Saturday, May 12, 2012


Last week's septic tank and drainage field excavations also gave us a chance to bury electrical power and data lines running to the house from the nearest utility pole. These conduits need to be buried 30" below the surface to protect them from inadvertent damage, whereas (strangely) the main water supply line only needs to be 12" below grade. The water line, which was laid weeks ago, is the white PVC pipe hanging in the air in this photo. It will be packed in clean (rock-free) fill to protect it from punctures after the electrical conduits are backfilled.

Why four conduits? Two are for power lines, one is for a telephone line and the fourth is for cable/internet service. Most likely, we won't use the telephone line, but it will be good to have the conduit in place, just in case. What else is buried outside tin box?

The big, sarcophagus-like concrete box is the septic tank. Its size (1,050 gallons) and that of the drainage field it leads to (666 square feet) are based on a plumbing code formula that relates septic tank capacity to the number of bedrooms in a house. This formula is somewhat dated, since it does not account for a number of ways we're reducing the volume of water passing through the system, including  graywater recycling, dual-flush toilets and low-flow faucets. Our septic system is thus going to be excessively large, though this means we should have no problem hosting Super Bowl parties.

The 4" PVC waste line leading to the septic tank has two cleanouts, which will let us service the tank. The cleanout closer to the house was the end of the plumbing system when our plumber first laid the pipes before the house's slab was poured. A second cleanout was added closer to the tank in order to allow it to be pumped out periodically. A tank this size needs to be emptied every two years or so to ensure that the drainage field works properly.

A biennial cleaning schedule might lead a more cynical homeowner to create a mnemonic along the lines of emptying the septic tank every time we hold a congressional election. But we're not that cynical.

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