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What is vapor encroachment?
Vapor intrusion is when harmful vapors seep into a building from the groundwater or soil beneath. Radon intrusion was the first vapor intrusion to be recognized, but it became apparent that other types of chemicals, like petroleum-based liquids or chlorinated solvents, could be an issue for indoor air quality. When these chemicals create indoor air pollution, it could be detrimental to occupants’ long term health.
Vapor encroachment is a broader term than vapor intrusion, as explained in the ASTM E2600-10 Standard for Vapor Encroachment Screening; vapor encroachment describes the potential for noxious subsurface gases to exist in groundwater or the soil on or near the target property, not just what is directly under the building.
How are building occupants exposed to these chemicals?
Vapor intrusion can happen through contaminated well water that gets into the house when there is negative pressure inside the house. Heating and cooling systems, exhaust fans, bathroom fans, fireplaces, and clothes dryers can all create depressurization that invites the influx of gases from the ground through drains, showers, concrete slab pores, cracks in foundations and walls, etc.
Vapor intrusion screening is can be triggered by new knowledge, such as learning of environmental conditions like a plume of contamination with adjacent or nearby properties to the site. Generally, vapor intrusion testing is a consideration during the due diligence phase of an industrial or commercial real estate transaction when particular attention is given to the nature of the building and previous uses of the site. Chemical vapor intrusion can impact residential homes, but radon is a more common concern.
A vapor intrusion assessment, also known as Pressure Field Extension (PFE) testing, is our reference point to determine system design. When we conduct our PFE testing, we look for potential exposure pathways, i.e. cracks/ ruptures in the slab, floor to wall joints, floor drains (not holding water), sewer lines, etc. The identification of potential exposure pathways for VOC’s to enter the structure is the first step in outlining a plan to seal those areas as part of our strategy to mitigate risks related to vapor intrusion.
ASTM E2600 - 15 offers suggestions on how to utilize vapor intrusion screening in real estate transactions. The extent of screening should be dictated by reasonably ascertained information, such as the nature of the building, previous uses of the site and surrounding conditions of the site in question. Vapor intrusion screening should be performed by a qualified professional. Since there are no general vapor intrusion licensing options, you should look for radon certifications, such as Radon Mitigator or Primary Radon Tester or the certifications offered by the National Radon Proficiency Program, such as Residential Mitigation Provider and Residential Measurement Provider. Reports are considered current if performed within the most recent 180 days. Vapor intrusion screening does NOT replace the need for Phase I and Phase II environmental site assessments as part of due diligence for purchasing real estate.
When do I need to check for vapor issues?
How do you address vapor intrusion?
The vapor mitigation solution will be based on the building foundation type and whether it is installed before construction or retrofitted after construction.
For buildings with a slab (concrete) foundation, a sub-slab depressurization system will be installed. These systems typically consist of installing solid core PVC pipes inside the slab; these pipes are connected to a fan that creates a negative vacuum under the slab. The vapors under the structure are discharged outside.
For buildings with a crawl space with an soil or gravel “floor”, sub-membrane depressurization systems are the best choice. An impermeable membrane, typically 6 to 12 millimeter thick plastic sheeting, is placed over the soil after the soil is dug out to allow perforated ventilation piping to capture, reroute, and discharge captured vapors through a discharge pipe.
These may be combined with other approaches, such as building over-pressurization, sealing openings, and passive venting.
What happens when the chemical vapors are vented into the air outside?
These molecules should not cause concern when they can disperse freely in fresh outdoor air but could be a concern to health over time in enclosed areas. It is important to select a qualified consultant and installer to establish the right vapor intrusion mitigation system.
Is it expensive to maintain?
Sub-slab and sub-membrane depressurization systems must operate on a continuous basis to effectively prevent vapor exposure. They use little electricity, are relatively quiet, and require little maintenance. Our comprehensive post-implementation report will include estimated costs to maintain. A licensed mitigator should periodically inspect the system to ensure its proper functionality.