The OUESO event was detonated in hole U10bf of the Nevada Test Site as indicated in figure 1.1. The device had a depth-of-budal (DOB) of 216 m in the alluvium of Area 2, about 460 m above the Paleozoic and about 360 m above the standing water level, as shown in figures 1.2 and 1.3(l). Stemming of the 1.63 m diameter emplacement hole followed the plan shown in figure 1.4. A 1.22 m diameter liner was grouted inside the emplacement hole between depths of 202 and 222.5 m. An additional exploratory hole (Ue2bf) was drilled 15 to the west of the emplacement hole. This hole was grouted from depth to 24 m below the surface and filled with naive backfill to the surface. A log of the stemming operations was maintained by Holmes & Narver(2). Detonation time was 08:00 PDT on August 11, 1982 and about 25.5 minutes later a subsurface collapse to a little greater than half the DOB occurred. Slight pressure change activity was detected about 54 hours later. No radiation arrivals were detected above the ground surface and the QUESO