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BY DON MEEHAN
CARE AND FEEDING OF SEPTIC TANKS
Approximately sixty-four percent of Island County residents have homes with septic tanks. Approximately 75 percent of our drinking water comes from aquifers underneath our homes. With this thought in mind, I felt the topic of septic tank care would be one which would interest many of you. A well designed, properly constructed, and adequately maintained septic tank system can serve a home as satisfactorily as can a city sewer. On the other hand, a system that does not receive the care and attention it deserves can become a burdensome expense to a homeowner as well as a menace to public health.
Because Island County soils have so much variability, septic system design is critical. Homeowners who fail to take account of the designed capabilities of their system may be facing serious problems down the road. Overloading a system beyond its design capabilities for long periods of time may lead to irreparable damage to the drainfield. Failing to perform maintenance can also cause system failure.
The purpose of a septic tank is to settle and treat household wastes such as soapy water from the laundry and the bath, discarded food scraps, and body wastes. The solids settle to the bottom of the tank, bacteria destroy some organic material by changing it into gasses, and the clarified liquid floats into the drainfield where it seeps into the soil. Filtration by the soil and soil microorganisms activity remove most of the impurities in the liquid wastes. Disease-causing organisms will be reduced to safe levels by the time the treated wastewater reaches groundwater in a properly designed, operated and maintained system.
Before getting into the proper approach for maintaining your system, I would like to address the role of oxygen in the breakdown of disease-causing microorganisms. These are the pathogenic bacteria, viruses, protozoa and helminths (worms).
When microbes from septic waste enter the soil structure through the septic system, they enter an environment that many are able to survive in. A significant part of this environment has to do with the number and types of soil microorganisms which attack those from septic wastes. Most soil bacteria require oxygen to survive. They are very competitive against waste microbes when oxygen is present. When soils become saturated with water, the oxygen levels drop. Soil bacteria become inactivated in these conditions, allowing many kinds of sewage bacteria to survive. In general, sewage bacteria and viruses are rapidly destroyed in soils with adequate oxygen levels.
Septic systems pushed over their design limits tend to saturate the soil with moisture, preventing proper in-flow to oxygen. Normally, bacteria and viruses are destroyed in the first two feet of soil, but not when soils are saturated. Under saturated conditions, the disease microorganisms will pass down into the underground water storage areas risking contamination of well water. Helminths (worms) are of sufficient size that their movement is restricted even when the soils are saturated.
System failures can be identified when inspection of the drainfield area reveals seepage. Indicators are wet spots, unpleasant odors, or lush growth of water-loving vegetation. Downspouts and storm water drains should not be connected into the system since these sources of water can legally be discharged on the surface. Location of these discharges near a drainfield would not be recommended unless special circumstances permitted it.
The septic tank needs to be inspected once every year and pumped out if necessary. Heavy volume and the kinds of solids passing through the system will govern the frequency of pumping the system. A simply designed stick can be made for measuring the scum layer and the sludge depth. The septic tank should be pumped when the total volume of solids (scum or floating layer plus sludge or bottom layer) equals one third of the liquid volume. For the typical home, this occurs every three to seven years.
Drainfields need to be cared for as well. They need to be protected from compaction from heavy vehicular traffic. Tree and shrub roots can be kept from clogging the lines by not planting woody plant species not suited for these locations. Even though chemicals exist for removal of roots, it would be wise to consult the Health Department for their advice.
Contrary to popular belief, recent research has demonstrated that softened water and the salt brine from water softeners do not damage drainfields, as long as the system was designed to handle the additional liquid volume.
Some things you should NOT DO include: flushing articles down the toilet or sink other than toilet paper and human wastes; dig up or allow animals to dig up the drainfield area; put concrete or other impervious layers over the drainfield (such as plastic in landscape situations); put more than two additional feet of soil over the drainfield; and take away soil from the drainfield area.
Keep in mind that the most common cause of failure seems to be failure to pump the septic tank frequently enough. If you do not know where your septic tank is located, this information is generally on file with the County Health Department if you provide them with your land's parcel number. Information about making the scum stick is obtained in the publications listed below.
A number of publications on septic systems are available from our office. Most cost 50 cents or less. They are titled "The Care and Feeding of Septic Tanks", "Soils and Septic Tanks", and "Septic System Waste Treatment in Soil". In addition to these publications I can also have a list of plant materials which can be used near septic system drainfields. The County Health Department also has a number of publication free to the public on care of septic systems and they include information about mound systems as well.
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