Types of Septic Systems

There are basically three types of septic systems. Not all homeowners are free to choose from all four types because local codes may not allow conventional systems to be installed where soil absorption or drain field space is limited. In addition, each has its own advantages and disadvantages. Most localities require an engineer to perform a site evaluation. The results of this evaluation will determine the homeowner’s options. Different systems require more or less frequent attention by the home owner; others require more frequent maintenance by septic system professionals. Installation costs also vary by type, so there is much to consider when choosing the system that's best for you.

Conventional Systems

Generally there are two types of conventional septic systems: those that use gravel in the drain field and those that use some form of chamber system. As its name suggests the older style graveled system contains a layer of gravel in the drain field. During construction, a drain field ditch 1 to 3 feet below ground level is constructed. Its length is determined by the anticipated flow of effluent into the system from the home or rural office, as well as the soil's ability to absorb water. Washed gravel is poured into the bottom of the ditch, then over and around a perforated plastic pipe.



Additional gravel is poured around and over the pipe, then the gravel is covered by a semi permeable barrier such as geotextile fabric so that backfill soil doesn't filter between the rocks and reduce the field's ability to absorb water. While some treatment of waste occurs in the septic tanks as bacteria within the tank operate on the waste, most of the treatment occurs as wastewater discharged from the tank enters the drain field and is filtered through the gravel and the soil below. Over time, bacteria and other organisms in the soil consume any organic material in the wastewater. These organisms multiply and form a layer called a biomat that sits on the soil layer. When sufficient oxygen is available, worms and other parasites feed on the bacteria as well as the material in the wastewater. When the drain field is in balance, these organisms keep the biomat from becoming so thick that it won't allow passage of wastewater to the soil below.

Graveled or stone septic systems have some potential drawbacks. First, the use of gravel automatically, limits the effluent's ability to reach the soil where the majority of filtration takes place. Depending on the size of the gravel, something like 50 to 75 percent of the potential infiltrative area is blocked by the surface of the gravel. In addition, though responsible contractors use only washed gravel, a certain amount of fines inevitably remain and drop to the soil level further reducing potential filtration. One further potential problem of graveled systems is the possibility of drain field overload. This may occur when the water table rises above the drain pipe and effectively shuts down the drain field’s ability to discharge water. If this happens, it will be noticeable as baths and toilets begin to back up. Then there is the possibility of drain field overload that may occur when there are additional guests in the house for long periods of time or at times when faucets or toilets have been left running for prolonged periods. Again, once the system is overwhelmed the drain field will fail to function and may become damaged to the point of needing to be replaced.

Gravel less conventional systems overcomes some of the drawbacks of graveled systems. These drain field systems consist of a series of connected chambers that are typically 15 to 40 inches in width. Typically these chambers are manufactured of molded high-density plastic in 10' to 12' foot lengths. Some systems include pipes within the chamber, others do not. CleanEarth Environmental exclusively uses the Infiltrator chamber system as we have found this system to most effective when allowed in Florida soils. Native soil is compacted slightly around the chambers to provide stability and then filled in above the chamber. When placed into service, waste water is carried by pipe from the septic tank to the chamber run and flows directly against the soil. As in the graveled system a bio mat forms on or near the soil level and works to consume solids that pass out of the septic tank. One real advantage of the chambered system is its ability to hold much larger amounts of water. This is useful in locales where the water table can rise close to the surface and in instances when there is a temporary surge as a result of extra guests. Obviously shock loading over prolonged periods of time is going to be detrimental to the biomat as oxygen will not be available to parasites during these periods.

Low-Pressure Dose Systems

Low-pressure dose systems (also known as low-pressure pipe systems) may offer an alternative where soil and topographical conditions do not permit placement of a conventional septic system. This is especially true where the topography requires the drain field to be located up-hill from the the septic tanks or where there is uneven terrain that would otherwise preclude placement of a conventional system.

Low-Pressure Dose Systems (LPDs) basically work like this: Beside the standard septic tank, an additional tank called a pumping chamber is installed. Under normal conditions, a low-pressure pump is turned on twice each day and forces wastewater in the pumping chamber to pass into the drain field. Under an LPD application, the drain field consists of small perforated pipes in shallow, gravel lined trenches 10" to 18" deep and 12" to 18" wide. Wastewater is pumped, or forced into the drain field to the point where the entire field is saturated. Then the field is left to drain. This creates good aerobic conditions (aerated) thus promoting good bio-processing by bacteria and other parasites. Shallow placement also promotes evapo-transpiration, where evaporation and grass and other shallow rooted vegetation help eliminate wastewater. In an LPD system, the pumping chamber is designed to contain at least on extra day of effluent. More flow will cause alarms to be activated. With an LPD installation the drain field is normally uphill from the septic tank to avoid the possibility of continuous distribution of effluent via gravity. When the drain fields are not located up-hill, the system will be designed is such a way that effluent will not leave the pumping chamber when the pump is turned off.

Beyond the topographical site advantages of LPDs mentioned above, there is a significant reduction in the land area required by the absorption field compared to conventional systems. In addition, the use of a low-pressure pump means that the entire drain field will be used uniformly. And narrow, shallow trenches reduce some of the enevitable soil-compaction that is commonly associated with the construction of conventional drain fields. But LPDs do have drawbacks: there is the potential for infiltration by roots and clogging of drain holes by solids that escape the pumping chamber. There is also the possibility of wastewater accumulation in the trenches. Finally, LPDs require regular maintenance. The addition of electricity, a pump and smaller drain field increase the possibility of system malfunctions. Consequently, most permitting authorities now require annual or semi-annual inspections by licensed septic professionals.

Aerobic Wastewater Treatment Systems

Clearly aerobic septic systems are the one system that can be applied in almost any situation where septic systems are required. When you own an aerobic system you are basically the owner of a small version of a municipal sewage plant. That is, your aerobic system mirrors many of the steps and activities performed by an urban waste treatment plant. Aerobic systems are similar to septic systems in that both treat wastewater using natural processes. However, unlike the conventional septic system, the aerobic system injects oxygen via a pump into the tank. This increase in oxygen increases the natural bacterial consumption of waste within the system. The best aerobic systems provide a pretreatment tank as well as a final treatment tank with unstabilized chlorine. At this point the resulting discharge water is clean enough and pure enough to be discharged via sprinklers directly over the absorption field. This is a real plus to home owners who don't want to clear trees to create an absorption field and to other homeowners on lots close to a body of water that might otherwise be subject to potential pollution.



Aerobic systems work like this: Wastewater and effulent enter a pre-treatment tank where grease, oils, toilet paper, and other solids and foreign materials are captured. This helps to reduce the amount of solids entering the aerobic chamber. Too many solids can clog the system and cause malfunctions. Next, the wastewater enters the aerobic chamber where air is compressed and forced into the wastewater to increase the growth of beneficial bacteria that consume the solids. However, not all solids are consumed by the bacteria, so the mixture next enters a setting or clarifying chamber where any remaining solids can settle. Next the treated water moves to a pumping chamber where is receives a final treatment of unstabilized chlorine. This is not the same chlorine as you use to shock your pool, but rather a highly concentrated, tablet form of chlorine specifically designed for the treatment of wastewater. A float valve within the pump chamber will signal the pump to discharge the water to absorption field. This treated water is then piped to the field and dispersed via pop-up sprinklers.

Typically aerobic systems cost little more than conventional septic systems to install and maintain. Systems are specially designed with alarms and control boxes to assure that they are functioning properly at all times. Usually they are less expensive to install than LPDs or conventional systems as there is no need to condition a drain field with sand and/or gravel. Because you are basically running your own wastewater treatment plant, it is essential to secure the services of a qualified professional in order to obtain the periodic certification letters required by most permitting agencies. This maintenance contract will assure you that your plant is functioning within specifications at all times. Manufacturers provide a two-year warranty contract as a part of the purchase price. At the end of this time you will need to either renew your maintenance contract or obtain one from another waste water treatment professional.

Regardless of the type of system you would like to install. CleanEarth Environmental can help with all your permitting and maintenance needs.