Septic System Design and Maintenance

Enlarge Image Image Gallery This illustration shows the complete septic system, from plumbing vent to septic tank to drain field. illustration by Nate Skow

Sometimes, we take things for granted. A hot shower, a load of laundry or a flush of the toilet may be just a routine part of our day, but it can add up to a lot of water down the drain. In fact, the average person uses between 50 and 70 gallons of indoor water each day, and the majority of us don’t give a second thought as to where all that wastewater is headed. Take a little time to understand septic system design, and you're sure to save a bundle of money in the long haul.

More than one-fourth of all homes in America have a septic system, and each one requires maintenance to keep it running properly. With prices for new septic systems ranging from $3,000 to more than $40,000, depending on the type of system and the cost of installation, proper maintenance can mean big savings.

How it works

Since most septic systems are underground and out of sight, they’re easily ignored until things go wrong. Whether you’re installing a brand-new system or you’ve
inherited an older one, becoming familiar with it can save headaches and dollars. Maintenance of a private system is the homeowner’s responsibility. Understanding how it works is the first step in caring for it. Most basic septic systems have three main components:

• Household wastewater pipe – Each time you turn on a faucet or flush a toilet, wastewater is carried through a pipe and into your septic system. The number of people living in your home and your water usage habits determine the flow going into the system. If a system isn’t designed to handle the volume of wastewater flowing into it, an overload occurs, and that can mean big problems for a homeowner.
• Septic tank – The size of the tank is determined by house size and water usage. It may also be mandated by state and/or local regulations. The number of bedrooms is a good guide. A three-bedroom house typically requires a 1,000-gallon tank, and it increases 250 gallons for each additional bedroom.
Inside the tank, the heavier solid material sinks to the bottom, and fats and grease float on top. The liquid effluent in between flows out to the drain field (or in some older installations, a rock-filled pit called a French drain) through a T-shaped outlet that helps prevent solids from escaping. A screen or filter is required in some states to prevent solids from escaping. The sludge –
solids that collect in the bottom of the tank – periodically has to be removed by pumping. Some tanks have risers with bolted lids that allow easy access for checking sludge levels without opening the tank.
• Drain field – An underground pipe carries the liquid effluent from the tank to the drain field, where it’s distributed into a series of shallow trenches lined with gravel and covered with soil, or plastic chambers covered with soil. The soil in the absorption field is loaded with bacteria, which purify the liquid waste before it makes its way into groundwater.
The area ideally should be covered with nothing but grass. Tree roots, heavy vehicles or even compaction from excess foot traffic can cause irreparable damage.