The Google link isn't showing the print.
However that figure at first sounds like gross overkill.
Back in the 70's early 80's when I had a specialist photographic company we put a life-size photograph of a F1 racing powerboat on the side of a truck, that was 5' x17'. The Developer, stop & fixer were sprayed onto the emulsion. That took a maximum of around 20 litres of Developer, less than 10 litres stop bath and probably 40 - 50 litres of Fixer.
So multiplying those figures by 3 for the 5' x 40' enlargement gives:
60 litres Dev = 16 US gallons,
less than 25 litres stop bath = 6.6 US Gallons
120 -160 litres Fixer = 32-40 US Gallons,
My figures are all erring on the high side. We always processed with over capacity on stop bath & fixer as they kept well, only developer would have been made up in fresh batches, So that indicates those 500 gallon figures are way out of proportion.
Ian