Arsenic and an Old Roof
Picture a hazardous waste containment facility with large tanks of arsenic being stored until it could be properly disposed. The vats were sitting on concrete secondary containment. The owner hired an unlicensed consultant to design a new roof for the building, who gave the project to a friend of his to re-cover a built-up roof and even added a little extra gravel to the roof to be sure it was well covered.
After the new roof was installed, there were approximately 10 pounds per square foot of built-up roofing and 17 pounds per square foot of re-cover roofing material on a structural steel deck designed for 20 pounds dead load per square foot and 20 pounds live load per square foot. In addition, re-cover drains were installed that reduced the size of the drainage pipes to about one-third of the required amount.
Because the size of the drains were reduced, the water built up on the roof to the overflows during the next heavy rain — four inches of water at waters weight of approximately 62 pounds per cubic foot. Guess what ended up with the arsenic in the secondary containment? You do the math.
Moral: Hire a competent contractor who makes sure the structure can withstand the weight of the designed roof.
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