The librarian can help you refine your search strategy, assist with retrieval of relevant materials and guide you through a maze of resources. This is the best starting place. This assignment involves many steps. Focusing on a more narrow aspect of pollution, e.g., will help focus research efforts. Good choice for supplementary sources, especially state and federal government publications.
Much government information is now available on the Web.
If you have difficulty locating solid resources, contact your librarian for help. Details of Most Efficient Search Sam needs both current and historical information. He might need to consider whether his historical information needs to be something written at that time, or if a more recent source that takes a retrospective look at the issue will better suit his needs. Sam may need to consult a few non-scholarly sources first, in order to gain a better understanding of the scope and complexity of his topic. The final works he chooses and will be citing in his paper need to be by professionals or scholars in the field, rather than popular press materials.