UK environmental authorities are predicting it will take months to clean up Salisbury following the nerve agent attack on Sergei Skripal and his daughter.
They now believe liquid was used for the poisoning and say that given the strength of the agent, simply washing it away is not an option.
Alistair Cunningham of Wiltshire Council Recovery Co-Ordination Group said: "With the liquid it will be treated with a caustic cleaning agent to break it down. It won't be washed away, it won't be diluted into the water course. It will be treated and broken down to a harmless substance and contaminated material will be removed as necessary."
Experts believe liquid was probably used because it was safer for the perpetrators than solids
Laurence Harwood, Professor of Organic Chemistry at the University of Reading says: "Solids always give off dust, and you don't need very much of this material to be contaminated and poisoned yourself."
Authorities need to clean not only the Skripals home but also any places they visited. The attack on the former spy and his daughter has sparked a Cold War-style diplomatic crisis between Russia and the West.
Russia denies any involvement.