Remediation

re·me·di·a·tion
/rəˌmēdēˈāSHən/
noun
the process of improving something or correcting something that is wrong, especially changing or stopping damage to the environment
Via Oxford dictonary

Environmental remediation is the cleanup of hazardous substances dealing with the removal, treatment and containment of pollution or contaminants from environmental media such as soil, groundwater, sediment. Remediation may be required by regulations before development of land revitalization projects.
Via Wikipedia