Septic Systems

Households that are not served by public sewers usually depend on septic tank systems to treat and dispose of wastewater.  A well designed, installed, and maintained septic system can provide years of reliable low-cost service.  When these systems fail to operate effectively, property damage, ground and surface water pollution, and disease outbreaks can occur.  therefore, it makes good sense to understand and care for your septic tank system.
    There are many different types of septic tank systems that can fit a wide range of soil and site conditions.  the following information will help you to understand a simple type of septic system, and keep it operating safely at the lowest possible cost.
    A "conventional" septic tank system has three working parts:

1. The septic tank
2. The drainfield with its replacement area
3. The surrounding soil

The Septic Tank

    The typical septic tank is a large buried rectangular, or cylindrical, container made of concrete, fiberglass, or polyethylene.  Wastewater from your toilet, bath, kitchen, laundry, etc. flows into the tank.  Heavy solids settle to the bottom where bacterial action partially decomposes them to digested sludge and gases.  Most of the lighter solids, such as fats and grease, rise to the top and form a scum layer.
    Septic tanks may have one or two compartments.  Two compartment tanks do a better job of settling solids and are required for new systems.  Tees or baffles are provided at the tank's inlet and outlet pipes.  The inlet tee slows the incoming wastes and reduces disturbance of the settled sludge.  The outlet tee keeps the solids or scum in the tank.  All tanks should have accessible covers for checking the condition of the baffles and for pumping both compartments.  If risers extend from the tank to or above the ground surface, they should be secure to prevent accidental entry into the tank.
    Solids that are not decomposed remain in the septic tank.  If not removed by periodic pumping, solids will accumulate until they eventually overflow into the drainfield.  Most septic tanks need to be pumped every 3 to 5 years, depending on the tank size, and the amount and type of solids entering the tank.

"Early Warning" Levels Inside Your Septic Tank
The septic tank should be pumped whenever:

Many products on the market, such as solvents, yeast, bacteria, and enzymes claim to improve septic tank performance, or reduce the need for routing pumping.  None have been found to be of benefit.  Some can cause solids to carry over to the drainfield, which results in early soil clogging and the need for a new drainfield.   Products containing organic solvents contribute to groundwater pollution.
    The wastewater leaving the septic tank is a liquid called effluent.   It has been partially treated but still contains disease-causing bacteria and other pollutants.  Discharging effluent onto the ground's surface or into surface and ground water is against Washington State Law.

The Drainfield

    The drainfield receives septic tank effluent.  It has a network of perforated pipes laid in gravel-filled trenches (2-3 feet wide), or beds (over 3 feet wide) in the soil.  Wastewater trickles out of the pipes, through the gravel layer, and into the soil.  The size and type of drainfield depends on the estimated daily wastewater flow and soil conditions.
    Every new drainfield is required to have a designated replacement area.   It must be maintained should the existing system need an addition or repair.

The Soil

    The soil below the drainfield provides the final treatment and disposal of the septic tank effluent.  After the effluent has passed into the soil, most of it percolates downward and outward, eventually entering the groundwater.  A small percentage is taken up by plants through their roots, or evaporates from the soil.
    The soil filters effluent as it passes through the pore spaces.   Chemical and biological processes treat the effluent before it reaches groundwater, or a restrictive layer such as hardpan, bedrock or clay soils.  These processes work best where the soil is somewhat dry, permeable, and contains plenty of oxygen for several feet below the drainfield.

System Failure

    Warning signs of a failure:

    If you notice any of these signs of if you suspect your septic tank system may be having problems - contact your local health agency for assistance.

Caring for Your System - the Ten Essentials

1. Practice water conservation
2. Keep accurate records
3. Inspect your system once a year
4. Pump out your septic tank when needed
5. Never flush harmful materials into the septic tank
   The following items cannot easily decompose in the tank:
       grease
       cooking fats
       newspaper
       paper towels
       rags
       coffee grounds
       sanitary napkins
       cigarettes
   The following items are harmful to the system's proper operation and may pollute the groundwater
       solvents
       oils
       paints
       pesticides
6. Keep all runoff away from your system
7. Protect your system from damage
8. Landscape your system properly
9. Never enter any septic tank
10. Check with your local health agency for help with system problems.

The in this page has been extracted from "Understanding And Caring For Your Septic Tank System", published by Washington State Department of Health