In every industry, the Environmental department is an overhead, the requirement rate is very low. You will face problems finding jobs, after completing your M.Tech. 

If you are interested in the branch do a course in Environment Policy and Law, and you will be able to find job positions in legal branch to support company's moves. 

Environmental Science doesn’t have much scope in India and pursuing an M.Sc in this field is not a good idea. 

I know a few people who have done their post-graduation in Environmental Science and most of them are working in call centers or preparing for Govt. jobs. You may get job opportunities in environmental consultancies but the pay is very low. It will be around INR 10,000-INR 15,000 per month. 

One of my relatives completed her M.Sc in Environment from a U.S country. She is working for a consultancy in Pune. She handles projects like counting trees in a city. This shows how limited opportunities are for Environmental Science in the country.