Both a civil or mechanical engineering program with an environmental engineer program would be a great academic endeavor. If your interests are in water quality, impacts to water, or in green building, then I?????????d suggest the civil engineering route. If you are interested in renewable energy, then I?????????d suggest the mechanical engineering route.
An engineering degree opens opportunities to apply your technical knowledge to solve problems or build infrastructure that has minimal impacts to the environment. You might also look into an environmental science degree if you want to study the scientific aspects of the environment.
My husband is a registered professional mechanical engineer but his degree is environmental engineering where he took courses in renewable energy (degree from California Polytechnic University ????????? San Luis Obispo). My degree is in civil engineering and most of my career was in facilities engineering and now I work in renewable energy development.
I hope this gives some insight.