To understand the problems of the drainage system it is essential to know how drainage has evolved and the particular areas within the system where failure can occur.
Prior to the 19th Century Public Health Acts, drainage was often simply the ejection of waste into an open gully in the street. A cesspool in the garden (for those properties that had a garden) with a 'privy' above became an alternative.
As a result of the Public Health Acts, local authorities were made responsible for the disposal of all waste material, and a network of below ground drains were developed, often extending into the sea for discharge. Although we may still use the same pipework, the use of sewerage treatment works has radically altered the basis of disposal.
However, the Property Manager, other than understanding that the majority of properties drain into a public system, need not concern himself with this, as any responsibilities relating to it lie with the relevant local or water authority/company.
All modern property is built with a two-type drainage system whereby rainwater and foul water are dealt with separately. The diagram overleaf shows a typical two-pipe system. However, in many cases both pipes will still drain into the same public system, and it is therefore feasible that foul smells can come from the rainwater system.
The use of 'P', 'S' and 'V' traps/bends attached to the WC, bidet, hand basin, sink, bath, shower etc. should prevent smells emitting from the apparatus. In each case the trap retains a level of water which stops smells being transmitted through. They can become blocked with waste material, but are usually readily accessible and can be cleared by physical or chemical means.
The standard problems with foul drainage are:
2. Cracked pipe.
3. Broken seal.
4. Loss of water in trap.
Considering each in turn, a blockage can occur because the fall of the pipe does not give an adequate flow, waste therefore stabilises in the pipe and, over a period of time, blocks further waste flow, as the majority of solid waste flows along the bottom of the pipe. To ensure an adequate flow a 100 mm waste pipe must have a fall of at least 1 in 40.
A cracked pipe below ground can also result in material from the surrounding ground invading the pipe and be the source of the blockage. Alternatively, a crack or a cracked seal can result in smells invading the surrounding area, as both will allow the foul air in the pipe to escape.
The loss of water in the trap will, obviously, allow the foul air to pass through the trap. But how can the water be lost? Normally regular use, assuming no damage to the trap, will keep the water level at the required level. However, in dry weather the water can evaporate if the system is not used for an extensive period.
These checks, in the main, also apply to the rainwater goods. But, due to the open nature of gutters and hoppers, there is an additional problem with blockages causing rainwater to pour over the edge of the gutter or hopper, thereby causing a potential damp problem within the property. Blockages can be caused by leaves, slipped tiles/slates, or as examples, a ball or dead bird. A regular ladder-based check of the gutter is therefore essential, particularly in the autumn in areas where deciduous trees abound.
Septic Tanks and CesspoolsEdit
In some rural areas homes are not connected to mains drainage, and septic tanks or cesspools (cesspits) are used. Originally a brick, stone or concrete box, modern ones are plastic, and all are buried near the property they serve. They collect all waste from the household drains, but a septic tank works like a simple sewage treatment works by separating solids from liquid, which can then soak away.
A cesspool is simply a container that must be regularly emptied, every week in some cases. Modern versions may be emptied less frequently - perhaps 10 times per year. Septic tanks also require 'de-sludging' at least once a year.
The most likely problem with older installations is lack of capacity – our water usage for washing clothes, dishes and ourselves has increased considerably over the years. An average family house should have a septic tank system with a total holding capacity of approximately 1000 gallons.
When a septic tank or its soakaway does not function properly it can cause odour nuisance, flooding and pollution, and it may be determined a statutory nuisance under Section 79 of the Environmental Protection Act 1990. A notice may be served requiring the person responsible for the septic tank to ensure that any nuisance is removed.
If the system is not effectively separating solids from liquids then the effluent leaving the septic tank will in time tend to clog the soakaway, which reduces the permeability of the soil and an excess of sewage in the system will result. This will build up in the drainage pipes and manholes and/or may rise above the soakaway and breakout onto the surface.
To rectify the problem the tank should be de-sludged, and the soakaway may need a jet clean, by a suitable contractor. It is possible that some repair work to the soakaway may be required. Prevention is far better than cure, and it is most important that a septic tank is emptied at least once a year.
In an ideal world with some anaerobic biological action, a good crust layer, regular emptying and adequately vented drainage pipe work a septic tank should not smell. However, it is not uncommon to get the occasional unpleasant odour, and fitting airtight access covers may resolve the issue.