The Role of Historical Research in Phase I ESAs

When many people think about historical research in a Phase I Environmental Site Assessment (ESA), aerial photographs are often the first source that comes to mind.  While historical air photos are valuable tools, relying on them alone can result in an incomplete understanding of a property’s environmental risk profile.
Historical research in a Phase I ESA is not simply about identifying visible changes over time.  It is about reconstructing land use, understanding regulatory context, and identifying potential environmental liabilities that may not be apparent from surface observations.
 
Beyond the Aerial Photograph
Aerial photographs provide useful insight into surface conditions, building footprints, vegetation patterns, and obvious site alterations.  However, they have limitations:

• Subsurface infrastructure such as underground storage tanks (USTs) is rarely visible.
• Temporary industrial activities may not leave obvious visual markers.
• Fill placement, grading, or minor spills may not be detectable.
• Resolution and frequency of historical coverage can vary significantly.

Aerial imagery tells part of the story; but rarely the entire story.
 
The Value of Documentary Research
Comprehensive historical research typically includes review of multiple documentary sources, such as:

• Historical city directories
• Fire insurance plans (where available)
• Land title records
• Municipal building permits
• Historical topographic maps
• Regulatory databases
• Local knowledge and interviews

Each of these sources contributes a different layer of information.  For example, city directories can reveal past occupants and business types that may indicate potential contaminating activities.  Fire insurance plans can identify historical fuel storage or industrial operations not evident in photographs.  Land titles may highlight ownership patterns associated with specific commercial uses. 
Environmental risk is often linked to historical operations that predate modern environmental regulations. Without documentary research, these risks can remain undiscovered.
 
The Role of Environmental Database Reports
An essential component of modern historical research is the review of environmental database reports, such as those provided by Environmental Risk Information Services (ERIS).
ERIS Reports compile regulatory information from federal, provincial, and municipal sources, identifying nearby contaminated sites, fuel storage tanks, waste facilities, spill records, and other environmentally sensitive activities.  In Alberta, this can include records from Alberta Environment and Protected Areas, the Alberta Energy Regulator, and other agencies.
 
The value of an ERIS Report lies not just in listing sites, but in supporting broader risk evaluation.  For example:

• Identifying adjacent or nearby fuel facilities that may present off-site migration risk.
• Confirming historical regulatory files associated with the subject property.
• Highlighting properties with historical contaminating activities that may influence site conditions.

Database reports are not substitutes for professional judgment.  However, they provide a structured and comprehensive framework for identifying recognized environmental conditions (RECs) and potential areas of concern that may warrant further evaluation.
 
Reconstructing the Site’s Story
Effective historical research requires synthesis.  It involves comparing aerial imagery with documentary evidence and regulatory data to identify inconsistencies, confirm uses, and evaluate plausibility.
For example:

• Aerial photographs may show an undeveloped lot, while directories indicate a fuel distributor operating at that address.
• Land records may reveal subdivision changes that affect historical boundaries.
• Database reports may identify contamination at an adjacent property, requiring evaluation of groundwater flow direction and potential migration pathways.

The objective is not to collect documents for their own sake.  The objective is to develop a defensible understanding of how the property has been used and whether those uses present environmental risk.
 
Professional Judgment and Defensibility
Historical research directly influences the defensibility of a Phase I ESA.  Incomplete or superficial research can result in missed contaminating activities, inadequate risk evaluation, or unsupported conclusions.

Conversely, thorough and well-documented historical analysis strengthens:

• Identification of recognized environmental conditions
• Development of the conceptual site model
• Rationale for conclusions and recommendations
• Overall credibility of the report

Environmental due diligence is ultimately about managing uncertainty.  Historical research reduces that uncertainty by providing context and evidence.

Aerial photographs remain a valuable and accessible tool in Phase I ESAs.  However, they represent only one component of a comprehensive historical review.
 
Robust historical research enables environmental professionals to move beyond surface observations and toward defensible, risk-informed conclusions.
 
In an era where environmental liability can have significant financial and regulatory implications, historical research is not simply a procedural step.  It is foundational to competent environmental practice.