PDF Version: Survival Homestead - Septic Systems
Black Water & Grey Water
There is no getting around it: we must talk about what to do with waste on the homestead. There are three types of waste we are concerned about, solid and liquid human waste (fecal matter and urine), and grey water. There are a few different ways to treat them.
Human waste is what comes out of our bodies and is disposed of with outhouses, composting toilets, and septic systems. When solid human waste and liquid human waste are mixed together and stored in a tank, it becomes known as “black water”. Black water is toxic, dangerous, gross, and stinky.
Grey water is waste water from sinks, showers, and laundry. Often this waste is directed into the septic system or city sewer, but it doesn’t have to be and there are some good reasons not to.
But first let’s look at ways to treat human waste on the homestead.
Outhhouses & Composting Toilets
Portable Toilet Rental
These are the blue plastic buildings you see at outdoor events. You rent the unit for a fee, and the rental company brings their truck and empties the unit as needed. Obviously there is not a lot of work involved, but the blue plastic buildings are ugly and you need to pay fees! And they stink!
An outhouse can be environmentally friendly as long as it is not located too close to a water source. It should be downhill from and at least 100’ from any surface water (creeks or ponds) or wells.
Biological activity in the pit breaks down the waste and turns it into compost, so it is safe for the environment. The smell can be mitigated by sprinkling sawdust, wood chips, or wood ashes in the pit after every use.
The pit can be dug as deep or shallow as you wish, but keep in mind the deeper it is, the longer you can use it before you have to dig a new hole and move the outhouse. When you dig the new hole for the outhouse you can put the removed soil into the old hole.
The outhouse is used for both solid and liquid human waste.
The advantages are that there is very little maintenance. The disadvantages are that there can be an odor and insects, and you have to dig the hole.
When building an outhouse, make it roomy with good air flow. Make it at least four feet wide by four feet deep.
These can be either purchased or built by the homesteader, and they can be either kept in the house or outdoors in an outhouse-style building.
In it’s simplest form, a composting toilet can be a 5 gallon bucket inside or under a wooden bench. A toilet seat is mounted to the top of the bench. After each use, the user sprinkles wood chips or sawdust on top. The bucket is emptied out as needed into a compost pile or pit.
When I built composting toilet, I simply cut four sides and a top from a piece of plywood. I made it just big enough to sit over the bucket. I used wood cleats inside to reinforce the corner joints and used plenty of screws. I used a jigsaw to cut a hole in the top slightly bigger than the bucket, so that the bucket protrudes from the hole a fraction of an inch. I then attached a (new) wood toilet seat.
If plenty of sawdust is used as a covering, there is very little odor and no insects.
Even the bucket composting toilet can be kept and used indoors and many people do this. But I keep mine outside in an outhouse style building.
There are commercial versions that use electricity to stir the waste and circulate air. If the homesteader prefers a nice composting toilet they can keep indoors they can be an option, but they are expensive. A nicer home made unit can be constructed, too.
In either case, if the users urinate into the composting toilet a lot, it can make a wet stinky mess that affects the composting action. Some composting toilets have a urine diverter to direct urine to another location. Although urine is high in salts, it is not really bad for the environment (as long as separation to drinking water is established) so urine can be directed to another place for disposal.
In my house, I have a greywater setup so that people can urinate in the toilet (the greywater system also serves the shower, sink, and laundry water) and a composting toilet outside for solid human waste.
There is a biological danger if the material from the composting toilet is not completely composted. At proper long term composting, the reactive temperatures are supposedly high enough to kill any pathogens, but if the material has not been properly composted, some harmful biologicals may remain. Be careful.
Also, some prescriptive medications are resistant to breakdown by biological activity. In other words, if someone in the family is taking drugs and uses the composting outhouse, those drugs will remain in the material produced. If the compost is fed to plants, the plants may suck up some of the medication chemicals.
The material created by the composting toilet can be used on gardens. It is up to the user whether or not to used it on food producing plants, although I would certainly not recommend it if a user is on prescription medication. On the other hand, there is no reason not to use the compost on ornamental plants or shrubs or trees that have a function aside from food production.
For more information on composting toilets, read Joseph Jenkins’ “The Humanure Handbook: A Guide to Composting Human Manure”.
A septic system does not simply take human waste and disperse it into the ground. A properly working septic system treats the waste, using natural and biological activity. In the septic tank, anaerobic bacteria digests the waste and breaks it down into harmless material. This is why you shouldn’t pour chemicals into your septic system; they harm the beneficial bacteria. Excess water is dispersed into the soil where it is cleaned and filtered.
There are three basic type of septic systems:
1. Standard Gravity
2. Pressure Distribution
3. Advanced Treatment
Typical Septic System
Standard Gravity Drain Septic System
Standard gravity drain septic systems work by using gravity to drain the effluent from the septic tank into a series of underground trenches that form a drain field. The parts of the system are the septic tank, the distribution box, and the drain field. This is the best type of septic system for a survival homestead because it follows the KISS rule. There are no electric pumps involved if the septic tank is lower than the house drain pipe, and the drain field is lower than the septic tank.
It is important to note that with gravity drain systems, all connecting pipe between the house and the septic tank, and the tank to distribution box, and the distribution box to drain field must be sloped at 1/8” to 1/4” per foot to allow the waste water to flow to its destination. The pipe in the drain field is flat, and has no slope.
Waste travels directly from the house to the septic tank, where the tank does a few separate jobs. The solids sink toward the bottom and greasy sludge floats on the top. Anaerobic bacteria digests the material in both locations. When the solids have settled to the bottom (”sludge”) and the lighter material has risen to the surface (”scum”), the resulting water is has been “clarified” and is now known as “effluent”. The effluent leaves the tank on the exit side, though a pipe Tee (also known as a “baffle”) that is positioned on the upper side of the tank wall. The reason a Tee is used is so that the material floating on top will remain above the level of the bottom of the Tee, preventing it from flowing to the drain field.
Most septic tanks are constructed of concrete. However, plastic and fiberglass tanks are available for sites unsuitable for the delivery truck. Some people make septic tanks out of concrete block, but they must be made water tight.
The size of the tank is important, because a tank that is too small will not properly “digest” the material. For a one or two bedroom home, a tank capacity of 1,000 – 1,200 gallons is typical. For a three bedroom home, a 1,500 gallon tank is typical.
With a gravity drain septic system, the the septic tank must be lower than the exit pipe from the house. This means that if the house has a basement with plumbing fixtures, the house drain pipe will probably be lower than the floor, and if the septic tank is near the house and not downhill, the tank will be very deep.
Typical septic tank
As waste enters the tank from the house, the “effluent” exits the other side of the tank , where it makes it way to a distribution box. Then multiple pipes carry the effluent to the drain field field. Because the system works by gravity, the drain field must be lower in elevation than the tank. As the effluent reached the drain field, it begins its final treatment by leeching into the soil.
Note: with a gravity drain septic system, the the drain field must be lower than the septic tank. If the septic tank is very deep, and it is not possible for the septic tank exit pipe to travel downhill to the drain field, a separate holding tank will need to be installed. This tank will contain a submersible sewage pump with a float switch. When the level of effluent reaches high enough to activate the pump, the effluent will be pumped to the drain field. Obviously this adds a level of complication and a potential failure point. In addition, you need a source of electricity to run the pump.
There are a few different ways to lay out the drain pipe. Older designs used what is known as a “serial” design, where the effluent travels to the first trench, then continues onto the second trench, and so on. The beginning pipes are overworked and prone to failure. In the “parallel” design, the outlet from the tank flows into a distribution box, then flows equally to a number of separate drain pipes. The distribution box is visible in the preceding illustration of a typical septic system.
Construction of the drain field is accomplished by excavating a series of rectangles with a level bottom. Trenches should be 3 feet in width, 2-3 feet deep, and each trench should be no longer than 100’. There should be 3 feet between the bottom of the trench and any hard pan, bedrock, or groundwater below.
A layer of clean gravel is placed on the bottom of the trench to within one or two feet of the surface. The rock should be ¾1-1/2” in size. Each trench will hold one length of perforated 4” PVC pipe and covered with another 2-3 inches of gravel. Then the gravel is covered with a layer of geotextile fabric (landscape fabric) to keep the soil from settling into the rock and clogging it. The remainder of the trench is filled with soil level with the surface of the ground.
Plastic Chamber Systems
The plastic chamber system replaces the perforated pipes with a series of interlocked high-density polyethylene (plastic) chambers that rest on the bottom of a shallow trench. They are open at the bottom allowing effluent to drain directly into the soil. The large volume of the chambers allows additional capacity, resulting in designs of a smaller size. These types of systems have become very popular.
Two vendors of the plastic chamber system are “Infiltrator Chamber®” and “Hancor®”.
Percolation Test & Soil Classification
Before you can decide on the size of your system, you have to do what is known as a Percolation Rate Test, or “Perc Test”. Most people have an approved (by the county) geologist or soil expert come out to your site. While he is there you excavate some holes about six feet deep in the random areas of the proposed drain field. (You need to hire a backhoe operator). The soil expert will crawl down into the hole and test the soil to see how well it will work for draining the effluent. It can’t drain too fast (too sandy) and it can’t drain too slow (too clayey). Also, of course, he will check to see if you reach bedrock or groundwater in the hole. Sometimes it is possible for the homeowners to dig the holes themselves and send the soil samples off to be tested.
The soil will be tested in accordance with the US Department of Agriculture Soil Conservation Classification System. If the test is not done correctly, you can either oversize the system causing needless work and expense, or worse yet, under size the system, leading to failure of the system. In any case, the soil sample that tests as the most restrictive should be used to size the system.
The soil will be classified into one of six basic groups:
1. Coarse sand (will probably need a Pressure Distribution System)
2. Medium Sand
3. Fine Sand
4. Very Fine Sand
5. Silt loams of good structure
6. Clay loams
We can do a simple test to get an idea of the soil classification. Dig up a sample as described above. Remove stones and larger organic material and break up the soil into small particles. Add two inches of this to a one quart mason jar and fill the jar three quarters full with water. (A tablespoon of dish washing detergent can be added to help the process). Shake the jar vigorously until well mixed and set on a shelf where it won’t be disturbed for at least a week.
The sand will settle to the bottom after a few minutes. After about an hour, the silt will settle on top of the sand. The Clay can take from a few days to a few weeks to finish settling on top of the silt. At this time each layer can be measured.
The proportions of the layers can be calculated with some simple math. If the sand at the bottom measures 25 millimeters and the measurement of all three layers combined is 80 millimeters, the proportion of sand is 25 / 80 = 31%.
Once the percentages of sand, clay and silt are determined, the soil status can be pinpointed on the USDA Soil Textural Triangle. For example, if the soil is 31% sand, 27% clay, and 42% silt, make a dot on the proper axis on the triangle, then intersect the lines as I have shown in the following diagram. In my example, the soil texture falls into the “clay loam” section of the triangle and almost falls into the “loam” section.
Illustration: Soil Texture Triangle
USDA Soil Texture Triangle
How To Size The Drain Field
The size of the drain field is determined by the amount of wastewater flow, slope of the ground, depth to ground water or bedrock and the characteristics of the soil. The two most important factors are the soil classification and the number of people living in the house. Local health departments will use the number of bedrooms in a house, assuming two people per bedroom. So a two bedroom house will be assumed to produce 240 gallons of waste water per day. Here are some factors and assumptions influencing the size of the drain field:
1. Every person will produce 60 gallons of waste water per day.
2. The size of the system will be in square feet of drain field.
3. Because each drain pipe trench is 3 feet wide, a 100 foot long trench would equal 300 square feet.
4. Each 60 gallons of waste water will need from 50 to 300 square feet of drain field, depending on the soil classification.
5. Each 60 gallons of waste water will need from 3 to 10 plastic chambers, depending on the soil classification.
Calculating Drain Field Size
The final size and design of the drain field will be determined by the local code authorities. Because there are so many variables that can affect the function of the septic system, getting a permit and doing it right are good ideas.
Don’t forget, drain field layout should have at least 2 equal sized trenches, to avoid the “serial” design drain field.
Permits & Rules
The state will have septic system design rules and the county may have even more restrictive rules. It is best to do some local research before designing the system. I live in a county with very few building codes. But they do want people to get a permit for septic systems. And I have a feeling there are very few areas where you can install a septic system without a permit.
I am not your typical guy who likes to get permission for everything I do, but I can see their point. If not designed properly, septic systems may malfunction or pollute the ground. I don’t want to deal with either of those problems.
When I talked to my county code enforcement agent about a septic system, he was open to the idea of my bringing in a hand-drawn design for approval, as long as the drawing had measurements and the soil passed an official percolation test. This would avoid having to pay an engineer to draw up my plans. He even said he might be able to come up with a plan used by someone else that I could use as a base to make my own.
My point is, it might not be a long, complicated, expensive process to get a permit and do it officially. I live in a very rural county in Montana, so everyone’s experience may not be like mine, but it’s worth it to find out. Also, if they ever find out you put in a septic system without a permit they will probably make you dig it up. So keep that in mind as well.
Emergency Septic System
In a hypothetical situation, after the collapse of law and order, the survival homesteader may need to construct a septic system using materials at hand. One way to do this is to build the system as described in the preceding text, but use a 50 gallon plastic barrel in place of the septic tank. Keep as much to the basic design principals as possible! Note that if you do this now and the authorities find out you’ll get in big trouble!
Other Septic Systems
Pressure Distribution Systems
If there is not enough soil depth at the drain field location to properly treat the effluent, or if the size of the drain field must be small and the soil consists of coarse sand, a pressure distribution system may be required. The size of the septic tank, but the effluent is pumped to the drain field through a small pipe. The effluent is spread along the entire length of each trench, resulting in better soil treatment.
Advanced Treatment Systems
Advanced treatment systems are required when the soil is very shallow (12-30 inches). These systems clean the wastewater before it is deposited into the ground. Most of the time, these treatment systems are followed by pressure distribution drain fields.
Most of what I learned about grey water I learned from Art Ludwig’s book: “The New Create an Oasis with Greywater: Choosing, Building, and Using Greywater Systems” and I recommend to anyone serious about installing a grey water system that they purchase it. The site where you can buy the book also has a ton of good free information and some example systems.
Laws vary by state as to what particular water can be directed to grey water reuse, or if it’s legal at all. For example, some states allow sink water, and other’s don’t. To find more specific information about what is legal and what is not, go to Art Ludwig’s “Gray Water Policy Center” web site at http://oasisdesign.net/greywater/law/.
Grey water is any household water that doesn’t include water from the toilet, although there may be an exception to that rule: if the toilet is used for urinating only. This includes water from the sinks, laundry, and shower drains.
There are some good reasons to direct grey water away from the sewer or septic system:
1. You might not have, or be able to construct, a septic or sewer system.
2. Reduce the amount of water directed to the septic or sewer system, relieving strain on the system.
3. Grey water can be used to safely irrigate food producing plants and trees, saving fresh water.
In the most popular designs, grey water is directed to a wood mulch pit with a tree or other beneficial plant growing in the center of the pit, on a raised mound. The high carbon material of the wood mulch breaks down the stinky part of the grey water, and at the same time the tree or plant gets irrigated.
Grey water mulch pit
Of course, directing the grey water to a different destination than the septic tank or sewer requires additional waste piping in the house. If the house is built with grey water reuse in mind it will be a lot easier than retrofitting an existing house.
When I talked to my county code official about installing a greywater system, his main concern was that I have enough water to direct to the septic system because it will not function properly without a minimal amount of water. I think a good solution to this would be to install a diverter valve in the main sanitary drain, so that grey water can be directed to either the reuse system or the septic system. The diverter valve can be on the 2” grey water drain line, and Art sells these valves at his web site.
Some things to keep in mind when designing a grey water system:
1. Don’t store grey water in holding tanks, ever. If stored in a tank, it will turn into black water!
2. Don’t plan on using grey water to flush the toilet. That is storing the water in a tank! It will turn stinky. Rain water would be better suited to filling the toilet tank.
3. Grey water should be routed directly to the mulch pits for use by the plants.
4. Don’t use pumps to move the grey water, unless as a last resort (for example: the grey water needs to go uphill)
5. Don’t worry about “filtering” the grey water. There is no benefit (unless you use a pump) and it adds costs and complications to the system.
6. Grey water should not be used to irrigate plants with a “sprinkler”. It is acceptable to irrigate by discharging the grey water onto the surface of the ground, for example by routing a discharge hose from the laundry to trees or bushes, as long as there is no danger of someone (or a pet) being exposed to the grey water. Ensure grey water doesn’t come in contact with plant stems or leaves; keep it on or in the ground.
7. For grey water piping, 2” pipe is preferable to 3” or 4” pipe
8. Local code officials may not be aware of state grey water laws or even know what grey water is. And they certainly will not allow urine to be included in grey water systems.
9. In some cases, sink water is not acceptable (legal) for use as grey water. In most cases, toilet water is not legal for use as grey water (see text below)
It is my personal opinion that toilet water can be directed to the grey water system as long as no one defecates in the toilet. If solid human waste is added to the grey water you no longer have grey water; you have black water. It is also my opinion that sink water is perfectly acceptable to use as grey water, although some states don’t support that opinion. My belief is that the particles in the sink water add nutrients to support the microbial organisms which break down the grey water into environmentally safe material.
How To Size The Mulch Pit
The size of the mulch pit containing plants or a tree should be four times the expected peak flow. So if the peak flow (for example from a shower) is 40 gallons, the mulch pit should be 160 gallons.
It is better to have multiple mulch pits rather than one large one. This allows more plants to be irrigated and prevents one mulch pit from becoming waterlogged. The grey water can be diverted by manually moving a hose to different piping inlets, or PVC sanitary fittings can be used to fork the underground pipes. It is important to use a style of fitting which will divide the grey water equally into each section, and not clog the fitting. Art Ludwig recommends cutting an access hole in each fitting so that they can be periodically inspected. Since the pipes are underground, a bucket should be placed over them to prevent filling in with soil. Using the fittings, one fork can branch into other forks, making the system versatile.
Grey Water Systems And Freezing Temperatures
There is not much information available about using grey water systems in freezing temperatures. When I built my cabin, I wasn’t sure if I was going to install a septic system, so I planned on using a grey water system for everything except black water. I simply directed all the waste water to what I call a “grey water pit”. The pit is four feet deep, four feet wide and four feet long and filled to the top with straw bales. There is no exposed piping or direct exposure to grey water. All house waste water, including toilet water) enters the pit about one foot below the surface. (Remember, even though we have a toilet, we don’t have black water in the house! We use the composting toilet outside.) At this time, my grey water system is designed to safely dispose of household water, rather than for irrigating plants.
After six months there has been some settling of the straw bales (and some mushrooms are growing on top), but there is no odor present. The carbon in the straw material is absorbing the grey water and biological activity is taking place. Although the 3” drain pipe leading to the pit is buried only 6”-12” below the surface, the system performed flawlessly over the past winter where temperatures were below zero degrees (F) for days at a time. The grey water pit also performed perfectly during those cold temperatures.
From my observations, I think a grey water system can be used in freezing temperatures as long as there is sufficient slope in the drain pipes to prevent pooling of water, and the grey water is discharged to a pit with high-carbon material to allow the biological process to occur. It may be that the biological process creates heat, as in a compost pile, that helps prevent the water from freezing. My “pit” is four feet deep and full of straw, which may act as an insulating barrier to the cold.
I’m not sure if a shallow grey water mulch pit built to irrigate a shrub or tree will function in sub-zero temperatures, because that type of mulch pit is much shallower than my pit. Of course, in freezing temperatures there is not much benefit in irrigating plants anyway. Perhaps a solution would be to route grey water to the plants in the growing season and route it to a deeper pit in the winter.