EWI Tests Superfund Site for Vapor Intrusion Using Sub-Slab Sampling Technique

On contaminated sites, concern over exposure to harmful chemicals can expand from groundwater and soil to indoor air. Such air pollution is called “vapor intrusion,” and “occurs when there is a migration of vapor-forming chemicals from any subsurface source (soil, water) into an overlying building,” according to the Environmental Protection Agency (EPA).

In summer 2019, Environmental Works, Inc. (EWI) tested for vapor intrusion in a building within the footprint of a Superfund site in southwest Missouri using sub-slab vapor sampling.

Jon McKinney, associate engineer at EWI who conducted the sampling, explained the process. “We drill a hole through the (concrete) slab and install a ‘pin’ that is sealed around the edges. This allows us to collect vapor samples from beneath a building.”

McKinney added that a “helium shroud” is used during sampling to guarantee that the air vapor being sampled is “not diluted by ambient air.”

According to the EPA, “recognition of soil vapor intrusion to buildings and other enclosed spaces occurred in the 1980s with concerns over radon intrusion. Subsequently, there was an increasing awareness that anthropogenic chemicals (e.g., petroleum hydrocarbons and chlorinated solvents) in soil, groundwater, and sewers and drainlines could also pose threats to indoor air quality via the vapor intrusion pathway. In buildings with lower concentrations of vapor-forming chemicals arising from vapor intrusion, the main concern is whether the chemicals may pose an unacceptable risk of health effects due to long-term (i.e., chronic) exposure to these lower levels.”

The vapor intrusion sampling was part of a larger project being carried out by EWI at the Superfund site. The owner of the property plans to demolish the building where the vapor sampling was conducted to make way for a new elevated building. The current building is close to a stream and is prone to flooding during major rain events.

“The EPA, as overseeing agency, requested that soil sampling and sub-slab sampling be done prior to any new construction in order to determine if there are any potential risks to the construction workers who would be doing the work, and/or any indoor inhalation risks for the future building,” said Bobbilynne Koepke, senior project manager in EWI’s Investigation/Remediation department and site project manager.

Heavy metals (including hexavalent chromium) and chlorinated solvents are of known concern on the Superfund site, said Koepke, adding that, of these, the chlorinated solvents were the driver for vapor intrusion sampling.

No contaminants of concern were identified during the vapor intrusion sampling event and subsequent analysis. However, a soil sample collected during the series of soil borings drilled within the proposed new building footprint showed levels of lead above the applicable screening level, according to Koepke.

“EWI has prepared a plan to address these concerns via limited excavation prior to construction, in order to eliminate the potential risk to construction workers who would help build the new building,” said Koepke.

EWI’s HAZWOPER-trained environmental field crews are experienced in dealing with impacted soil and groundwater and can safely excavate these areas using appropriate equipment and personal protective equipment (PPE) ahead of regular construction crews being onsite.