Role of Historical Source Review in Environmental Assessments

Share the knowledge

A Phase I Environmental Site Assessment (ESA) is fundamentally an investigation into the past. While the site visit and interviews provide a snapshot of current conditions, it is the historical source review that reveals how a property has evolved over time—and whether past uses may have introduced environmental risks.

Historical source review is one of the most critical components of a Phase I ESA. It allows environmental professionals to identify potential contamination pathways, legacy risks, and Recognized Environmental Conditions (RECs) that may not be visible today. In many cases, the most significant environmental liabilities originate from activities that occurred decades earlier.

This article explores the purpose and objective of historical research, the key sources reviewed, and how findings are analyzed and reported within the Phase I ESA process.

Purpose and Objective of Historical Source Review

The primary objective of historical source review is to reconstruct the environmental history of a property and its surrounding area. This involves identifying past uses and activities that could have resulted in the release of hazardous substances or petroleum products.

Understanding Past Land Use

Land use changes over time. A property that is currently:

A commercial office
A residential development
Vacant land

…may previously have been:

A gas station
An industrial facility
A dry cleaner
Agricultural land with pesticide use

Historical research helps uncover these transitions and evaluate whether they present environmental concerns.

Identifying Recognized Environmental Conditions (RECs)

A central goal of a Phase I ESA is to identify Recognized Environmental Conditions (RECs)—defined as the presence or likely presence of hazardous substances due to a release or potential release.

Historical sources help identify:

Former underground storage tanks (USTs)
Industrial operations
Waste disposal practices
Chemical storage areas

Without historical review, many RECs would remain undetected.

Supporting All Appropriate Inquiry (AAI)

In jurisdictions such as the United States, historical research is essential for meeting All Appropriate Inquiry (AAI) requirements under CERCLA.

A properly conducted historical review:

Demonstrates due diligence
Supports liability protections
Strengthens the defensibility of the ESA

Evaluating Adjacent Properties

Environmental risk is not confined to property boundaries. Contamination can migrate through:

Soil
Groundwater
Air pathways

Historical research extends beyond the subject site to include adjacent and nearby properties, identifying off-site sources that could impact the property.

Filling Gaps in Site Knowledge

Interviews and site inspections may not reveal:

Activities from decades ago
Demolished structures
Temporary industrial uses

Historical records provide a long-term perspective that fills these gaps.

Key Historical Sources Reviewed

A comprehensive historical source review relies on multiple data sources. Each provides a different perspective, and together they create a more complete picture of site history.

Aerial Photographs

Aerial photographs are one of the most valuable tools in historical research.

They allow environmental professionals to:

Observe site development over time
Identify structures, tanks, and operational areas
Detect changes in land use

Aerial imagery often spans several decades, providing a visual timeline of the property.

Fire Insurance Maps (e.g., Sanborn Maps)

Fire insurance maps, such as those produced by Sanborn Map Company, provide detailed information about:

Building footprints
Construction materials
Industrial uses
Storage tanks

These maps are particularly useful in urban areas and can reveal historical uses not evident in other sources.

City Directories

City directories list businesses and occupants at specific addresses over time.

They help identify:

Types of businesses operating on-site
Duration of operations
Changes in occupancy

For example, a property currently used as retail may have previously housed:

Auto repair shops
Manufacturing facilities
Chemical storage operations

Topographic Maps

Topographic maps provide information about:

Terrain and elevation
Natural features such as streams and wetlands
Historical land development

They can indicate:

Potential drainage patterns
Areas where contaminants may migrate

Building Permits and Records

Municipal records such as building permits and planning documents can reveal:

Construction history
Renovations or expansions
Installation or removal of tanks

These records help establish a timeline of structural and operational changes.

Environmental Databases

While not strictly historical in the traditional sense, regulatory databases provide:

Records of spills and contamination
Registered storage tanks
Cleanup activities

These databases complement historical sources by identifying known environmental issues.

Historical Reports and Previous ESAs

If available, previous environmental reports can provide:

Past findings
Sampling results
Identified risks

These documents help build continuity in environmental assessment.

Interviews and Local Knowledge

Interviews with:

Property owners
Occupants
Local authorities

…can provide insights not captured in written records, such as:

Informal site uses
Anecdotal evidence of spills or dumping

Combining Multiple Sources

No single source is sufficient on its own. Environmental professionals must:

Cross-reference multiple data sources
Identify inconsistencies
Fill gaps where data is missing

This layered approach ensures a comprehensive and defensible historical review.

Analysis and Interpretation of Historical Data

Collecting historical data is only the first step. The real value lies in analyzing and interpreting the information to identify environmental risks.

Establishing a Chronological Narrative

Environmental professionals develop a timeline that:

Tracks changes in land use
Identifies periods of higher risk
Highlights key transitions

This narrative helps stakeholders understand how the site has evolved.

Identifying High-Risk Activities

Certain historical uses are associated with higher environmental risk, including:

Gas stations and fuel storage
Dry cleaning operations
Manufacturing and industrial processes
Waste disposal and landfills

These uses are flagged for further evaluation.

Assessing Data Gaps

In some cases, historical records may be incomplete or unavailable.

Data gaps are:

Identified and documented
Evaluated for potential impact on conclusions

Significant gaps may lead to:

Conservative assumptions
Recommendations for further investigation

Evaluating Migration Pathways

Historical information is used to assess whether contaminants could:

Migrate onto the site from nearby properties
Move through soil or groundwater

This is particularly important in densely developed or industrial areas.

Determining Recognized Environmental Conditions (RECs)

Based on the analysis, environmental professionals determine whether:

RECs are present
Potential RECs exist
Conditions have been addressed (historical RECs)

This classification is a key outcome of the Phase I ESA.

Reporting Historical Findings

The findings of the historical source review are documented in the Phase I ESA report.

Clear and Defensible Documentation

Reports must:

Clearly describe historical sources reviewed
Summarize findings
Provide supporting evidence

This ensures that the ESA is:

Transparent
Defensible
Compliant with standards

Integration with Other ESA Components

Historical findings are integrated with:

Site inspection observations
Interviews
Regulatory database results

This holistic approach strengthens conclusions.

Supporting Conclusions and Recommendations

The historical review directly informs:

Identification of RECs
Recommendations for further investigation (e.g., Phase II ESA)
Risk assessments

Communicating Risk to Stakeholders

The report must translate technical findings into:

Clear, understandable language
Actionable insights

Stakeholders—including buyers, lenders, and developers—rely on this information to make decisions.

Challenges in Historical Source Review

Despite its importance, historical research presents several challenges.

Incomplete or Missing Records

Older records may:

Be unavailable
Contain gaps
Lack detail

Environmental professionals must work with incomplete information.

Inconsistent Data Quality

Different sources may:

Provide conflicting information
Use different terminology
Vary in accuracy

Careful interpretation is required.

Time and Cost Constraints

Clients often expect:

Fast turnaround
Cost efficiency

Balancing thorough research with project timelines can be challenging.

Urban vs. Rural Differences

Urban areas often have more detailed records
Rural areas may have limited documentation

This affects the depth of historical analysis.

Best Practices for Effective Historical Review

To ensure high-quality results, environmental professionals should:

Use multiple sources to cross-verify information
Document all sources and limitations
Identify and address data gaps
Apply professional judgment and experience
Maintain compliance with ASTM standards

The Strategic Value of Historical Research

Historical source review is not just a technical requirement—it is a strategic tool.

It enables stakeholders to:

Understand long-term environmental risk
Make informed investment decisions
Plan for redevelopment and remediation
Protect against liability

Conclusion

The role of historical source review in Phase I Environmental Site Assessments is both foundational and indispensable. By reconstructing the past, environmental professionals can identify risks that are not immediately visible, ensuring that stakeholders are fully informed before making critical decisions.

From uncovering legacy contamination to supporting regulatory compliance and liability protection under frameworks like CERCLA, historical research provides the context necessary for accurate and defensible environmental assessments.

In an industry where unseen risks can carry significant consequences, the ability to understand and interpret a property’s history is essential. A thorough and well-executed historical source review transforms a Phase I ESA from a procedural requirement into a powerful tool for risk management and strategic planning.

👉 Learn more about our Automated Environmental Site Assessment Solution

The Role of Historical Source Review in Phase I Environmental Site Assessments