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They sent it in the mail which cost $0.44. They also processed the check which probably cost a few cents as well. If you think about the trees cut to make the paper and the chemicals to make the magnetic ink and carbon footprint of the processing; this check for one cent put a hole is the ozone the size of 2,486 football fields.
Luckily for the Washington Gas Light Company, they probably own a logging company, a magnetic ink company and a company that will sell you carbon credits for a small, outrageous fee. In sending this check, they made $1.3 million dollars.
Thanks @athikerpickle!