In procurement documents posted on the Web Tuesday, the Department of Defense said the contract would encompass "all activities associated with the operation and maintenance, including repairs, of the two-acre Pentagon Memorial."

"Principle duties are keeping the area free of litter, raking the gravel areas to ensure smoothness, removal of gravel from unit pools, polishing metal surfaces, cleaning stone faces and assuring the pools remain clear," the document states.

The aim is to be unobtrusive while maintaining the memorial's "pristine appearance" and and "solemnity," and to honor visitors' privacy, the document says.

The memorial "is a unique structure serving as a work of art, a memorial of significant emotional power, and a functioning park with landscaping and moving water features."

"Each of these aspects presents major challenges to the performance of this contract. In combination, they require considerable orchestration of contractor resources coupled with a deep sensitivity to the significance of the memorial and the concerns of victims' families and the general public," the document concludes.