I was asked about review courses here and figured the topic needed more than just a short answer. Many organizations have workshops on environmental or geological topics that are low-cost or free, partially to fulfill an educational mission, and partially to support professionals who have continuing education requirements. I suggested looking up your local professional organization, but here are some links to other options, some of which I've mentioned before:
1. Clu-in.org has a bunch of free webinars focused on environmental topics. I prefer live webinars, but they also have archived presentations as well.
2. Trainex.org is a separate site with links on clu-in. It includes a number of classroom courses in addition to videos and online courses. It's intended for EPA and other government personnel, but non-government folks can generally take the courses if they pay the course fee. The course fees are generally lower than the next option...
3. The national ground water association has events listed here, which include brownbags, webinars, and short courses. Some of their more interesting webinars are member-only.
4. Conferences are generally a good option, but unless you have a generous expense account, their usefulness depends on where they're held and how expensive they are. Some organizations to keep in mind for geology/environmental consulting stuff (in the US):
a. NGWA lists their conferences plus a lot of water supply stuff here
b. Geological Society of America has section meetings, a big annual meeting, and subject-specific conferences
c. the Association for Environmental Health and Sciences has meetings on the east and west coast
d. the National Association for Environmental Professionals has one annual meeting coming up
e. Battelle has a set of three conferences.
f. RemTEC is every 2 years - next one in 2015.
g. The National Environmental Monitoring Symposium
So there are a bunch of options out there for continuing ed credits or just expanding your knowledge...