Septic System Basics

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SOIL ABSORPTION SYSTEMS

A common misconception is that the key component of a septic system is the septic tank. "The soil absorption system, or leach field, is where the real treatment occurs," Joe says.

After the septic tank has settled out solids, clarified wastewater is dispersed through perforated pipes into the soil. In Septic Tank Practices, Peter Warshall says soil is the key to clean water. It acts as a "physical strainer, chemical renovator and a biological recycler" for the wastewater passing through it. Your soil absorption system may be called a leach field, leach bed, soil absorption field, seepage bed or mound, but all act similarly.

Beneath and to the sides of the pipes, a black, jellylike mat or biomat forms. This thin layer of anaerobic organisms helps regulate the flow of wastewater to the soil and preys on potentially pathogenic bacteria, viruses and parasites. It also converts nutrients into a form that can be used by plants or releases nutrients into the atmosphere as gases. The biomat also is a common trouble spot for clogging, as it has low permeability. Failing to pump out your septic system or discharging too much wastewater down the drain can lead to a buildup of organic material, which causes the biomat to grow too thick.

Your leach field may be a series of trenches into which wastewater flows by gravity. If your system is older, your leach field may be buried 5 feet deep. More modern leach fields use drip-irrigation lines, usually buried only 6 to 8 inches tinder the surface to keep wastewater in the zone of microbiological activity and within the root zones of plants. Some septic owners use alternating fields: a shallow leach field in summer, when plants can use wastewater nutrients; and a deeper leach field in winter, when plants are dormant. A diverter valve switches the flow.

Leach fields work best when the soil surrounding them is well-drained. Don't do anything that could compact the soil, such as driving heavy trucks over it (a lawn mower is fine). Grass planted over your leach field helps keep the soil aerated. Don't plant trees with deep roots, especially invasive species such as willows.

If your property does not have permeable soils or the soil is too permeable for filtering, your leach field may need to be built up with sand to create a mound system. Instead of distributing wastewater underneath the soil surface, wastewater is pumped up onto the mound, where it percolates through a layer of sand before contacting native soil.

PUMPING IT

"A few times a year, I'll be called out to pump a system, and the homeowner doesn't know where it is," Joe says. "After a little probing, we'll find it under their new house addition or a driveway! When you buy a house, locate the septic system. Better yet, check out the system before you buy the house."

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