Septic Tanks

Septic Tank Maintenance and LMWD Septic Tank Pumping Requirement

All customers of the Lookout Mountain Water District treat their household wastewater through an Individual Sewage Disposal System (ISDS), in most cases this is commonly called a septic tank and a leaching field.   LMWD requires that water users pump their septic tank once every two to four years; this resolution was adopted in 1997 and was a requirement of a water decree.

Source for ISDS information below: Jefferson County Department of Health and Environment


Please see the Jefferson County website:

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.

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. 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.

Recommended frequency for pumping/cleaning of tank in years:

Tank Size (Gallons)

Household Size
(Number of People)








500 5.8 2.6 1.5 1.0 0.7 0.4
750 9.1 4.2 2.6 1.8 1.3 1.0
900 11.0 5.2 3.3 2.3 1.7 1.3
1000 12.4 5.9 3.7 2.6 2.0 1.5
1250 15.6 7.5 4.8 3.4 2.6 2.0
1500 18.9 9.1 5.9 4.2 3.3 2.6
1750 22.1 10.7 6.9 5.0 3.9 3.1
2000 25.4 12.4 8.0 5.9 4.5 3.7
2250 28.6 14.0 9.1 6.7 5.2 4.2
2500 31.9 15.6 10.2 7.5 5.9 4.8