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Solids: The Enemy of the Septic Tank and aerated wastewater

September, 11th, 2016

When a tank inspection reveals excessive solids accumulation, sticking with a three- to five-year pumpout schedule is not enough.

If a tank is operating properly, solids are retained and take up increasingly more volume. At some time they must be removed. (If there is little accumulation of solids, either the household is extremely conservative with water use and waste generation or there is a problem causing solids to pass through the tank.)

When there is little clear zone left, proper solids separation will no longer occur, detention time for settling is further reduced, and solids will wash out of the tank, eventually clog the soil treatment area, and cause system failure.

Research on solids accumulation shows the interval between pumping depends on tank size, number of people in the house, and the nature of the sewage (which in turn depends on household habits and lifestyles). Many Local Governments recommend a three- to five-year pumpout interval. This interval is probably reasonable, but checking sludge levels at the time of service can provide a better estimate for the necessary pumpout interval.

Solids are the enemy of a septic tank, but unfortunately many tanks are not regularly assessed for accumulation.

Does your septic tank have an effluent filter, is the effluent filter clogging regularly? Most septics do not have a filter but they are cheap prevention to having a clogged drain field, however they require periodic cleaning and an accurate way of detecting your tank requires pumping.

Also is your aerated wastewater treatment system (AWTS) burning out pumps? This can also mean the sludge level is high and has moved throughout the tank and requires pumping out the solids.

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