Engineers' Angle | Stinky problem, absorption pits
Several persons who have problems with their absorption pits have found the use of a cesspool emptier inconvenient and costly. They have repeatedly asked for suggestions for a permanent fix to this issue.
A failing absorption pit can become a source of pollution and a public-health concern. Further, the problem may contribute to damage of property, depreciation in the value of the real estate, pollution in ground and surface water, and outbreaks in disease. Once an absorption pit fails to operate effectively, efforts should be made to apply curative measures.
There are some basic considerations to ensure that your absorption pit works properly for the longest possible time, but first the operation of an absorption pit will be explained.
An absorption pit, with the absence of a septic tank, operates as primary and secondary treatment systems. The process of treating the waste can simply be described as follows.
1. Effluent entering the pit from a building consists of both liquid and solids.
2. The effluent is broken down by naturally occurring bacteria.
3. The liquid is then removed from the pit by percolation through the surrounding wall and soil.
Considering the steps in the process, the operation of the absorption pit can be affected by a number of issues. First, harmful chemicals, especially from detergents, can kill useful bacteria, and this action then slows down the decomposition of waste.
With no intervention, the pit will become less efficient and, over time, become clogged with heavy sludge. Second, the soil in the vicinity of the pit may have poor percolation as a result of its nature and this could lead to the pores in the soil becoming blocked or saturated.
This would again result in the reduction of the percolation rate of the treated waste and, with time, the accumulated liquid and solid exceed will the capacity of the pit.
Possible solutions to the problem of blockage are:
a) Connect your waste pipe to the public sewer system. The National Water Commission is extending the sewer network in the city, and if the service is available, the utility company will facilitate the request for connection. The flow of waste to the public system prevents the contamination of the groundwater.
b) In the absence of a public sewer system, consider installing a septic tank. This provision helps to treat and break down solids, hence reducing the possibility of the pit becoming clogged.
c) Blockages to your absorption pit may require some form of cleaning or replacement of the perimeter wall. In the past, cleaning was done manually, with someone entering the absorption pit and cleaning the sides (with the proper gear). This practice is, however, not encouraged in most areas because of health, safety and environmental concerns. However, there are chemicals that are available to unblock pits clogged by sludge. Additionally, the material forming the wall of the chamber can be replaced. An expert visiting your home could give you a definite solution.
d) One method of prolonging the lifespan of absorption pit is to reduce the amount of chemicals, especially detergents, entering the pit. This will help to preserve bacteria that aid in breaking down and treating the sewage.
e) Grease traps are used to trap fatty oils, grease, and sludge, and to separate the oil from water. Without the traps, oil and grease enter the absorption pit and clog the pores in the soil and subsequently reduce the percolation rate. To clean the trap, the lid of the grease trap should be removed and the accumulated grease and oils extracted on a regular basis. The interval between cleaning will depend on the amount of grease generated from your activities, but a good practice is to inspect and clean at least once per month.
Generally, it is always better to ensure that your sewage disposal system is designed and constructed by a professional according to best practices. The location for your absorption pit is also critical. Pits located in water-logged areas are more likely to have problems. A well-designed system should perform adequately for 25 to 30 years.
- Damian Cummings is a professional civil engineer who lectures in the Civil Engineering Department in the School of Engineering at the University of Technology, Jamaica. Send questions and comments to, firstname.lastname@example.org or email@example.com. You may also leave your comments for the JIE's Technical Committee at our Facebook page: Jamaica Institution of Engineers JIE.