Columbia with the Army in attendance on 20 October 1943, Keith proposed switching the development effort to the Johnson barrier. Urey balked at this, fearing this would destroy morale at the SAM Laboratories. The issue was put to Groves at a meeting on 3November 1943, and he decided to pursue development of both the Johnson and the Norris-Adler barriers. Groves summoned British help, in the form of Wallace Akers and fifteen members of the British gaseous diffusion project, who would review the progress made thus far. Their verdict was that while the new barrier was potentially superior, Keith's undertaking to build a new facility to produce the new barrier in just four months, produce all the barriers required in another four and have the production facility up and running in just twelve "would be something of a miraculous achievement". On 16 January 1944, Groves ruled in favor of the Johnson barrier. Johnson built a pilot plant for the new process at the Nash Building. Taylor analyzed the sample barriers produced and pronounced only 5percent of them to be of acceptable quality. Edward Mack Jr. created his own pilot plant at Schermerhorn Hall at Columbia, and Groves obtained of nickel from the International Nickel Company. With plenty of nickel to work with, by April 1944, both pilot plants were producing barriers of acceptable quality 45 percent of the time. Construction The site chosen was at the Clinton Engineer Works in Tennessee. The area was inspected by representatives of the Manhattan District, Kellex and Union Carbide on 18 January 1943. Consideration was also given to sites near the Shasta Dam in California and the Big Bend of the Columbia River in Washington state. The lower humidity of these areas made them more suitable for a gaseous diffusion plant, but the Clinton Engineer Works site was immediately available and otherwise suitable. Groves decided on the site in April 1943. Under the contract, Kellex had responsibility not just for the design and engineering of the K-25 plant, but for its construction as well. The prime construction contractor was J. A. Jones Construction from Charlotte, North Carolina. It had impressed Groves with its work on several major Army construction projects, such as Camp Shelby, Mississippi. There were more than sixty subcontractors. Kellex engaged another construction company, Ford, Bacon & Davis, to build the fluorine and nitrogen facilities, and the conditioning plant. Construction work was initially