FREE WW Collection Systems Questions and Answers

Question 1

What is the generally accepted minimum self-cleansing velocity in a sanitary sewer to prevent the deposition of solids?

Accepted Answer

2.0 fps

Answer

A minimum velocity of 2.0 feet per second (fps) is the industry standard for designing sanitary sewers. This velocity is typically sufficient to keep solids in suspension and prevent them from settling and accumulating in the pipe, which could lead to blockages and reduced capacity.

Question 2

Which piece of equipment is most effective for removing heavy grease blockages from a sewer line?

Accepted Answer

High-Pressure Water Jetter

Answer

A high-pressure water jetter is the most effective tool for clearing grease blockages. The powerful stream of water can cut through the hardened grease, emulsify it, and flush it downstream. Mechanical rodders may poke a hole through the grease but often leave much of the blockage behind.

Question 3

In a wastewater lift station, what is the primary function of a check valve?

Accepted Answer

To prevent backflow into the wet well

Answer

A check valve is a one-way valve installed on the discharge side of a pump. Its purpose is to prevent the water that has just been pumped up the force main from flowing back down into the wet well when the pump shuts off. This prevents the pump from having to re-pump the same water and protects it from backflow damage.

Question 4

The characteristic 'rotten egg' smell in a collection system is caused by the presence of which gas?

Accepted Answer

Hydrogen Sulfide (H₂S)

Answer

Hydrogen sulfide (H₂S) is a gas produced by the anaerobic (without oxygen) decomposition of organic matter containing sulfur. It is well-known for its distinct and unpleasant rotten egg odor. In addition to being an odor nuisance, H₂S is toxic and highly corrosive to concrete and metal pipes.

Question 5

What is the most critical first step that must be taken before an employee enters a manhole?

Accepted Answer

Test the atmosphere with a calibrated gas meter

Answer

Testing the atmosphere within the confined space is the most critical first step. Manholes can contain hazardous atmospheres, including oxygen deficiency, toxic gases (like H₂S), and explosive gases (like methane). A calibrated gas meter must be used to verify the space is safe for entry according to OSHA regulations.

Wastewater Operator Certification Practice Test

Wastewater Operator Certification Practice Test

FREE WW Collection Systems Questions and Answers