"Specialists spent three days transporting and applying decontamination agents. The results will be announced after samples of the soil have been examined in ten days' time," he said.
The three previous stages were done in July and August.
The maximum permissible level of toxic agents in the soil was brought down from 8,850 times greater than was permissible to 9.2 times, the source said.
A Proton-M carrier rocket with three Glonass M satellites was launched from Site 81 of the Baikonur cosmodrome on July 2.
It fell apart almost immediately after the launch and exploded. The rocket was carrying some 600 tonnes of heptyl, amyl and kerosene.
Kazakhstan Environmental Protection Minister Nurlan Kapparov said a few days ago that decontamination efforts should continue until the soil is completely clear of toxic agents.
Voice of Russia, Interfax