[en] A series of experiments involving high explosives and radioactive materials were conducted at Los Alamos, New Mexico, primarily to understand certain safety aspects of operational nuclear weapons. The experiments were conducted underground in large diameter holes as deep as 120 ft. The location was selected because it had geologic and hydrologic characteristics that assured complete containment of the experiments and precluded any possible contamination of groundwater. Important features verified by the USGS included the absence of any recharge and about 1200 feet of dry rock above the groundwater aquifer. Residual materials dispersed by detonation of the high explosives remain at the bottom of the experimental holes. The materials of significance from an environmental standpoint include about 40 kg of plutonium, 93 kg of enriched uranium, at least 82 kg of depleted uranium, 13 kg of beryllium, and an undetermined amount of lead. Environmental monitoring has been carried out regularly since the time of the experiments. Results of measurements confirm that there has been no contamination of groundwater. Minor surface soil contamination dating from the time of the experimental operations has been detected in small surface drainages near the experimental area. None of the surface contamination has been measurable at Laboratory boundaries or points of public access on a state highway. 14 refs., 8 figs