Housing...Inside and Out

April 10, 1997
Septic Systems: Enzyme Additives & Pumping (April Part I)

 

Enzyme and Septic System Additives: Are They Worth It?

An aspect of onsite septic systems that is important to understand, is whether Enzyme Treatments and Septic System Additives are necessary and worth the trouble and expense. Many companies advertise an enzyme additive which can be added to your septic system, and is intended to enhance the biological degradation and decrease the amount of solids in a septic tank. While there is nothing detrimental in these additives, the only thing that will actually increase the biological decomposition rate of septic wastes, is to increase the temperature of the septic tank. Some of these additives cost from $100 to $200 but will do very little to improve the performance and decomposition rate in septic systems. They are definitely not advisable, especially for the price. The most important thing to understand about additives, is that not much you can add to your system will improve its performance except to raise the temperature. Everything that is important to the degradation of septic wastes is already in your tank. Therefore nothing need be added for it to work well.

How Often Should I Pump My Septic System?

Extension agents are often asked: how regularly should a septic system be pumped in order to keep it functional? This is a difficult question to answer for all cases because systems are site specific and the amount of use is crucial. Generally it is suggested that every two years a septic system be pumped out. The reason for this is that most septic tanks are nothing more than long term storage tanks.

However if your house has a large number of people living in it, more than the bedroom design would normally accommodate, (more than two people per bedroom) then it's likely that your septic tank load will be higher than normal and pumping it every year might be in order. Another crucial factor is the amount of absorption your septic system can handle in terms of soil leaching. You may have "tight" soil which has a very low "hydraulic conductivity", and can't accept much water. The soil may have a poor percolation test result because water flows through it very slowly. In such cases, it also may be necessary to pump it more often so that slow leaching does not limit the performance of your septic disposal system.

You may also find that after ten years or so, a leach field begins to fail. This is a common occurrence because a healthy leach field will get a regular flow of bacteria from the fluids exiting the septic tank. These bacteria create organic slimes in the soil which clog the soil pores and cut down enormously on the absorption capacity of the soils. An interesting suggestion has been made recently which could help deal with this problem. Consider installing two parallel leach trenches, two parallel leach systems which could be alternatively used by valving both of them.

The scenario would go like this: one trench of the leach system would be used for a period of two years and then the valve closed. The other is then opened by its valve, so that the second parallel system would then serve as the leach field for the next two years, while the original, having been closed down, would lie fallow and recover from the bacterial loading that it had received. This drying out and "lying fallow", by switching every two years alternatively, from one leach system to another, could and probably should in most cases, enable the leach field(s) to last indefinitely. This is a system that has recently been suggested by engineers and experienced people in the industry and hasn't been tested widely, but seems to make very good sense. And if it's possible to afford such an option, it's highly recommended. Obviously it costs twice as much for the leach field that's twice the size in order that each can handle the leach requirements separately over alternating two year periods.


Written by Dr. Francis Graham (Retired)

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