Phase 1 Site Assessment and Phase 2 Site Assessment A Phase I/One Environmental Site Assessment (ESA) is the assessment of historical and current environmental activities of a property. We look at numerous environmental database records, fire insurance plans, city directories, aerial photographs, and also conduct a visual site visit and interviews with knowledgeable people to identify environmental concerns at the property. The Phase I/One Environmental Site Assessment GTA ESA is either conducted in accordance with the Ontario Regulation 153/04 (as amended 407/19) if filing a Record of Site Condition (RSC), or in accordance with CSA Standard Z768-01 if used for due diligence/financing purposes.