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Alternative Septic System Designs for wet, steep, rocky, small, poor percolation sites SepticAPedia ©   Search This Web site - inspect-ny.com Alternative septic system designs for problem sites Description of alternative septic systems, design criteria, product sources Aerobic septic systems, cesspools, dosing systems, drywells, evaporation/transpiration, gravelless, & graywater systems Media filter systems, septic filters, graywater filters, septic mound systems, raised bed septics, sand bed septic systems Residential sewage treatment systems, waterless or low-water toilet alternatives, product sources

This document discusses alternative septic system designs for difficult building sites such as wet sites, steep sites, rocky sites, limited space, bad soils with no percolation or sandy soils with too fast percolation, and other difficult site conditions. We provide detailed articles about each alternative septic system design choice, listing its features, design requirements, inspection details, maintenance needs, product sources. We include links to septic design engineers, advanced septic system products and septic design books and building codes. This document is a chapter provides in our Septic Systems Online Book.

Examples of advanced septic designs include aerobic septic systems, chemical, composting, incinerating & waterless toilets, evaporation-transpiration (ET) septic systems, septic media filters, greywater systems, holding tank septic systems, mound septics, raised bed septics, pressure dosing septic systems, sand bed filters, peat beds, constructed wetlands, wastewater lagoons, constructed wetlands, and septic disinfection systems.

Consultants in this field can be listed at our alternative septic designers page at no charge by contacting me. Also see The Septic System Information Website. Massachusetts Title 5 Licensed Septic System Inspector, & New York State H.I. License # 16000005303. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

ALTERNATIVE SEPTIC SYSTEM DESIGNS - Onsite Wastewater Treatment Methods for Difficult Sites

This document catalogs alternative septic system designs and provides links to detailed descriptions of these designs for onsite wastewater treatment. "Septic System Alternative Designs" refers to any onsite wastewater disposal method other than the widely used conventional septic tank and leach field. In the U.S. most states require that an "alternative septic system" be designed by a professional and submitted to the local health department for approval.

Alternative onsite wastewater disposal systems can reduce the soil absorption area or leach field size requirement substantially and can in fact in some cases reduce the needed area to zero. For problem sites where space or soil conditions make it difficult to install a conventional leach field or where an existing septic system has failed, these designs are very important alternatives.

The alternative septic system designer conducts the site and soil inspection and testing, prepares the system design and installation plan, supervises the septic system construction, and certifies that the system was installed as designed.

Alternative septic system designs are used for new or replacement septic systems on difficult sites where soil conditions (such as a rocky site, limited soil percolation rate, or high ground water level), or other terrain conditions (such as limited space for a septic system or steeply sloped sites) do not permit the installation of a conventional septic tank and drainfield system.

Examples of site conditions that lead to consideration of an alternative septic design include:

• Bad soils: building sites with soils with very low percolation rates or no soil percolation such as clay soils
• Difficult soils: building sites with other soil problems such as too-fast percolation rate, perhaps too sandy
• Failed septic systems: sites where an existing septic system has failed and there is limited space or other constraints on septic system repair
• Rocky building sites or sites with bedrock and not enough topsoil to treat and dispose of wastewater.
• Small building sites which lack adequate space to install a conventional septic drainfield
• Steep building sites which do not permit installation of a conventional drainfield or sand bed
• Wet building sites with high groundwater or subject to surface runoff (that cannot be fully diverted)

General Categories of Onsite Residential Wastewater Treatment Systems

Because various texts provide so many different views of categorizing wastewater systems, I've made this simple list which groups wastewater treatment systems into a few major categories:

1. Conventional Septic Tank and Drainfields in native soils for effluent absorption and treatment. Up to 45% of effluent treatment, often less, occurs in the septic tank, the remainder occurring in the drainfield.
2. Raised Bed and Septic Mound systems which take a similar approach as conventional systems cited above, but which require extra steps of soil preparation or the necessity to bring in fill to treat effluent. A common raised bed design is the sand-lined filter bed septic system.
3. Advanced Material Media Filtration systems (sand beds, filter beds, peat filters, synthetic textile filters, rotating biological contractor systems, trickling filters, foam media filters including above-ground self-contained systems)
4. Aerobic Septic Systems which insert additional oxygen into and agitate sewage in the primary treatment tank
5. Wetlands and Constructed Wetlands for sewage or effluent treatment. This category may also include greenhouse treatment systems or other methods involving the use of constructed or natural water/land formations.
6. Disinfection Systems which perform a final treatment of effluent by use of disinfectant chemicals (chlorine) or perhaps UV light so that effluent can be discharged to the surface or to ground water or even streams and waterways.
7. Waterless and Low-Water and Greywater-Separation systems, which may not really treat effluent, may not discharge anything into the environment, but which form another set of alternative designs where water supply or land use restrictions mean that a conventional system is not permitted. Examples include composting toilets, incinerating toilets, chemical toilets, and graywater systems.

Our Master List of Septic System and Wastewater Treatment Alternative Designs below offers a complete list of alternative septic system designs and major septic system component designs along with a description of each septic system/onsite wastewater treatment approach. For each system we link to articles providing more in-depth design, installation, repair, inspection, maintenance and product source information.

Levels of Wastewater Treatment - How Sanitary is the Final Effluent?

In case the above list of wastewater treatment categories is not enough, there are also various levels of degree of treatment of septic effluent achieved by different versions of these systems, by natural wetlands septic systems, or by use of septic effluent disinfection systems. For example, you may read about more than one type of gravity dosing or pressure-dosing sand filter beds system which look a lot alike but which achieve different degrees of effluent treatment.

Jantrania (see Alternative Septic Designers) describes eleven Onsite Wastewater Treatment Types in a confusing list (Table 1.3 in his text) since the same type of system may appear more than once (drainfields) depending on the level of treatment achieved by a specific implementation. In the same text the author proposes a Pollution Scale numbered from 0 Drinking Water) to 10 (Sewage). (p.36). An overall sewage treatment level of 50% would be 5.0 on this scale, and a treatment level of 100% would mean that the output of the system was equivalent to drinking water in purity.

Because over time the concentration of contaminants in incoming sewage and wastewater varies by type of use, level of building occupancy, changing soil moisture and temperature, and other factors, it is risky to assume that a regulation or a septic system design level requiring or claiming 90% treatment (pollution scale 1.0) is always producing effluent treated to exactly that level. Awareness of the variation in level of contaminants in sewage arriving at a treatment system, as well as awareness of variations in site conditions (level of ground water, temperature, frequency of inspection and maintenance) is behind the very conservative standards adopted by many health departments regulating septic system installations.

The terms percentage of treatment and level of treatment of sewage or wastewater are used in different and perhaps confusing ways. A writer may say that "45% of the effluent treatment occurs in the septic tank". I take this to mean that whatever the overall or final level of wastewater treatment that the whole system is going to provide, from input to the system to final discharge of effluent into the environment, 45% of it is occurring inside the septic tank. This does not necessarily mean that the effluent discharged from the septic tank is 45% of the way along the pollution scale or nearly half way to being pure drinking water. The term "level of treatment" should be reserved to mean the overall or final degree of purity of the effluent which is discharged to the environment.

Sewage contaminants- what's in sewage, and typical sewage contaminant levels are discussed in more detail at Septic system contaminants.

General Categories of Wastewater Dispersal Methods

Adding to the complexity of what to call various septic systems, there are also categories of methods of septic effluent dispersal (to the final treatment and soil absorption or other efflluent disposal system) such as:

1. Gravity-Fed Perforated Pipe in Gravel-Filled Trenches: these are conventional gravity-fed drainfields, using gravity to permit wastewater to flow from the septic tank to the absorption system or drainfield. Wastewater moves out of the septic tank to the drain field by gravity in response to and equal in volume to new waste entering the septic tank. The absorption system consists of perforated pipes in gravity-filled trenches dug into native soils.
2. Drip or Spray systems which may disperse effluent above or below ground.
3. Gravity Dosing systems, which distribute wastewater to the drain field in irregular batches or "doses", permitting the absorption system to rest and recover between doses.
4. Pressure Dosing effluent dispersal methods for septic effluent handling such as sprinkler dispersal, and intermittent effluent dosing systems which using pressure dosing by pressure manifold, rigid pipe systems, or pressurized drip irrigation systems

An individual septic system design may use a combination of these methods to treat, disperse, and dispose of septic effluent. For example, a sand filter bed septic system might be fed by gravity, by a gravity-operated dosing system, or by a pump operated pressure dosing system.

Keeping these types of of septic systems (treatment methods) and these types of wastewater dispersal systems (disposal methods) in mind when reviewing various off-the-shelf packaged septic systems or wastewater treatment systems with interesting but non-descriptive names (like the "magic bullet treatment box") will help you to understand the general approach which has been taken in any specific case and will help you choose among alternative septic system designs and products. Further reading will be needed to understand the installation cost, maintenance cost, and level of management required of each type of septic system. I collect and publish here additional details on alternative septic system design, installation costs, and maintenance costs.

Links at the left of this page and most of our septic information website pages offer descriptions, design suggestions, product sources for each of these septic system types.

Jantrania (see Alternative Septic Designers) sorts alternative or advanced onsite wastewater treatment systems into five major groups: aerobic septic effluent. treatment systems, media filters, natural systems such as wetlands, waterless toilet systems, and disinfection systems. Here, however, our list of septic system designs and effluent. treatment alternatives is organized alphabetically and includes not only alternative methods of primary treatment but also methods of effluent final treatment, dispersal, and disposal. Conventional gravity septic tank and effluent drain field systems (Jantrania/Gross wastewater system type I) are discussed at the "Septic Systems Home" and "Septic Design Basics" links at the left of these pages.

Master List of Septic System Types & Onsite Wastewater Treatment Alternative Designs

Each of the links below presents a document with more in-depth information about each of these alternative septic system designs.

• Chemical Toilets: use a chemically treated reservoir located directly below the toilet seat. The chemicals reduce odors and perform partial (incomplete) disinfection of the waste. Chemical toilets have limited storage capacity and must be pumped and periodically cleaned by a septic company. Similar to simple chemical toilets but more sophisticated in design are recirculating toilets which separate the waste from the chemical and then re circulate the fluid through the toilet tank.
• Composting Toilets: may be used where the water supply is limited or not available at all, or where a building owner for other reasons wishes to conserve water use. Other wastewater treatment will still be required for handling graywater from sinks and showers.
• Disinfection Septic Systems: use chlorination or ultraviolet light (UV) to disinfect wastewater effluent before it is discharged to the environment.
• Dosing Systems, Pressure or Gravity: Dosing systems permit the septic system drain field to rest between effluent doses and, depending on design, may alternate use of drainfield sections. Two broad types of dosing systems are Gravity-Dosing (effluent flows from an effluent tank to the absorption system by gravity) or Pressure-Dosing (effluent is pumped from a dosing chamber to the absorption field).
  See Gravity Dosing Septic Systems
  and Pressure-dosed Drainfield Septic Systems for details.

• Evaporation-Transpiration (ET) Septic Systems: and Evapo-Transpiration Absorption Septic Systems (ETA) dispose of septic effluent from the septic tank by providing a surface area intended to allow the effluent to evaporate. ET systems depend entirely on evaporation while ETA systems make use of both evaporation and (limited) soil absorption of septic effluent. (Jantrania/Gross wastewater system type IX if effluent is treated to level 2 or better). ET beds may be used with or without intermediate storage tanks and with or without effluent recycling systems.
• Filter bed effluent treatment systems (if treated to level 2 effluent or better, Jantrania/Gross wastewater system type VIII) - see various filter media types listed here such as sand beds, fabric filters, etc. Filter beds may be
  Mound Systems or
  Raised Bed septic systems,
  Media Filter septic systems, septic systems or Sand-Bed filter septic systems.
  Readers should distinguish between types of septic filter beds (listed above) and other septic filter products such as
  in-tank septic filters.

• Greywater Septic Systems: refer to systems which reduce the liquid effluent load on a septic system by separating greywater (or graywater) from sinks and showers from blackwater (black water) from toilets. When we inspect a home which uses a separate drywell to handle greywater we presume that the owners discovered that their septic system, or at least its leach field, was of limited capacity or life.
• Gravity or Siphon Dosing Septic Systems: move septic effluent from the septic tank to a final effluent treatment/dispersal/disposal system such as a drainfield by accumulating septic effluent in a dosing tank or chamber and periodically sending the "dose" of effluent to the drainfield. To move effluent from the dosing tank to the drainfield a "gravity" dosing system uses a mechanical device such as a bell siphon system, tipping tank, or float valve to determine when the dosing tank is full and ready to send effluent to the drainfield at intermittent frequencies or in "doses". Effluent flows from the dosing tank to the drainfield by gravity. Gravity/siphon dosing systems usually require a larger effluent holding tank or chamber than pressure dosing systems. While some gravity dosing systems do not require electricity to operate, other "gravity" dosing system designs which place the dosing tank uphill and distant from the septic tank, can require an effluent pump to move wastewater from the septic tank to the remote dosing chamber/tank. Dosing systems permit the drain field to rest between doses and, depending on design, may alternate use of drainfield sections.
• "Gravity trench systems" is a generic term to describe distribution of septic effluent into a treatment and dispersal/disposal system using perforated pipes buried in gravel-filled trenches dug into the soil. An example is the conventional septic drainfield but gravity trenches can be used in other designs such as with gravity or pressure dosing systems. Gravity trench effluent systems may also be designed for "level 2 or better" effluent treatment (Jantrania/Gross wastewater system type V).
• Greenhouse treatment of septic effluent to level 3 or better (Jantrania/Gross wastewater system type XI). Greenhouses, like ET beds, may be used with or without storage tanks and effluent recycling systems. The system uses an enclosed "greenhouse" constructed around plants and a mini "constructed wetlands" to treat effluent. Greenhouse wastewater treatment systems permit maintaining the treatment system at a higher temperature than otherwise might be possible, such as in a cold or cool climate area.
  Also see Constructed and Natural Wetland Septic Systems
  and also Lagoon Systems.

• Holding Tank Septic Systems: use a sealed tank to hold household waste and wastewater until the tank can be pumped out by a septic pumping company. Most jurisdictions do not permit septic holding tanks as a permanent wastewater handling method for full-time occupied residences, but holding tanks may be permitted during new home construction and in other special cases. In New York State we've seen holding tank systems in use on small-lot properties located along the Hudson River. Generally such systems will not be acceptable for full time occupied residences as even a large tank of several thousand gallons will require frequent and costly pumping and disposal.
• Incinerator Toilet Septic Systems: incinerating toilets use electricity or gas to burn the waste placed into these systems. Like chemical toilets and holding tanks they have limited capacity, are used where water is not available or must be conserved, and they do not address the handling of remaining graywater from sinks and showers. My favorite of this type was the "Destroylet" incinerator toilet which was electric/propane fueled and which is no longer on the market. Each flush resulted in a more than 10-minute burn cycle which produced a pretty smelly exhaust.
• Latrine or simple trench systems, useful in remote and impoverished areas to improve sanitation and thus the quality of drinking water and other special, extremely low-cost waste handling, wastewater treatment systems are ignored by most modern texts on onsite wastewater treatment, excepting perhaps military manuals which address field toilets and sanitation for military operations. This topic needs considerably more attention as a step in assisting rural, poor areas in developing nations. Articles, illustrations, and text contributions are wanted; additions to this special topic will be provided as they are developed at this website. Inadequate disposal and treatment of human and animal waste in poor areas is a major cause of dysentery and often high infant and child mortality. Meanwhile see the helpful but inadequate resource sketches at http://www.africanwater.org/ecosan_main.htm"the African Water Page and Ecological Sanitation" and http://peacecorps.mtu.edu/erda/links.htm a peace corps site on composting latrines
• Lagoon systems: also known as "pond systems" for onsite wastewater treatment are less often found in use for single family residential wastewater treatment. A residential lagoon system may use a conventional septic tank, but effluent from the tank flows to a storage pond or lagoon for further treatment. Lagoon systems require comparatively large land areas and are more likely to be found therefore in rural areas or where a common wastewater treatment system has been designed to serve multiple dwellings. Also see Constructed Wetland Septic Systems
• Media Filter Septic Systems: use a conventional septic tank followed by any of several methods to further filter and treat septic effluent before it is discharged to the soil, soil surface, or waterway. Treatment is by both actual filtration and ultimately by a biochemical process as the filter "matures" and includes its own biomass. Both natural media filter septic systems (such as sand, gravel, or peat) and synthetic media filter septic systems (foam cubes, glass, slag) are used.
• Mound Septic Systems: a wastewater absorption trench system which has been constructed using "suitable soil-fill material" which has been placed on top of the natural soil on a building lot. Mound systems are often confused with "raised systems" (see below) but have different design requirements, are generally smaller in total size, and depend on the fill material for successful wastewater treatment. Also see "Raised Systems" below.
• Pressure-dosed Drainfield Septic Systems: pressure dosing systems use a separate dosing chamber and pump, located downstream from the septic tank, to move effluent into a drainfield which in turn distributes effluent through a pressure-fed network of distribution pipes. (Jantrania/Gross wastewater system type II or if treated to level 2 or better effluent, system type VI) Pressure dosing is used in a variety of disposal field designs including mounds and sand beds, and have the advantage of being able to distribute effluent uniformly throughout the absorption system, and the disadvantage of added system cost and complexity, along with the requirement for electricity for system operation.
  An alternative but possibly less long-term reliable version of a drainfield dosing system that may not require electricity is the siphon system. Also see Dosing Systems, Gravity/Siphon.
• Raised Septic System: a wastewater absorption trench system which has been constructed in soil-fill material which has been placed on top of the natural soil on a building lot. Raised systems are often confused with "mound systems" (see below) but have different design requirements, and make at least partial use of existing soils for wastewater treatment. Also see "Mound Systems" above.
• Sand: Intermittent Sand Filter Septic System: wastewater effluent from the septic tank is intermittently distributed over the surface of a specially prepared bed of sand placed atop the existing soil surface. Effluent which has passed through the sand is collected by additional pipes at the bottom of the sand bed. The sand is not visible as it's covered by topsoil.
• Spray effluent dispersal systems, treating effluent to level 3 or better (Jantrania/Gross wastewater system type X). Spray systems are normally above ground effluent dispersal systems.
• Septic tank and graywater filters are products used at a septic tank outlet or at a graywater tank inlet or outlet to prevent suspended solids from reaching and clogging the soil absorption system. Readers should distinguish between in-tank septic or graywater filters and types of septic media filter and bed systems such as:
  mound systems or
  raised bed septic systems,
  media filter septic systems, septic systems or sand-bed systems.
• Steep Slope Septic Designs - how to install sewer lines from building to septic tank; how to install septic drainfields, leach field systems at steep or sloped sites.
• Trenches for effluent dispersal, gravity fed or pressure dosed, with gravel or gravelless systems are discussed under conventional septic and drainfield pages, pressure dosing, or gravelless systems. Also see "Gravity Trenches" above.
• Waterless toilets and graywater systems: see the various toilet types and greywater/graywater links on this page such as chemical toilets, composting toilets, and incinerating toilets. (Jantrania/Gross wastewater system type IV). Also see Greywater Septic Systems.
• Wetland Septic Systems or "natural" septic systems use a constructed wetlands area (or a greenhouse) to treat septic effluent. These systems are more common in Louisiana, Mississippi, Tennessee, South Dakota, and Florida where both municipal wetland septic designs and private homeowner wetland septic system designs are in use. "Wetlands" may include both visible water such as open ponds, and underground water located in constructed beds which are covered with soil. Also see Lagoon Systems.

The Septic Systems Online Book - Where Are We?

• This Chapter: SEPTIC DESIGN ALTERNATIVES
    AEROBIC SYSTEMS
    CESSPOOLS
    DOSING SYSTEMS GRAVITY/SIPHON
    DOSING SYSTEMS PRESSURE
    DRYWELLS
    EVAPORATION-TRANSPIRATION
    GRAVELLESS SYSTEMS
    GREYWATER SYSTEMS
    LAGOON SYSTEMS
    MEDIA FILTER SYSTEMS
    SEPTIC & GREYWATER FILTERS
    MOUND SYSTEMS
    RAISED BED SYSTEMS
    SAND BED SYSTEMS
    SEWAGE TREATMENT SYSTEMS
    WATERLESS LOW WATER TOILETS
• Next Chapter: SEPTIC INSPECTIONS
• First Chapter: SEPTIC SYSTEMS ONLINE BOOK

Technical Reviewers

More Information on Septic System Testing and Building Diagnostic Inspections and Repairs

• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
• The Home Buyer's Guide to Septic Systems
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
• Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.

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