Phase II Vapor Intrusion Assessment

          Vapor Intrusion refers to the process by which volatile chemicals migrate from a subsurface source into the indoor air of buildings. Soil vapors and gases enter the building through cracks or penetrations in basement floors/walls, including openings around sump pumps, pipes or electrical wires which pass through the foundation (similar to how radon gas enters the building).

          Vapor Intrusion can occur whether the building is old or new, or whether the building is constructed on grade or has a crawl space or basement. In most cases, operation of the building's HVAC system and internal exhaust systems can exacerbate the problem by increasing the pressure differential.

The sources of the subsurface volatile chemicals are contaminated soils and/or groundwater resulting from:

• Buried waste and drums
• Underground piping systems
• Underground storage tanks
• Impoundments and lagoons
• Chemical use and spills
• Improper disposal

          Inhalation is the primary route of exposure to building occupants. Indoor air chemical concentrations can exceed odor thresholds for specific chemicals resulting in malodor, IAQ concerns and occupant complaints. Several volatile chemicals (VOCs, SVOCs) are also carcinogenic. As a result, vapor intrusion is a Phase II ESA concern addressed in 39 states. Seven states (CA, PA, NY, NJ, MA, CT, NH) have codified vapor intrusion in a regulation or law. In March 2008, ASTM published a new standard (E 2600-08) entitled "Assessment of Vapor Intrusion in Structures on Property involved in Real Estate Transactions" which adopts voluntary consensus standards of good practice to evaluate the potential migration of soil gas/vapors from contaminated soil and groundwater into existing or planned structures.

AET's scope of services for Vapor Intrusion per ASTM/EPA protocol include:

Tier 1 Non-numeric Screening: Formulation of a professional opinion of no further action based on historical research and site reconnaissance that there are no sources of contamination within a certain distance at the property (typically based on a distance of not less then 100 feet).

Tier 2 Numeric Screening: Verification of no further action for vapor intrusion by the collection of soil and groundwater samples to screen the property for the presence of contamination.

Tier 3 Site-Specific Screening: Develop a conceptual site model and implementation of a vapor intrusion investigative plan to document current and potential human exposures to subsurface vapors at the property.  Relevant site-specific air sampling data is collected beneath the building foundation or slab, subsurface walls, within crawl spaces, indoor air, as well as outdoors for quality control comparisons. Air sampling results are compared to typical background concentrations of select VOCs listed in the ASTM standard and various state regulations. (See Project Profile).

Tier 4 Vapor Intrusion Mitigation: Design and implementation of engineering controls to minimize and/or eliminate soil vapor intrusion into the building. Engineering controls include sealing infiltration points and actively manipulating pressure differential within the building in comparison to the surrounding environment. Incorporation of vapor barriers can be designed into new construction. Sub-slab depressurization systems can be added to existing buildings which draw vapors from the soil beneath the occupied building areas and discharge collected vapors into the atmosphere. Additional controls can include HVAC modifications, room pressurization, and passive ventilation systems.

To view representative AET project profiles click here

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