36 © The Containment of Underground Nuclear Explosions Photo credit Cwaar' matt 8 wr gy Blanca containmentfailure, 1958. kilotons. Thefirst few tests after Rainier, however, were detonated at greater depths than this formula requires because it was more convenient to mine tunnels deeper in the Mesa. It was not until “*Blanca,’” October 30, 1958, that a test was conducted exactly at 300 (yield)'” feet to test the depth scale. The containment of the Blanca explosion, however, was unsuccessful and resulted in a surface venting of radioactive material. As a consequence,the depth scale was modified to include the addition of a few hundredfeet as a safety factor and thus became: 300 (yield)? plus-a-tew hundredfeet.’ Today, the general depth of burial can be approx: mated by the equation: Depth = 400 (yield) . where depth is measured in feet and s.erd on kilotons.'? The minimum depth of burial. however, is 600 feet.'3 Consequently, depths ot bunul van from 600 feet for a low-yield device. to shout 2.100 feet for a large-yield test. The depth is scaled to the '2**Bublic Safety for Nuclear Weapons Tesis."’ United States Environmental Protection Agency, January, 1984. '3The 600-foot depth was chosen as a minimum after a statistical study showed thatthe likelihood of a seep of radioactive material fo the surges for explosions buried 600 feet or more was about 1/2 as great as for explosionsat less than 500 feet, even if they were buried at the same wale Jeoth in each case.