National Park Service officials said they will begin taking land for the Flight 93 memorial in Somerset County from property owners because negotiations have been unsuccessful.

The service said it will condemn about 500 acres still needed for the memorial to be built in time for the 10th anniversary of the 2001 terrorist attacks.

Randall Musser, who is one of seven landowners affected, said he is surprised by the Park Service's actions but understands the agency must move forward with land acquisition to finish the memorial by 2011.

Park Service representatives said they have been working with landowners for years, but negotiations have not been successful.

Musser said while there have been talks about negotiating, they have never sat down and discussed anything.

On Tuesday, Musser said a Park Services appraisers came to look at his land. Before he heard back from the appraiser, he received a letter informing him the Park Service would be using government powers to take the land.

Park Service officials said, even with homeowners willing to sell, title questions and other claims can arise that could delay the project. The Park Service will need about 1,500 acres to construct the memorial, and 500 of those acres will come from the landowners.

Flight 93 was traveling from Newark, N.J., to San Francisco when it was diverted by hijackers with the likely goal of crashing it into the White House or Capitol. The official 9/11 Commission report said the hijackers crashed the plane into a Pennsylvania field as passengers tried to wrest control of the cockpit.

Construction on the memorial is set to begin by the end of the year.

The park service planned to publicly release further details later Thursday. Stay with WJACTV.com and WJAC-TV News for continuing coverage.