This set of Civil Engineering Drawing Multiple Choice Questions & Answers (MCQs) focuses on “Design of Septic Tanks”.
1. A __________ is a chamber made of concrete, fiberglass, PVC or plastic, through which domestic wastewater, sewage flows for primary treatment.
a) drainage tank
b) pit latrine tank
c) harvesting water tank
d) septic tank
Explanation: Septic tank systems are a type of onsite sewage facility (OSSF). They can be used in areas that are not connected to a sewerage system, such as rural areas. The treated liquid effluent is commonly disposed in a septic drain field which provides further treatment. However, groundwater pollution may occur and can be a problem.
2. The term “septic” refers to ____________
a) anaerobic bacterial environment that develops in the tank
b) refers to safety and precaution
c) drainage of waste materials
d) aerobic bacterial environment that develops in the tank
Explanation: The term “septic” refers to the anaerobic bacterial environment that develops in the tank which decomposes or mineralizes the waste discharged into the tank. Septic tanks can be coupled with other onsite wastewater treatment units such as biofilters or aerobic systems involving artificially forced aeration.
Explanation: A septic tank collects and treats wastewater at a property that is not connected to the mains sewer system. Installed underground, a septic tank makes use of natural processes to treat the sewage it stores. Usually made up of two chambers or compartments, the tank receives wastewater from an inlet pipe. Wastewater enters the first chamber and separates over time, with solids settling at the bottom, oils and greases forming a layer of scum at the top, and a layer of relatively clear water remaining in the middle.
4. Septic tank is usually consists of brick wall in cement not less than _______
a) 20 cm
b) 100 cm
c) 80 cm
d) 200 cm
Explanation: Septic tank is usually consists of brick wall in cement not less than 20cm(9”) thick and the foundation floor are of cement concrete 1:3:6 or 1:2:4. Both inside and outside faces of wall and floor are plastered with a minimum thickness of 12mm thick cement mortar 1:3 and all inside corners are rounded.
5. Connecting pipe should be _______ mm minimum diameter.
Explanation: It may be of R.C.C, Hume pipe, cast iron pipe, S.W. Inlet and outlet may be made through T-junction pipe or baffle wall of precast R.C.C. may be provided at a distance 1/5 of length of the septic tank so that the inlet sewage may not disturb the working of the tank.
6. Soak pit shall not be less than ____________
a) 45 cm
b) 90 cm
c) 50 cm
d) 100 cm
Explanation: Soak pit shall not be less than 90 cm in diameter and not less than 1.5 m in depth below invert level of the inlet pipe. The pit is constructed with lining of dry brick or stone with open joints backed with at least 7.5 cm thick coarse aggregate.
7. A _________ is a type of toilet that collects human faeces in a hole in the ground.
b) septic tank
c) pit toilet
Explanation: A pit latrine or pit toilet is a type of toilet that collects human faeces in a hole in the ground. They use either no water or one to three litres per flush with pour-flush pit latrines. When properly built and maintained they can decrease the spread of disease by reducing the amount of human faeces in the environment from open defecation. This decreases the transfer of pathogens between faeces and food by flies.
8. The pit is typically at least ____________ deep and ___________ across.
a) 14 meters, 10 m
b) 30 meters, 15 m
c) 3 meters, 1 m
d) 11 meters, 9 m
Explanation: The World Health Organization recommends they be built a reasonable distance from the house balancing issues of easy access versus that of smell. The distance from groundwater and surface water should be as large as possible to decrease the risk of groundwater pollution. The hole in the slab should not be larger than 25 cm (9.8 inches) to prevent children falling in. Light should be prevented from entering the pit to reduce access by flies. This may require the use of a lid to cover the hole in the floor when not in use.
9. The size of the faeces drop hole in the floor or slab should not be larger than ____________
b) 25 cm
c) 45 cm
d) 250 mm
Explanation: The user positions themself over the small drop hole during use. The size of the feces drop hole in the floor or slab should not be larger than 25 centimeters (9.8 inches) to prevent children falling in. Light should be prevented from entering the pit to reduce access by flies. This requires the use of a lid to cover the hole in the floor when not in use. However, in practice, such a lid is not commonly used as it is easy to lose it or for the lid to get very filthy.
10. As of 2013 pit latrines are used by an estimated ____________ people.
a) 1.77 billion
b) 2.77 million
c) 1.77 billion
d) 4.66 billion
Explanation: This is mostly in the developing world as well as in rural and wilderness areas. In 2011 about 2.5 billion people did not have access to a proper toilet and one billion resort to open defecation in their surroundings. Southern Asia and Sub-Saharan Africa have the poorest access to toilets. In developing countries the cost of a simple pit toilet is typically between 25 and 60 USD. Ongoing maintenance costs are between 1.5 and 4 USD per person per year which are often not taken into consideration.
11. As a very general guideline it is recommended that the bottom of the pit should be at least _______ above groundwater level.
a) 0.5 m
b) 2 m
c) 12 m
d) 20 m
Explanation: As a very general guideline it is recommended that the bottom of the pit should be at least 2 m above groundwater level, and a minimum horizontal distance of 30 m between a pit and a water source is normally recommended to limit exposure to microbial contamination.However, no general statement should be made regarding the minimum lateral separation distances required to prevent contamination of a well from a pit latrine. For example, even 50 m lateral separation distance might not be sufficient in a strongly karstified system with a down gradient supply well or spring, while 10 m lateral separation distance is completely sufficient if there is a well developed clay cover layer and the annular space of the groundwater well is well sealed.
12. A _____________ houses the squatting pan or toilet seat and provides privacy and protection from the weather for the user.
Explanation: A shelter, shed, small building or “super-structure” houses the squatting pan or toilet seat and provides privacy and protection from the weather for the user. Ideally, the shelter or small building should have hand washing facilities available inside or on the outside (e.g. supplied with water from a rainwater harvesting tank on the roof of the shelter) although this is unfortunately rarely the case in practice. In the shelter, anal cleansing materials (e.g. toilet paper) and a solid waste bin should also be available. A more substantial structure may also be built, commonly known as an outhouse.
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