Environmental reporters with ambitions to do investigative projects using databases will find an enormously rich collection of ideas, tips, examples, and tools in the new Data Journalism Handbook, released by the Open Knowledge Foundation and the European Journalism Centre.
In true open-source tradition the book is the product of hacking in the best sense — a volunteer collaboration of scores of gumshoes and geeks with smarts and hard-won real-world experience. It started barely six months ago at a London workshop, and grew to include an international array of contributors. Some of the best material is the collection of case studies. Although European in flavor, it includes some US contributors.
- "The Data Journalism Handbook (1.0 Beta),"  Open Knowledge Foundation, accessed May 16, 2012, edited by Jonathan Gray, Liliana Bounegru, and Lucy Chambers, distributed under Creative Commons Attribution-ShareAlike license.
If you are interested in data journalism (once aka computer-assisted reporting, and now often evolved as data viz), you should be sure to check out these few of the many additional resources:
- National Institute of Computer-Assisted Reporting,  Investigative Reporters and Editors. A lot of the action in this seminal community can be accessed via the NICAR-L listserve. 
- The New Precision Journalism,  by Philip Meyer.
- Journalism in the Age of Data,  Stanford Knight Center, 2012, by Geoff McGhee.
- Data Journalism Blog,  created by Marianne Bouchart.
- Data Driven Journalism,  a Dutch website.
- Data Journalism Awards website,  by the Global Editors Network, supported by Google.
- "5 Tips for Getting Started in Data Journalism,"  Poynter Institute, October 6, 2011, by Troy Thibodeaux.
- The Wikipedia article on "Data Driven Journalism"  has a list of books on the subject. See also "Database Journalism." 
- Explore EPA's Envirofacts  and ECHO  if you haven't already. Drill deep and find riches.
- "Digital Journalist's Legal Guide,"  Reporters Committee for Freedom of the Press.