On October 11, ExxonMobil released its investigative report on the results of soil and sediment tests  from Mayflower and Lake Conway. The company submitted the 81-page report to the Arkansas Department of Environmental Quality (ADEQ) as part of its cleanup obligations, and the document is supposed to provide a definitive picture of the environmental situation in the wake of the Pegasus oil spill.
ADEQ has been studying the report in the weeks since, and on Monday, it sent a reply to Exxon  asking that the oil giant to reevaluate some of its conclusions and continue testing. The agency also forwarded a letter  from the Arkansas Game and Fish Commission (AGFC) with more critiques of the report. To assist in conducting an independent evaluation of the data, AGFC hired two environmental consulting companies with a history of investigating oil spills.
Perhaps the most important point in either regulator's reply is the Game and Fish Commission's rebuttal of how Exxon's report treats a class of pollutant called polyaromatic hydrocarbons, or PAHs. Game and Fish says that Exxon's figure for PAH contamination may misrepresent the amount of toxins still in the environment.
These chemicals are found in petroleum and are especially dangerous for two reasons: They're toxic in low doses, and they don't easily degrade — that is, they stick around in the environment. As with many complex organic compounds, PAHs come in a great assortment of varieties, each one detectible as a distinct species with its own intimidating name ("Acenaphthene," "Acenaphthylene," "Anthracene," "Benzo(a)Anthracene," etc).
Exxon's report examines the toxicity effects of 38 separate PAHs, 16 of which are designated as "priority PAHs." But, says the letter from AGFC to Exxon, that is only about half of the total PAHs present in the source oil. That is, Exxon may have failed to analyze some compounds that should be factored into the overall toxicity picture.
ADEQ's requests to ExxonMobil for more testing:
AGFC's letter to ADEQ, weighing in on Exxon's results: