Chemical reactivity : The substances which react violently or produce flame on contact with water can be given suitable chemical treatment to convert them into nonreactive form before running into the drainage.
Example: Sodium metal.
Those substances which generate heat on mixing with water are treated carefully with large quantity of water in a safe area.
Example: Calcium oxide.
Acidic chemical wastes are first treated with large quantity of sodium carbonate anddhen with a large quantity of water. The treatment with sodium carbonate neutralises the acid since the former is a base.