is a closed landfill automatically a brownfield?

Amanda, Landfills are one of the largest sources of pollution in communities throughout the U.S., so I’m certain as much leeway as possible would be afforded to any project attempting to rehabilitate a landfill site. However, there are certain protocol that should be adhered to. A landfill site meets the definition of a brownfield if environmental contamination has been identified, or presumed to exist by virtue of the type of materials deposited, such as a municipal solid waste landfill that receives household waste. Absent a site being designated a brownfield by a recognized government agency, the documentation you are required to submit is an acceptable environmental site assessment and remediation plan. I can’t determine if your comprehensive “Final Closure and Post-Closure Maintenance Plan” meets the threshold. If you have any doubt, have an environmental firm review your report. If it doesn't, I would recommend contracting an environmental firm to have one done.

Also, in case your project happens to be a medical-related facility I think I remember reading that the health care supplement explicitly excludes building on a prior landfill. See SSPr 2. (Again only for healthcare).

Ryan, you are correct. LEED 2009 for Healthcare SSp2 Environmental Site Assessment "Sites that are contaminated due to the past existence of a landfill on the site are prohibited..."