Vapor encroachment screening assesses potential risks of contaminant vapors migrating from soil or groundwater into buildings. The initial screening assessment uses soil, gas, and groundwater sampling. This step is followed by a comparison with conservative screening levels, determining the need for further investigation. 

Vapor encroachment method is also an important part of Phase 1 Environmental Site Assessment (ESA). It identifies harmful chemicals present in vapor that comes from contaminated soil on the subsurface.

Vapor Encroachment Screening Methods

Vapor encroachment screening is an important environmental assessment method to find out threats from hazardous vapor from contaminated soil or water. These vapors often contain volatile organic compounds (VOCs) from sources like fuel spills, dry cleaners or industrial wastes. Therefore, the vapor migrated from the soil impacts the air quality of buildings. The steps involved in this process are:

1. Initial Screening (Tier 1)

  • Soil Gas Sampling: Soil samples are collected from contaminated sources and buildings to identify the concentration of volatile organic compounds.  
  • Groundwater Sampling: Groundwater samples are collected to assess the chances of VOCs migrating from the soil to the buildings.
  • Pathway Assessment: It involves analyzing soil and water data to find the pathway VOCs from the building's source. 

2. Sampling Technique

  • Driven Probe Rod: This is a method to install soil gas probes that are suitable for moderate to high permeability soils.
  • Burial of Soil Gas Sampling Tubes: This is another method of inspecting soil gas, and it is also suitable for moderate to high permeability soil.  

Types of Vapor Encroachment Screening Methods

The vapor encroachment screening method assesses the risk of vapor intrusion. Vapor intrusion is when the soil vapor containing contaminants migrates into the building. The types of VES method are:

  • Tier 1 Vapor Encroachment Screen: The first step in detecting vapor encroachment is based on readily available data and soil characteristics. It includes a search distance test to find suspected contaminated sites, determine chemical concentrations, and assess vapor intrusion. 
  • Tier 1 Vapor Encroachment Screen: This more in-depth assessment step involves collecting soil vapor samples and analyzing them to find contaminants. Sub-slab soil sampling is the common method of evidence in vapor intrusion investigation. This step identifies the extent and concentration of contaminants in soil vapor, aiding health risks.
  • Preemptive Vapor Mitigation (PVM): It is an emerging method aiming to omit vapor encroachment as a recognized environmental condition (REC). It involves the implementation of mitigation steps before vapor intrusion is confirmed, like installing sub-slab depressurization systems. PVM is also a cost-effective approach to address vapor intrusion issues.

Key Benefits

VES is a two-tiered approach offering various benefits by identifying risks of contaminated vapor coming from the soil into the buildings. This approach offers protection to public health and facilitates responsible real estate transactions. The benefits are:

  • Preventing Health Issues: VES prevents health issues related to exposure to VOC after addressing vapor intrusion. It also identifies other hazardous substances causing headaches, nausea, or increased risk of cancer.
  • Mitigation Strategies: VES helps to implement mitigation strategies such as sub-slab depressurization systems or other methods to reduce vapor intrusion.
  • Due Diligence: VES is an important part of environmental due diligence in real estate transactions. It ensures that buyers are aware of vapor intrusion issues.
  • Reducing Liability: VES reduces liabilities associated with contaminated properties by assessing vapor intrusion risks. Thus, it encourages making informed decisions about property acquisition, development or remediation. These steps ensure that the project is undertaken responsibly.    

Vapor Encroachment & Vapor Intrusion: How They Are Different?

The VE approach assesses the risk of chemicals migrating into the vadose zone from contaminated soil. On the other hand, VI refers to the presence of that harmful vapor inside a building. The differences are:

1. Vapor Encroachment

The VE approach evaluates the likelihood of chemicals from contaminated soil groundwater entering the vadose zone. It includes preliminary assessments such as vapor encroachment screening to find out potential risks. 

2. Vapor Intrusion

VI focuses on the actual presence of contaminated vapors inside the building. VI generally occurs when vapors migrate through the ground and enter the building through cracks or any other openings. It is found by an investigation involving soil sampling to determine the concentration of vapors. If soil vapor concentration exceeds the established screening level, Human Health Risk Assessment is necessary to find site-specific risks.   

Conclusion

To sum up, vapor encroachment screening methods protect public health by identifying and addressing risks from contaminated soil and groundwater vapor entering the building. It ensures safer indoor air quality and prevents health issues.

The environmental consultants also take part in the VES approach by analyzing the historical and current use of the property and surrounding areas to find contamination sources. It includes reviewing databases, maps and past environmental reports.