New pat of Arlington called the Millennium Project. It is a new way of burying caskets. Double stacking them in concrete boxes.:
The Millennium Project, the first expansion of the cemetery space in nearly 40 years, cost around $81.7 million. The expansion space was taken out of a recreation spot for a nearby military base, a construction staging area for the cemetery and National Park Service woodland, according to The Washington Post.
The expansion features a new system for saving space and efficiency, Army Col. Mike Peloquin, the cemetery’s director of engineering, said in the Post report.
Concrete boxes used for burials will be double stacked, with space for two caskets. The concrete containers will be about 18 inches under the ground surface, and spaced closely together.
According to Renea Yates, the deputy superintendent for cemetery administration, the expansion will add decades onto the life of the cemetery. However, continued expansion will still be needed as the cemetery continues to delay the inevitable day when there is no more room left for burials in the military cemetery.
https://www.militarytimes.com/news/your-military/2018/06/05/expansion-of-arlington-national-cemetery-to-open-soon-with-6000-pre-dug-graves/