18 @ The Containment of Underground Nuclear Explosions Photo credit: Department of Energy Aerial View of Yucca Flat Edgerton, Germeshausen & Greer (EG&G), Fenix & Scisson, Inc., and Holmes & Narver, Inc. REECo has 5,000 employees at the test site for construction, maintenance, and operational support, which includes large diameter drilling and tunneling, on-site radiation monitoring, and operation of base camps. EG&Ghas 2,200 employees, whodesign,fabricate, and operate the diagnostic and scientific equipment. Fenix & Scisson, Inc. handles the design, research, inspection, and procurement for the drilling and mining activities. Holmes & Narver, Inc. has responsibility for architectural design, engineering design, and inspection. In addition to contractors, several government agencies provide support to the testing program: the Environmental Protection Agency (EPA) has responsibility for radiation monitoring outside the Nevada Test Site; the National Oceanic and Atmospheric Administration (NOAA) provides weather analyses and predictions; and the United States Geological Survey (USGS)provides geological, geophysical, and hydrological assessments of test locations. TYPES OF NUCLEARTESTS Presently, an average of more than 12 tests per year are conductedat the NevadaTestSite. Eachtest is either at the bottom of a vertical drill hole or at the end of a horizontal tunnel. The vertical drill hole tests are the most common (representing over 90% of all tests conducted) and occur either on Yucca Flat or, if they are large-yield tests, on Pahute Mesa. Mostvertical drill hole tests are for the purpose of developing new weapon systems. Horizontal tunnel tests are more costly and time-consuming. They only occur once or twice a year and are located in tunnels mined in the Rainier and Aqueduct Mesas. Tunnel tests are generally for evaluating the effects (radiation, ground shock, etc.) of various weapons on military hardware and systems. In addition, the United Kingdomalso tests at a rate of about once a year at the Nevada Test Site. It takes 6 to 8 weeks to drill a hole depending on depth and location. The holes used by Livermore and Los Alamos differ slightly. Los Alamos typically uses holes with diameters that range from about 4