D1 & D2 Practice Exam 1

What is static head? - Answer-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? - Answer-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? - Answer-95% If the water has low pH, what does it indicate? - Answer-Corrosive water What is the purpose of a mechanical seal? - Answer-Prevents water leakage from the pump What could cause a chlorine gas cylinder to frost? - Answer-Feed rate is too high Which chemicals are formed when chlorine gas is injected into water? - Answer-Hypochlorous acid and hydrochloric acid Which of the following is true about the effectiveness of chlorine? - Answer-The lower the pH, the better the disinfection with chlorine. What does a high C factor for a pipe indicate? - Answer-Smooth pipe interior What is the disadvantage of having a tree formation in the water distribution system! - Answer-Dead-end mains If chlorine is injected into cold water, how would the cold temperature affect the effectiveness of chlorine? - Answer-More contact time would be required If a confined space has 20.9% oxygen content, what does this tell you? - Answer-Confined space is safe to enter What could be the problem if an excessive amount of water is leaking from the stuffing box? - Answer-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? - Answer-Foot valve What problem could arise due to excessive air bubbles in a pipeline? - Answer-Air pocket forms at the high points