My totally non-swag is that someone is reading as a category on a worksheet something that is a subcategory of something.   I'm guessing that Public Works tracks the supplies and equipment for drainage in a sub-account of Public Works Supplies and Equipment.  Apparently though they do not have similar ( or maybe they do and no one has pointed them out) accounts in their Labor account and other main accounts.  As Joe has often pointed out  it would take a week of coaching from our bookkeeper to really be able to come up with the real number.