Cesspool

A cesspit, or cesspool, is a term with various meanings: it is either used to describe an underground holding tank (sealed at the bottom) or a soak pit (not sealed at the bottom). It can be used for the temporary collection and storage of feces, excreta or fecal sludge as part of an on-site sanitation system and has some similarities with septic tanks or with soak pits. Traditionally, it was a deep cylindrical chamber dug into the earth, having approximate dimensions of 1 metre diameter and 2–3 metres depth. Their appearance was similar to that of a hand-dug water well.

The pit can be lined with bricks or concrete, covered with a slab and needing to be emptied frequently when it is used like an underground holding tank. In other cases (if soil and groundwater conditions allow) it is not constructed watertight, to allow liquid to leach out (similar to a pit latrine or to a soak pit).

In the UK a cesspit is a sealed tank for the reception and temporary storage of sewage; in North America this is simply referred to as a "holding tank". Because it is sealed, the tank must be emptied frequently — in many cases as often as weekly. Because of the need for frequent emptying, the cost of maintenance of a cesspit can be very high.

A cesspool was at one time built like a dry well lined with loose-fitting brick or stone, used for the disposal of sewage via infiltration into the soil. Liquids leaked out through the soil as conditions allowed, while solids decayed and collected as composted matter in the base of the cesspool. As the solids accumulated, eventually the particulate solids blocked the escape of liquids, causing the cesspool to drain more slowly or to overflow.

A biofilm forms in the loose soil surrounding a cesspool or pit latrine which provides some degree of attenuation of the pollutants present, but a very deep cesspool can allow raw sewage to directly enter groundwater with minimal biological cleansing, leading to groundwater pollution and undrinkable water supplies. It is for this reason that deep water wells on the property must be drilled far from the cesspool.

Most residential waste cesspools in use in the US today are rudimentary septic systems, consisting of a concrete-capped pit lined with concrete masonry units (cinder blocks) laid on their sides with perforated drain field piping (weeping tile) extending outward below the level of the intake connection. The concrete cover will often have a cleanout pipe extending above ground. Some are constructed with concrete walls on one or more sides.

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