Failures In Real Estate Inspections
The term "failure" (or "failed septic system") has a broader meaning when used in septic inspections for real estate transactions than when used by your local health department.
In either case, sewage coming out of the ground (sometimes called a "blowout") or backing up into the house, usually due to an inability of the leaching area to handle the daily flow, is considered a failure. A repair to the system would be required by the health department to eliminate the health hazard.
However, in inspecting a septic system for real estate transactions there is an attempt to determine how well the system is handling the current discharges from the house and evaluate whether the system will handle the needs of the buyer. If the inspector finds the liquid level in the tank to be abnormally high (higher than the tank outlet pipe feeding the leaching area), it indicates that the leaching area is having trouble soaking down the daily flow. Also, if the liquid level in the leaching area is abnormally high (the components are "underwater") it similarly means there is no reserve soak-down capacity and the system could "blow-out" with just a slight increase in daily flow.
The system may then fail the inspection even though the system has not failed in the eyes of the health department (sewage has not come out of the ground or backed up into the house, causing a health hazard), and the homeowner may be unaware of any problem. This broader meaning of the term "failure" causes some confusion.
Septic inspections became common in the 1980's, after a surge in real estate prices was followed by a drop. Some people walked away from houses that they owed more on than they could get if they sold them. The banks ended up with a few houses that needed expensive septic systems in order to be resold, and after that they started insisting on septic evaluations prior to mortgaging a house. Now it has become routine.
Note: A flood-test (or "push-test", or "flow-test"), where abnormal quantities of water are discharged to a septic system during an inspection, should be avoided. It can lead to wrong conclusions and can damage the system. Consider this: even when a washing machine is dischaging, and at the same time someone flushes a toilet and uses a sink to wash their hands the system receives less than twenty gallons. Observation of this type of normal flow during an inspection is an acceptable practice. Too often, though, these flood-tests are an attempt to overwhelm the system with hundreds of gallons of water. This requires the system to have a surge capacity beyond what most older, functioning systems can demonstrate, and does not help evaluate whether the system will work well on a normal basis for the buyer. Normal flows to a system are intermittent, never steady. The system is sized, and it's function is predicated, on the expectation of this intermittent dosing.
Despite this, flood-tests remain common.