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EPA Sketch of an aerobic septic tank design using an aspirated mixer in the treatment tank Alternative Septic System Designs
Septic systems for wet, steep, rocky, small, poor percolation sites

  • SEPTIC SYSTEM DESIGN ALTERNATIVES - CONTENTS: How to design, building, inspect, test & matinatin 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
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Guide to alternative septic system designs:

This article provides a master list (links at the "More Reading" links at the bottom of this article ) of all 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, sites close to a lake, river or stream, 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 discussed in this article series 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, peat filter septics, raised bed septics, pressure dosing septic systems, sand bed filters, peat beds, constructed wetlands, wastewater lagoons, constructed wetlands, and septic disinfection systems.



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Alternative Septic System Designs: Onsite Wastewater Treatment Methods for Difficult Sites

Sketch of a Septic Mound System using a pumping stationThis article describes just about every type of alternative septic system design 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.

Sketch: septic mound system design. [Click to enlarge any image]

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:

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: [Readers should see our Master List of Septic System Types or our list of alternative septic system designs and products in the links at the left of these pages.]

  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. Some "advanced" septic system designs may be simple modifications to a conventional septic tank and leachfield, such
    as ALTERNATING BED SEPTIC SYSTEMS.
  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.
    See MOUND SEPTIC SYSTEMS
    and
    see  RAISED BED SEPTIC SYSTEMS
  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).
    See MEDIA FILTER SEPTIC SYSTEMS
  4. AEROBIC SEPTIC SYSTEMS which insert additional oxygen into and agitate sewage in the primary treatment tank
    See AEROBIC SEPTIC SYSTEMS
  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. Also see LAGOON SEPTIC SYSTEMS
  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. Also see AEROBIC SEPTIC SYSTEMS
  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.

    See GREYWATER SYSTEMS

    and ALTERNATIVE & WATERLESS TOILETS.

    See EVAPORATION-TRANSPIRATION SEPTIC SYSTEMS for wastewater treatment and disposal in areas where there is no electrical power and limited or no place for effluent disposal.

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 effluent 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.

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. Technical reviewers welcomed and are listed at Reviewers.

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Continue reading at AEROBIC SEPTIC SYSTEMS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see ALTERNATIVE SEPTIC DESIGN FAQs - questions & answers posted originally at this article

Or see ALTERNATIVE SEPTIC DESIGNERS

Or see SEPTIC SYSTEM DESIGN BASICS - home

Or see TYPES OF SEPTIC SYSTEMS - master list

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INDEX to RELATED ARTICLES: ARTICLE INDEX to SEPTIC SYSTEMS

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