For an MTech in Environmental Engineering, the best option will be to attempt GRE or IELTS and pursuing a Ph.D. abroad. 

There are several research job opportunities for Environmental Engineering students in India but these jobs do not pay well. The reason behind this is the Govt. has not taken initiative to improve in this field. Which is not the case abroad. 

If your only alternatives are institutes like NIT Durgapur, it will be better to go for IIEST Shibpur. Pursue a B.E. in Civil Engineering and after that do your MTech in Environmental Engineering. You will get way better research exposure at IIEST Shibpur.