Former Fuel Infrastructure and Vapor Risk: Understanding Subsurface Conditions at a Commercial Property in Monrovia, California
Background
When properties have a history of fuel storage, automotive repair, or industrial operations, historical uses can create uncertainty during transactions, refinancing efforts, or redevelopment planning. For lenders, buyers, and property owners, understanding whether past operations have created ongoing environmental liabilities is an important part of managing risk and keeping projects moving forward.
McAlister GeoScience recently completed a Phase II Environmental Site Assessment (ESA) involving soil vapor sampling at a commercial property in Monrovia, California with a history of automotive and fuel-related operations. Previous due diligence identified Recognized Environmental Conditions (RECs) associated with historical site uses, including former fuel infrastructure and automotive service activities, prompting additional investigation into potential subsurface impacts.
Environmental Investigation Approach
Following recommendations from the prior Phase I ESA, McAlister GeoScience designed a targeted investigation to evaluate whether historical fuel infrastructure remained onsite and whether former operations had affected subsurface conditions.
The investigation began with a geophysical survey utilizing multiple technologies, including:
- Ground-Penetrating Radar (GPR)
- Electromagnetic pipe detection
- High-power metal detection equipment
This work helped identify potential subsurface anomalies and areas where underground storage tanks (USTs) and associated infrastructure were historically suspected to exist. Based on the geophysical findings, five soil vapor sampling locations were selected in areas associated with historical operations and suspected former fuel system locations. Although geophysical results were somewhat inconclusive, identified anomalies generally aligned with the expected location of historical fuel infrastructure. Findings suggested that former USTs, associated piping, and related components had likely been removed previously.
What Soil Vapor Sampling Revealed
Soil vapor investigations are commonly used to evaluate volatile compounds that may migrate through subsurface soils from historical petroleum or solvent-related activities. Because vapor pathways can create concerns for future occupancy or redevelopment, understanding these conditions early can help stakeholders make informed decisions. Laboratory analysis identified several volatile organic compounds (VOCs) commonly associated with petroleum products and automotive operations.
Select compounds, including benzene and ethylbenzene, exceeded applicable California commercial and industrial Environmental Screening Levels (ESLs) in isolated sample locations. However, the overall dataset indicated impacts were limited in extent. Using California regulatory guidance and federal risk evaluation methodologies, site-specific risk calculations were completed to evaluate potential exposure conditions. Calculated Cancer Risk and Hazard Index values were classified within low-priority thresholds.
Outcome: Supporting Transaction Confidence Through Targeted Investigation
Environmental findings do not always translate into material risk.
While historical operations and former fuel infrastructure warranted additional investigation, the results demonstrated that remaining vapor impacts were not present at concentrations expected to pose significant risks to human health or the environment under current or anticipated commercial use scenarios. The investigation concluded that no additional environmental investigation or corrective action was warranted at this time.
For commercial real estate transactions, targeted investigations like soil vapor assessments provide more than regulatory compliance—they provide clarity. Identifying and evaluating potential concerns early helps lenders, buyers, and owners better understand risk, reduce uncertainty, and maintain transaction momentum.
Environmental due diligence works best when it provides actionable answers rather than unnecessary complexity.
If you want to learn more or need help with an upcoming project, reach out to the team at McAlister GeoScience for more!