The geotechnogenic system a cavity of underground nuclear explosion -geological environment - surface ecosystems is considered, for the object of peaceful underground nuclear explosion (PUNE) "Crystal" (Russia, Yakutia) as an example. New data on the radioactive pollution of surface and underground waters were obtained. Geophysical transient electromagnetic sounding, in other words - time-domain electromagnetic sounding method (TDEM) along two profiles above the epicentre of PUNE was applied. The revealed geoelectric layers conform to the geological structure of the area. There is a local geotechnogenic anomaly under the epicentre of the explosion: it is a sharp rise of the aquifer levels by 260-300 m up to the cavity of PUNE. Mining of the kimberlite pipe "Udachnyi" at a distance of 3.5 km to southwest from the "Crystal" PUNE object caused destabilization of the system PUNE cavity-geological environment. Deepening of the open-cast mine and its drying promoted the formation of a great cone of depression around the mine. Radioactive underground brines from the zone of explosion moved to this depression, mixing with the brines of underlying horizons in the cone of depression. The brines from the open-pit mine were drawn into the tailings dump and injected under the ground. The ecological risk is connected with possible environmental pollution by the drainage of tailings dump and by infiltration of underground waters from the burial ground through fractured zones of tectonic faults.
