Preventing Vapor Intrusion from Landfills
[caption id="attachment_369" align="aligncenter" width="850"] This figure depicts the migration of volatile chemicals from contaminated soil and groundwater plumes into buildings. Volatile chemicals are shown to enter buildings through cracks in the foundation and openings for utility lines. Atmospheric conditions and building ventilation are shown to influence vapor intrusion (Credit: EPA)[/caption]
What is Vapor Intrusion?According to the US Environmental Protection Agency (EPA), vapor intrusion can be defined as the "migration of hazardous vapors from any subsurface contaminant source, such as contaminated soil vapour extraction or groundwater or contaminated conduit(s), into an overlying building or unoccupied structure via any opening or conduit." When certain chemicals are released into subsurface layers of soils as either solids or liquids they may form dangerous vapors that could potentially migrate through subsurface soils and enter drains, basements, buildings, etc through cracks or holes. Depending on the composition of the gas in question, it could be either toxic or explosive (or both), posing a safety risk to humans working or living in these spaces.
Assessing the Vapor Intrusion RiskAs landfill gas is composed largely of methane, a toxic and highly explosive gas, the risk of vapor intrusion from landfill sites is high. Vapor intrusion of methane poses both an asphyxiation and explosion hazard that poses a serous risk to human health and safety. Consequently, it is imperative that landfills (and other sites where hazardous vapors pose a risk) carefully consider the vapor intrusion pathway and undertake regular monitoring to assess methane concentrations and to check for rogue gases.
Vapor Intrusion Screening-level CalculatorThe US Environmental Protection Agency (EPA) has developed a Vapor Intrusion Screening-Level (VISL) Calculator, a technical resource that enables operators to identify and assess situations where there is a high risk of hazardous vapor intrusion. The VISL Calculator, which is presented as a Microsoft Excel spreadsheet, provides the following services:
- It identifies hazardous vapor-forming chemicals that could potentially pose a health or safety risk when inhaled.
- It recommends screening-level concentrations of hazardous vapors and gases for groundwater, near-source and sub-slab soils, as well as indoor air derived from benchmark exposure scenarios for residential or non-residential buildings, a cancer risk level of 1/million, and a hazard risk of 1 for possible non-carcinogenic effects.
- It allows operators to calculate screening-levels for a specific site by imputing user-defined hazard risk levels for the target site/building, site specific exposure scenarios, as well as site- or semi-site specific factors that could reduce these hazards.
Benefits of Using the Vapor Intrusion Screening-Level CalculatorThe VISL Calculator can assist operators to determine whether a vapor intrusion pathway could potentially pose a health and/or safety risk to humans by:
- Determining whether there are any hazardous volatile chemicals that could endanger humans due to vapor intrusion present
- Helping to determine whether any volatile chemicals that are found to be present are present at levels that could pose an explosion hazard
- Comparing vapor extraction systems levels of subsurface soils and indoor air against screening levels recommended by the VISL Calculator
- Using this data for prioritizing sites and buildings for monitoring and for implementing appropriate safety precautions.
Featured Image: Vapor Intrusion, by EPAReference: Oswar Vapor Intrusion Technical Guide.