The National Park Service’s planning document, obtained by the Washington Post on Wednesday, concluded that President Donald Trump’s planned 250-foot triumphal arch in Washington, D.C., will likely contribute to adverse effects to historic properties. The document stated that “such adverse effects cannot be fully avoided while retaining the location-dependent purpose of the Undertaking.”

The planning document identified roughly 37 nearby historic sites that could be affected by the arch’s construction, including the Lincoln Memorial, the National Mall, the Washington Monument, the Pentagon and the U.S. Capitol. The Park Service singled out the symbolic alignment among Arlington House, Arlington National Cemetery, Arlington Memorial Bridge and the Lincoln Memorial — sites that face each other to represent the reunification of the United States after the Civil War — and warned the arch could interfere with that relationship.

The agency outlined a package of mitigation measures that could accompany construction: installing vibration plates near the Arlington Memorial Bridge and other sensitive sites, enforcing limits on noise-generating activities, prohibiting unnecessary lighting and limiting work hours. The Park Service also proposed developing digital programs to explain the commemorative relationship between the Lincoln Memorial and Arlington House, illustrate the before-and-after Potomac River skyline, and describe the significance of triumphal arches.

Veterans, preservationists and lawmakers have consistently raised objections. Veterans filed a lawsuit in September seeking to halt construction, alleging the arch would harm the symbolic relationship of historic sites representing the reconciliation of war or disrupt burials at Arlington National Cemetery. Some lawmakers have shared fears that the arch could further complicate Washington’s airspace.

The Park Service circulated the document among preservationists and other groups to review and sign by noon Monday, according to an email obtained by the Washington Post. Should local preservation officers decline to sign, the disagreement could trigger another process involving the Advisory Council on Historic Preservation, a federal agency.

The Trump administration does not need the preservationists’ consent to move forward. The administration has already received approval from the U.S. Commission on Fine Arts, a federal advisory council composed of Trump appointees, and preliminary approval from the National Capital Planning Commission.

Trump has been emphatic about the arch, insisting it stand 250 feet tall to mark the United States’ 250th anniversary. A photograph distributed by Getty Images shows the president holding models of the arch while delivering remarks in the East Room of the White House on October 15, 2025.

The Guardian asked the Park Service for comment.