D2 Practice 1 Flashcards
What is static head?
The vertical distance between a reference point to the water surface, when the water is not moving
How long must water remain stagnant and undisturbed in the pipe before a first-draw sample is collected for lead and copper analysis?
At least 6 hours
If at least 40 samples per month are collected from a public water system, what is the minimum percentage of routine/repeat samples that must test negative for total coliform?
95%
If the water has low pH, what does that indicate?
Corrosive water
What is the purpose of a mechanical seal?
Prevents water leakage from the pump
What could cause a chlorine gas cylinder to frost?
Feed rate is too high
Which chemicals are formed when chlorine gas is injected into water?
Hypochlorous acid and hydrochloric acid
What’s true about the effectiveness of chlorine?
The lower the pH, the better the disinfection with chlorine
What does a high C factor for a pipe indicate?
Smooth pipe interior
What is the disadvantage of having a tree formation in the water distribution system?
Dead-end mains
If chlorine is injected into cold water, how would the cold temperature affect the effectiveness of chlorine?
More contact time would be required
If a confined space has 20.9% oxygen content, what does this tell you?
Confined space is safe to enter
What could be the problem if an excessive amount of water is leaking from the stuffing box?
Packings may need to be replaced, or the packing gland may need to be tightened
What is installed on the suction pipe of a pump to prevent water from draining out of the pump, and towards the suction pipe?
Foot valve
What problem could arise due to excessive air bubbles in a pipeline?
Air pocket forms at the high points
What is formed when chlorine reacts with ammonia?
Chloramine
What is the disadvantage of using ozone for disinfection?
Lack of disinfectant residuals
Which water source is the most protected from pathogens?
Deep well
What is used to restrict leakage from the impeller discharge to the pump suction?
Wear rings
What is trihalomethane?
Disinfection by-product (DBP)
What is the recommended minimum flushing velocity?
2.5 ft/s (5 ft/s preferred)
What is monochloramine?
Combined chlorine
Which of the following is the most powerful disinfectant?
Monochloramine, chlorine, dichloramine, trichloramine
Chlorine
What is the advantage of a compound meter?
It’s capable of measuring a wide range of flow