Navajo Water Project Working to Secure Its Path - Eminent Domain?

Jimmy Detsoi touted a proposal that he thought would get unanimous support from people in a small Navajo community where raising livestock is synonymous with culture and tradition, the advent of the massive federal Navajo-Gallup Water Supply Project. He had identified nine residents with livestock grazing permits on a patch of northwest New Mexico land that is in the path of the 280-mile, $1 billion pipeline project that will bring water closer to thousands of Navajos on the eastern side of the reservation. More than 40 percent of Navajo residences across the 27,000 square-mile reservation still do not have running water, and many have the arduous task of hauling water miles for basic uses like cooking, washing and drinking. The pipeline also will bring water relief to the city of Gallup, N.M., and parts of the Jicarilla Apache Nation. Detsoi, the grazing official in Twin Lakes, N.M., was seeking approval from the permit holders for the pipeline to cross their lands. One refused. The man told tribal officials that the destruction of vegetation and being unable to access a road would cause too many problems. The start of project construction this year is dependent on completion of various permitting, land acquisition and contract activities. Tribal officials are hesitant to use eminent domain, which allows the tribe to seize property for economic development, against grazing rights holders because it brings back harsh memories of when the federal government pushed Navajos off their land and forcibly relocated some of them...more

I'm confused (what's new?) about this eminent domain thing.  The article says:

 The right to graze livestock is sometimes treated as land ownership, which doesn't exist for tribal members on the reservation because the land is held in trust by the federal government. To Detsoi, grazing permit holders aren't giving up much by allowing the water pipeline and could benefit from the grass seed that's planted as part of reclamation. "A lot of people think they own the land," he said. "We've been trying to tell them, we don't own the land. The land still belongs to the government."

And the Navajo President says:

 While consent is preferred, Navajo President Ben Shelly has warned that he will enforce eminent domain along the project that is on the fast track by President Barack Obama's administration and came as the result of years of negotiation on tribal water rights.

How can something be treated as property "sometimes"?  I can understand if the feds own the land and have delegated the right of eminent domain, but just what are they condemning?   The feds own the land so it must be the grazing permit?