Drainage, Waste & VentQuestion 9 of 120
A 3 in horizontal drain is run 72 ft at 1/8 in per ft. The invert at the upstream end is at elevation 100.00 ft. What is the invert elevation at the downstream end?
a.99.85 ft
b.99.90 ft
c.99.25 ft
d.98.50 ft
Explanation
The fall is 72 ft x 1/8 in = 9 in, and 9 in equals 0.75 ft, so the downstream invert is 100.00 - 0.75 = 99.25 ft. The 99.85 ft and 99.90 ft answers understate the drop by treating the fall as inches of elevation rather than converting to feet, and 98.50 ft doubles the correct fall.
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