ISDS Operations & Maintenance

Back to ISDS Main Page >>

What's an individual sewage disposal system and how does it work?
The typical ISDS consists of a Septic Tank and Absorption Bed (sometimes called the leaching field). The septic tank is usually made of concrete or other durable materials. Most tanks will have a capacity of 1,000 gallons or more and will be divided into two compartments. Sewage (or effluent) from the dwelling flows through a building sewer and enters the first compartment of the tank. Here, bacterial decomposition occurs and materials which cannot be digested settle to the bottom as sludge or float to the top to form a scum layer.

The remaining liquid then flows into the second compartment of the tank through a series of baffles, where additional treatment occurs. Although most tanks are non-mechanical, some will have a motor or aerator which agitates the sewage. These mechanisms are an integral part of the tank and should not be removed or disconnected as this may seriously affect the operation of the system.

From the tank, the effluent is piped to the Absorption Bed and enters a series of perforated pipes bedded in gravel and underlying soil before flowing naturally back into the groundwater system. The filtering action of the soil removes most of the harmful bacteria. The result is a high degree of treatment occurring in a natural, environmentally sound process.

Not all contaminants can be removed by these systems. Nitrates, a chemical by-product of human waste, are not removed and may impact the groundwater. Distance separation from wells and proper system maintenance is necessary to increase treatment effectiveness as well as the life span of the system.

Care and Feeding of Your ISDS
One of the most important factors in proper ISDS operation is being careful of what goes into the system. An ISDS is designed to treat only household wastewater. Although typical household soaps and cleaners should not cause a problem, liquids such as paints, solvents, thinners, pesticides, or photographic chemicals should never be poured down the drain. These materials can damage your system and seriously pollute the groundwater. Likewise, items such as disposable diapers, cigarette butts, and sanitary napkins should be kept out of the system. Kitchen wastes such as bones, eggshells, and coffee grounds do not readily decompose and should be thrown out rather than put through the garbage grinder. Grease is probably the worst enemy of your ISDS; pans should be wiped clean prior to washing and excess grease or drippings should never be poured down the drain.

Unlike a public sewer, your ISDS is designed to accept a certain sewage flow (about 75 gallons per person per day) with a safety factor for peak water use periods. Prolonged overloading of the system may result in sluggish drains, backups, or surfacing of sewage in the bed. Therefore, it is recommended that heavy water use be spaced; don't do multiple loads of laundry back to back or permit three or four showers to be taken in a row. This will allow the system to accept the flow evenly without serious overloading.
(view the Septic System Maintenance brochure)

Pumping Tank
Since some materials in sewage cannot be decomposed, they must be periodically removed by a licensed systems cleaner who will pump this material from the tank. If you have a 2-compartment tank, both sides should be pumped. The pumper should also remove all of the water from the tank; this will allow a "rest period" for the leaching field. Failure to regularly pump the tank may result in sludge being carried into the leaching field where it can plug the soil pores and cause failure. Since repairing a failing absorption bed may cost many thousands of dollars, the cost of routine pumping represents a very reasonable investment in protecting your ISDS. See following chart for recommended frequency of pumping or cleaning of tank.

 Estimated septic system tank pumping frequency - years

Absorption Bed
This is where treated wastewater enters the soil, and failures are common in this component of the ISDS. Since the plastic (PVC) pipes in the bed are usually one foot deep or less, they are quite susceptible to damage. Vehicles should never be driven or parked on an absorption bed. In addition, to the potential pipe damage, the soil may be compacted. This will prevent proper absorption of the sewage. Animals such as cattle or horses may also compact the soil and damage pipes. If your ISDS is in a pasture, it should be fenced to keep out livestock.

Erosion can seriously affect an ISDS by removing the soil cover and allowing sewage to escape from the bed. This can be prevented by maintaining proper drainage and establishing a good vegetative cover (excluding trees) above the bed. If the bed is located in a lawn area, watering should be restricted to prevent saturation of the ground.

Repairs
Despite the best of care, some systems may malfunction. If your ISDS should back up into the dwelling or leak from the absorption bed, contact the Jefferson County Public Health at 303-271-5700 at once. We can advise you on procedures to repair the system.

Additives
In normal amounts, household chemicals should not affect the proper functioning of your ISDS. Additives which are claimed to improve the operation of the system will probably not cause any harm, but they are not needed to assure proper operation of the system. Beware of any claims that a chemical additive will "rejuvenate" the system or make it "as good as new." Common baking soda, however, may lessen any odors from the tank and, if necessary may be added for this reason.

Summary
In summary, do not dispose of items that will destroy the natural digestion processes in your ISDS, or overload the system with excessive water. Have the tank regularly inspected and pumped. If you adhere to these few simple rules, your ISDS will prove to be a safe and economical onsite method for disposing of your rural wastewater.

Last Modified: Jun 8, 2009 02:43 PM