Who is the best person to talk to when determining a career path?

Before anything I suggest you to take a couple of online career exams. These would at least give you a broad idea of what you want deep down. Secondly, do your own research. Look up these careers online and try to educate yourself. Talking to your school career adviser should be your next step. He would tell you what to expect and avoid.

I hope you the best with your search.

This is a good question. As mentioned in Wael's answer, doing your own research on line is the best way to start. Since you already have a field identified (environmental science), you can take that and break it down further by looking at job sites like Glass door, Monster, etc. (there are a ton of them out there) and plugging in that as a search term. This will bring up a list of positions in that field that you can review and see if anything sounds interesting. Job descriptions are often vague and intimidating so as to discourage the casual job seeker who is not serious about the position, but don't get discouraged. You are just seeking information. Look at the qualifications needed to perform the task. Note the ones you are interested in and then consider what it is that you like about them. Not just the overall requirement itself, but what is it about that item that makes it interesting. Is it something that is repeated daily and can be considered as following a formula or is it something that is new every day and poses new problems/challenges? Depending on your personality and what you like to do, you then used those items to decide which skills to build (software, finance, chemical, engineering, etc.).
There are also sources at the college you are planning on attending. The career councilors are available to assist and they have contacts in the various fields that they can point you to so you can set up one on one time to find out about the various careers and get advice on how to prepare. Job fairs and college recruiters are also good sources of information.
Having the willingness to reach out to these resources is the first step in being successful so don't worry about not knowing what questions to ask, just start asking general questions and that will open the discussion to the ones you really want answered. All of these resources are there to help and there is no rejection to fear from any of them so reach out and get started! If you come across the odd person who doesn't seem to care (very rare, but still a possibility), go on to the next person. There are a lot of choices out there so don't get discouraged if someone is having a bad day and comes across badly. You are in control of these discussions so feel the power and use it to your advantage. Good luck!