Environmental assessment needs to be done only if construction area is above 20,000 sq.m.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/statue-unity-needs-no-clearance
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/hindu-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/gujarat
[4] http://admin.indiaenvironmentportal.org.in/thesaurus/environment-clearance-ec
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/environment-impact-assessment-eia
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/narmada