The black oily sheen that showed up in Calvary Cemetery in South Portland this summer looked like countless other spills.
But pollution investigators working with forensic chemists determined with the certainty of a DNA sample that the oil came from a malfunctioning piece of equipment at the Rigby Rail Yard a half-mile away.
Environmental law enforcement officers charged with tracking down polluters and ensuring they pay for cleanup are using techniques similar to those found in police crime labs to fix blame and hold people accountable for the damage to wildlife and habitat.
"There are what we call fingerprints," said Chief Petty Officer Ann Logan, marine science technician with the Coast Guard in South Portland. "Everybody's bilge is a little bit different. Everybody's fuel tank is a little different. Some may have residual water from another place they've been."
That telltale rainbow pattern on the surface of the water, as unnaturally attractive as it is deadly to the marine environment, represents a complex mixture of molecules minutely different for every batch of oil and every tank of gasoline.
Chemists are able to separate the petroleum products from the water in a sample, then measure those thousands of components precisely to determine whether they have a match. "We can tell the difference between different tanks on the same ship depending on the quantities and the cargo and so forth," said Wayne Gronlund, manager of the Coast Guard's Marine Safety Laboratory in Groton, Conn. The lab handles oil spill fingerprinting cases from across the country. The Maine DEP relies on the Health and Environmental Testing Lab in Augusta for similar analysis.
Like traditional police work, forensic science is no substitute for shoe leather detective work. The technology that labs use to analyze oil samples can tell basically what type of petroleum product a spill is -- diesel, gasoline, heating oil -- but it can't say where it originated. To find a match, chemists need samples taken from suspects.
To find them, investigators track the oil sheen, but that can be misleading because of the winds and currents that move oil around, and the movement of boats themselves. They also look for an incriminating stain on boats.
In the Calvary Pond spill, members of the Coast Guard and the state DEP teamed up to track the source. The state agency handles most spills on land and in fresh water, but because the Calvary Pond drains directly into the Fore River, the Coast Guard also shared jurisdiction.
When the first spill occurred in August, investigators started taking samples from several likely suspects, including a nearby oil change service station.
When they realized the spill was emanating from the stormwater system, they started opening manhole covers looking for oily residue. Through the process of elimination, they were able to work their way back to the drains coming from the rail yard. Samples showed the oil came from a malfunctioning oil-water separator that was overwhelmed during a large rain, spilling about 500 gallons of waste oil into the stormwater system.
The yard's owner, Portland Terminal Co., at first disputed its responsibility, according to the DEP. But confronted with the chemical analysis, it acquiesced.
State officials say the cleanup costs for the spill could top $200,000 and the yard will have to undergo an elaborate environmental assessment to prevent future spills.