Septic Systems in Oregon

A septic system is the most common form of onsite sewage treatment for homes that are not connected to the public sewer system. A septic system consists of a septic tank, where solids settle and decompose, and a drainfield where liquid discharged from the tank is treated by bacteria in the soil. You could also run into Sand Filter and Pressure Distribution Maintenance systems or Alternative Treatment Technology systems, depending on the age of the system, where the water table is located, and the quality of the soil at the house.

Septic System Basics

  • The Tank

The septic tank is designed to collect all of the sewage that comes from your home. For example, every time you do a load of laundry, you are creating sewage that travels to your septic tank. When sewage enters the septic tank, the solids or sludge sink to the bottom of the tank and oils or scum float to the top of the tank. All of the liquid between the sludge and scum layers is called sewage. Once the tank is full, sewage is displaced from the septic tank to the drainfield. Over time, the scum and sludge levels i the tank increase to a point when the tank needs to be pumped by a licensed sewage disposal service to remove the solids. When you buy a home with a septic system, as part of the septic system inspection, the tank is likely to be pumped. Discuss with the septic system evaluator how often you should get the tank pumped from that point on.

  • The Drainfield

The soil absorption field may be a drainfield (also called leach field) or a seepage bed. The soil absorption field consists of a series of trenches that sit below the ground. These trenches are filled with a porous material and covered with soil. Sewage from the septic tank is dispersed into the trenches. Microbes then break down the sewage, as it moves down through the soil profile below the trenches. Note that you will not want to build anything on top of this field, and a large lot that you might think is an investment in developable land may not be because of this field. Occasionally, this field is in somebody else’s yard, so as part of your inspection, you will want to figure out where the boundaries of the field are.

Getting Systems Inspected

The Oregon DEQ requires that inspectors be one of the following: an installer, a maintenance provider, a wastewater specialist, an environmental health specialist, or a  National Association of Wastewater Technicians (NAWT) certified inspector with experience inspecting existing septic systems. Here is a link to professionals who have signed up with the Oregon DEQ’s official SepticSmart program:

Here are some more good links about septic inspections:

Maintaining a Septic System

Congratulations on your new home purchase! Now, you have to remember to maintain that septic system. Here are some do’s and don’ts:

  • DON’T flush material that will not easily decompose, such as hair, diapers, cigarette butts, matches, or feminine hygiene products.
  • DON’T wash or flush medicines or hazardous chemicals like paint, paint thinner and bleach into the system. They kill the bacteria needed to decompose wastes in the septic tank and drain field.
  • DON’T drive over the septic tank or drainfield.
  • DON’T flush flushable wipes. Many septic tank pumpers and city public works employees are finding they don’t break down and cause serious headaches.
  • DON’T plant anything over or near the drain field except grass. Roots from nearby trees or shrubs may clog and damage drain lines.
  • DON’T dig in your drain field or build anything over it.
  • DON’T cover the drain field with a hard surface such as concrete or asphalt.
  • DON’T make or allow repairs to your septic system without obtaining the required permit. Use professionally licensed septic contractors when needed.
  • DON’T use septic tank additives. These products usually do not help and some may even be harmful to your system.
  • DON’T allow backwash from home water softeners or condensate from an air conditioner or heat pump to enter the septic system.
  • DON’T enter your tank. Any work to the tank should be done from outside. Gases that can be generated in the tank and/or oxygen depletion can be fatal.
  • DO conserve water to avoid overloading the system.
  • DO use substitutes for household hazardous waste.
  • DO learn the location of your septic tank and drain field. Keep a sketch of it handy with your maintenance records for service visits.
  • DO cover the drain field with a grass cover to prevent erosion and remove excess water.
  • DO keep your septic tank cover accessible for inspections and pumpings. Install risers if necessary.
  • DO keep a detailed record of repairs, pumpings, inspections, permits issued, and other maintenance activities.
  • DO divert other sources of water, like roof drains, house footing drains, and sump pumps, away from the septic system. Excessive water keeps the soil in the drain field from naturally cleansing the wastewater.
  • DO have your septic tank pumped out regularly by a DEQ licensed contractor.
  • DO call a professional whenever you experience problems with your system, or if there are any signs of system failure.

What happens if you don’t pump your tank often enough? If that tank gets too full of solids, there are a lot of differently possibilities (to the right is a picture that shows drainfield lines that have burst because solids were pushed into them), but some of the things you might experience are:

  • Water and sewage from toilets, drains, and sinks are backing up into the home
  • Bathtubs, showers, and sinks drain very slowly.
  • Gurgling sounds in the plumbing system.
  • Standing water or damp spots near the septic tank or drainfield.
  • Bad odors around the septic tank or drainfield.
  • Bright green, spongy lush grass over the septic tank or drainfield, even during dry weather