Water enters storage tanks through atmospheric humidity and condensation, via leaks or through spill traps around the filler openings of underground tanks. Tank design is part of the problem, especially where water sumps don't drain adequately. Water is the key to microbial growth, Mr. Chesneau said. He believes more water than before is entering the diesel supply, although this is disputed by some in the petroleum industry. Fuel is spending less time in tanks at distribution points, where water used to settle out before the diesel was delivered, he said.
Airborne microbes get into the tanks via leaks or vents.
They also ride on dirt or other debris that finds its way into the system. Once bugs have colonized a fuel system, they establish a complex micro-environment and fuel conditions rapidly deteriorate. Killing the bugs now becomes the easy part. You have to alter the pH to stop the corrosion from continuing. The interior of an underground tank apparently has become a more comfortable place for bugs since the advent of low-sulfur diesel.