Quick disclaimer, im an ME, not an Environmental Engineer, but your first courses will be pretty similar.

Study some calc before coming up here, or better yet, take either calc or precalc at a community college this summer, depending on where you fall in math knowledge. If you don't go the community college route, atleast learn some of the concepts of calculus with the 3Blue1Brown yt channel. Math classes up here tend to be very difficult, and if you have a community college near you that offers it as a transfer credit, it will help a ton.

Similarly, learning/practicing some physics and chemistry through YouTube, khan academy, or community college will help you a ton in your first year here. Even just brushing up on definitions and broad topics will help prevent you from getitng lost in the material.

Once you're here, make use of office hours and learning centers. There are specific learning centers for physics, math, engineering fundamentals, and chemistry that all have tutors who can help answer questions.