mitigation plan
Mitigation of what? For a definition of mitigation, check a dictionary.
In environmental science, it means reducing the pollution effects of something (usual human activity), such as air pollution by power plants, ozone layer depletion by chorofluorocarbon release, polution of lakes due to industrial and agricultural runoff, or the extinction of fish species due to the building of dams, overfishing and the destruction of spawning habitat.