Environmental Engineering
The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about

0.05 to 0.5 ppm
0.5 to 1.0 ppm
1.0 to 5.0 ppm
0.01 to 0.05 ppm

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Environmental Engineering
Scour valves are provided

At every summit of rising mains
At the foot of rising main along the slope to prevent back running of water
At street corners to control the flow of water
At every depression and dead ends to drain out the waste water that may collect there

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