A treatment process that minimises contaminant spread by converting waste into a solid impermeable mass with low surface-to-volume ratio, reducing mobility through physical encapsulation. Uses binding agents (typically cement, lime, or proprietary binders) mixed with contaminated materials. Solidification combined with stabilisation (S/S) is widely used in the UK for contaminated land remediation and hazardous waste treatment, following Environment Agency guidance and STARNET protocols.