Underground tunnel for nuclear waste located 650 metres below the surface in 900 metre thick salt beds. For 20 years the Waste Isolation and Pilot Plant (WIPP) at Carlsbad, New Mexico, USA was tested for its suitability for storing nuclear waste. In 1999 it became operational for the storage of transuranic waste. This consists of radioisotopes heavier than uranium that are byproducts of nuclear weapons research and production.