An attorney we work with asked me to look at a phase I environmental site assessment (ESA) for his client. His client was really interested in the property, which already had a solid lease.
The ESA disclosed a historically recognized environmental concern (HREC) and a recognized environmental concern (REC). Both had to do with a release of gasoline from a former underground storage tank (UST) at the property. The property had environmental case closure with very low levels of gasoline contamination left in place.
The question posed by the attorney’s client boiled down to the Phase I recommendation - “Complete a Vapor Intrusion Assessment and Prepare a Soil Management Plan”.
“Is this necessary?” the client asked.
I told them that the recommendation was very conservative based on the information provided by the ESA. I let them know that if they planned to redevelop the property, the county would probably look to them to voluntarily investigate for vapor intrusion and prepare a soil management plan as part of the redevelopment.
I advised that the recommendation was overly conservative given their intention to hold the property as is. I also told them that it was unlikely a vapor intrusion assessment would disclose a vapor intrusion problem.
As we were wrapping up, a question came up, “What is a vapor intrusion assessment?”
I started my answer with an explanation of vapor intrusion.
What is Vapor Intrusion?
As a liquid chemical evaporates, it turns from a liquid into a vapor or gas. All liquids evaporate to some extent, and the extent to which a liquid evaporates shows its volatility. The more volatile a liquid is, the more quickly it turns into vapor.
When a liquid chemical leaks into the ground, it enters the soil and groundwater. Once in groundwater, the chemical moves along with the groundwater. As this process unfolds, and depending on its volatility, some of the released chemicals turn into a vapor and enter the space of dry soil above the groundwater. The vapor can leak up through the ground and enter a building causing a buildup of chemical vapors in the building. This process is vapor intrusion.
What is a Vapor Intrusion Assessment?
As time goes on, groundwater carries the dissolved chemical downstream from the chemical release. At the same time, a vapor plume (just like the billowing smoke that forms above a smokestack) forms in the soil above the affected groundwater. The area of the vapor plume mirrors the area of chemically-affected soil and groundwater.
A vapor intrusion assessment uses the link between the vapor plume and affected soil and groundwater to confirm whether there is contaminated soil and/or groundwater in an area and to determine whether any detected contamination poses a human health risk due to vapor intrusion.
In practice, a vapor intrusion assessment involves collecting soil vapor samples from small wells spread across the area you are investigating, and testing the soil vapor samples for suspected contaminants.
Typically, detected contamination levels in soil vapor are used to estimate how much area is contaminated, identify areas of high contamination or “hot-spots”, and gauge potential human health risks by comparing detected levels with published environmental screening levels (ESLs).
What are the Advantages of a Vapor Intrusion Assessment?
A vapor intrusion assessment has some real advantages over the more traditional phase II soil and groundwater assessment for figuring out where soil and groundwater contamination is, where the highest levels of contamination are, and whether soil vapor intrusion poses a human health risk.
Number one, a soil vapor assessment costs much less than a soil and groundwater assessment, generates less waste, is less intrusive, and provides information that can be used to target a groundwater and soil investigation, and possible cleanup. Additionally, a soil vapor assessment can be used to examine vapor intrusion health risks.
Of course, a soil vapor assessment does not provide all the information a soil and groundwater investigation can, but it gets you well down the road and allows more efficient and cost-effective phases of investigation and cleanup.
Our recommendation: Before drilling for soil and groundwater samples, use a soil vapor assessment to get a valuable overview.
In this article, we took a look at soil vapor intrusion, explained what a soil vapor assessment is, and described some of the advantages a soil vapor assessment has over a traditional phase II soil and groundwater investigation.
If you have a Phase I ESA that recommends verifying an HREC or REC, go ahead and get a second opinion, and if necessary, consider using a soil vapor assessment to confirm the ESA recommendation. With over 30 years of experience in conducting soil vapor assessments and reaping their advantages, we can help. Please call us at 831-475-8141 or click below to schedule a free consultation.