NOTE: Originally posted by EDR (Environmental Data Resources) blog by Tony.

Ask Tony

An extension of the popular “Ask Tony” column in EDR’s ESA Report newsletter, this blog will address the technical aspects of conducting a Phase I ESA. Topics will cover vapor intrusion, reliance, REC determinations, consultant liability, decisions about whether sources are “reasonably ascertainable,” Phase I updates and contract language.
astm vapor intrusion

Welcome ASTM E 2600 Vapor Intrusion Standard!

Vapor intrusion into structures on a property can potentially create significant liability and have a material impact on property value. As such, it is a growing concern for property owners, prospective purchasers of property and the environmental professionals conducting due diligence. To respond to this industry concern, ASTM recently approved ASTM E 2600, Standard Practice for Assessment of Vapor Intrusion into Structures on Property Involved in Real Estate Transactions. The standard describes a process consisting of four tiers to assess if a vapor intrusion condition (VIC) exists. The first two tiers are screening tiers designed to quickly and inexpensively identify a potential vapor intrusion condition (pVIC). If the potential for vapor intrusion cannot reasonably be screened out at the Tier 1 and/or Tier 2 levels and assuming the transaction is going to proceed, the process identifies three options:  (1) proceed with a more site-specific and comprehensive investigation (Tier 3), in the hope that this investigation will eliminate vapor intrusion concerns; (2) proceed directly to mitigation (Tier 4), on the assumption that mitigation conducted pre-emptively may be more cost effective to address a pVIC; or (3) gain more certainty on the presence of a pVIC through additional investigation.

Prior to initiating the screening evaluation, it is assumed that (1) the structure(s) on the property being investigated are not designed to be intrinsically safe from vapor intrusion; and (2) there are no significant preferential pathways, natural or man-made, which can accelerate the movement of vapors into structures on the target property (TP) from contaminated soil and/or groundwater either on the TP or nearby.

The information required in Tier 1 is the same information collected as part of an ASTM E 1527 Phase I. The first test in the screening process is a search distance test to identify if there are any known or suspect contaminated sites in the area of concern (AOC). If there are none, no further action is required.

The standard identifies a primary and secondary AOC in the search distance test, distinguished by whether the radius search is completely around a target property (primary AOC) or limited solely to the up-gradient direction (secondary AOC). Also, the search distances are different for sites contaminated with [non-petroleum hydrocarbon] COC (such as chlorinated volatile organics) versus sites contaminated with petroleum hydrocarbon COC. The search distances are shorter for petroleum hydrocarbons because they are known to undergo significant bio-degradation in the vadose zone in the presence of oxygen.

To identify the AOC for contaminated sites with [non-petroleum hydrocarbon] COC, the search distance is 1/3 mile around a TP, and beyond that a source of contamination is only of concern if it is up-gradient of the TP (up to the search distances identified in the ASTM E 1527 Phase I standard). For sites with petroleum hydrocarbon COC, the search distance is 1/10 mile around a TP, and beyond that a source of petroleum hydrocarbon contamination is only of concern if it is up-gradient of the TP (up to the search distances identified in the ASTM E 1527 Phase I standard). Hence, for example, a gas station site with a release would be in the primary AOC if located anywhere within 1/10 mile of the TP. It would be in the secondary AOC if located up-gradient of the TP between 1/10 mile and 1/2 mile (the ASTM E 1527-specified search distance).

If a known or suspect contaminated site is located in the AOC, then the next check typically would be to determine if there is a hydraulic or physical barrier between the potentially impacted structure on the TP and the source of contamination. For example, if there is a river between the source of contamination and the structure, the river will likely act as a hydraulic barrier to any migrating contaminant vapors. Hence, this suspect source of contamination in the AOC may be eliminated from concern.

If there are no hydraulic or physical barriers, the next check would be to determine if the known or suspect contaminated site in the AOC may have released a COC. If not, the site may be eliminated from concern.

If COCs are likely to be present at a contaminated site in the AOC (e.g., perchloroethylene from a former dry cleaner), then the location of this site relative to the TP becomes important. If the source of contamination is located up-gradient of the TP, there is much greater concern than if it is located down-gradient or cross-gradient. To understand why, it is necessary to understand the definition of the critical distance in the standard. Effectively, the critical distance is the distance over which contaminant vapors can potentially migrate in any direction through the vadose zone along a path of least resistance, for example, from a contaminated groundwater plume into a structure on the TP.

The standard identifies the critical distance (CD) conservatively and distinguishes between [non-petroleum hydrocarbon] COC and petroleum hydrocarbon COC. If the CD is less than 100 feet (except for dissolved petroleum hydrocarbon COC in which case the CD is shorter: less than 30 feet), then it is presumed that contaminant vapors can potentially impact a structure on the TP. If the CD is greater than or equal to 100 feet (or 30 feet for dissolved petroleum hydrocarbon COC), then it is presumed unlikely that contaminant vapors can impact a structure on the TP. The CD for petroleum hydrocarbon COC in free product form (LNAPL) is the same as for [non-petroleum hydrocarbon] COC (i.e., 100 feet).

If a source of contamination is located down-gradient from a TP, it can be eliminated from concern if it is beyond the CD. If the source of contamination is cross-gradient, it can be eliminated if it is beyond the CD plus a “buffer” to account for the width of the plume at the edge nearest the TP or contamination puddling above the water table (a condition that may, for example, be associated with a gasoline spill). If the source of contamination is up-gradient of the TP or on the TP, then it can not be eliminated at this step.

If the source of contamination has not been eliminated from concern, then the environmental professional may be able to eliminate the source using experience with local subsurface geology and soil characteristics. For example, if the soil is all clay or otherwise has a very low permeability, this might eliminate the source from concern, depending on its location.

The Tier 1 assessment concludes either that vapor intrusion is not a likely concern for the property or that a pVIC exists. If a pVIC exists, further investigation may be to proceed to Tier 2, or to proceed pre-emptively to mitigation as described in Tier 4, or take some other course of action (e.g., withdraw from the deal).

More refined screening takes place in Tier 2. If data is available in state regulatory files or elsewhere that can provide insight into the extent of contamination associated with the source (e.g., plume delineation, COC concentrations, etc.) and the status of any remediation, then the screening methodology continues by assessing whether the nearest plume edge is beyond the CD. If so, the source may be eliminated from concern. If not, then the COC concentration(s) are compared to existing generic state risk-based concentrations (RBCs) that have typically been established for soil, soil gas and groundwater. If concentrations are below the state RBCs, then the source may be eliminated from concern. If above, then the environmental professional may determine RBCs on a site-specific basis, e.g., using the ASTM E 1739 standard.(5) If COC concentrations are below the site-specific RBCs, the source may be eliminated from concern.

If there is no plume information associated with the source of contamination (or if the site-specific RBCs have been exceeded), then it may be appropriate to evaluate whether or not sampling (e.g., soil, soil gas and/or groundwater at or near the TP) is a viable option. Sampling should not be pursued unless it is believed that useful information can be collected. If sampling is not pursued, then a pVIC is presumed to exist. If sampling is conducted and the results indicate that vapor intrusion is unlikely, then the source of contamination may be eliminated from concern.

In summary, a source of contamination may be eliminated in the Tier 1 and Tier 2 screening methodology if:

1. The source is not in the AOC;
2. There is a hydraulic/physical barrier between the source and the TP;
3. The presence of COCs is unlikely;
4. The source is down-gradient and beyond the CD;
5. The source is cross-gradient and beyond the CD plus a “buffer” for account for plume width/puddling;
6. Subsurface geology and soil characteristics are such that vapor intrusion is unlikely;
7. The nearest plume edge to a structure is beyond the CD;
8. COC concentrations are below state generic RBCs;
9. COC concentrations are below site-specific RBCs; or
10. Sampling results indicate that vapor intrusion is unlikely to be a concern.

If a pVIC remains after the Tier 1 and Tier 2 screening, the environmental professional and client may choose to proceed to a Tier 3 investigation, proceed directly to pre-emptive mitigation in Tier 4, or take some other action (such as not pursuing the deal).

If you have any questions on the standard or would like to share vapor intrusion experiences, you are welcome to participate on this blog.

Tony Buonicore is a Consultant and chaired the ASTM Task Group responsible for developing the vapor intrusion assessment standard. He can be reached at 800-238-1841 or ajb@edrnet.com.

6 Comments

1. By

fred @ psi on 3/11/2008
Tony - as always, the CRE community, including the environmental consultants, appreciates your leadership in forging an industry-standard concensus for bringing this issue to predictable ‘endpoints.’ The emerging interest by many jurisdictions in impact by vapors was looming as a spectre that complicated and frustrated a lot of deals. Now we have common ground to create some certainty in outcomes - and the markets always respond favorably to certainty.

2. By

pcoyne on 3/11/2008
Hi Fred and Anthony. Good to see you on here. Can you give a sanitized example of some of the “complicated and frustrated” deals that you’ve seen out there? How did the VI issue surface, how was it dealt with, what were the factors? I think sharing case studies is going to hasten the learning curve for the market.

3. By

abuonicore on 3/12/2008
Fred, thanks for the kind words. I also will be teaching the ASTM vapor intrusion course. It is a full day course. In it I will take the Tier 1 and Tier 2 screening from the standard and translate it into Phase I language using a flowchart I developed for an article that will be published in the April issue of Pollution Engineering.

4. By

abuonicore on 3/13/2008
As we all know, if a target property (TP) and source of contamination are separated by a river, the river acts as a hydraulic barrier for groundwater plume migration. As such, this source of contamination would not be of concern from a vapor intrusion viewpoint on the TP. What other physical and hydraulic barriers might exist that would do similarly? Wetlands have been suggested (hydraulic barrier), along with buildings with multistory underground parking (physical barrier) and major roadways with significant underground utility corridors (physical barrier) running perpendicular to the line connecting the TP and the source of contamination. Any one have other experience the industry can benefit by?

5. By

oriona on 6/2/2008
Tony, I would like some clarification on the necessity to review regualtory files for a Tier 1. Based on my take on the standard and your Draft White Paper, it appears that if a site (petroleum release or non petroleum release) is identified within the critical distance, regardless if it is down- or cross-gradient, and if groundwater has been impacted, then one would need to review the files to determine the extent of the plume. Is this correct?

6. By

abuonicore on 6/29/2008
There is a requirement in the E 1527 Phase I standard to conduct a government records check. However, this is typically accomplished by reviewing information collected by third party data providers. I am sure you are also aware that limitations established by many state agencies often prohibits regulatory file reviews at their offices in the timeframe available to complete the Phase I. Now let me address your critical distance question. For a Tier 1 screen, if a known or suspect contaminated site is: (1) downgradient within the critical distance; (2) cross-gradient within the critical distance plus a “buffer” to account for plume width; or (3) upgradient within the AOC, then a pVIC would exist at the conclusion of the Tier 1 screen. Proceeding to the Tier 2 screen would entail review of the files associated with these known or suspect contaminated sites to assess actual plume characteristics and dimensions. If the actual distance from the nearest edge of the contaminated plume to the nearest structure as determined from review of the files exceeds the E 2600 critical distance criteria, then there would be no pVIC. Refer also to my April 2008 Pollution Engineering article (www.pollutionengineering.com).

This entry was posted on Monday, August 25th, 2008 at 2:32 pm and is filed under ●Environmental Engineering.

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