Volatile organic compounds (VOCs) and predominantly trichloroethylene (TCE) have long been recognized as dangerous and persistent groundwater pollutants. Numerous epidemiological studies have established that TCE is a likely human carcinogen with the strongest evidence supporting a causal link to kidney, liver and lymphoma cancers. In the past, the most common route of exposure was through contaminated well water, whether by ingestion, inhalation of vapors or though contact with the skin. In many jurisdictions, government regulators were less aggressive where a plume of TCE or other VOCs was discovered in an area serviced by a public water supply, believing that residents were not being exposed.
In recent years, however, the danger of vapor intrusion is finally getting the attention it deserves from regulators and legislators across the country. One of the largest vapor intrusion sites discovered to date is in Endicott, New York. A plume of TCE and other VOCs are contaminating the air in hundreds of Endicott homes, requiring the installation of hundreds of individual vapor intrusion remediation systems. Faraci Lange, LLP, a Rochester, New York law firm, is involved in toxic chemical exposure litigation commenced against IBM on behalf of the victims of this contamination.
What is vapor intrusion?TCE and other VOCs are by definition volatile. What this means is that when dissolved into or mixed with groundwater, they do not tend to stay put. Instead, they tend to revert to a gaseous phase and drift upward through the soil toward the surface. Whether a particular VOC plume in the groundwater will present a vapor intrusion problem is a function of a number of variables.
First and foremost, the concentrations found in the plume are important. Obviously, the higher the concentrations, the more unstable the plume and the more likely vapor intrusion will occur. Second is the depth of the plume. Groundwater plumes can be shallow, meaning that they are contained in what is termed the "overburden" groundwater, or they can be found in deeper, more permanent groundwater layers. The more shallow the plume, the less distance vapors volatizing out of the plume have to travel before getting to the surface. Therefore, more shallow plumes present a greater likelihood of intrusion. The nature of the soil above the groundwater plume is also an important factor. Soils that are relatively impervious to gas transport are less likely to permit volatized vapors a path to the surface. Conversely, sandy and coarse soils with multiple air spaces present ideal conditions for vapor intrusion.
Even when vapor intrusion is present in a particular neighborhood, the risks to the residents will not be uniform. Homes with deeper and more porous basements will allow more intrusion than those with more sealed foundations and slabs. Other factors, such as the time of year and the circulation inside the house, will play important roles.
What can be done to protect residents from vapor intrusion?Because of their volatile nature, attempts to remove TCE and most VOCs from groundwater typically involve what are referred to as pump and treat remediation systems. Contaminated groundwater is pumped to the surface to air strippers which permit the volatilization of VOCs into a tower. From the tower, the VOCs are discharged into the atmosphere or captured in various charcoal type filters for disposal. However, this process is neither fast nor highly efficient. Over many years, this type of technology can reduce the concentrations found in a particular plume. Unfortunately, the presence of the contaminant can never be eliminated completely.
When vapor intrusion is discovered, individual remediation systems must be installed on a house by house basis. This process involves drilling into the foundation and installing a suction system that pulls vapors from beneath the subslab and vents them out above the roof of the house. In order to be effective, these systems need to run 24 hours per day, 7 days per week. They also require effective sealing of all points of entry into the home, including basement floor cracks and utility service entries, to prevent vapor intrusion.
Communities in which there had been confidence that a groundwater problem was harmless are being reinvestigated now by authorities who are looking for the insidious hazard of vapor intrusion. Given the thousands of known TCE plumes throughout the United States, it is extremely likely that vapor intrusion similar to that discovered in Endicott, New York is occurring in numerous other communities and causing potential future illness to thousands.