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A system consisting of a septic tank and percolation area is frequently used for the treatment of sewage from a dwelling house in a rural setting - Leaving Cert Construction Studies - Question 8 - 2006
Question 8
A system consisting of a septic tank and percolation area is frequently used for the treatment of sewage from a dwelling house in a rural setting. (a) Using notes a... show full transcript
Worked Solution & Example Answer:A system consisting of a septic tank and percolation area is frequently used for the treatment of sewage from a dwelling house in a rural setting - Leaving Cert Construction Studies - Question 8 - 2006
Step 1
Design of the septic tank
Answer
The design of the septic tank consists of pre-cast units or can be constructed on site. It generally has the following characteristics:
- The tank receives wastewater from the dwelling house via a dip pipe with a diameter of 100 mm.
- It is constructed on a reinforced concrete foundation.
- The minimum size of the tank is 2725 litres.
- The tank length should be three times its width, and it must maintain a minimum distance of 1.5 metres below the water level.
- The capacity of the tank can be calculated using the formula:
where P is the number of persons served (minimum of 4 persons). - The tank may be pre-cast or built in situ.
Step 2
Location of the septic tank
Answer
The location of the septic tank must adhere to the following guidelines:
- It should be at a minimum distance of 7 meters from the dwelling it serves and at least 20 meters from the nearest point of any other dwelling.
- The site must be suitable for regularly emptying when needed.
- The tank must be installed in an area where adequate percolation can be achieved. It is important to perform percolation tests on all sites where a dwelling house is to be built.
- Additionally, the tank must be located at least 3 meters from a road or boundary and at least 30 meters away from any well or drinking source.
Step 3
Function of the percolation area
Answer
The function of the percolation area is crucial for treating septic tank effluent, and it serves to:
- Facilitate the percolation of the septic tank effluent and replace soils that act as the final stage of treatment.
- Allow wastewater to infiltrate the soil, where it is further treated by the action of aerobic bacteria.
- Prevent effluent from reaching the underlying groundwater directly, promoting filtration before entering the aquifer.
Step 4
List one advantage and one disadvantage of a septic tank and percolation area system
Answer
Advantages of a septic tank and percolation area:
- It is suitable for dwelling houses in rural areas as it offers an independent sewage treatment solution and does not require connection to a municipal sewage system.
- It is a relatively cheap system to operate and requires low maintenance if constructed properly.
Disadvantage:
- It may not adequately treat the waste in rural areas, leading to potential pollution of nearby watercourses. There is a risk of the effluent reaching rivers and wells, which can be harmful to the environment.