Treatment starts with a three-chamber concrete tank with a total capacity of 2,210 gallons.
The backhoe operator dug this hole in less than an hour. The bottom of the hole is not visible from the cab of the backhoe, so the operator was essentially digging blind.
The drain field consists of six 1 1/4-inch PVC lines connected through cross fittings to the 2-inch line from the septic tank.
Three floats in the pump chamber of the septic tank must be located precisely in order for the system to work correctly.
If effluent rises too high in the tank, an alarm will be tripped.
Holes at the top of the distribution piping allow effluent to be distributed evenly across the drain field. The pipes will be protected by the black plastic covers in the background.
The drain field and tank after the system has been backfilled and leveled.
Image Credit: All images: Matt Bath
Editor’s note: This is one in a series of blogs detailing the construction of a net-zero energy house in Point Roberts, Washington, by an owner/builder with relatively little building experience. You’ll find Matt Bath’s full blog, Saving Sustainably, here. If you want to follow project costs, you can keep an eye on a budget worksheet here.
Standard treatment of sewage hasn’t changed much over the years. Nature actually had it figured out pretty well before humans even attempted to manage it. Given enough time, soil and the organisms that inhabit it are extremely adept at breaking down harmful toxins and dispersing the safer compounds into underground waterways. The only thing a septic system does is harness this awesome power.
Designing a proper system starts with a soils test and/or “perc” test. A soils test involves removing a deep core of soil and analyzing what appears in the different layers. Soil is then classified into sand, gravel, loam, clay, and all sorts of combinations of those types. A perc test involves filling a deep hole with water and timing how long it takes water to percolate through the soil at the bottom of the hole. (The soil must be prepped by soaking it thoroughly first and most counties require you to have a license to complete the test.) Both tests can give a pretty good indication of how well a particular patch of soil will perform at breaking down the effluent — what sewage becomes after sitting for a period of time.
Soils and perc tests
In my state, the soils test or perc test must be completed by a licensed septic designer. The designer I hired charged $150 and found my soil to be “sandy loam” for the top inch and “medium sand” for the next 2 feet until reaching the water table at 28 inches. This is the depth at which dry soil becomes saturated with water due to an underground spring.
The county and state health codes dictate what kind of dispersal system can be used for a given type of soil. Conditions on my site allowed me to use a gravity distributed system, which is the simplest type.
The next step in the design called for locating the area of the lot where the drain field would be located. Health codes dictate setbacks for the field of 5 feet from property lines, 10 feet from water lines, and 100 feet from natural water supplies. I have a natural canal on one end of my property, and the 100-foot setback took up a substantial amount of the lot.
The drain field needed to be 400 square feet, and there also needed to be a reserve field of the same area set at least 6 feet away from the main field. I had a problem here because it was impossible to fit both fields into the setbacks. Fortunately, by using the next system up from gravity I was able to use smaller fields that fit within the setbacks.
A pressure distributed system
I will be installing what is called a pressure distributed system. It’s basically the same as a gravity type system but with the addition of a pump. This balances the distribution of effluent more evenly across the field, thus allowing a smaller field area.
The sewage from the house exits the main drain pipe and enters a three-compartment concrete septic tank (see Image #2 below).
The first compartment is aptly named the trash chamber, and allows the sewage to separate into solids on the bottom, a layer of sludge on the top, and a cleaner liquid in the middle. This liquid is allowed to enter the second compartment, called the digestion chamber. In order to exit this chamber, the sewage must decompose into small enough particles to pass through a filter. A pump sits at the bottom of the last compartment, the clarifier chamber. When the level of liquid in the chamber causes a float to reach a certain height, some of the liquid is pumped out of of the tank and through a pipe to the drain field.
There are two more floats: the first to ensure the pump doesn’t run too often and the second to sound an alarm if the pump isn’t working and the tank is getting full.
The experienced backhoe operator I hired was able to dig the 9 foot by 15 foot hole to a depth of 77 inches in less than an hour (see Image #3 below). I would have liked to do it myself, and I realize now, after having seen it done, that with the right person checking the depth for me I could have done it. But it would have taken me at least five times as long. The hardest part about digging a hole that deep is that you aren’t able to see the bottom of the hole from inside the cockpit of the excavator, so you’re basically digging blind.
Once the hole was dug, I climbed down on a ladder and made sure the bottom of the hole was nice and flat. We hit the water table around 6 feet down, so I was working in about 6 inches or so of water. Once I was sure I had made a nice bed for the tank I climbed back out and we got started on digging the field. This part could have very easily been done by hand since the depth of the drain field is only 7 inches. But since the excavator was already there, it made quick work of the job.
The field is 9 feet by 35 feet, and it must be flat and level. The first step is finding the lowest spot, then and digging down 7 inches from there. Once that is done it’s simply a matter of matching that depth to the remainder of the field. I used a 6-foot level and also a rotary laser level to check the depth, and a rake and shovel to fine-tune things.
Adding the piping
The pipes that disperse the effluent to the drain field are made from 2-inch PVC reduced to 1 1/4-inch PVC using two cross fittings and a tee fitting. In image #4 below, you can see how the 2-inch pipe enters the field and is attached to cross fittings underneath the black tunnels. The design allows the 2-inch pipe to branch into six separate 1 1/4-inch pipes and disperse the effluent into the the field evenly.
The PVC is very simple to glue together with primer and cement. Once the pieces are glued, a 1/8-inch hole must be drilled at the top of each 1 1/4-inch line every 2 feet, starting 1 foot from the place it tees off from the main 2-inch pipe. Those pipes are then covered with the large, black gravelless chambers. The holes allow the effluent to spray out and cover as much of the area of the entire field as possible.
The gravelless chambers are exactly what they sound like. Instead of covering the PVC lines with gravel, you use the plastic chambers. They are cheaper and much easier to install than shoveling gravel. The chambers help direct the effluent sprayed from the pipes into the soil and also ensure that the pipes will be protected from human activity above.
Installing the tank
Around this time the septic tank manufacturer arrived with the tank on the back of a flatbed. The driver used a small crane on the back of the truck to hoist the massive tank into the air and lower it into the hole we had prepared.
I had a hose all ready to start filling the tank with some water as soon as it was dropped. This helps to give it some added weight and ensure it settles into the soil. The backhoe operator also added soil around the sides but left the top and the inlet and outlet ports on the sides exposed.
The electrical cable was too short
The tank installation went smoothly, but for the second time in my build I underestimated the amount of wire I needed and now I’m stuck with a couple pieces that are too short. I’ll have to return to the electrical supply store to get longer pieces. An important part of working solo is knowing where your deficiencies are and I tend to cut things just a little too close so I don’t waste a thing. With wire, hopefully this will be the last time I underestimate the length I need!
I began the day by running 1 1/2-inch PVC from the tank to the drain field. I learned a lot from the mistakes I made running electrical conduit, and the end result was a well planned and perfectly aligned run. The next step was attaching the float switches inside the pump chamber of the septic tank. There are three floats that will work together to operate the pump.
The float switches are bell-shaped plastic parts attached to low-voltage cords. They are very simple but ingeniously designed. When the water is low, gravity pulls the float down so the heavier bell end is down. When the water level raises, the bell end floats upward, causing a sliding metal part inside the float to meet another metal part in the middle and complete the circuit.
Placing floats correctly
The floats must be placed on the PVC pole precisely (see Image #5 below). The first float was to be placed 13 inches from the bottom of the tank. This switch controls the “redundant off” function in the control panel. Basically, it ensures that the pump continues to run until the effluent level is low enough to lower the float. Without it, the pump would wear out a lot faster because it would run so often. Imagine if you took out the garbage to the street every time you had a piece of trash! It’s much more efficient to have a small container and only empty it when the container is full.
The second float is placed 20 inches from the bottom of the tank. Once the effluent level is high enough to raise this float, the pump activates and continues to run until the “redundant off” float is lowered.
The third float is the high-level switch, and is placed 35 inches from the bottom of the tank. This activates an alarm and a siren if the float is raised, and will allow me sufficient time to figure out what is wrong and fix it before the effluent level gets so high that the tank is full (see Image #6 below).
The control panel is mounted on a post
You can see in Image #6 how I’ve mounted the control panel on a 2Ã—6 pressure-treated post and run wires through 3/4-inch conduit from the panel down towards the pump chamber riser. Tomorrow I will buy a rubber grommet to make a seal as I drill a hole through the side of the riser and run the conduit into the junction box. The last step will be running some 12/2 UF cable from my temporary power pole underground to the control panel.
The other part I still need is the flexible hose assembly that will connect the pump to the 1 1/2-inch PVC I talked about in the beginning of this post. Once that is hooked up, it’s just a matter of filling the tank with water and checking to ensure everything is working properly.
Ready for another inspection
You can see my $7,000, high-powered sprinkler system at work in Image #7 below. Hard to believe that underneath the plastic “infiltrators” you see in the background and 12 inches of soil, that spray is going to be the last step in safely disposing of my sewage.
Today, the septic designer brought over a hose assembly and we hooked it up. The hose assembly attaches to the pump at the bottom of the tank and makes three 90-degree turns before exiting the tank and going through the PVC pipes I assembled a few days ago.
Now it was time to fill up the pump chamber with water and test the system. It was necessary to fill up the chamber with water for two reasons. First, you never want to run any kind of water pump without water in it because air has much lower resistance than water and the motor will burn out without that resistance (so make sure you aren’t out of windshield wiper fluid!). Second, the panel won’t operate the pump unless both the redundant off and pump on floats have been activated, and I’m not too keen on climbing down into the tank and flipping them upside down by hand.
After 10 minutes or so I had enough water in the tank to activate both floats and I turned on the power to the control panel. The pump activated and we got the beautiful water show you see in the photo. The septic designer called the inspector for an appointment so I can replicate the display for him and he will sign off on it.
The final steps involved making inspection ports from 6-inch PVC and placing them over each of the ends of the drain lines. Each port has a plastic cap that can be lifted off to expose the 90-degree long sweep at the end of the line. If for any reason the drain lines get clogged, you can take off the cap, reach down inside the PVC and unscrew the plug for the line in order to flush it out.
Toward the end of the day, the backhoe operator came back and expertly returned the soil over everything, driving back and forth to compact the soil (see Image #8 below).
Totally out of sight now, you can hardly tell that anything was done! What better way to “save sustainably” than to build your own septic system on your lot rather than take up a ton of land with a giant sewage treatment plant? Obviously, those are necessary with high-density residential areas, but in neighborhoods like mine, it really is too bad that more homes don’t have their own septic systems.
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