Septic, Mound, and Holding Tank Systems in Wisconsin Under Comm 83

by Russell Knetzger, AICP, Milwaukee, WI

and Barry Sullivan, Ozaukee County, WI , Sanitation & Zoning Specialist

May, 2000, revised April, 2005

Septic Systems provide non-electrified gravity flow soil absorption sewage treatment.  Sewage effluent flows from the plumbing connections of the building into a "tank" (usually cement) buried in the ground just outside the building being serviced.  The tank has an outlet positioned below a baffle system to retain greases at the tank top, and to encourage settlement of grits and solids to the tank bottom.  The goal is that only clear effluent exits the tank via the outlet.  Greases and solids are intended to break down inside the septic tank via microbial action, and gradually dissolve and become part of the clear effluent.

The outlet from the septic tank connects to a series of  drainage tile placed through a layer of gravel that has been dug into or placed upon the surface of the unpaved natural ground surface.  Prior to 1980 the tile were made of cement, but since then “Sch 40” plastic piping is used. As the effluent seeps out of the tile lines into the gravel, microbial action on the gravel surfaces continues to purify the effluent of disease organisms.

The effluent is then supposed to soak into the ground and return to being a part of the ground water systems. 

The problem with septic tanks is that solids over time can buiup in the tank bottom to the outlet level, so that new effluent is reaching the tile lines carrying too much solid material.  Slim builds up in the tile lines nearest the tank, preventing any soaking into the gravel. Over time the slime occupies more and more of the entire tile field, to the degree that untreated effluent reaches the outer limits of the tile field, and bubbles-to the ground surface.

Such effluent is odorous and potentially hazardous.  It is carrying high levels of dissolved nutrients and potential disease organisms, so that if the effluent reaches water bodies, the organisms and nutrients degrade the water quality.

Periodic pumping of solids from the bottom of the tank might prevent the slime buildup.  The problem is that such "septic tank-tile field" systems became culturally identified as "maintenance free" systems.  Pumping only occurs after the tile field has become clogged and is emitting untreated effluent.  Pumping at that point might provide some temporary hydraulic relief, but basically the entire system has become non-functional and a new field should be installed.

Another problem with such septic tank/tile field systems is that if the underlying soils are impervious to water (clays) the effluent cannot soak in except in the driest of weather.  The effluent will collect upon or move along the clay layer and reach the surface, in an insufficiently treated state. Also, many older systems are located in zones of seasonal saturation and/or groundwater, in which case effluent is reaching the water table in an under treated condition.

An opposite problem is underlying soils can be too thin or too pervious, especially if they  lie over fractured rock.  The under-treated effluent can travel through the thin soil and down the cracks or porous soils into the ground water source used for drinking and cooking.

Mound Systems are basically septic tank/tile fields as described above, but they add two features: (1) storaqeand then surge electric pumping of the effluent from the tank into  small diameter Sch 40 type tile lines; (2) special suitable sandfill  soils trucked onto the site to become the  absorption field, thereby overcoming shortcomings in the natural soil of the site.

In theory, if effluent is collected in the tank in the same manner as a household sump pump, and then periodically forcefully discharged over the entire  absorption field, that pressurized discharge utilizes the treatment and soaking action of the whole field, not just the portion nearest the tank.  Using the whole field also allows the field to dry out between discharges, thereby  reducing the formation of slime.

By trucking in proper sandfill soils, and mounding them up on the natural soil surface (hence the name "mound system") some inadequacies of the underlying natural soil may be overcome.

Given the experimental nature of mound systems, they were allowed in Wisconsin only on a test basis, starting in the mid-1970s.  Each mound installed was registered and monitored under a University of Wisconsin study program.  By the mid-1980s mounds were judged workable, and are now routinely allowed by permit, except a minimum amount of topsoil must be present and a minimum distance must exist from the bottom of the mound to the seasonal high ground water table.

However, the permit process for all ground treatment systems, both septic and mound, was shifted by the state legislature away from towns, villages, and cities, and given only to counties.  The county through its state-mandated “county sanitarian" department administers a strict code set by state administrative rule.  Initially the Department of Health, Industry, Labor and Human Relations (DILHR) was given this rule-making role, but now it rests with the Department of Commerce.

As part of this new county administered system, soil borings are now required of every application.  Such borings are taken only by licensed soil testers so that results of underlying soil perviousness cannot be faked as they were under the previous system of "soil percolation tests.” Such "Perc tests" were taken by master plumbers, who could tailor results by choosing dry months and by inadequately saturating the soil with water before the test.  Even with licensed soil testers, county staff often initially insisted upon being present at the site as borings  were performed and read. County presence during the borings is now an option. Most counties do not require their staff presence unless the property owner of a failing “POWTS” (private onsite wasterwater treatment system) is Wisconsin Fund eligible.

Besides soil porosity, ground water table location is critical under the new rules.  Soil borings show the seasonal high ground water level by “soil mottling", (a permanent soil discoloration that experienced testers can read) and this higher level is used, not some lower level where the ground water might actually be at the time of soil testing.

Generally 24 inches of natural soil to the ground water or zones of seasonal saturation or bedrock is required, though an “A+4" variance system is possible in some cases, where the "A Horizon" of soil, the topsoil, is at least 4 inches above the highest ground water level. It is also possible to have an “A+0” mound system

Holding Tanks.  In cases where a tile field is not practical (inadequate lot size, such as cottages on small lake lots), or soils and water table levels do not meet the state sanitary code, holding tanks are authorized under the state code.

A holding tank is simply a tight, leak-proof steel drum that acts as a temporary collection for all sewage effluent.  When the tank nears its full point the tank contents are then pumped into a truck operated by a state licensed waste hauler.  The effluent is trucked to the nearest community having a public sewage treatment system, and dumped under permit via a special metered manhole into that system for treatment.

All pumping and disposal records are monitored by the county sanitarian department, as well as the receiving municipality, which will invoice the hauler for the gallonage being received and treated.

In spite of this tight security, holding tanks are regarded as "systems of last resort" and "failure prone." Pump-ing and trucking is quite expensive,  beginning at $25 per week, and rising well above that for homes with a large family or careless use of household water.  The failure element relates to the ease with which owners may illicitly equip the tank with a sump pump, and eject the untreated effluent onto the ground surface, such as nearby road ditches.

Given the extreme nuisance holding tanks can become if illicitly pumped by owners, the legislature granted the right to local communities to outright ban the use of holding tanks, or to severely regulate them to specific limited existing emergency situations alluded to above (failed septic system on small existing lot, etc.) The county may not issue a permit for a holding tank unless the local ordinance allows for it. However, state regulations are written so that communities that permit holding tanks can reclassify them from systems of last resort to systems of choice.

"Comm 83”. As University of Wisconsin monitoring of the experimental mound systems through the 1980s was showing positive results, groups for and against the legalization of mounds began speaking out. Much publicity has attached during the 1990s to a proposed revision of the state administrative rules governing on-site soil absorption sewage treatment (the broad category for septic and mound systems).

Called "Comm 83," these rule changes are a shortened name for “Chapter 83" of the Wisconsin Administrative Regulations which are published and administered by the Department of Commerce (“Comm") for septic and mound systems.

Environmentalists  were  fearful the new regulations were too lenient in terms of protecting water sources, and cities were fearful additional town lands would qualify for development, thereby worsening the "urban sprawl" phenomenon that  was becoming so prevalent during the 1990s.  Basically Comm 83  was being characterized by opponents as only lessening the minimum distance between the bottom of  an absorption field  through the layer of natural topsoil to the top of the seasonal high water table.

The legislature finally intervened and allowed adoption of Comm 83 providing towns do land use planning.  The "Smart Growth" law adopted by the legislature in October 1999 is commonly thought of as the mechanism that would provide financial grants to towns for such planning, and provide a framework into which the plans would need to fit.

Accordingly the legislature allowed Comm 83 to go forward, and Comm 83  became operative July 1, 2000.

There is some opinion that the Smart Growth law does not in fact address the land use planning issues related to Comm 83, and “l000 Friends of Wisconsin”, one of the authors of the Smart Growth law, brought a lawsuit seeking to again delay implementation of Comm 83.  However, the July 1, 2000 date of implementation of Comm 83 did take place, and still stands.

While the minimum distance below the bottom of an absorption field is being lessened by Comm 83, that is occurring within a change in the total regulatory framework of Comm 83.

Previously  Comm 83  was  "prescriptive based" (describing exactly what distances, soil types, etc. must exist).  It was changed by the new July 1, 2000 rules to “performance based,” which does not do away with soils information and distances, but which shifts the emphasis to quality of effluent treatment based upon the designed use of electrification and pressurization to achieve desired levels of effluent treatment..

In effect emphasis is being placed by the July 1, 2000 rules upon the design and operation of each soil absorption system, given the soils and water table distances found, rather than upon more generalized, but fixed criteria.

The switch is occurring because some early mound systems are failing, and it is thought these failures can be prevented in the future with adjusted designs.  It is also thought that non-mound “septic systems" would benefit from pressurized discharge pumping of effluent to replace the traditional “dribble out” method that has led to eventual system failure from accumulation of slime.

Readers needing more detailed or up to date information are encouraged to learn more about the Wis-consin Administrative Plumbing Code known as “Comm 83” by going to:


Chapter 85 deals with Soil and Site Evaluation.

At the above website readers can page to see the individual component manuals that are used in the design of the POWTS.

WAPA Annual Chapter Report 2008