By Melissa Gaskill of Nature magazine

There is only one official source of data on pollution caused by offshore drilling in U.S. waters: the National Response Center, an online reporting system for oil and chemical spills managed by the U.S. Coast Guard. But watchdog groups say that the system's reliance on self-reporting means its data are fundamentally flawed.

One of those groups is SkyTruth of Shepherdstown, W. Va., founded by geologist John Amos in 2001 to monitor the effects of human activity on the environment using remote-sensing and mapping technologies. Amos monitored satellite images of the Gulf of Mexico during the Deepwater Horizon disaster, noticed a separate slick, and traced it to the former Taylor Energy platform 23051.

According to NRC reports analyzed by Amos, an average of 14 gallons per day had been spilling from that rig for several months, says Amos. "But our image analysis shows the leak rate must be greater, possibly by a factor of 10." Assuming oil needs to be at least 1 micrometer thick to create a visible sheen, he explains, and assuming that an oil slick that thin has a 72-hour lifespan at the surface, a leak of 14 gallons per day could only create a visible sheen 1.6 kilometers long by 91 meters wide. "We repeatedly observed, and NRC reports describe, slicks much larger," Amos says.

Small claims

It is a common problem. Amos had previously found a slick nearly 34 km long that was blamed on a spill of just 7 gallons (See Skytruth's reports).

Then, in March 2011, oil washed ashore on Grand Isle, La. Workers at the Department of Wildlife and Fisheries traced the spill to an apparent source at West Delta Block 117, about 32 km to the southwest. Anglo-Suisse Offshore Partners (ASOP) of Houston, Texas, had reported three discharges from its Platform E there, totaling less than 5 gallons. But, says Amos, "enough came ashore that the Coast Guard had to mount a clean-up response, which certainly suggests more than a few gallons."

The Coast Guard collected oil samples from the ASOP well and the slick, which were sent to Louisiana State University in Baton Rouge for chemical fingerprinting. Ed Overton, professor emeritus at the university's School of the Coast and Environment, says the samples matched. "All oil contains the same molecular structures, but oil from different sources contains different levels of hundreds of various compounds," says Overton, who developed the first methods for analyzing components as a method of "fingerprinting" oil samples in the late 1970s, and has continued to be involved in refining the technology.

ASOP did take responsibility for the clean-up, which had been largely completed by April 6, but the company did not return phone calls from Nature requesting comment.

Amos thinks that the Taylor and Grand Isle incidents illustrate the reporting system's flaw. "There is a strong incentive to under-report incidents. Who is going to get in a helicopter and fly 50 miles offshore for a 2-gallon spill? You report so you won't get fined, but report small because you know that will keep everybody behind their desks. We need some kind of independent verification."

The Coast Guard conducts a telephone investigation of every report, according to Petty Officer Nathan Thompson, and determines an appropriate course of action on the basis of that. There is no threshold amount that triggers a response. "It depends on the location, the reporting party and other factors," Thompson says. "If a company had a history of a lot of spills, or if a spill occurred in a more environmentally sensitive area, we'd probably go out. Sometimes we have to prioritize. In Louisiana, we get a lot of reports of spills from unknown sources, and we go out to those every single time."

Guessing game

Overton also suspects that spills are routinely underestimated given that fines are linked to volume, but points out that estimating spill volume is not an exact science. "Sheens can cover a lot of area and not represent much oil," he explains.

"We need research on better spectral methods to estimate the thickness of sheens."

More accurate data are vital as offshore drilling ramps back up post-Deepwater Horizon, Amos says. "NRC reports are the only comprehensive offshore spill database. But if the government and citizens rely on them to know how much pollution is caused by offshore oil and gas production, our drilling policy is based on fundamentally inaccurate data."

Accurate or not, the data are difficult to use, says Eric Schaeffer, former head of civil enforcement at the US Environmental Protection Agency and now director of the non-profit organization the Environmental Integrity Project, headquartered in Washington, D.C. "The data are pretty scattered, nomenclature is not consistent. At the time of release, you don't necessarily know how much has spilled, yet have an immediate obligation to report. But there isn't correction and updating of information later. Simple things such as spelling out how you did the numbers would be really valuable."

Carrie Beth Lasley, a researcher at the University of New Orleans Center for Hazards Assessment, Response and Technology, adds that mandatory annual inspections of platforms--or at the very least after a hurricane--are also needed.

Amos would like someone to monitor satellite images to identify unreported and under-reported spills. "We were able to document the leak from the Taylor platform because, during the BP spill, multiple satellite imaging systems were trained on that part of the Gulf on a daily basis," he says. "But once BP was plugged, the data stream slowed to the normal daily trickle. Satellites are overhead all the time, but only on when a paying customer wants an image."

The hardware and personnel for a Gulf-wide monitoring system already exist, he notes, at the University of Miami's Center for Southeastern Tropical Advanced Remote Sensing in Florida. "We have tremendous assets we aren't using, and that's a shame."

As part of an effort to rectify this, on April 19, SkyTruth announced it was forming a consortium with North Carolina-based SouthWings, a non-profit organization of private pilots, and Waterkeeper Alliance, a worldwide organization promoting clean water, to monitor pollution. "It's a coordinated approach, SkyTruth using satellite images to detect and map potential oil slicks and pinpoint potential sources, SouthWings and Waterkeeper using that information to coordinate overflights and on-the-water investigations and sampling," Amos says.

This article is reproduced with permission from the magazine Nature. The article was first published on April 21, 2011.