Phase I Initial Site Investigation Report is a document which contains the results of Preliminary Response Actions undertaken at a disposal site. The purpose of a Phase I Report is to record information in a standardized format in order to facilitate the evaluation and Tier Classification of a disposal site in those cases where Comprehensive Response Actions may need to be undertaken or support a Response Action Outcome Statement filed prior to Tier Classification of a disposal site.

Content of a Phase I Report includes:

• general disposal site information (defines and describes the disposal site and surrounding area),
• disposal site map,
• disposal site history
• potentially responsible parties,
• site hydrogeological characteristics (details of subsurface investigations and a preliminary or generalized description and depiction of site hydrogeologic conditions),
• nature and extent of contamination,
• migration pathways and exposure potential,
• evaluation for the need to conduct Immediate Response Actions, and
• conclusions (summary of findings and statement of conclusions with respect to the site and the outcome of Initial Site Investigation Activities).

Possible Outcomes of a Phase I Report are the determination for the necessity for Comprehensive Response Actions and Tier Classification or the filing of Response Action Outcome Statement submitted to the Department indicating the achievement of the requirements of a "Class A" or "Class B" Response Action Outcome.