the market such as Infiltrator. These chambers offer unique performance characteristics that enhance installation and overall systems performance.

This type of system is the most inexpensive discharge system available. However many areas do not have the native soils present to allow this type of system. Talk to your installer or soil tester about what would be best for your lot. If you are currently looking at a piece of property, you should know what type of system you will be able to install.

These systems will include aerobic treatment units, sand filters, peat moss treatment, constructed wetlands, and the list goes on. Most POWTS relied on the discharge bed to perform treatment of the effluent. These systems all have one thing in common and that is they pretreat effluent before discharge to the soil.

Aerobic Treatment Units (ATU) work in similar fashion to municipal wastewater treatment plants. The effluent is held while large quantities of oxygen are injected. The oxygen allows for aerobic bacteria, bacteria requiring oxygen to survive, to consume the solids in the effluent. This bacteria is much more effective than anaerobic bacteria, bacteria not needing an oxygen source. Most aerobic units have been tested by the National Sanitation Foundation, NSF. A NSF class one rating is the highest issued and probably the type you want to pursue.

Sand filters inject effluent in measured quantities through a layer of sand. This allows also for aerobic bacterial action, discussed above. Sand filters can be single pass or recirculating. Single pass sand filtes require a larger area and more material. Recirculating sand filters are smaller and easier to construct. Sand filters can be made of several types of materials. These materials can be course sands or fine stones. These materials must be clean.

Other types of systems such as peat moss beds, constructed wetlands, subsurface drip irrigation's systems, etc. are also availible. If you are having problems getting a POWTS approved for your lot or home you may want to talk to a soil tester, installer familiar with these systems, or a representative of Lake Shore Burial Vault. We would be glad to assist you in finding the most effective and inexpensive system available.

A certified soil tester must complete a detailed analysis of your soil characteristics (and other site limitations i.e. set backs, slopes, etc.) to determine the type of system your lot requires. The most important item the soil tester is looking for is depth to a "limiting factor" such as high groundwater or high bedrock. They will insure that mandates of vertical separation between the bottom of the soil absorption system and high groundwater or high bedrock in most instances are met.