Benton County, Oregon

Making Benton County a Better Place to Live
Printed on Mar 28, 2015 @ 11:46 AM

Benton County Environmental Health – Septic System

A Homeowners Guide to Operation and Maintenance

This document outlines the principles of septic system operation and explains the maintenance procedures necessary to prolong the life of the system. If neglected, the septic system can fail and lead to potential health hazards. If properly operated and maintained, the system can provide many years of trouble-free service.

The standard household septic system is a two part sewage treatment and disposal system buried in the ground. It consists of a septic tank and disposal field.

What Does Household Sewage Consist of?

Household sewage is a combination of wastewater from several sources, including sinks, showers, washing machines, garbage grinders, and dishwashers. The largest source of sewage is the toilet.

The Septic Tank

Untreated household sewage will quickly clog all but the most porous gravels if applied directly to the soil. The function of the septic tank is to allow separation of the solids from the sewage so that the remaining liquid (effluent) can be absorbed into the ground without clogging the soil. Within the tank three important processes take place. The heavier solid particles in the sewage settle to the bottom of the tank, forming a layer of sludge. Lighter materials, including fats and grease, float to the surface and form a scum layer. Bacteria (called anaerobes, because they live without oxygen) live in the septic tank and slowly digest some of the solids into gaseous and liquid components. This helps to reduce sludge build up.

Sludge and scum are stored within the tank rather than being allowed to flow into the disposal field where they would quickly clog the soil and cause the system to fail prematurely. As the tank fills with sludge and grease, efficiency of treatment decreases. Sludge and scum are removed when a septic tank is pumped.

The Disposal Field

The disposal field generally consists of a network of perforated pipes laid in gravel-filled trenches. After partial treatment in the septic tank, the sewage effluent flows into the distribution box or a series of drop boxes, then out through the perforated pipe and into the gravel-filled trenches. The gravel acts as a media for aerobic bacteria and other organisms to feed on the sewage.

In the soil below the disposal trenches, solid particles and disease causing bacteria are filtered out. Soil bacteria destroy many of the toxins and pollutants while other toxins and pollutants become bonded to clay particles. While these mechanisms remove many pollutants, some trace constituents such as Nitrates may reach groundwater tables.

Finding Your Septic System

In order to take proper care of a system the homeowner must know where it is located. If the septic tank's access manhole is at ground level, it should be easy to locate. Most access manholes are buried somewhere under the lawn or garden. To locate the septic tank, look under the house or in the basement to find where and in what direction the sewer pipe goes out. Septic tank locations are sometimes indicated by either lush or stunted grass growth, and /or mounded or depressed areas which differ from the rest of the yard. Any likely spot can be probed with a metal rod. A tank installed under current rules should be a minimum of five feet from the house foundation. Most systems installed since 1992 have tracer wire from the foundation to the tank and to the first box.

If this doesn't work, ask someone who may have seen the system installed or pumped (a neighbor, the builder, or a previous owner). Benton County Environmental Health Office has records showing the location of most newer septic systems. The more recent the installation the more likely we are to have the record. The installation records of increasingly older systems may be incomplete or nonexistent. If all else fails, turn the job over to a local septic tank pumper.

Once the tank has been located it should be permanently marked with a stake or flagstone and its location should be recorded in your files.

Septic Tank Pumping

Don't wait until your system shows signs of failure to have your septic tank pumped. The recommended pumping interval is every three to five years. You must call a licensed pumper to do the work. Proper pumping equipment will clean out scum, sludge, and all liquid. The pumped sewage will be disposed of at an approved facility. A thorough pumping service should also include an inspection of the inlet and outlet fittings, and the overall integrity of the tank.

A licensed pumper is assigned an official license number from the Department of Environmental Quality (DEQ). The license number should be given to you upon request and can be verified through the Environmental Health Office. The Environmental Health Office has a list of local licensed pumpers, or you can consult the Yellow Pages of your telephone directory.

It is not necessary to leave any of the sludge in the tank as "seed." Incoming sewage contains all the bacteria needed for proper operation.

The use of enzymes and other additives has not been shown to be of significant value. While their use may not harm the system, some may pose environmental hazards to the disposal field area or ground water. They do not take the place of regular maintenance.

Predicting System Failure

Septic systems generally give little warning that they are about to fail. However, the following symptoms often indicate that the system is becoming clogged:

  • Sewage odor near the septic tank, or disposal trenches.
  • Fixtures and toilets backing up or draining more slowly.
  • Sewage on the ground or over the disposal trenches as indicated by wet spongy ground or ponding of a grayish black liquid.

Reasons for System Failure

If the sewage effluent cannot be absorbed into the soil near the disposal field, sewage will backup and overflow onto the surface of the ground or inside the dwelling. There are four major causes of this problem:

  • High Water Table
    During wet periods the groundwater table rises. If the water table rises into the disposal field, sewage may be forced up to the ground surface. This is the result of improper disposal field location and may be improved by relocating the disposal field into an area of drier soil or by creating artificial drainage around the system.
  • Soil Clogging
    If sludge or scum from the septic tank overflows into the disposal field, the soil will become clogged. This usually means a new disposal field must be installed. However, this situation can occasionally be corrected by flushing the system and allowing it to rest for 6-12 months. The problem can be avoided by regular pumping of the septic tank.
  • Mineral Deposits
    If the soil in the disposal field area is continuously wet or flooded due to either a high winter water table or excessive sewage flows, mineral deposits which clog the soil will form. Such clogging can often be corrected by allowing the area to dry out and rest for 6-12 months. Reducing the volume of sewage from the dwelling can help prevent this type of failure. Home water use can be reduced by using the methods mentioned at the end of this document.
  • Roots
    The roots of certain trees and shrubs planted over the disposal field area can enter and block pipes. Removal of these plants is usually required. Avoid planting willow, cottonwood, poplar, and dogwood trees in the disposal field area.

If Repairs Are Needed

Should any of the symptoms that indicate system failure appear, do the following:

Contact the Environmental Health Office. An Environmental Health Specialist can visit your property to assess the situation. Repairs may not be warranted or only minor repairs or improvements may be needed. However, in most cases the disposal field must be replaced with a new one.

  • If minor repairs or improvements are needed, a repair permit must be obtained prior to any work being done on the system. Applications for repair permits are taken at the Benton County Development Department, located at 360 SW Avery, in Corvallis. Be careful not to mistake your permit receipt for the actual permit, which is issued by the Environmental Health Office only after examination of the replacement area is made.
  • Once you have submitted your application for a repair permit, a sanitarian from the Environmental Health Office will designate a disposal field replacement area. The designation of a replacement area will depend primarily on soil conditions, the size of the parcel, and distances from buildings, wells, property lines, and other items that require a setback. You may be required to provide one or more test pits for a thorough examination of the soil conditions. Work may not begin on the system until the permit has been issued.
  • All work must be inspected and approved by the Environmental Health Office prior to backfilling.

Protecting Your Septic System

Pump the tank regularly, every three to five years. Sludge build up varies with each family. Ask what frequency your pumper recommends. Do not wait until failure symptoms show up.

To protect your septic system against premature failure follow these simple procedures:

  • Minimize water use in the home. Excess water will decrease the effectiveness of the septic tank and lead to flooding of the disposal field.
  • Do not connect basement sumps, roof drains, or footing drains into the septic system.
  • Use water saving plumbing fixtures where possible (faucet aerators, low-flow showers, low-flow toilets, etc.) and run dishwashers and washing machines with full loads. Fix leaky faucets and toilets promptly.
  • Do not dispose of the following into a septic system: coarse organic matter-vegetable trimmings (such as vegetable trimmings or coffee grounds), tampons, diapers, condoms, baby wipes, etc. These will clog the septic tank with sludge and will require more frequent tank pumping. Use of a garbage disposal may shorten disposal field life. Home composting is an excellent alternative means of disposing of vegetable food waste.
  • Fats and grease – cooking oil, bacon grease, etc., will overflow the tank baffles and clog the disposal trenches.
  • Chemicals such as pesticides, disinfectants, motor oil, acids, medicines, paint and paint thinners, etc. will kill the bacteria that decompose organic matter in the tank, and cause increased sludge build up. More frequent pumping of the tank will be required to keep this system operating.
  • Follow current code when siting and installing any new septic disposal field. Improper location or construction will result in an early system failure.
  • Keep heavy vehicles off the disposal field area. Their weight could crush pipes and lead to extensive repairs.
  • Don't plant deep rooted trees or shrubs over the disposal trenches as their roots may clog pipes.
  • Do plant grass turf or other shallow rooting plants over the disposal field. Proper vegetation helps take moisture from the ground and the system. However, use care in landscaping so you don't cut or dig too deeply into the disposal field area.
  • Vegetable gardening is not recommended for the disposal field area Deep rototilling may adversely affect the disposal field trenches. Also, there is a possibility that root crops may become contaminated.
  • Do keep a maintenance record of your septic system. Include a plot plan showing the location of the septic tank and disposal lines.