“NLC”) the predecessor-in-interest of the appellant herein (formerly known as ST-CMS Electric Company Private Limited ) had set up a 250 MW lignite-based thermal power project in 1992 and had entered into Power Purchase Agreement (“PPA”) on 04.11.1993 with Tamil Nadu Electricity Board (“TNEB”), the predecessor of second respondent Tamil Nadu Generation and Distribution Corporation Limited (“TANGEDCO”), the said PPA having been amended and restated on 20.11.1996 followed by certain modifications through addendums dated 09.10.1997, 27.01.1998, 22.01.1999 and 25.08.1999. Prior to the said events, in the run-up for setting up of the said power project, NLC had approached the Ministry of Environment, Forest and Climate Change (“MOEF&CC”) of the Government of India for environmental clearance which concededly was granted by Office Memorandum dated 23.12.1988 under the then prevalent Environment (Protection) Rules, 1986, framed under Environment (Protection) Act, 1986. The said Rules were amended by Notification dated 07.12.2015 through Environment (Protection) Amendment Rules 2015 in terms of which there is a mandate to all thermal power projects, existing as well as new, to comply with the norms under the said regulatory framework,