1. What is the maximum allowable velocity in public water mains?
a) 3 ft/sec
b) 8 ft/sec
c) 10 ft/sec
d) 12 ft/sec
Explanation: The velocity of 3 ft/sec is considered to be minimum to keep the foreign particles moving in sewers. The Washington State Department of Health (DOH) recommends a maximum velocity of 8 ft/sec but permits greater velocities during fire flow conditions.
2. The increasing flow velocity in water systems not only creates noise but also leads to the wear and tear of the pipes.
a) True
b) False
Explanation: The minimum flow velocity is 3 ft/sec to keep the foreign particles moving. In certain mains higher velocity is required such as fire hydrants. If the velocity is increased higher than the limits, the foreign particles moving with higher speeds may cause abrasion against the inner walls of the sewer which leads to wear and tear of the sewers.
3. Storm water is collected from streets into the __________ which in turn discharged into main drains of open type.
a) Link drains
b) Lateral drains
c) Sub mains
d) Interseptal mains
Explanation: Lateral drains are small diameters of pipe which is aligned on one side of the curb line that collects wastewater from different sources like residences, schools, etc. Link drains collect storm water from streets and conveys it to the min drains.
4. The depth in open drain should preferably be kept _______ the man height.
a) Less than
b) Greater than
c) Equal to
d) Sufficient to
Explanation: Open drains often carry storm water. In rainy seasons the water level increases in the drains. If it contains clogging or any operations to be done, it becomes difficult if the depth is more.
5. Which of the following is considered if sewers are placed on the softer grounds?
a) The trench is excavated to confirm the shape of the pipe
b) Sewers are laid embedded in the concrete
c) The width of the trench is kept to 15 cm
d) The desired slope is considered
Explanation: The bottom of the trench is kept at a width of 15 cm and top as 60 cm. This is to facilitate the joining of pipes. When the ground is not hard enough, it becomes necessary to insert pipes on harder surfaces. Hence sewers are embedded in concrete surfaces.
6. In India which type of sewer systems are preferred?
a) Partial
b) Combined
c) Direct
d) Separate
Explanation: It becomes uneconomical to lay separate systems for both sanitary sewage and stormwater. Hence a combined system is used in countries like India which is a developing country and also because the rainfall is moderate.
7. Partial sewers carry a part of stormwater to sanitary sewers.
a) True
b) False
Explanation: In partial sewer systems a part of stormwater during rain is allowed to enter sanitary sewer while the remaining stormwater is carried through open drains to the point of disposal.
8. Two sets of sewers are laid in _________ system.
a) Partial
b) Separate
c) Combined
d) Partially combined
Explanation: In separate systems, two sets of sewers are laid. The sanitary sewage is carried through sanitary sewers while the storm sewage is carried through storm sewers. The sewage is carried to the treatment plant and stormwater is disposed of to the river.
9. Which of the following is an advantage of separate sewers?
a) Rivers are polluted
b) Size of the sewers are small
c) It proves economical
d) Nuisance potential is reduced
Explanation: In separate sewer systems, as two sets of sewers are used, the quantity of wastewater flow will also be less in sewers. Hence the size of the sewers will be small. As two sewers are used, it doesn’t prove to be economical.
10. When only one set of sewers are used to carry both sanitary sewage and storm water, it is called as __________ system.
a) Partial
b) Direct
c) Combined
d) Separate
Explanation: In separate systems, two sets of sewers are used to carry sanitary sewage and storm/ surface water separately. In the combined system, a single sewer with a larger size is used to carry both sanitary sewage and surface water together.