DIY Network

The Drainage System: Alternative to Sewer System From "Blueprint for Home Building" episode DBHB-202

Figure A

You've learned about the drain, waste and vent parts of your plumbing system in the first three segments of this episode, but what if you live in a region where your municipality doesn't provide a sewer system? For that, host Jeff Wilson takes a look at the most common alternative -- a septic system.

Today more than 25 million households in the United States utilize a septic system. A typical septic system consists of two parts:

1. Septic tank (figure A).

2. Drain field.

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Figure B

When the waste product leaves the building, it goes into a septic tank, which is a watertight, oxygen-free holding tank generally made of pre-cast concrete or fiberglass. It separates the waste water into three components (figure B -- an illustration of the three components):

1. Solids (or sludge).

2. Floatables (or scum layer).

3. Zone of relatively clear water.

The solids are broken into liquid with the use of bacteria that are able to thrive in an oxygen-free environment. When the solids begin to breakdown, gasses are generated, which assist in stirring the tank and are then vented through the vent stack in the home's plumbing system.

The oxygen-free conditions inside the septic tank also deactivate some of the disease germs that are found in sewage. The heavier content settles as lighter water passes over it into the clear zone.

Then you have a cesspool that distributes the water into the ground-water system, leaches it out through a leach field and then distributes it out through the ground water. From the clear zone of the septic tank, the wastewater flows into the drain field for the secondary treatment stage of the sewage.

Figure C

The drain field (figure C) is generally a series of perforated pipes or slotted panels that are usually surrounded by a layer of gravel, tire chips or other lightweight materials such as Styrofoam pieces.

At this point bacteria continue deactivating the disease germs that remain in the wastewater. Further filtration occurs as gravity draws the heavier water downward through the soil layers. Meanwhile, some water has risen up the surface and begins to evaporate.

Note: In some areas septic systems need to be elevated to prevent contamination of high water tables. These systems are called "mounded systems," which may also be found where other types of soils exist such as clay or bedrock.

If you are in the position of having to go with a septic system, generally it costs between $3,000 and $5,000 for installation. The average size for a four-person household is 1,500 gallons, which can accommodate 200 to 400 gallons of water flow per day.

For more information on your home's plumbing system, check out our Home IQ online package. Scroll down to the "Plumbing and Electric" section.

In the next episode of Blueprint for Home Building our host focuses on the design options for the best flooring choice for the rooms of your new home.

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