Onsite Septic Systems for Container Homes

Onsite Septic Systems

For most of us, an “off-grid location” is associated with the lack of access to the municipal electrical system. However, in a wider sense, the “off-grid” location also means no access to Municipal Utility Facilities of which the most important are Water and Sewer Systems.

The solutions for electricity and water at off-grid locations were already addressed by the series of articles encompassed by:

In this series of articles, we will address issues related to Onsite Sewage Disposal Systems (typically referred to as Individual Septic Systems).

These days, it’s hard to imagine a house without running water. Less obvious (because less “visible”) is the fact that all used water going down the drain must be collected and processed (biologically treated) before being recycled back into nature. In towns, it is accomplished by an underground network of pipes carrying it into Sewage Processing Plants. At typical locations of container houses – (usually far from Municipal Utility Facilities), you are on your own. However, these days (unlike in the remote past) the disposal of household sewage is highly regulated by law. What goes down the drain, must end-up in the Septic System comprised of a Tank (collector), Disposal System (network of Pipes), and zillions of microorganisms processing the waste (the latter come on their own for free).

septic system container homes

These days the place for old rural cesspool-type septic systems can only be in memories of nostalgic past. The truth is that in most countries, they are illegal!

Sources of photos: Left- “What is a cesspool?”, (Village Septic) ; Right: “The RI Cesspool Act goes into effect”, (Hogan Associates, RI, USA).

Each of the mentioned above systems (Electrical, Water and Septic) must meet relevant government-imposed standards. The most technologically advanced (and expensive) are systems harvesting electrical energy. The individual water harvesting systems are much less costly and relatively simple, provided you only want to have utility water (drinking quality water must meet more stringent requirements increasing cost and complexity). The individual septic systems are based on traditional rural solutions and do not require any sophisticated hardware. However, due to increasingly more demanding environmental restrictions, from the legal point of view, they seem to be the most challenging of all three.

Provided you have the required skills and basic technical knowledge, theoretically, you can build the Energy and Water harvesting systems for your home in the DIY process. Before “turning them ON” you may still need a final inspection by a Local Authority, however, if you followed the local building codes, most likely it will be a formality.
In contrast, the construction of the Septic System requires close collaboration with the Environmental Agency and Local Authorities well before you start to design the system. By doing it on your own, most likely you will lose time and money!

In short words – the Septic System must eliminate solid waste and reduce contaminants contained in the wastewater to the acceptable levels (subject to environmental laws) then, recirculate in form of clean water back to nature. In the simplest form, the Septic System is composed of a tank(s), a network of pipes, drain-field (soil acting as a filter and “treatment plant”), and an invisible but crucial army of microorganisms that actually do the job by decomposing organic matter contained in the sewage.

Conventional Septic System in its simplest form: Two-compartment tank, Distribution Network (pipes), natural filter (soil), and not shown on this picture zillions of bacteria. Source: The Natural Home (askinglot.com)

The configuration and size of the Septic System depend on the combination of many factors, of which the most important are:

1. Daily Volume of Sewage

Most local authorities will calculate the expected sewage flow volume based on the household’s size determined by the number of bedrooms and/or a number of permanent inhabitants, level of luxuriousness, and (in remote locations – by the available volume of freshwater…. Whatever stipulates the law, it all comes down to the daily amount of produced sewage/wastewater that must be collected, retained for a limited time, treated, and subsequently discharged over a leaching bed.
The daily volume of sewage determines the size of the septic tank(s) and, (in the first approximation) the area of the drain-field.

Statistical data for a typical American household. Source: City of Jal, New Mexico (USA)

For details see:  Household-Generated Sewage

  1. Wastewater Treatment Concept

Traditionally all household-generated wastewater is sent to the septic system. While usually. it is the simplest and most economical solution, for houses in remote, off-grid locations it may be beneficial to separate Blackwater (toilets, kitchen sink, and dishwasher) from Greywater (bathtub, shower, washing machine, bath sinks).  This will not only reduce the volume of generated wastewater and size of the Septic System as well as demand for freshwater but will also allow for the reuse of pre-treated greywater (flushing toilets, irrigation…). Note that usually, it is much easier to meet restrictions governing the disposal of greywater.

A possible implementation of the greywater “drain-field”. Source:  “From Laundry to Landscape: Tap Into Greywater” by Laura Allen and Cleo Woelfle-Erskine (Mother Earth News)

The complexity of the conventional (simplest) onsite Septic System. Source: “Septic Tanks – What you Need to Know”, County Clean Group (UK)

For details see:

  1. Geological Profile and the Type of Soil

The drain field is the final stage of an Onsite Septic System. It acts as a Wastewater Treatment Plan. Such municipal or industrial plants are built according to well-defined specifications.  In contrast, the natural drain-field has the properties created by Mother Nature, so under normal circumstances, you must accept it “as-it-is”. The only parameters that you may have an influence on are its size and location within the borders of your property. Unfortunately, it may not guarantee that the drain-field will meet the necessary requirements.

In short – it all comes down to the permeability and percolation of the soil, or in other words, its ability to absorb and “process” (purify) wastewater to meet environmental restrictions applying to the given land.

Usually, the combined effect of absorption and percolation is expressed by the Hydraulic Load Rate (HLR) of the given soil. It sets the limit for the maximum amount of wastewater (in gallons per square feet per day) that can be safely discharged over a future drain-field. “Safely” in this case means – preventing the build-up of biomass, eliminating health hazards (pathogens), and decontaminating to the level required by environmental protection laws before reaching the groundwater table.

Permeability of different types of soil. Source: “Permeability: Soils, DimensionRIFT (YouTube)

In some cases, the Percolation Test may not give full answers, and a more thorough examination of the soil intended for use as a drain-field will be needed.  LTAR (Long Term Acceptance Test) requires digging an 8ft deep inspection trench to allow an authorized engineer for visual inspection of the soil.  Basically, it makes it possible to identify and examine individual layers of the soil (topsoil, sand, clay, bedrock) as well as its geological profile (including the depth of the water table).

Another important aspect is the topography and geological profile (slopes of the terrain, location of the groundwater table, etc…). Note, that it may be “physically” more difficult to locate the drain-field on the near slope inclined towards the house, or watercourse.

The movement of the contaminated plume is determined by the local geology (here outwards from the house). Source: US- EPA (

The good news is, that to some extent, the natural drain-field can be “re-engineered” to meet relevant requirements (for example adding artificial sound mounds).

For details see:  Designing Drain-fields (TBD)

  1. Lot Size and topography

Obviously, the household wastewater is not the sort of Cuckoo’s egg you may toss at your neighbor’s yard. It means, that given the limited size of the terrain that can be used for the leach bed and maximum HLR of your soil you either will have to minimize the amount of produced wastewater or use a more complex (and pricey) septic system. Because in the end –the Septic System must comply with all relevant environmental restrictions!

Note, that due to specific health hazards-related restrictions existing wells, lot’s borders, nearby watercourse, trees, veggie garden(s), pools), etc… may significantly reduce the area available for the Septic System.

Source: Septic Smart – Understanding your home’s septic system” – RVCA.ca, Ontario, Canada

  1. Climate zone

The operation of conventional Septic Systems will be strongly affected by low temperatures. Performance of Septic Systems designed for individual households almost entirely depends on the biological treatment of the wastewater (decomposition of organic solids by bacteria). To be effective, such a process requires the temperature in the range of 60 to 100 deg F (approximately 15 to 40 deg C). At lower temperatures, the process slows down or even stops, which will affect the level of clarity and purification of effluent leaving the septic tank to the distribution system.

septic system

If the Septic System is not protected against freezing temperatures, the bacteria may stop their activity putting the whole system to off-use status! Source: “Does Cold Weather Affect Septic Systems?”, Home Stratosphere, (BC, Canada)

If this is not enough – temperatures below the freezing point will also severely impact the operation of the disposal system. It’s not only about the possibility that the pre-treated wastewater will freeze in the pipes or but also about the impact on the biodegradation process in the subsurface soil.

  1. Lifestyle and habits

The raw residential sewage is composed of water (about 99%), organic matter (human feces, food leftovers …), chemicals (detergents, soaps, cleaners ….), non-degradable inorganic matter, and invisible but potentially harmful toxins and microorganisms (pathogens, microbes, parasites…).

Example of Natural & Eco-Friendly Cleaning Products … Source: The Good Trade. Note – this picture serves as a reminder that we cannot endlessly ask our Planet to deliver, it’s time we start to take care of our Mother Nature. We are NOT endorsing any particular cleaning product!

Connected to municipal water and sewer systems, usually, we do not pay much attention to how much water comes out of water taps and what goes down the drain. Somehow, we assume that the source of water is unlimited, and the drain will graciously “suck” whatever we throw-in.

Moving to an off-grid location (typical for container-based homes), we must change this common but false perception of “limitlessness”, and face the reality that both, the water source and the Septic System have limited capacities, and the latter is also sensitive to solid, especially non-biodegradable waste.

As much as it may be tempting, get used to daily “eco-showers” reserving such pleasures for special occasions. Source: Seattle Bathtub Guy Seattle, USA).

That is why, when moving to the house serviced by an individual onsite Septic System, it will be important to scale-down “business-as-usual” activities. Lower use of water (what anyhow may be imposed by its availability or rather limitations), compositing of all organic leftovers, and setting a “Do-Not-Flush” policy for all other, non-biodegradable and toxic waste that can be collected and disposed of at designed for that purpose facilities.

  1. Types of Septic Systems

Constraints imposed by such factors as the type of the soil and its geological profile, size of the lot and its topography, climate zone, and volume of generated sewage will also have a huge impact on the configuration and size of the first stage of the Septic System – Tanks. In most cases, the conventional Type-1 (anaerobic) septic system will do the job. However, just to give you an idea, the mentioned constraints may force you to build a Type-2 septic system (Type-1 plus an extra aerobic stage) or even a Type-3 septic system (Type-2 with an extra disinfection stage). In short – that means, increased complexity, cost, size, and maintenance!

Configuration of the Type-1 Septic System. Source: “Septic Installation” – Redline Excavating Ltd, (BC, Canada)

Compared to:

Configuration of the Type-3 Septic System. Source: “Septic Installation” – Redline Excavating Ltd, (BC, Canada)

For more details see:

So, What’s Next?        

Rather than trying to solve all these problems on your own, we strongly suggest putting all facts on the paper, write relevant questions, and contact licensed experts. To make it clear – the primary source of information (copy of the Individual Sewage Disposal System (ISDS) Regulations) is your local authority. However, you can be sure that before the final approval, officials will refer you to the licensed (and insured) specialist to avoid liability (if any legal issue related to the project will arise in the future).

One thing you can do however on your own is the graphical plan of the septic system. For that purpose, you can use a copy of your property survey as it will show the location of your house, driveway, property lines, as well as crucial measurements. This paper is a “starting page” for your project, the page where you can mark details of the current (or planed) landscape – like the direction of slopes (if any), location of a shed, trees, veggie gardens, wells, swimming pool, lake, watercourse (if any) including these located on neighbors’ properties near the fence.  Proper identification of all these factors is crucial to make the design of your onsite Septic System acceptable to relevant authorities (and the whole effort as much painless as possible).

Sketch of the plan for an on-site septic system. Source: County of Santa Clara, Consumer Protection Division, (USA)

Note that often you may also have to include into the plan a spare area for the future secondary leach-field (Drain-field), in a case, the primary one will become unfunctional!

The following picture, with typical landscape features, shows potential challenges you will face when making plans for your onsite septic system. Keep in mind that minimum-distance requirements are shown here only as examples – the actual limits may differ between countries, states, and even local communities (they also depend on the environmental zone of protection).

The preliminary plan of the onsite septic system must consider the local geology and the suitability of the soil for wastewater disposal. Such factors like the depth of the soil, eventual presence of sand, clay or bedrock, terrain’s slope(s), as well as the level of the groundwater table will determine not only the size of the drain-field (by far the largest area of the system) but also the type of the required Septic System. It means – the necessary stages of wastewater treatment and subsequently the number and size of corresponding tanks. For that, you will have to hire the authorized service for soil percolation (HLR) or LTAR tests.

Practical Notes:

    1. Our Eco-Consciousness (as a society) is rapidly growing, and the local environmental regulations follow these changes. In other words, what was good enough (legal) last year, may not meet today’s requirements.
    2. For an “average person” (in other words, for someone not familiar with the subject), it may be difficult to identify and understand relevant EPA and Local Authority regulations. What makes it worse, is that some regulations related to onsite wastewater treatment systems are either not clearly defined or even do not exist (greywater is a good example). That, in turn, will create confusion and open an area for personal interpretations.
    3. The Local Authority is there to provide regulations and issue the final authorization paper. They may (but are not obliged to) assist you with guidelines, provide contact points to licensed private services, inspectors, etc…. However, meeting the relevant regulations is Your Responsibility, failing to meet them is Your Liability.

We do not promise that designing an onsite Wastewater Treatment and Disposal System is an easy task. This EPA’s design manual has “only” 409 pages, but it will be just for the start (good luck if you go for it).

Personally, I’m a sort of DIY guy, but in this case, due to legal and financial implications, I will strongly suggest contacting government-licensed specialists (it does not hurt to carefully check references). Be sure, that once you get familiar with the matter, having the required skills and determination, you will be able to significantly contribute to the construction of the system. It is important, however, to start construction works with “educated decisions”, as well as a well-engineered and legalized plan in your hands.

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