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How much oil is spilling in to the Gulf of Mexico? And, yes, it does matter.

Lisa Suatoni

Posted May 20, 2010

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Soon after the explosion of the Deepwater Horizon rig, the coast guard and BP estimated that 42,000 gallons (1000 barrels) were leaking from the well each day into the Gulf of Mexico.  Within a week this estimate was revised by the government to 210,000 gallons (5,000 barrels) a day.

This round estimate of 210,000 gallons has stuck – accepted with certainty by the federal government - despite multiple independent estimates that suggest the spill is substantially larger.

Oil Slick Size

Initial estimates were based on oil slick size, following the Bonn Convention method.  However, independent estimates – also based on the size of the oil slick – questioned the widely reported value of 210,000 gallons per day. 

In a statement to the press, Dr. Robert Howarth of Cornell University pointed out that the government’s figure rested at the lower bound of potential spillage rates using oil-slick size as an estimator.  His own estimate ranged from 170,000 gallons to 630,000 gallons (4047 to 15,000 barrels) per day.

Using satellite imagery of the oil slick and thickness estimates from visual descriptions, John Amos of Sky Truth and Dr. Ian MacDonald of Florida State University estimated a minimum average flow rate of 1.1 million gallons (26,500 barrels) per day – five times the original estimate.  Differences between their calculations and the governments can not be identified because the government’s computation has not been made public.

In truth, it appears that oil-slick size is not the best estimator given the depth of the spill, the heavy use of dispersants during the response, and the evidence that a substantial amount of oil is remaining below the surface (quite possibly the result of physical dispersion of the hot liquid during entry into the cold, high pressured deep waters), resulting in a likelihood of underestimating the spillage rates.

Other Available Methods

Experts point out that a range of alternative, and more suitable, methodologies exist.  They include direct physical measures of velocity with flow meters (this would, admittedly, be challenging), acoustic methods, and visual analysis of particle flow from the leaking pipe (particle image velocimetry).

Immediately following the release of footage of the leak, a number of updated measures were provided by independent scientists.  According to an NPR story, Steven Wereley, an associate professor of mechanical engineering at Purdue University, conducted visual analysis of the leaking pipe estimating between 2 and 3.5 million gallons (56,000 barrels to 84,000 barrels) per day.  According to NPR other scientists employing similar methods also generated estimates in the millions of gallons (or 10,000s of barrels) per day.

 Why the size of the spill matters

 BP and the federal government repeatedly argue that measuring the volume of oil entering the Gulf is not a priority, that a more precise measure of flow rate is not important.  Their rationale is that it would not influence the response in any way.

We disagree for a number of reasons:

  1. Scale. The flow rate estimates differ by a factor of ten.  Differences on this scale are not quibbles; they are big, fundamental differences. 
  2. Response. The discrepancy is sufficiently large enough to influence response strategies.  For example, to promote the efficacy of dispersants, they are applied at a specific ratio to the volume of oil.  This is not possible if the volume is unknown, by this large of a degree.  In addition, the ability to successfully cap the well, engineer a dome, or pump the oil to the surface depends on a good estimate of the oil flow rate (both in terms of volume of oil and the force with which it is exiting the pipe).
  3. Law. Under the Oil Pollution Act of 1990, a natural resource damage assessment (NRDA) must be conducted.  This entails assessing the input of oil, its fate (i.e., where it goes, what it coats and contaminates), and the damage it caused.  The ability to fully conduct this accounting – or ‘mass balance’ - requires knowing the initial volume of oil.
  4. Financial Penalty. Following discharge of oil into a water body, the federal Clean Water Act allows for a civil penalty of up to $1,000 per barrel of oil spilled. This penalty can not be calculated to its fullest extent without knowing the total volume of oil.
  5. Future emergency plans. Knowing the magnitude of this spill is necessary to inform future emergency response plans.  Substantial underestimates of the volume of oil leaking from Deepwater Horizon will leave us unprepared in the future.

There are multiple reasons why BP may not want the true amount of oil to be known.  Just take for example, the $1000 per barrel of oil spill civil penalty under the Clean Water Act.  Using the “official” number of 5,000 barrels per day, their current tally is $140 million (and counting).  Using some of the higher estimates provided by visual analysis of the leaking pipe, BP’s current tally is in the billions (and counting).

The bigger mystery is why the federal government is sitting on the sidelines.  Why has the federal government been reluctant - and so slow - to undertake its own assessment of the size of the spill, particularly given the available expertise and alternative methods? 

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Michelle BroeMay 20 2010 02:48 PM

Thank you, Ms.Suatoni, for taking up this important issue. Why is our government lying to us about the size of the oil gusher(spill is just too inadequate of a word) ? Is it because this administration is lying in bed with BP ?This is an enviomental catastrophy worse than we have ever seen before.Where were the enviormental safeguards ? This kind of carelessness is criminal.We now have an ecological catastrophy; we have trashed the Gulf of Mexico- The Florida Keys the fragile coral reefs, the jewel in the crown of this enviorment, the wetlands of Louisianna where thousands of species of our fellow creatures breed & nest , these extraordinary places will take generations to recover. And some species will never recover from this criminal damage. Let's call for a national moratorium on all offshore oildrilling until the proper safeguards are in place.

Jon PerkinsMay 20 2010 03:12 PM

Its funny seeing the way people are simply ignoring all these new estimates and concerns! BP has the cap on things and isn't letting people see whats really going on because its already costing them in the BILLIONS in lost revenue and bed publicity. they're screwed and they're just trying to put a good face on things. Its like a kid who lit the kitchen on fire and went and hid under the bed hoping no one would notice! THE annoying part is PEOPLE ARE LETTING THEM GET AWAY WITH IT!

This is going to effect generations. world economies, the entire fishing industry and several Eco systems resulting in the extinction and endangerment of several species and the financial ruin of tens of thousands of families.

Gulf Spill May Far Exceed Official Estimates

Michele CatonMay 20 2010 10:27 PM

I am so devastated by this.. I wish I lived in a country where the government cared about their effects on the environment. Action needs to be taken immediately.. ugh this is so frustrating as a 20 year old. I want to do something. The people in power are blinded by greed and not sticking up for what is right. :( My heart is broken as an animal lover and what I thought was a smart government.. but I've lost faith in them. All I can do is pray

Regan NelsonMay 21 2010 12:31 PM

Great article, Lisa. I thought this news article from the Kansas City Star was also useful:

Mandy SmithbergerMay 21 2010 05:07 PM

It also matters in terms of revenue--if the government decides to collect royalties on the oil spilled (as they should), an accurate calculation of the amount of oil lost is millions. It won't cover the cost of the clean up by a long shot, but it's still revenue that taxpayers deserve for the loss of their natural resources.

MichaelMay 23 2010 12:27 AM

A fascinating point about the measurements of the accident, Lisa. NRDC is so far the only credible source I've seen which mentions at least one crystal clear reason why BP would hide the spill rate. Excellent work, thanks!

It costs BP, Halliburton and Transocean much more money because the leak is bigger. I knew there was more to this than meets the casual eye.

I'll be discussing your article here on my radio show, Blue Planet Almanac on 5-24-10. With us we'll have John Amos of SkyTruth, marine biologist David E. Guggenheim and NWF ambassador Leilani Munter. Today John co-authored an excellent NY Times Op Ed piece about the importance of getting the spill rate right, "The Measure of a Disaster."

Thanks again for your work!

Ken SmithMay 23 2010 08:43 PM

Calculating how much oil is spewing into the bottom of our food chain, which would be impossible to live without, is a very simple process. all I needed was the diameter of the hole, preasure reading, giving me a pretty accurate 100 gallons per second, you can do the rest of the math if you want to bother with it. Suffice it to say, I will not be spending another minute doing anything someone else wants me to do.Dont think for one second, that the powers to be would share this information with anyone. After all, they want to avoid a panic.

Dennie KirtleyMay 30 2010 02:29 AM

911 was the biggest recent marker of our lives. It changed us all. This oil spill dwarfs even 911. It's an earth changer. We are in humongous trouble.

BP's approach all along was "let's not waste time calculating flow rates". They have been in this business for decades. You think for a second they didn't know what the flow rate was? Not on your life! The oil companies live, eat and breathe this stuff.

We have been duped by BP and abandoned by President Obama who on day one could've and should've commandeered a fleet of supertankers to suck this oil stright up out of the water. Forget all of BP's "we're operating in outer space" bullcrap. We have the technology to bring in the supertankers and pull this oil out of the water right now. They did it in the Persian Gulf in the First Gulf War. We can't wait any longer for the BP scientists to continue "carefully taking their time getting it right".

DavidJun 1 2010 12:16 AM

BP's activities following the blowout have been carefully choreographed to lead toward their original end-goal: BP having access to all of that oil ! BP has used the media to make people believe that "relief wells" are the answer (they are drilling MORE wells, so that they will have access to the oil even after they cap the first one)
BP should immediately (if not sooner) be nationalized, as they have created damage FAR BEYOND the value of their company.

Roni DinaJun 29 2010 10:34 PM

What is the measurement of the hole that is leaking oil in the Gulf?

davidSep 14 2010 12:41 AM

BP's activities following the blowout have been carefully choreographed to lead toward their original end-goal: BP having access to all of that oil ! BP has used the media to make people believe that "relief wells" are the answer (they are drilling MORE wells, so that they will have access to the oil even after they cap the first one)
BP should immediately (if not sooner) be nationalized, as they have created damage FAR BEYOND the value of their company. i really dont care about this

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