The Middlesex Sampling Plant on Mountain Avenue in Middlesex, New Jersey, is a 9.6 acres (38,800 m2) site which was initially used to stockpile pitchblende uranium ore. From 1943 to 1955, under the direction of the Manhattan Project and its successor agency, the United States Atomic Energy Commission (AEC), it was used to crush, dry, screen, weigh, assay, store, package, and ship uranium ore, along with thorium and beryllium ores, for the development of the atomic bomb.

[1] The site was used from 1955 to 1967 for the sampling and storage of thorium residues, and was decontaminated, certified, and released for unrestricted use in 1967.

[2] During the decontamination process, radioactive materials were carried away by wind and rain to the yards of nearby residents.

[3] The facility was used by the United States Marine Corps as a reserve training center from 1969 until 1979, when the U.S. Department of Energy (DOE) took over and cleaned up the residential properties.

[4] In April 2024, the site was officially transferred to the Borough to build its public works facility and a warehouse with an adjoining road.