See original version at Center for Public Integrity

In an economically distressed pocket of southwest Detroit known by its ZIP code — 48217 – the weekend of Sept. 7-9 was one of the worst, pollution-wise, that residents like Theresa Shaw could ever remember.

"I started smelling it on Thursday," said Shaw, who immediately suspected the Marathon Petroleum Co. refinery a half-mile from her house. "I kept the windows closed because I couldn't breathe. On Friday, I thought, 'What the heck are they doing?' My eyes were just burning, my throat was hurting, my stomach was hurting. I was having migraine headaches.

"The smell, it was like this burning tar, with that benzene and that sulfur. I wanted to scream."

Shaw retreated to her sister's house on the north side of town. Responding to citizen complaints, the Michigan Department of Environmental Quality traced the powerful odor to Marathon, which had been cleaning several large vessels, and wrote up the company for a nuisance violation.

Marathon says it's "committed to environmental responsibility" and acted quickly to correct the odor problem, a byproduct of plant maintenance.

But the episode further eroded residents' trust in the company and underscored their fears about a $2.2 billion refinery expansion that will allow Marathon to process more high-sulfur Canadian crude oil.

The build-out, nearly complete, won't add to the air pollution burden, Marathon promises. In fact, the Ohio-based company vows, emissions of some pollutants will go down, and job numbers will go up.

Shaw isn't buying it. "They've disrespected us in this neighborhood over and over and over again," she said.

The conflict in southwest Detroit is one piece of a larger environmental struggle being waged in communities nationwide. At the core of the debate: plans by a number of oil companies to step up refining of heavier, dirtier crude, much of it from Alberta's tar sands formation, a deposit whose reserves are eclipsed only by Saudi Arabia's vast oil fields.

From the Great Lakes to Texas, people in already polluted neighborhoods are watching warily as refineries grow to accommodate the Canadian oil. Thus far, much of the controversy over tar sands has centered on the environmental damage caused by extraction and the risks of a spill from the proposed Keystone XL pipeline, which would carry the fuel to Gulf Coast refineries.

But the next stage in the process has been largely overlooked: The oil has to be refined somewhere.

Heavy oil from Canada is already reaching Marathon and other refineries. Between 2006 and 2011, imports of such crude more than tripled, a Center for Public Integrity analysis of data from the U.S. Energy Information Administration found.

Some worry that government approval of Keystone XL would accelerate this trend, providing wider access to tar sands. Construction has begun on the southern portion of the pipeline, between Oklahoma and Texas, but the northern section is on hold, pending further analysis by the U.S. Department of State. The thick, asphalt-like crude, known as bitumen, requires more processing than lighter forms of oil, which could lead to increases in pollution if not controlled. The burden would fall most often on communities, like southwest Detroit, populated mainly by low-income people of color.

The Environmental Protection Agency expressed concern about this prospect in June 2011. Commenting on a draft State Department environmental assessment of Keystone XL, the EPA urged the department to "provide a clearer analysis of potential environmental and health impacts to communities from refinery air emissions and other environmental stressors."

Yet the EPA has conducted no evaluations of its own and isn't keeping track of the refinery expansions around the nation, an agency spokeswoman said in a statement to the Center.

The State Department has looked only at the possible effects of Keystone XL and maintains that there's no evidence the pipeline's potential approval has prompted any of the current refinery expansions. The department referred Center inquiries to its published evaluations, one of which says that significant expansions should trigger rules requiring refiners to install better pollution-control equipment.

However, some advocates contend that companies are underestimating the projects' air impact in an attempt to avoid such requirements.

"This has all been done very quietly in the regulatory backrooms, and people aren't aware of it," said Josh Mogerman, who tracks developments related to tar sands for the Natural Resources Defense Council. "These refineries have a lot of problems, and it's hard to believe that's going to get better by moving to process one of the dirtiest fuels on the planet."

Two trade groups representing the oil industry, the American Petroleum Institute and the American Fuel & Petrochemical Manufacturers, did not respond to interview requests, but both have supported increased use of tar sands, arguing that America would benefit economically and secure a more stable energy source.

'Sacrifice zones'

Typically, the refinery expansions are unfolding in places that have long suffered from air and water pollution.

> Email Jim Morris and Chris Hamby