VI Questions to Ponder for Thursday…

Here are some questions MassDEP would like you to think about and hopes to discuss with you on Thursday, February 9 at the Vapor Intrusion-related MCP Amendments discussion.

Please consider providing comments on this Blog to facilitate a wide-ranging & open discussion during this process.

Hope to see you Thursday!  – Liz Callahan (

MassDEP is rewriting portions of the Massachusetts Contingency Plan (MCP) with the goal of providing clearer rules for owners, operators, LSPs and other interested parties dealing with sites where volatilization of contaminants under or near a building has caused the intrusion of vapor-phase contaminants into a building’s indoor air or could result in vapor intrusion as the result of future development.

MassDEP is focusing on the following topics:

  1. Clarifying the rules for completing Immediate Response Actions (IRAs) addressing Vapor Intrusion as a Critical Exposure Pathway (CEP)
  2. Clarifying the rules for source elimination and control
  3. Evaluation of MCP closure tools and other “stopping points”: Response Action Outcomes (RAOs) – both Permanent Solutions and Temporary Solutions — and Remedy Operation Status (ROS)

IRA Completion

  1. What has been your experience with completing an IRA?  What are the circumstances in which it is not clear when an IRA Completion Statement can be filed?

Source Elimination/Control 

  1. How should we define “source elimination/control” to ensure that people are appropriately addressing the source and have a clear standard to meet?  The current requirement is that a “source [of OHM] . . . which is resulting or is likely to result in an increase in concentrations . . . is eliminated or controlled.”  310 CMR 40.1003(5).
    1. What options should MassDEP consider for creating a measurable standard for whether source has been controlled?
    2. Some ideas:

i.      requiring groundwater concentrations to be ≤ 1% of contaminant solubility limit (consistent with EPA guidance; also in MassDEP Interim VI guidance)

ii.      require that plume be stable and non-advancing

iii.      require that the concentration at the downgradient edge of a plume be non-detect, below GW-2, or meeting some other standard

MCP Closure and Future Use

  1. What are the factual circumstances in which achievement of a Permanent Solution is difficult under the MCP when addressing VI?
  2. Where Permanent Solution cannot be achieved, when are Sites winding up in Temporary Solutions and when in Remedy Operation Status (ROS)?
  3. How does the choice between a passive venting system and an active Sub-slab Depressurization System (SSDSs) influence the choice of MCP closure/stopping place?
  4. How do different MCP stopping places affect transferability of property?
  5. How do buyers understand the ongoing site responsibilities (and ideally how would they)?
  6. What information is appropriate to put future owners/operators on notice of potential VI problems for future building scenarios?
  7. How do closure mechanisms deal with sites with groundwater concentrations exceeding GW-2 but where GW-2 does not apply now because there is no building that would trigger GW-2?
  8. What role should Activity and Use Limitations (AULs) have?
  9. Would a new category of Response Action Outcome (RAO) specifically designed for closure of sites with VI be helpful?
  10. What are appropriate O&M and reporting requirements (regardless of closure or MCP status) for sites with venting systems?
    1. What aspects of O&M should an LSP do?  What aspects could owner do?
    2. When is indoor air sampling indicated?
    3. Some ideas for SSDSs in particular:

i.    Perform initial tests to make sure SSDS is working

ii.  Maintain differential pressures ≥ pressures established as adequate to prevent vapor intrusion

iii.  Conduct annual checks of differential pressure until operation of system is no longer necessary to ensure No Significant Risk (NSR)

iv. Operate system continuously until operation of system is no longer necessary to ensure NSR

v.  Send MassDEP notice of unscheduled shutdowns

vi. Within 72 hours of unscheduled shutdown, have system back online within 30 days, unless DEP sets an interim deadline

vii. Specify a procedure for providing notice of scheduled shutdowns

     11.  What role can remote sensing technology play in monitoring SSDSs?  Is it readily available for this application?


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