Types of Septic Systems

So you need a septic system. Did you know that means you’re going to have to pick a type of system? There’s a wide variety of system types out there, but before diving into the details of every one, the ten in this post (considered the most common by the EPA) are a great place to start.

The type of system best-suited for you will depend on things like your household size, soil type, lot size, surrounding water bodies, and more. Here’s the very basics on both conventional types of septic systems and common alternative systems.

Septic Tank

The septic tank itself is a buried, watertight holding tank built to hold and do light treatment on a household’s wastewater. Solid matter settles to the bottom of the tank while liquids are discharged to treat and disperse in the soil. Read more about the septic tank here >>

Conventional System

The most conventional kinds of systems have a septic tank and a trench or a drainfield for liquids to disperse into. The practice of using gravel or stone for this drainfield goes back decades — the stone filters out larger contaminants and microbes in the soil below further treats the water. These systems have large footprints and won’t suit all residential sites; though they are most commonly installed in single-family homes or small businesses.  

Chamber System

Gravelless systems have begun to replace traditional gravel systems in recent years. There are many forms of gravelless drainfield, and they offer a smaller carbon footprint than a gravel system does. In a common type of gravelless system, chamber systems, a series of chamber pipes carries the wastewater directly from the tank into the soil. These systems are ideal for areas with higher groundwater tables and where the septic usage volume is more variable. Read more about chamber systems >>

Drip Distribution System

This type of system can be used in many kinds of drainfields. The tank discharge is slowly dripped out in a wide reaching array of shallowly-placed lateral pipes. Drip distribution does require electrical power to regulate the timed drip delivery, and therefore require higher costs and more maintenance. Read more about drip distribution >>

Aerobic Treatment Units

ATUs are like a miniature municipal sewage plant. The treatment tank is injected with oxygen to stimulate natural bacterial activity for further treatment., and some can have additional  tanks to perform more disinfection and pathogen reduction processes. These systems work well in smaller lots, poor soil conditions, and areas with a high water table or nearby surface water. Read more about aerobic treatment >>

Mound System

A mound system will require building an artificial sand mound for the wastewater to be pumped into and flow through before reaching the native soil. This works well in places with shallow soil or bedrock and with high water tables. They do require more space and maintenance than the average. Read more about mound systems >>

Recirculating Sand Filter System

This type of system is more expensive than most conventional systems, but performs a high level of nutrient treatment. After leaving the septic tank, the wastewater will flow into a pump tank which pumps it at a low volume through a sand filter contained with PVC or concrete. Then, like a mound system, the water will filter into the native soil. Read more about recirculating sand filters >>

Evapotranspiration System

In this kind of system, the wastewater will never reach the soil or the groundwater. Instead, it evaporates from the drainfield into the air. This is only workable in arid, hot conditions with shallow soil. Read more about evapotranspiration systems >>

Constructed Wetland System

As the name suggests, this type of system imitates the treatment processes of natural wetlands. After leaving the septic tank, pathogens and other nutrients will be filtered from the wastewater by microbes, plants, and other media, before reaching a drainfield. The plants in these systems need to be able to survive in constantly wet conditions. Only artificial wetlands should be used to treat wastewater; real natural wetlands are not a wastewater disposal or treatment option. Read more about constructed wetland systems >>

Cluster/Community System

Essentially, a cluster or community system is a septic system large enough to handle the wastewater of two or more households or buildings. You’re likely to find them in rural subdivisions, and they will be subject to common ownership. Read more about cluster systems >>

More Information:

• Find diagrams of each type of system at EPA Septic.

• Peruse decentralized wastewater technology fact sheets.

• 5 Factors to Consider When Choosing a Septic Tank from Pete’s Outflow Technicians

• 10 Different Types of Septic Systems + How to Choose the Right One from The Original Plumber. See here for additional info on outdated systems and other FAQs.

A Bored Well Drilling Demonstration

On October 20, 2021, the Illinois State Water Survey staff were invited to a bored well drilling demonstration in North Central Illinois. Professor Mike Phillips, from Illinois Valley Community College, invited ISWS staff to view the construction of a new bored well. Reynold’s Well Drilling, Riverton, IL, was contracted to construct the well. Reynold’s Well Drilling only installs large-diameter bored wells, typically 30-40 wells every year. According to the driller onsite, they have been busier in the last 5-6 years. The entire process took 4-5 hours and was estimated to cost around $15,000. Reynolds was contracted to drill the well and a separate contractor, Lutes H2O Well Drilling Inc. was contracted to install the distribution lines to home the following day.

Regarding the existing hand-dug large diameter well on the property, the owner mentioned that the sample from that well was tested in 1999 when the home was purchased. The test results showed that the drinking water was high in coliform bacteria, nitrates, iron, and manganese. In response, the Phillips installed a UV treatment system and water softener. The water hasn’t been tested since the initial test in 1999. The old well is brick lined well and about 23 feet deep. The water yield for the old well was 5 gallons per minute.


Figure 1. Well Cover for Brick Lined Well

Figure 2. A View Down into the Brick Lined Well

Figure 3. Drill Rig, Trailer, and Water Truck

The process began with selection of a location for the new well. They chose a location in the front yard and approximately 15-20 feet from the driveway. The drillers began by setting up their truck over the chosen location. Once in place, they started digging, using a 36-inch dirt bucket that removes 1ft of dirt per pass.

Figure 4. Drill Rig Set up over the Well Location

The digging continued for several passes, and a large mound of dirt accumulated near the new well. Once there was a depth of 16 ft removed, a metal sleeve was placed in the top 16 feet of the new well. The sleeve worked as a guard to prevent the dirt along the sides from caving in, which allowed the drillers to continue to dig deeper.

Figure 5. Drill Cuttings

Figure 6. Metal Sleeve to Prevent Cave In

Figure 7. Metal Sleeve In Place in the Borehole

Figure 8. Water From the Bucket Indicates Saturated Material

Drilling continued until water was evident in the drill cuttings. When the driller determined they were at a sufficient depth, they prepared the well for installation.

The well was constructed from a single length of fiberglass casing. To allow water into the well, thin slits were cut into the bottom section of the well. Centralizers were attached in three places equidistant apart which acted as stabilizers to position well casing upright and center it in the borehole. Water was pumped into the annulus to hold pressure to the sides to prevent caving, while a vertical metal beam was used to hold down the fiberglass well casing, so it didn’t float. Filter sand and gravel placed in the annulus served to both hold the well in place, allow for additional water storage around the well, and to help filter the water in the formation before it can get into the well.

Figure 9. Driller Cutting Slits in the Well Casing

Figure 10. Close Up of the Cut Slits in the Well Casing

Figure 11. Fastening Centralizers and A Lid to Lower the Casing into the Well Borehole

Figure 12. Lowering the Well Casing into the Borehole

Figure 13. Adding Water into the Annulus Around the Well

Figure 14. Adding Sand and Gravel into the Annulus Around the Well

To finish the well, water is pumped from the new well until it runs clear, a cap is added to the fiberglass well screen, a submersible pump is installed, and a 6-inch PVC well casing is installed from the fiberglass well cap to the surface. The sleeve is then removed, and the upper portion of the well bore is filled with clay or concrete. At the end of the drilling process, the total depth of the borehole was 43 ft on the bottom, 13 ft at the top, and the top of the water was reached at 22ft. The well will be able to provide 8 gallons/minute. The last responsibility for the driller is to complete a well log and file it with the county health department.


Figure 15. Developing the Well by Pumping It Until the Water Runs Clear

Figure 16. The Fiberglass Cap and 6-inch PVC Casing that will Extend to the Surface

A Gradual Return to In-Person Outreach for the Illinois State Water Survey

In August and early September, staff from the Illinois State Water Survey participated in both the 2021 Illinois State Fair in Springfield, IL and the 2021 Farm Progress Show in Decatur, IL. At the Illinois State Fair, the ISWS had a booth in the “Conservation World” from August 13-15 and August 20-22. According to the Illinois Department of Agriculture, the 2021 Illinois State Fair saw over 472,000 visitors, making it the second highest attended fair since the department began tracking formal attendance numbers in 2014.

In addition, the ISWS had a booth in the “Partners in Conservation” tent from August 31-September 2 at the Farm Progress Show. The Farm Progress Show is the nation’s largest outdoor farm event and attendees and included producers from 46 states and around the world. ISWS estimated to have directly helped at least 278 private well owners at the Illinois State Fair over 6 days and at least 230 private well owners at the Farm Progress Show over 3 days, with many signing up for the Private Well Class.

The Private Well Class program is a free, grant-funded program that provides education and outreach, both online and in-person, to boost knowledge and competency of well owners as well as the thousands of dedicated environmental health, cooperative extension, and water well professionals that serve well owners every day.

Staff not only discussed the water cycle and the role that groundwater has in it, but also had an interactive sand tank flow model that demonstrates how groundwater moves in an aquifer and how contamination can affect private wells using colored dye. The display included a working hand pump for kids to try, which demonstrated how everyone in the “good old days” got water from a well. Private well owners in attendance also had the opportunity to chat with our Privatewellclass.org staff and experts. Information was provided on how to sign up for the free 10-lesson Private Well Class, how to get your well water tested, and where to find other resources available for well owners who want to learn more about how to properly care for their well.