Understanding Septic Systems

Image Gallery Under most conditions, a septic tank will need to be pumped out by a professional every two to five years. STEVE MAXWELL

A septic system is the most common way to treat household wastewater if connections to a municipal sewer aren’t available where you live. But few people who rely on septic systems understand how they actually work. And without correct knowledge, you’re open to misinformation or accidental mismanagement that could cost you lots of money.

The word septic means “absence of oxygen” and that's the state of affairs in the first part of every septic system — the tank. This is where raw sewage is broken down by anaerobic bacteria, liquefying most of the solids. Indigestible bits settle out into the bottom of the tank, a bacterial scum develops on the surface of the sewage, and excess liquid flows out of the tank into a network of perforated pipes buried underground. This area is large, and extends beyond the tank. It's called a leaching bed, or weeping bed, and it's the place where 90 percent of sewage purification occurs as nutrient-rich wastewater dribbles out of holes in the pipes. After this happens, soil microbes, insects and roots of grass purify the water. (Don’t plant vegetables in this area.)

Keep Things Flowing Smoothly

Septic systems can function for decades, as long as the soil around the perforated pipes remains porous enough to allow wastewater to drain away. But after the soil loses this porosity, sewage backs up and you’ll have a major problem.

Routine maintenance of your septic system is aimed at retaining the all-important porosity of the leaching bed, and this is the reason septic tanks need to be pumped out every two to five years by a professional (gases produced by a septic system can be deadly). Because the septic digestion of incoming waste is never complete, an indigestible sludge slowly builds up in the bottom of the tank. And while this is normal, it means the effective size of the tank is constantly getting smaller. If tank capacity is reduced enough, solids are forced out into the leaching pipes where they'll clog the soil and ruin your system.

Few people realize how bad washing machine lint is for septic systems. The small particle size of lint means that it doesn't settle to the bottom of the tank. If you're washing machine filter allows enough lint to slip past, it'll clog your leaching bed prematurely.

When the Water is Rising

The first thing to look at if your septic system goes bad is sewage loading immediately before the problem occurred. Did you have a lot of house guests? Have you been doing a lot of laundry? Backed up main drains or a swampy back yard might be caused by temporary overloading of the system. Limit water use for a few days and see what happens. If the problem remains, you could have a congested leaching bed, though not necessarily.