Compiled Draft Guidance for Summer Review


MassDEP has compiled the draft chapters from the three sub-Workgroups to provide a single DRAFT document for Workgroup review and comment during the summer meeting hiatus.

Word Document (111 pages, 712 KB): July 2009 Draft IA Guidance

Please submit comments by replying to this blog post or by email to Gerard.Martin@state.ma.us.
[MassDEP will accept comments throughout the summer, but comments submittede earlier in the summer will be more readily considered in the next draft that is currently being developed by MassDEP staff.  Be reassured, however, that ALL comments received will be considered for either the next or subsequent drafts… we won’t discard them.]

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10 Responses

  1. The USEPA’s Office of Inspector General (OIG) released a report on Monday 12/14/09, which says OSWER’s lack of final guidance on vapor intrusion is impeding efforts to address indoor air risks. I have summarized OIG’s recommendations here:

    1. Identify what remains valid and what needs to be updated in the 2002 OSWER Draft guidance;
    2. Issue a final VI guidance document;
    3. Train EPA and state staff on the new guidance; and
    4. Finalize toxicity values for TCE and PCE in IRIS.

    In response, OSWER has agreed to the following milestones:
    1. By Aug. 2010, identify and publicly report on the parts of the 2002 draft vapor intrusion guidance that are still valid and the parts that should be updated;
    2. By Nov. 2012, issue final vapor intrusion guidance; and
    3. By May 2013, train EPA and State staff on the new guidance.

    OSWER indicated that it will seek public input on how it will accomplish these tasks.

    Some topics called out specifically include use of multiple lines of evidence, how to address risks from petroleum hydrocarbons, Superfund 5-year reviews, preemptive mitigation and OM&M of mitigation systems including termination.

    Perhaps the Workgroup should discuss how USEPA’s coming changes could affect MassDEP’s draft guidance since at least some of the topics called-out in the report have been hot topics for Mass and we could stand to benefit from USEPA’s work.

  2. MassDEP has received comments from Wes Stimpson on the July 2009 DRAFT Indoor Air Guidance. The redline/strikeout version of the comments may be downloaded here:

    MS Word Document (635 KB)

  3. MassDEP has received joint comments from AMEC Earth and Environmental (AMEC) and GEI Consultants, Inc. (GEI) of the July 2009 DRAFT Indoor Air Guidance. The cover letter and comments may be downloaded here:

    Cover letter (PDF, 138 KB)

    Comments and Letter (PDF, 1 MB)

  4. Multiple Lines of Evidence: The draft guidance in general, and the Confidence Chart on pages 13 and 14 in specific, ignore the concept of Multiple Lines of Evidence. Using Multiple Lines of Evidence is not only the best way to evaluate the vapor intrusion pathway but is also the best way to understand the influences of background sources on indoor air measurements. All of the “more certain” or “higher confidence” EPC data sets in the Confidence Chart rely on one line of evidence only (measured indoor air concentration). This approach is problematic because it forces the regulated community to rely on one line of evidence with all of its inherent spatial and temporal variability influenced by weather, engineered controls, background sources and others.

    Each individual line of evidence has its own inherent variability; however, they are different for each line. For example, sampling methods are a significant source of data variability for soil gas but tend to be a smaller source for indoor and outdoor air. The reason is that indoor and outdoor air sampling methods do not vary much between practitioners, while soil gas sampling methods vary from practitioner to practitioner, and some methods in use are inappropriate altogether. Background sources of VOCs, on the other hand, are a significant source of variability in indoor air but are a smaller source of variability in soil gas the deeper the sample is collected. Sound sampling protocols can go a long way toward reducing variability in soil gas measurements, a relatively easy task; whereas, removing background effects from indoor air is much harder. This is how multiple lines of evidence can act together to reduce uncertainty when properly applied.

    Also, it would be more appropriate to discuss “Planning and Design of a Sampling Program” after discussing Multiple Lines of Evidence. A plan to collect data should come from a data gap analysis. The data gap analysis is best performed using a conceptual site model and hypotheses to be tested. Multiple lines of evidence and the development of the conceptual site model go hand-in-hand.

  5. Conceptual Site Model (CSM): The CSM, as described in the Draft Guidance, is not presented in a way that is likely to be used by vapor intrusion practitioners. The language is too general and provides no guidance on how to integrate the CSM into the process of site evaluation and decision-making. One way to make practical use of the excerpt from ITRC’s guidance would be to offer a set of “modular” or commonly-used VI CSM templates with suggested add-on components. For example, the CSM templates could begin with a series of simple schematics to choose from:
    –Residential, slab-on-grade over thick vadose zone
    –Residential, slab-on-grade over thin vadose zone
    –Commercial, slab-on-grade over ….
    –Residential, basement over thick vadose zone
    –Etc.
    The user selects a template and then Guidance could offer a series of common “add-ons” for each medium. Examples of media would be soil, GW data, construction details, underground utilities, atmospheric information, and so on. Under soil, common choices might be: glacial till, bedrock, sand, silt etc.

    Walking through such an exercise would guide practitioners through the conditions and processes present on site, and assist in making the decision about which conditions and processes are most important to vapor intrusion.

  6. Conceptual Site Model (CSM): The CSM, as described in the Draft Guidance, is not presented in a way that is likely to be used by vapor intrusion practitioners. The language is general and provides no guidance on how to integrate the CSM into the process of site evaluation and decision-making. One way to make practical use of the excerpt from ITRC’s guidance would be to offer a set of “modular” or commonly-used CSM templates with add-on components. For example, the CSM templates could begin with a series of simple schematics to choose from:
    –Residential, slab-on-grade over thick vadose zone
    –Residential, slab-on-grade over thin vadose zone
    –Commercial, slab-on-grade over ….
    –Residential, basement over thick vadose zone
    –Etc.
    The user selects a template, then the Guidance could offer a series of common “add-ons” for each medium. Examples of media would be soil, GW data, construction details, underground utilities, atmospheric information, and so on. Under soil, common choices might be: glacial till, bedrock, sand, silt etc.

    Walking through such an exercise would guide practitioners through the conditions and processes present on site, and assist in making the decisions about which conditions and processes are most important to vapor intrusion.

  7. Post-RAO/AUL Sampling

    Section 4.5.2 requires post-RAO/AUL sub-slab soil gas and potentially indoor air sampling at buildings with passive ventilation systems. Requiring chemical sampling after RAO is problematic because it calls into question the permanence of a Permanent Solution under the MCP. Furthermore, screening sub-slab soil gas concentrations against risk-based concentrations at a building with a ventilation system that has been demonstrated to be effective does not make sense. At such buildings, sub-slab soil gas concentration is not an indicator of the passive venting system performance or effectiveness. This section also suggests that if sub-slab soil gas concentrations exceed 100 x “the acceptable indoor air concentrations”, troubleshooting of the system should be conducted followed by additional sub-slab soil gas sampling. This implies that troubleshooting the system will decrease sub-slab concentrations, which it will not. The focus of the guidance should be on demonstrating that the passive system is effective at maintaining a condition of NSR (regardless of the sub-slab concentrations), and then the AUL should be used to prevent modifications to the venting system. If sub-slab concentrations were all below 100 x “acceptable indoor air concentrations,” it is unlikely that a venting system would even be required to maintain a condition of NSR in the first place.

  8. Phased Assessment Approach

    Guidance should be more proscriptive on how to conduct a pathway assessment by including a phased assessment approach, which moves from evaluation of soil and/or groundwater data, to soil gas data, and then to sub-slab and/or indoor air data. Conclusions about whether to proceed to the next step should be based on risk-based screening conducted at each phase. Each successive phase should use progressively more site specific information.

  9. Use of Threshold Values

    There are multiple references to the department’s draft Threshold Values (TVs) in the draft guidance document. Depending on the VOC, these TVs are either a risk-based concentration, a typical indoor air concentration (TIAC), or a laboratory reporting limit (RL). The comparison of soil gas data to 10X the TV in Section 3.1.1 is problematic because many of the TVs are TIACs or RLs that are below risk-based concentrations. Requiring subsurface concentrations to be low enough not to exceed TIACs or RLs is not consistent with the Regulation and essentially assumes that a CEP exists before such a condition has been demonstrated. This is similar to the idea of a “potential CEP”, and as we have discussed in the workgroup, potential CEPs do not exist under the regulation. Further, this idea of comparing subsurface concentrations to concentrations based on TIACs or RLS that are below risk-based concentrations is even more problematic for non-residential (or school) buildings, where the concept of CEP does not apply. “Screening” soil gas data should entail comparing measured values to soil gas concentrations derived from indoor air risk-based concentrations or TIACs when they are greater than risk-based concentrations, if the Department deems this appropriate.

  10. CEP Feasibility Evaluations (Section 2.3.2): The premise of this section is not consistent with the regulation, specifically 310 CMR 40.0414(3)a.

    The option to evaluate the feasibility of mitigating or eliminating a CEP is available to a PRP as long as an Imminent Hazard does not exist; accordingly, the Department cannot require CEP mitigation/elimination at sites where current risks do not pose an Imminent Hazard but could or do pose a Significant Risk (i.e., IH> current risk > NSR). Such a requirement is currently indicated in Section 2.3.3.1: “when indoor air contaminant concentrations from vapor intrusion pose a Significant Risk for building occupants, the benefits of reducing exposure are also presumed to outweigh the costs.” This statement is contrary to 310 CMR 40.0414(3)a.

    Contrary to the current draft text, rebutting the requirement to mitigate/eliminate a CEP is not an option when the CEP poses an Imminent Hazard (310 CMR 40.0414(3)a); therefore, Section 2.3.3.1 should not discuss feasibility evaluations for buildings where an Imminent Hazard exists, and Sections 2.3.3.1 and 2.3.3.2 should be combined so that there is not a difference in approach for sites where current risks are less than Significant Risk levels (i.e., NSR> current risk) or greater than significant risk levels (i.e., IH> current risk > NSR) as long as an imminent hazard does not exist.

    Section 2.3.3.2 – As mentioned above, Sections 2.3.3.1 and 2.3.3.2 should be combined into one section entitled: Evaluation of Feasibility of Initial CEP Mitigation where an Imminent Hazard does not exist. Currently, both Options A and B outlined under Section 2.3.3.2 seem to prescriptive. The Department should consider a more general approach listing issues to be considered in an initial CEP feasibility evaluation:
     Technological Feasibility
     Benefit: Risk Reduction
    • Do current risks pose a Significant Risk or not?
    • What risks are expected post-mitigation? Would they be significantly lower than pre-mitigation risks?
     Costs
    • Should consider up-front cost to install; and
    • Cost to operate and monitor, and the guidance should provide specific recommendations as to what time frame should be considered here – the length of time assumed for O&M will significantly affect the overall cost.

    The Guidance should then provide context for what dollar amount would exceed what level of risk reduction, e.g.
     If risk reduction is large (i.e., SR to NSR or NSR to background/ND), the dollar amount to conclude infeasibility should be larger than for situations where the risk reduction is small. The guidance should provide context for dollar amounts to be considered infeasible in the form of either specific dollar amounts or as a percent of overall project costs, as is the current approach in the Feasibility Guidance for achieving background.
     Then, if risk reduction is small (i.e., NSR to background or NSR to ND), the dollar amount to conclude infeasibility should be smaller. Again, the guidance should provide context for dollar amounts to be considered infeasible in the form either of specific dollar amounts or as a percent of overall project costs.

    Section 2.3.4 – As with initial CEP feasibility evaluations, this section needs to be revised to make it clear that the option to rebut the requirement to mitigate/eliminate a CEP is available as long as an Imminent Hazard (not a Significant Risk) does not exist, as specified at 310 CMR 40.0414(3)a. Again, a more general approach would be more helpful here. The Guidance should list issues to be considered in an “continuing” CEP feasibility evaluation:
     Technological Feasibility: technological feasibility will no longer be significant as technology would already be in place
     Benefit
    • Compare current risk level (i.e., mitigated risk) to risk level if mitigation was terminated
    • Could also consider information about how well site is characterized, source control, etc., relating to the potential for risks to increase in the future; however, specifics about exposure, type of COC (carcinogen or not), comparisons to “screening levels” in soil or groundwater are just redundant ways of evaluating current risks.
     Costs
    • Cost to continue to operate. Again, assumed time period is critical here; Guidance should be clear about what time period should be considered, or LSP should be allowed to use professional judgment to identify and appropriate, site-specific time period.
    Once the benefit (change in risk) and cost have been identified, Guidance should provide context for comparing the two:
     If change in risk from terminating mitigation is large (i.e., NSR to SR or background/ND to SR), the dollar amount to conclude infeasibility would be larger than for situations where the change in risk is small. The guidance should provide context for dollar amounts to be considered infeasible in the form of either specific dollar amounts or as a percent of overall project costs, as is the current approach in the Feasibility Guidance for achieving background.
     If change in risk from terminating mitigation is small (i.e., background/ND to NSR or background/ND to some fraction of NSR), the dollar amount to conclude infeasibility should be smaller. The guidance should provide context for dollar amounts to be considered infeasible in the form either of specific dollar amounts or as a percent of overall project costs.

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