Vapor Intrusion

What is Vapor Intrusion?

Vapor intrusion (VI) is the migration of organic chemicals in vapor phase from the subsurface into overlying buildings.  Vapors are generated by contaminants in soil and groundwater, travel through the soil layer into interior building spaces, and can be harmful to building occupants even if the contaminant concentrations are below regulatory standards.  The potential for impacts from VI is based on the following criteria:

  • the building is occupied, even if only on a temporary basis;
  • there is a pathway from the contaminant source to building occupants, usually through cracks or utility penetrations in the building ground floor slab, basement walls or exposed areas (e.g., crawlspace floors); and
  • a soil or groundwater contaminant source is less than 100 feet laterally or vertically from the building.

VI can contribute to adverse health issues among building occupants, especially those more susceptible to airborne contaminants, and can cause fear and anxiety among building occupants, businesses, and property owners.  A VI assessment of a property that meets the qualifying criteria is essential because a lack of understanding about indoor air issues and evaluation techniques may over-simplify, under-state, or over-state the problem.   Indoor air quality is often overlooked in many environmental investigations when contamination is present near inhabited structures.  The EPA and state environmental regulatory agencies have developed both screening and action levels for soil-gas and indoor-air contaminants to determine if VI poses a health threat to building occupants without mitigation measures.

Vapor Intrusion Experience

Duncklee & Dunham has conducted VI assessments and designed soil gas VI mitigation systems (VIMS) for commercial, residential, academic, and municipal facilities in North Carolina and Virginia in accordance with EPA’s Technical Guidance, the North Carolina Inactive Hazardous Sites Program, and differing state and federal regulatory requirements.  We utilize both traditional, short-term methods (e.g., Summa canisters) and more innovative, long-term methods (i.e. passive gas samplers) to collect samples in these assessments.   Target contaminants include petroleum hydrocarbons, volatile organic compounds (VOCs), chlorinated VOCs, and semi-volatile organic compounds.  We have also collected soil gas samples using soil vapor monitoring wells and Vapor Pins® and have experience in collection protocols for sub-slab and crawl-space soil gas.  Duncklee & Dunham has also conducted sub-slab soil gas analysis for radon in areas where the potential for radon intrusion is high due to underlying geologic formations.

Duncklee & Dunham has also designed passive and active VIMS for new and existing buildings.  Our VIMS design experience includes pre-construction networks of passive and active horizontal vent piping, sub-slab vapor barriers (asphaltic, HDPE, and composite membranes), and post-construction passive and active vertical vent piping networks and floor sealants.  We have designed, provided construction oversight, and tested systems installed on Brownfield and Greenfield properties for academic, commercial, residential and municipal uses. 

Duncklee & Dunham hosted a vapor intrusion symposium for our clients that provided an overview of vapor intrusion assessments and guidelines to follow on evaluating vapor intrusion in North Carolina.  Our Director of Engineering, Andrew Rodak, is a member of ITRC’s Vapor Intrusion Mitigation Team, which is preparing technical documents and training materials of vapor mitigation strategies for use by regulators to evaluate the adequacy of VIMS design submittals.