Water Supply and Sanitary Engineering MCQ with Answers (NEC Chapter 6)

Chapter 6: Water Supply, Sanitation and Environment MCQ

191 questions with answers. Practise by sub-section or take a timed test.

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Free practice by EngineeringNepal.com.np. Questions are written and checked by our team; always confirm the current exam format in the official notice.

Water Supply, Sanitation and Environment MCQ: what this set covers

Public health engineering appears in the NEC exam, in the Lok Sewa sanitary group and in KUKL and municipal recruitment. These questions cover demand and population forecasting, treatment units, distribution, sewers, BOD and treatment processes, septic tanks, and the BES, IEE and EIA system under the Environment Protection Act 2076.

There are 191 questions in this chapter, each with the answer and a short explanation. Choose a sub-section, pick how many questions you want, and either see the answer straight away or take it as a timed test. Your mistakes are saved in your browser, so you can come back and practise only those.

Code	Sub-section	Questions here
6.1	Water sources, quality and demand	32
6.2	Intake and distribution systems	31
6.3	Water treatment	32
6.4	Sewer design and construction	32
6.5	Wastewater treatment and disposal	32
6.6	Environmental assessment and disasters	32

Sample questions with answers

A few questions from each sub-section are shown below. Tap a question to see the answer. Use the practice tool above for the full set.

6.1 Water sources, quality and demand

A geological formation that holds water in its pores but cannot transmit it in usable quantity, such as a thick clay bed, is called:

Aquifer
Aquiclude
Aquifuge
Perched water table

Answer: B. An aquiclude (e.g. clay) is porous and stores water but its permeability is too low to yield water. An aquifuge (e.g. solid granite) neither stores nor transmits water.

A well tapping a confined aquifer in which water rises above the ground surface without pumping is known as:

Dug well
Gravity well
Flowing artesian well
Infiltration well

Answer: C. In a confined aquifer the water is under pressure; when the piezometric surface lies above ground level, water flows out on its own and the well is a flowing artesian well.

6.2 Intake and distribution systems

A river intake for a town water supply should preferably be located:

Just downstream of the town's sewage outfall
Upstream of the town and its waste discharge points
At the outer side of a sharp bend where scour is greatest
Where the river is shallowest in the dry season

Answer: B. Locating the intake upstream of the town keeps it away from its own sewage and drainage, and it should also be on a stable, straight reach with adequate depth in the dry season.

Reservoir and lake intake towers are provided with inlet ports at several levels mainly to:

Reduce the cost of the tower
Increase the velocity of entry
Draw water of the best available quality as the water level changes
Allow fish to pass downstream

Answer: C. Water quality varies with depth (algae near the top, silt and low oxygen near the bottom) and the level fluctuates, so multi-level ports let the operator draw the best layer.

6.3 Water treatment

A rectangular sedimentation tank is 30 m long, 10 m wide and 4 m deep. If it treats 6 ML of water per day, the detention time is:

2.4 hours
4.0 hours
4.8 hours
6.0 hours

Answer: C. Volume = 30 x 10 x 4 = 1200 m3. Flow = 6000 m3/day = 250 m3/h. Detention time = 1200 / 250 = 4.8 h.

A settling tank 30 m long and 8 m wide receives 4800 m3 of water per day. Its surface overflow rate is:

2 m3/m2/day
40 m3/m2/day
200 m3/m2/day
20 m3/m2/day

Answer: D. Surface overflow rate = Q / plan area = 4800 / (30 x 8) = 4800 / 240 = 20 m3 per m2 per day.

6.4 Sewer design and construction

In a separate system of sewerage:

Sanitary sewage and storm water are carried in two different sets of sewers
Sanitary sewage and storm water flow in the same sewer
Only storm water is collected
Part of the storm water, mainly from roofs, enters the sanitary sewer

Answer: A. The separate system has one sewer for domestic and industrial wastewater and another for storm water. When some roof and yard water is admitted into the sanitary sewer it is called a partially separate system.

A major disadvantage of the combined system of sewerage is that:

Self-cleansing velocity is never achieved
It needs two sets of pipes in every street
The treatment plant receives very large and variable flows during rain
House connections are impossible

Answer: C. Combined sewers are large and carry diluted sewage in storms, overloading treatment plants and pumps; overflows discharge untreated sewage to rivers.

6.5 Wastewater treatment and disposal

The conventional BOD5 test used in textbooks and Nepal's effluent standards is carried out by incubating the sample for:

5 days at 20 degrees C
2 days at 30 degrees C
5 days at 35 degrees C
24 hours at 20 degrees C

Answer: A. BOD5 at 20 degrees C is the conventional measure of the oxygen used by microorganisms in aerobic decomposition of organic matter. (Indian IS 3025 also allows an equivalent 3-day test at 27 degrees C.)

In a BOD test, 5 ml of sewage is diluted to 300 ml. The initial DO is 8 mg/l and the DO after 5 days is 2 mg/l. The BOD5 of the sewage is:

6 mg/l
120 mg/l
360 mg/l
480 mg/l

Answer: C. Dilution fraction P = 5/300 = 1/60. BOD5 = (D1 - D2) / P = (8 - 2) x 60 = 360 mg/l.

6.6 Environmental assessment and disasters

In Nepal's environmental assessment system, BES stands for:

Basic Environmental Survey
Baseline Ecological Study
Brief Environmental Study
Biological Environment Statement

Answer: C. Brief Environmental Study (BES) is the lowest level of environmental study introduced by the Environment Protection Act 2076, below IEE and EIA.

Under the Environment Protection Act 2076, depending on its nature and size, a development proposal requires which level of environmental study?

BES, IEE or EIA
IEE or EIA only
PEE, IEE or EIA
Only EIA for all projects

Answer: A. EPA 2076 and EPR 2077 classify proposals into three levels: Brief Environmental Study, Initial Environmental Examination and Environmental Impact Assessment, according to the schedules.

Full mock tests

When you have covered every chapter, take a full NEC licence mock test or Lok Sewa model test. The NEC mock follows the real pattern of 80 questions and 100 marks in 2 hours.