MARSHALL, Mich. As the Obama administration inches closer to a decision on whether to approve construction of the much-debated Keystone XL pipeline, costly cleanup efforts in two communities stricken by oil spills portend the potential hazards of transporting heavy Canadian crude. It has been three years since an Enbridge Energy pipeline ruptured beneath this small western Michigan town, spewing more than 840,000 gallons of thick oil sands crude into the Kalamazoo River and Talmadge Creek, the largest oil pipeline failure in the country's history. Last March, an Exxon Mobil pipeline burst in Mayflower, Ark., releasing thousands of gallons of oil and forcing the evacuation of 22 homes. Both pipeline companies have spent tens of millions of dollars trying to recover the heavy crude, similar to the product Keystone XL would carry. River and floodplain ecosystems have been restored, and neighborhoods are still being refurbished. Legal battles are being waged, and residents' lives have been forever changed. "All oil spills are pretty ugly and not easy to clean up," said Stephen
K. Hamilton, a professor of aquatic ecology at Michigan State University who is advising the Environmental Protection Agency and the state on the cleanup in Marshall. "But this kind of an oil spill is even harder to clean up because of its tendency to stick to surfaces and its tendency to become submerged." Before July 26, 2010, hardly anyone in Marshall had heard of Enbridge Energy Partners, a Houston firm whose parent company is based in Calgary, Alberta. On a recent midsummer morning, the Kalamazoo looked almost the way it once did. Towering oak trees draped over the water in the heat. Hawks patrolled the deep green riverbanks. An elderly couple lugged fishing tackle toward a shady area. If not for two motorboats whirring downstream and three men probing the water with poles, there would have been no sign that anything had gone wrong. Much of Kalamazoo's plant and animal life has returned. But ridding the water of all the oil, some of which sank to the river floor and continues to generate a kaleidoscopic sheen, has proved elusive. Though a 40-mile stretch of the river has reopened after being closed for two years and most of the oil has been recovered or has evaporated, vestiges of the spill are everywhere. "For Sale" signs dot the rolling cornfields and soy farms. Once-coveted riverfront homes sit vacant. Matt Davis, a real estate agent here, said he had struggled to sell homes since the spill. "Enbridge hopes people forget," Mr. Davis said. "But this is my town. This is where I grew up. Enbridge isn't from around here. "We didn't ask for them to have their pipeline burst in our backyard. Make it right. Take care of the mess you made."In Mat, the E.P.A. found that Enbridge had drastically underestimated the amount of oil still in the river. The agency estimated that 180,000 gallons had most likely drifted to the bottom, more than then 100 times Enbridge's projection.