Plutonium dispersal near Groom Lake
Shot SMOKY was fired atop a steel tower in Area 2, adjacent to some hills. It had a yield of 44 kilotons. SMOKY's dusty cloud deposited radioactive fallout over the Groom Lake area.
The first shot of Operation Plumbbob was a safety experiment called Project 57. Such tests were usually conducted to determine that a weapon or warhead damaged in an accident will not detonate with a nuclear yield, even if some or all of the high-explosive components burn or detonate. Because the non-nuclear explosion would disperse nuclear materials, such as plutonium, the Project 57 test was mainly used for developing decontamination and radiation monitoring techniques.
On the morning of 24 April 1957, an XW-25 warhead was subjected to a one-point detonation. Only the bottom detonator was fired. The warhead's high-explosive charge destroyed the weapon and spread plutonium over nearly 900 acres of the surrounding landscape. The primary hazard from plutonium is the danger of inhaling microscopic particles. Alpha radiation emitted by the material is very weak, but can damage soft tissue (as in the lungs).
Ground Zero for Project 57 was only five miles northwest of Groom Dry Lake. Initially, no fallout was detected at Watertown. It was later determined that there was minor alpha activity for 12 days following the shot, but it was well below operational guidelines.
Blast effects at Watertown
The following month saw the beginning of full-scale nuclear detonations for Operation Plumbbob. A DOE database of Estimates of Exposure Rates and Times of Fallout Arrival Near the Nevada Test Site lists six of these shots as having deposited measurable fallout at Watertown. The first to do so was the fourth detonation, called WILSON, which was fired on 18 June 1957. It was a 10-kiloton device, lofted on a balloon to height of 500-feet above Area 9 in the northern part of Yucca Flat. The mushroom cloud climbed to 30,779-feet where a steady wind blew it northeast. Meanwhile, WILSON's stem was blown in the opposite direction towards California. Balloon shots were somewhat cleaner than tower shots because there was no steel structure to vaporize and contribute to the fallout cloud.