Request for Comments: Draft of Assessment Sections 3.1 through 3.4

MassDEP is seeking comments on the latest draft version of the Assessment section in the new Vapor Intrusion Guidance .  The link is provided below (scroll down and keep clicking). 



The latest draft is intended as a starting point for discussion and does not reflect the current position of MassDEP.  Please identify and comment on sections that you consider need more clarification, are superfluous, and/or are incorrect.   Providing case examples is often helpful in this regard.




3 Responses

  1. Section, specifically the soil gas section, states that the “US EPA divides soil gas samples into several types. Including near-slab…”. What document released by the EPA makes this distinction? The 2002 guidance does not include the near slab terminology. Perhaps the author has confused this with the NJDEP guidance, which does use this terminology and, to my knowledge, is the first guidance document that did?

  2. Section 3.3.1 – The following sentence is problematic and inconsistent with discussions we have had in the Regulatory Subgroup meetings:

    “It is the Department’s opinion that indoor air sampling should be performed in order to determine if a pathway exists.”

    Specifically, in the Regulatory Subgroup we have discussed use of GW-2 standards as a way of screening out the possibility of vapor intrusion at sites where there is no other evidence of vapor intrusion. We have discussed conditions when use of GW-2 standards in this way would not be appropriate, but at sites that do not meet these conditions and where there is no other known evidence of vapor intrusion, the draft of the Regulatory section of this document indicates that use of GW-2 standards is appropriate to determine if a vapor intrusion pathway exists. This broad statement that indoor air sampling is needed to determine if a pathway exists is therefore inappropriate.

  3. Section 3.1.3 – the second paragraph in this section is problematic for sites undergoing redevelopment or property transactions. This paragraphs states: (1) that when modeling is used to estimate indoor air concentrations in proposed (un-constructed) buildings, post-construction indoor air sampling should be conducted to confirm the vapor intrusion modeling results, and (2) if a building is constructed with a vapor barrier and/or sub-slab depressurization (SSD) system intended to eliminate a potential vapor intrusion pathway, confirmation of the effectiveness of the barrier or SSD system should be demonstrated

    In current practice, RAOs are often filed after indoor air modeling has been used to demonstrate that a condition of No Significant Risk will exist in a proposed building but prior to completion of building construction. Is this second paragraph suggesting that filing an RAO at this type of site must be delayed until after construction is complete and indoor air samples have been collected? This is a significant implication that should be clarified. Alternatively, if an RAO is filed before construction is complete, is this paragraph requiring post-RAO monitoring? This would be a new requirement, and it is unclear how results of such indoor air sampling would be communicated with the Department at a closed site.

    This section also should address directly the implication of the recommended post-construction indoor air modeling at buildings where vapor barriers have been installed for reasons other the VOC intrusion (e.g. moisture); specifically, evaluating the need for AULs in these cases should be discussed explicitly.

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