WPI is a technical institute with a focus on engineering. They do a great job preparing their students for jobs as practicing engineers.
Brown is a university with a broad arts and sciences curriculum. The sciences are very strong and you will find lots of sharp students there. The school of engineering is fairly research-oriented, although they do offer ABET accredited degrees in biomedical engineering, chemical engineering, computer engineering, electrical engineering, materials engineering, and mechanical engineering. No civil engineering though…
Make sure that you know what civil engineers do. They work infrastructure projects like roads, bridges, and buildings. As @usbalumnus says, an ABET accredited bachelors degree is important because it is the first step toward becoming a Professional Engineer. A PE license is very helpful to anybody who wants to work in civil engineering. WPI might be more appropriate than Brown if you are sure you want to be a civil engineer.
Environmental engineering may not be what you think it is. Many environmental engineers design landfills or write environmental impact statements for companies that plan development projects. Look over the courses that a civil and environmental engineer takes.
If you are interested in sustainable energy, you might find your place in an electrical engineering program or a mechanical engineering program. For example many wind energy engineering groups find their home in mechanical engineering departments.