Frequently I am asked whether pumping is required during a septic tank inspection to determine if it is watertight, structurally sound and operating properly. My answer to that question is always an emphatic YES!

Many state and local governments struggle with this question for inspections conducted to determine system compliance or at the time of real estate transfer. The bottom-line discussion usually starts with a mention of the additional pumping cost to the homeowner and the insistence by some professionals that the watertightness and soundness of a tank can be determined by simply observing the contents and its operating level.

While these are two important conditions that should be evaluated during tank inspection, they do not tell the inspector or permitting authority everything they need to know to be assured the tank is watertight and operating the way it should.

EXAMINE THE LAYERS

The contents of the tank should be separated into three distinct layers: a sludge layer at the bottom of the tank, a clear liquid zone and a floating scum layer. If these do not exist, the inspector must determine if there is a problem with the tank itself or with the homeowner’s usage of the system. The operating level of the tank should be at the invert of the outlet. If the water level is above the invert, there is likely a problem downstream; if it is below this level, the tank is probably leaking.

Watertightness is the key to whether the tank is acceptable or not. If a tank is not watertight, there can be at least two types of problems. First, excess water can enter the tank and move to the drainfield, causing premature hydraulic failure. And untreated wastewater from a leaky tank presents a health risk to humans and can contribute to environmental problems such as phosphorus contributions to surface waters, causing algal blooms.

While operating at the proper level is an indicator that the tank is in good condition, pumping the tank will allow the inspector to visually evaluate tank walls, corners where walls and the lid meet, tank seams, openings and the tank bottoms for signs of cracks and leakage.

An argument against pumping tanks during inspections in my part of the world deserves some discussion. Here’s how it goes:

“It is common knowledge that a septic tank should not be pumped during the winter or just before winter because doing so removes the biological activity that generates heat, which keeps a tank from freezing.” Or, “Conversely, an empty tank is susceptible to cracking as the surrounding soil freezes and expands. … Thousands of seasonal lakeshore properties that are not occupied during the winter will be at risk.” And, “In areas with high water tables, an empty tank could pop out of the ground due to frost heaving.”

ANAEROBIC DIGESTION

Septic tanks are actually mini-anaerobic digesters, and pretreatment of the wastewater is through the processes of anaerobic digestion. Anaerobic digestion is a complex set of processes through which bacteria break down organic matter without oxygen. As the bacteria “work,” they generate biogas. They do not generate heat in the process; in fact, for the process to be most efficient at breaking down the organic material, the temperature should be about 95 degrees F. As an aside, the most common biogases produced are methane and carbon dioxide. This is why proper tank venting is so important; without venting, the gases can accumulate to toxic and explosive levels.

At temperatures less than 95 degrees F, the process is less efficient and there will be additional solids accumulation. This is probably the reason we need to pump our tanks in colder northern climates more often as part of regular maintenance than in the South or West. We see less breakdown and more solids accumulation in Wisconsin and Minnesota, for example. The temperature of the tank in the winter is dependent on all use factors, including the temperature of the water put in, whether the tank is insulated and the extremes of our climate.

If the tank is not going to be used, there would be some concern about soil pressures due to freezing and thawing, as well as potential tank buoyancy problems. But these inspections are to be conducted on operating systems, so sewage will quickly be returned to the tank from the house and the risk would be no higher for these problems than pumping the tank in the middle of the summer.

This is an example where the lack of knowledge about the processes involved in wastewater treatment can result in bad regulatory decisions, such as deciding not to have tanks pumped during inspections.