my friends think becoming an environmental engineer is a good idea

Hi Pneuma, 
I'm not sure why your friends are discouraging you! But, regardless of the reason, it's YOUR career, and not theirs, so you should make the decision for yourself. Of course it's good to get input from people who are knowledgeable - for example, talking to people who are working as environmental engineers can give you an accurate picture of what the field is like. I can connect you with those people if you're interested. It may also be good to consult with some of your teachers and professors in the areas you're interested in (probably natural sciences, math and mechanics, based on your desire to be an Env Eng). They might be able to tell you even more paths that may be worthwhile to check out. 

And after all that, if your friends don't support you and your decisions... get some new friends!

Good luck. 
Molly