Q:
FC on Shaker Road asks: “How often should I pump my septic tank?”
A:
The Massachusetts Department of Environmental Protection recommends pumping your septic tank every three years. But this is a general recommendation if your household generates typical wastewater quantities and your septic system is a modern Title V-compliant septic system.
Civil engineer Gary Shepard from Ross Associates in Ayer describes a septic tank as a settling basin. “Solids sink to the bottom where they are partially digested by anaerobic bacteria. This accumulation of solids is known as sludge,” Shepard said. “Scum” consisting of grease, oils, soaps, and anything lighter than water, floats to the top of the tank. Effluent (the liquid between the scum and the sludge) leaves the septic tank relatively free of solids. Colonies of aerobic bacteria form a layer at the bottom of the leach field known as the “biomat” and purify the effluent by consuming its harmful components, thereby preventing contamination to the groundwater.
Eventually, dead cell bodies clog the biomat’s pores and water can no longer pass through them, causing catastrophic failure—sewage can back up into the house or bubble up in the yard, requiring your leach field to be replaced. While this will naturally happen to all leaching systems, it should take decades. If sludge and scum accumulate (due to infrequent pumping or abuse of your system) to the point at which they flow out of the tank into the leach field, they will accelerate clogging of the pores and cause a premature failure of the system.
So what can you do to encourage a healthy system? The rate at which the sludge accumulates varies depending on how much wastewater you introduce into your septic tank. You want a healthy level of bacteria to break down the solids introduced into your tank, so to keep them healthy you should limit or avoid chemicals that kill the bacteria. Some household cleaners (for example, bleach) kill off significant numbers of these important bacteria, so limit them as much as possible.
Also avoid putting indigestible objects into your tank—bathroom tissues are septic system friendly, but paper towels and facial tissues are not—they will not break down in the tank. No plastics, coffee grounds, or uneaten food should be put down the drain. If you have a garbage disposer, you are adding a significant amount of additional stress on your septic tank, easily doubling the amount of solids introduced into your tank.
If your household is large, generates a large amount of wastewater, or has an older or undersized septic system, increase the frequency of the septic pumping, as often as annually. If you are very gentle on your septic system (there are only one or two of you, or you are rarely home), you may be able to go for four or five years between pumpings.
Pumping companies will advise frequent (annual) pumping. This is good practice, but may be more frequent than is necessary to protect the proper functioning of your septic system. Since each pumping may cost about $300, you don’t want to pump more frequently than is necessary.
The best advice is to observe the pumping process and gauge how well your habits are treating your septic tank. Little sludge accumulation in your tank, means you can decrease the frequency of pumping. Given the cost of septic systems, be conservative and err on the side of more frequent pumping.
Pressed for Details is written by South Shaker Road resident and former Planning Board member Marc Sevigny, who welcomes your questions about living in Harvard. Send them to PressedForDetails@charter.net.