Entry
, last edited January 19, 2012There has been considerable confusion over the distances in the screening tiers of E 2600-08. The distances in Tier 1 relate to establishing the area of concern. They are measured from the initial source of known or suspect contamination, e.g., a dry cleaner or a gas station with leaking underground storage tanks, to the nearest structure on the target property. Information is extracted directly from the Phase I investigation to conduct this screening. Just because a source is within the area of concern does not mean there is a vapor intrusion problem, only that it is possible and further investigation is necessary. The further investigation is described in Tier 2 screening. At the Tier 2 level, either detailed information related to the source of contamination and the contaminated plume is reviewed (typically via a state regulatory file review), or invasive sampling, such as soil gas sampling, is conducted. The distances in Tier 2 relate to the distance between the edge of a contaminated plume and the nearest structure on the target property, e.g., critical distance. If the contaminated plume is within the critical distance criteria in E 2600, then contaminant concentrations have to be compared with generic state screening levels or site-specific risk-based screening levels. Only after conducting this level of investigation, is it possible to assess whether or not there is the potential for a vapor intrusion problem. If the potential exists, only a full scale vapor intrusion investigation (referenced in Tier 3 of E 2600) would be able to confirm that a vapor intrusion problem does indeed exist. Such an investigation will usually follow vapor intrusion guidance, policy or regulation established by the state where the target property is located, and E 2600 refers the user to such guidance, policy or regulation. As an alternative to this more comprehensive and costly investigation, it is possible to proceed directly to mitigation.
Comment
Tony,
The process of Tier 1 to Tier 2 to Tier 3 is methodical in nature, much like what was typically done back when groundwater ingestion was the major exposure pathway driving things. Back then, one would do a water well survey, evaluate public water supplies, check zoning/ordinances, do windshield surveys, and even go door to door to ask if folks used a well. Now with VI, nothing short of poking one's nose in everyone's basement (I use nose figuratively here) can be done to buy some time, right? Typically, (back in the day) you could chase plumes and free product and feel comfortable that you could wait until after the nature and extent of contamination was determined before you decided on a corrective action.
How do you (or others on the forum) recommend we address timing. It's a whole lot easier to tell a resident that he isn't being exposed to groundwater contamination (via ingestion) while the assessment is being completed (typically months, sometimes many months), than it is to tell that same resident that his acute exposure is insignificant and we'll take care of the chronic after many months of studying. Aren't we really looking at vapor mitigation on the front end and then backing off after assessment is complete, particularly if free product is present?
Thoughts from the peanut gallery?
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Many, if not most, states are in the process of issuing their own guidance on vapor intrusion. I'd therefore recommend deferring to the preference of your state when conducting VI studies, rather than putting too much stock in the ASTM standard. The ASTM standard is so vague as to be of very limited value in my opinion. The "distances" in E 2600-08 really constitute only a very general rule of thumb.
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The NJDEP has specific requirements and timetable for a vapor intrusion receptor evaluation and vapor intrusion investigations. If you are 100 feet from LNAPL or non-petroleum related ground water contamination, a vapor intrusion investigation must be done. Within 150 days of identifying that a vapor intrusion investigation is required, subslab soil gas and, if necessary, indoor air quality sampling must be performed. This investigation is performed on the structures within 100 feet of the edge of the plume that exceeds the ground water screening level.
Should indoor air quality be found to contain compounds of concern for the site and those compounds are at level greater than the indoor air screening level, you have five days to mitigate impacts to the receptors. Mitigation can be additional ventilation (positive pressure), sealing/repairing floors, treating indoor air, etc. You then have 60 days to install a vapor mitigation system (e.g. subslab depressurziation).
So the advice to check state regulations is sound as some states, such as NJ, are very specific regarding VI investigations.
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The revised ASTM vapor intrusion standard is in the process of going to ballot. The standard has been redirected solely to screening for vapors to encroach upon a property, i.e., identify if a vapor encroachment condition or a VEC exists. Two tiers of screening are included in the standard, both very prescriptive with respect to distances. If a VEC exists or is likely to exist, it will be the responsibility of the EP conducting the Phase I to decide if this VEC constitutes a REC.
The existence of a VEC does not automatically mean there is a vapor intrusion problem, only that vapors may be encroaching upon the subsurface of the property. Whether or not these vapors may be migrating into a structure on the property would require further investigation and the standard indicates that state vapor intrusion guidance (if it exists in that state, and it does for almost half the states) should be followed.
A summary of the revisions in the standard is provided below:
(1) In view of the considerable uncertainty still surrounding vapor intrusion evaluation and the fact that substantially all of the federal and state agency vapor intrusion investigation publications have been issued as guidance rather than regulations, the revised E 2600 standard has been changed to a standard guide rather than a standard practice. This is similar to the standard guides E 2018 for property condition assessment and E 1739 for risk-based corrective action applied at petroleum release sites.
(2) The standard has been re-focused solely on screening and the title of the standard has been revised accordingly.
(3) The standard has been revised to be consistent in approach and methodology to the E 1527 Phase I ESA.
(4) The standard has been modified to make clear and underscore the critical importance of relying on the environmental professional’s judgment and expertise in conducting the vapor encroachment screening and in making determinations when conducting the screening. Thus, for example, the revised standard eliminates the presumptions that were part of the original E 2600 standard.
(5) The intent of the screening is to identify if a vapor encroachment condition (VEC) exists, is likely to exist, or can be ruled out in connection with the target property. Use of the VEC term is analogous to, but not the equivalent of, the identification of a recognized environmental condition (REC) in an ASTM E 1527 Phase I. The terms VIC (vapor intrusion condition) and pVIC have been eliminated from the revised standard. The revised standard has been greatly simplified to focus only on the potential for migrating vapors to reach the subsurface of the target property. Further investigation to assess the possibility of vapor intrusion into structures on the target property (analogous to a Phase II to address a REC that has been identified through an E 1527 Phase I) is beyond the scope of the revised E 2600 screening standard. As such, the original E 2600 standard Sections 10 and 11 referencing vapor intrusion assessment and mitigation have been moved to the appendix (see Appendix 7). Also, all references to vapor intrusion assessment and mitigation (including terminology) have been removed from the text of the standard (i.e., the main body of the revised document). The revised standard focuses solely on screening for VECs.
(6) Since the revised standard focuses solely on the identification of VECs in connection with the target property, comparison with risk based concentrations (RBCs) in Tier 2 has been removed from the body of the document and relocated to the Appendix (refer to Appendix 7). An RBC comparison analysis may be a part of a further investigation should a VEC be identified. Again, this would be analogous to, but not the equivalent of, undertaking further investigation arising from identification of a REC in a Phase I.
(7) Findings are limited to whether a VEC exists, likely exists, cannot be ruled out, or can be ruled out because a VEC does not or is not likely to exist.
(8) The revised standard clarifies the relationship between E 1527 and E 2600 and eliminates the confusion that resulted from the text of the original E 2600 standard.
(9) In Tier 1 the secondary area of concern that was identified in the original E 2600-08 standard has been eliminated.
The proposed revisions to the E 2600 standard are designed to clarify much of the confusion experienced in the marketplace. The revised E 2600 standard now deals solely with evaluation of the potential for migrating vapors to encroach upon a target property. If vapors do or are likely to encroach upon a target property, the person commissioning the vapor encroachment screening (VES) can evaluate whether to conduct further investigation of the target property. Moreover, if the VEC screening is conducted in conjunction with an E 1527 Phase I, whether the VEC constitutes a REC is a decision made by the environmental professional performing the screening based on the application of her or his expertise and professional judgment in performance of the REC analysis established in E 1527.
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