D61 MASTER THE DAY

What type of manhole is constructed at the start of a branch sewer and is less than 1m deep?

• Normal manhole
• Drop manhole
• Shallow manhole
• Deep manhole

Answer explanation

Shallow manholes (0.75–0.9m) are inspection chambers constructed at the start of branch sewers.

Which zone of pollution is known for maximum anaerobic decomposition and gas evolution?

• Clear water zone
• Zone of active decomposition
• Zone of recovery
• Zone of degradation

Answer explanation

In the active decomposition zone, DO reaches zero and anaerobic processes dominate with H2S evolution.

Which type of storm regulator works on siphonic action to divert excess water?

• Leaping weir
• Overflow weir
• Siphon spillway
• Catch basin

Answer explanation

Siphon spillways use siphonic action to move excess stormwater from the combined sewer to channels.

In which type of lake does the euphotic zone extend up to the hypolimnion?

• Mesotrophic lake
• Eutrophic lake
• Oligotrophic lake
• Senescent lake

Answer explanation

Oligotrophic lakes are deep with clear water; light penetrates to the hypolimnion supporting equilibrium.

What is the minimum cover diameter for a circular manhole cover as per IS?

• 40 cm
• 50 cm
• 60 cm
• 70 cm

Answer explanation

IS 1742 recommends a minimum diameter of 50 cm for circular manhole covers.

What happens during thermal stratification in lakes during summer?

• Water becomes uniform in temperature
• Epilimnion rises and mixes
• Three distinct layers form
• Water freezes

Answer explanation

During summer, lakes stratify into epilimnion, metalimnion, and hypolimnion due to temperature differences.

Which material is typically used for manhole walls?

• PVC
• Steel
• Brick, stone or concrete
• Plastic

Answer explanation

Manhole walls are made from brickwork, stone masonry or concrete for strength and durability.

Where are grease traps usually located in a sewer system?

• At sewer outlet
• Near sewage treatment plant
• Near kitchens and garages
• At inlets

Answer explanation

Grease and oil traps are installed near kitchens, garages or workshops to remove fats before sewage entry.

Which pipe is inclined from sewer to ground surface and covered at top?

• Drop pipe
• Lamp hole
• Cleanout
• Flushing pipe

Answer explanation

Cleanouts are inclined pipes ending at ground level, used for cleaning where manholes are not provided.

What is the effect of adding lime to a eutrophic lake?

• Reduces nitrogen
• Increases turbidity
• Removes phosphorus
• Promotes algal bloom

Answer explanation

Lime is added to eutrophic lakes to remove phosphorus and control eutrophication.