Clean up operations commenced at Maralinga with Operation Clean Up in 1963 and Operation Hercules in 1964. These involved the removal of major hazards to permit entry to the test sites. A major clean up operation codenamed Operation Brumby was conducted in 1967. Attempts were made to dilute the concentration of radioactive material by turning over and mixing the surface soil. Highly contaminated soil from Wewak was buried in the Marcoo crater, and the debris pits were capped. Over time, the short-lived isotopes decayed away, leaving plutonium, with its half-life of 24,100 years, as the main radioactive hazard. In January 1979, the British Government agreed to the "repatriation" of recoverable plutonium that had been buried at Maralinga.