MSU --
I took the Civil with Env Depth a few times before switching to Civil with WR Depth, but I obviously needed Env-type reference materials. The Env reference books I used are as follows:
Environmental
1. Wastewater Engineering: Treatment, Disposal, Reuse, 3rd Edition, Metcalf & Eddy (ISBN 0070416907)
2. Water Supply and Pollution Control, 5th Edition, Viessman & Hammer (ISBN 0065000587)
3. Water Quality and Treatment, 4th Edition, American Water Works Association (ISBN 0070015406)
4. Water Chemistry, Snoeyink & Jenkins, (ISBN 0471051969)
5. Handbook of Environmental Engineering Calculations, C.C. Lee and Shar Dun Lin (ISBN 0070381836) NOTE: I just saw where the 2nd Edition (April 2007) is coming out.
Best of luck in your preparations.
JR