Great Lakes Legacy Reauthorization Act of 2008

Great Lakes Legacy Reauthorization Act of 2008 - Amends the Federal Water Pollution Control Act (commonly known as the Clean Water Act) to define: (1) "site characterization" as a process for monitoring and evaluating sediment contamination under the Environmental Protection Agency's (EPA) guidance for the assessment of contaminated sediment in an area of concern in the United States; and (2) "potentially responsible party" to mean an individual or entity that may be liable under any federal or state authority used to facilitate the cleanup and protection of the Great Lakes.

Includes aquatic habitat restoration activities among activities the Great Lakes National Program Office is authorized to implement for the remediation of sediment contamination in areas of concern.

Prohibits the Administrator from implementing such a remediation project unless: (1) each nonfederal sponsor has entered into a written agreement under which each party agrees to carry out its responsibilities and requirements for the project; and (2) the Administrator provides assurance that EPA has conducted a reasonable inquiry to identify potentially responsible parties.

Revises provisions concerning the nonfederal share of project costs.

Requires the Administrator to implement, at federal expense, one site characterization per site within a project for the remediation of contaminated sediment. Repeals a prohibition against implementing a project unless the nonfederal sponsor agrees to maintain aggregate expenditures from all other sources for remediation programs in the area of concern or above the average level of such expenditures in the two fiscal years preceding the date the project is initiated.

Authorizes appropriations through FY2010 for: (1) such remediation projects; (2) a public information program to provide information relating to such remediation; and (3) the development and use of innovative approaches, technologies, and techniques for such remediation. Limits to 20% of the amount of funds appropriated for remediation projects that may be used for site characterization.