Their prime concern is that the mining will damage the natural barrier against salinity ingress.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/rajkot-farmers-protest-ultratech-limestone-mining-projects
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/indian-express-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/gujarat
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/mining
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rajkot-d
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/cement-industry
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/farmers
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/state-pollution-control-board-spcb-0
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/public-hearing