By now, you already know that at least 84,000 gallons of crude spilled from an ExxonMobil pipeline, swamping an Arkansas subdivision on Friday, and causing the evacuation of 22 homes. In addition to the loss of wildlife, damage to property, and environmental and human health hazards posed by the spill, it may have implications for the Keystone XL pipeline currently under consideration by the Obama administration.

There is a lot more to the story that’s important to understand. Here are six crucial things.

1.Not Your Average Crude

InsideClimate News reported shortly after the spill that an Exxon official confirmed the pipeline was “transporting a heavy form of crude from the Canadian tar sands region.” Specifically, it has been identified as Wabasca Heavy, Lisa Song writes, “which is a type of diluted bitumen, or dilbit, from Alberta’s tar sands region” although you won’t hear any Exxon folks calling it tar sands.

Dilbit is some seriously nasty stuff. She writes about a previous dilbit spill by Enbridge in Michigan’s Kalamazoo River in 2010:

Dilbit is a mixture of heavy bitumen and diluents–light hydrocarbons used to thin the bitumen so it can flow through pipelines. While most conventional crude oils will float on water, the bitumen began sinking into the river as the diluents evaporated, leaving a sludge of submerged oil that defied traditional cleanup methods. Earlier this month, the EPA ordered Enbridge, Inc., the Canadian company that owns the pipeline, to dredge sunken oil from the riverbed. The cleanup has cost more than $820 million to date and could top $1 billion once the order is carried out.

The Arkansas spill wasn’t as big as the Michigan spill and it was farther from main water bodies, but it’s still serious business. If you want to know more about how dangerous tar sands/dilbit can be, the Dilbit Disaster is a must-read.

2.Not Your Average Pipeline

The Pegasus pipeline running more than 850 miles between Patoka, Illinois and Nederland, Texas, is 20 inches in diameter and was built in the 1940s to carry crude from Texas to Illinois. But in 2006 the flow was reversed in order to carry Canadian tar sands to Texas. As Ben Jervey wrote for DeSmog blog, the flow was reversed to “help relieve the tar sands crude bottleneck in Cushing, Oklahoma. (The same reason given by proponents for the construction of Keystone XL.)”

The pipeline was built to carry 65,000 barrels a day, but Exxon was allowed to expand that to 95,000 barrels a day just a few years ago.

All of these facts bring up some basic questions. What effect does a higher capacity have on the pipeline? What effect does reversing the flow have on the pipeline? And what effect does switching from conventional crude to dilbit have on the pipeline, considering it was built to have a much thinner crude flowing through it?

John H. Cushman Jr. wrote for InsideClimate News:

Seven years ago, when Exxon, the pipeline’s operator, turned it into a higher-volume line for diluted bitumen from Canada flowing under greater pressure to refineries on the Gulf Coast, federal rules did not require a new permit application or safety reviews, according to federal officials. “Our regulations don’t specify how much product a pipeline carries. There is no regulation if they want to change the type of crude they carry,” said Damon Hill, a spokesman for the Pipeline and Hazardous Materials Safety Administration, a part of the Transportation Department. “As far as reversing the flow of a pipeline, it is not a safety issue.” To reverse the line that runs from Patoka, Ill. to Nederland, Tex. required 240,000 man-hours of work on pump stations, valves, bypasses and integrity tests, Exxon said when it opened the line. But only after the spill occurred did the agency step in with an order, issued Tuesday, that clamps down on the Pegasus pipeline, for example by limiting the pressure at which it may operate once it reopens. Noting that the pipeline’s flow was reversed in 2006 so that it could carry Canadian tar sands crude 850 miles from Illinois to Texas, the agency’s corrective action order remarked that “a change in the direction of flow can affect the hydraulic and stress demands on the pipeline.”

3.Tax Exempt?

Who’s footing the bill for the cleanup? The government has an Oil Spill Liability Trust Fund that companies which transport oil must pay into. But, as it turns out, the bitumen that Exxon was transporting in its pipeline isn’t oil by government standards. Erin O’Sullivan writes for Oil Change International:

In a January 2011 memorandum, the IRS determined that to generate revenues for the oil spill trust fund, Congress only intended to tax conventional crude, and not tar sands or other unconventional oils. This exemption remains to this day, even though the United States moves billions of gallons of tar sands crude through its pipeline system every year. The trust fund is liable for tar sands oil spill cleanups without collecting any revenue from tar sands transport. If the fund goes broke, the American taxpayer foots the cleanup bill.

Keep this in mind as Exxon tries to wiggle out of connecting the contents of its pipeline with tar sands.

4.No Media Access

It feels like BP’s Deepwater Horizon disaster all over again when it comes to media access. Lisa Song reported that the command center for cleanup is tightly controlled by Exxon, with even the parking lot off limits and guarded by security. She wrote:

The stakes are high and Exxon is running the show here, with federal agencies so far publicly invisible. The phone number of the command center in Mayflower goes to an ExxonMobil answering service based in Texas, and each day it is Exxon that distributes a unified command press release–which contains the logos of Exxon, Faulkner County and the city of Mayflower–with official updates on the progress of the cleanup. A request for a media tour of the spill site today was turned down by an Exxon spokesperson, who emerged from the command center to speak with a reporter at the gate. All areas being cleaned up so far have also been off limits. There is no central location where members of the media can gather to ask questions.

5.Under Investigation

Exxon may be feeling a little bit of heat as the Pipeline and Hazardous Materials Safety Administration has ordered a corrective action, which puts the broken pipeline under lockdown for the time being (pretty much a no-brainer). Jeannie Nuss reported for the AP that, “the order signed by Jeffrey Wiese, associate administrator for pipeline safety, says ‘continued operation of the Pegasus Pipeline would be hazardous to life, property, and the environment.’”

But that’s not all. She writes:

The federal agency’s order comes as Arkansas’ attorney general promised a state investigation into the cause and impact of the spill and other officials say they plan to ask Exxon to move the Pegasus pipeline to protect drinking water. “There are many questions and concerns remaining as to the long-term impacts, environmental or otherwise, from this spill,” Arkansas Attorney General Dustin McDaniel wrote to ExxonMobil executives Tuesday. He also asked ExxonMobil to preserve records pending his investigation.

6.Effects on Keystone XL

So, how is this going to affect decisions about the Keystone XL pipeline? Those who have been against the pipeline because of its environmental risks have new fodder. Others who were previously in favor or indifferent may have second thoughts, especially considering that the Pegasus pipeline capacity was only about a tenth of what the Keystone XL would carry.

Any pipeline poses risks, but tar sands pipelines pose even more risks than conventional oil. “TransCanada’s first Keystone pipeline leaked 12 times in its first 12 months,” wrote Sierra Club’s Michael Brune. “Because tar sands must be pumped at higher pressures and temperatures than conventional oil, it corrodes pipes faster.”

Just days before the Arkansas spill, a coalition of environmental groups, led by the National Wildlife Federation, as well as landowners, and others filed a petition with the Pipeline and Hazardous Materials Safety Administration and the EPA, calling on them to enact stronger safety regulations for pipelines carrying tar sands oil. The petition may well pick up more backers in the spill’s aftermath.

Originally published on AlterNet.