Septic Systems

Approximately 25% of the housing units in the United States are served by septic tanks or cesspools (private, subsurface wastewater systems), according to a 1995 American housing survey by the U.S. Census Bureau. That means there are currently more than 25 million septic systems in the United States. Further, each year about 400,000 new systems are built. In Canada, there are about 3 million active septic systems and about 40,000 new systems built each year.

The following is a brief summary of some things you should know about septic systems. For more information, a particularly good publication is The Septic System Owner’s Manual by Lloyd Kahn, Blair Allen, and Julie Jones. It is published by Shelter Publications of Bolinas, California. Their Web site is www.shelterpub.com.

A typical septic system consists of two basic components: a septic tank and an underground disposal field. Wastewater flows from the house to the septic tank. Effluent, after the solids have settled out of the wastewater, flows from the tank to the drainage field.

Most septic systems operate by gravity. Thus, it is a passive system, perhaps one of the best passive systems we have to serve our homes.

For various reasons (typically, site topography and soil characteristics), some septic systems will require a pump (an effluent pump) to pump effluent from the septic tank to the drainage field. Others may require a pump (sewage ejection or grinder pump) to pump the wastewater from the house to the septic tank. The simpler system is the one using an effluent pump. A sewage ejection or grinder pump is a more complex piece of equipment that requires more maintenance. Duel ejection pumps are sometimes installed so one can serve as a backup in the event of a problem. Both types of pump should be equipped with a high-water alarm to alert you if there is any problem with the system. All septic system pumps should be maintained on regular basis.

Fundamentally, the septic tank has several functions:
1. To receive all wastewater from the house.
2. To allow solids to settle from the wastewater.
3. To facilitate decomposition of the accumulated solids.
4. To provide storage for accumulated solids.
5. To allow the wastewater without the solids (the effluent) to flow to the drainage field.

For most single-family homes, the septic tank will range from 500 to 1,500 gallons in capacity. Most modern septic tanks are concrete, fiberglass, or plastic. The majority of tanks are prefabricated units. Most older tanks are wood or steel.

The disposal field is sometimes called a drainage field, leach field, or absorption field. It is intended to purify and disperse the effluent flowing from the septic tank. Disposal fields typically consist of either perforated distribution pipe or chambers. Chambers are typically concrete or plastic. The type of soil in which the drainage field is located and how well it will absorb the effluent will dictate the size and configuration of the disposal field. Also, in most states and provinces, the number of bedrooms dictates the minimum system size of the septic tank and disposal field. There are many regional variations of the components of and configuration used for disposal fields. Some even include the ability to chemically treat the effluent to facilitate purification and recycling.

Ultimately, the water and nutrients from the effluent will recycle back into the environment to nurture plant growth and/or evaporate into the atmosphere.

The most serious problem for a septic system occurs when solids flow into the disposal field. This can cause a backup of the system because the drainage field becomes blocked. To minimize the risk of damaging the drainage field, it’s important to pump out the septic tank on a regular basis. In most areas of North America, it is recommended that a septic tank be pumped out every 3 to 5 years. In some areas, however, a 10-year cycle is possible based on how the system is used, the type of soil, and other factors. At a minimum, we recommend opening the tank and inspecting it every 3 to 5 years and then pumping when evidence indicates a need. A qualified technician should do the inspection. Those qualifications vary regionally. You should check with the state or county plumbing inspector for more information. Call any licensed sewage contractor listed in the yellow pages.

Here is a summary of key points regarding your septic system:
1. Open and inspect the tank every 3–5 years.
2. Expect to replace a wood or steel septic tank soon.
3. Pump the septic tank every 5–10 years, depending on inspection findings.
4. Most disposal fields will last 20–30 years or more, depending on soil type and use.
5. Effluent pumps will typically last 20–30 years, assuming normal use and regular maintenance.
6. Sewage ejection (grinder) pumps will last 10–20 years, assuming normal use and regular maintenance.
7. If you want to add a bedroom, you may have to enlarge your septic system.

Septic systems are natural, effective, reliable, and passive systems for disposing of wastewater. With proper maintenance, most will serve for many, many years. For more information, we recommend The Septic Systems Owner’s Manual noted above.

Ann Arbor Home Inspection Inspector
P.O. Box 7300, Ann Arbor, Michigan 48107
Phone: (734)369-3003 • Email: richard@annarborhomeinspection.com