November 2014 Newsletter

Summary of Observations of FY 13 NOAFs Addressing Vapor Intrusion   
By: Allen Wyman, LSP, Permanent Environmental Solutions, LLC, and Loss Prevention Committee Chair

The Loss Prevention Committee (LPC) identified 29 MassDEP Audits for FY 2013 in which one or more vapor intrusion violations were noted.  Given the timing of MassDEP guidance and the LPC’s desire that information be timely, Notices of Audit Findings (NOAFs) relative to Opinions completed prior to 2005 were disregarded.  Further, NOAFs resulting from Level II Audits were disregarded.  Level II Audits are often field inspections of active remedial/mitigation systems and/or compliance with AUL obligations and do not focus on the technical adequacies of the Opinion.  Given these specifications, the LPC reviewed 15 Audits of completed Opinions.  Key issues from these NOAFs are noted below along with considerations for minimizing audit risks. 

Insufficient Evidence to Rule Out Site-Related Sources:  At one site, the VOC concentrations in indoor air samples collected in 2013 were greater than the documented 1992 background, 2008 Typical Indoor Air Concentrations (TIACs), and 2011 Threshold Value levels. Yet no additional actions were taken and no evidence was provided to adequately demonstrate that the contaminants were not site related.  At another site the identification of contaminants of concern (such as benzene, TCE, and PCE) in indoor air were attributed to other indoor sources without providing adequate proof.  Further, indoor air contaminants within one building at another site were above Threshold Values, yet were disregarded because the contaminants of concern were not identified in soil or groundwater samples from the site.

Considerations for Minimizing Audit Risks:
If indoor air concentrations are above the Threshold Values then, as stated in the December 2011 Interim Final Vapor Intrusion Guidance (VI Guidance), “…any conclusion that discounts the indoor air measurements should be justified through the use of additional Lines of Evidence that demonstrate that indoor air contamination is not site-related. Such Lines of Evidence may include a comparison of indoor air concentrations to outdoor (ambient) air concentrations to determine whether indoor air concentrations may be resulting from exchange with outdoor air rather than vapor intrusion. The identification of indoor sources of the specific contaminants of concern may also be a relevant Line of Evidence. The removal and/or quantification of such indoor sources would best support their significance in indoor air sampling results. Either of these Lines of Evidence may support the conclusion that contamination is attributable to a non-site-related source.”

Additional evidence might include sub-slab soil gas sampling to assess a possible pathway, or the lack thereof. In the case of contaminants in indoor air but not in groundwater, MassDEP’s VI Guidance recommends that one weigh the adequacy of data such as soil vapor, groundwater, and indoor air results. Even though, in one case, there were no contaminants reported in the groundwater and the indoor air contaminants deemed non-site related, MassDEP believed the lack of soil vapor data was a “significant omission” given the many other variables that influence vapor migration. MassDEP noted that groundwater samples from wells closest to the building were diluted by the laboratory, resulting in analytical detection limits above the Method 1, GW-2 standards for TCE and carbon tetrachloride. Similarly, the analytical detection limits for two soil samples collected nearest to the building “were raised via laboratory dilution to levels 10 times the reportable concentrations. Therefore, it may not be definitively concluded TCE, DCE and other VOCs do not exist in soil or groundwater at the site or that such contaminants are present at levels below Method 1 GW-2 standards.” MassDEP also deemed insufficient the elimination of contaminants of concern without justification or via simply stating they are the result of specific interior sources. Given this, consideration should be given to presenting multiple lines of evidence.

MCP 310 CMR 40.0901(4) states that the characterization of risk of harm to health shall take into consideration guidance published by MassDEP. As seen in these NOAFs, LSPs should take care in doing so. In these cases, either no or insufficient justification was provided for eliminating the contaminants of concern from further consideration. These NOAFs identified MassDEP’s reasoning behind each violation in the context of MassDEP policies in existence at the time the opinions were completed. Based on these NOAFs, LSPs should base their decisions on MassDEP guidance or clearly provide a rationale supporting an alternative approach.

Lack of an AUL to Prevent Certain Uses: At another site, the results of indoor air samples collected in 2012 were less than commercial/industrial limits but greater than residential limits. No AUL was implemented.

Considerations for Minimizing Audit Risks:
If a site is closed when indoor air contaminants are below those allowed under applicable current use (such as industrial), yet above levels allowed under more conservative conditions (such as a residence), an AUL is necessary (1995, Guidance for Disposal Site Risk Characterization, S. 2.1.2). In short, if the risk characterization is dependent upon a specific use or intended use of the property, an AUL must be implemented to prevent the uses that were not considered. If the risk characterization does not consider a residence or daycare, then a deed restriction must be implemented preventing the use of that property as a residence or daycare.

Inadequate Assessment of Vapor Migration Pathway: For several commercial and residential sites, there was a lack of or inadequate technical justification for the absence of indoor air or sub-slab vapor sampling. This occurred at sites where contaminants of concern were noted in monitoring wells at which groundwater was assigned category GW-2. In one case, no indoor air samples were collected in certain residences at the disposal site; the rationale provided was that CVOCs were non-detect in indoor air at other residences at the disposal site where higher groundwater concentrations were reported. In another case indoor air and/or sub-slab vapor samples in one section of a building were not collected based on the results of one round of indoor air testing conducted in an adjacent portion of the structure.

Considerations for Minimizing Audit Risks:
In the NOAF, MassDEP found it inadequate to qualitatively determine that the indoor air at two residences would not be impacted because the indoor air in other buildings in the area (with higher groundwater contaminant levels) were not impacted. MassDEP stated that, given the many variables controlling vapor intrusion (contaminant concentrations in soil and groundwater, soil conditions, building construction, weather conditions, etc.), the potential impact to indoor air should be evaluated separately at each structure.

In another instance, MassDEP found it insufficient to forego sub-slab vapor and/or indoor air sampling in one section of a building (a former dry cleaner) based on the results of indoor air testing in the vacant space next door. In the NOAF, MassDEP pointed toward two issues. One issue was related directly to the vacant space, stating, “Due to the variability associated with this pathway, one round of testing in one section of the building does not adequately characterize indoor air throughout the year, especially during the heating season.” Relative to the former dry cleaner, MassDEP stated, “Due to the high levels of PCE in groundwater along with the lack of sub-slab data, vapor intrusion cannot be ruled out…Indoor air and sub-slab soil gas testing is necessary to determine the extent, if any, of vapor intrusion into [former dry cleaner].”

Inappropriate Use of Averaging: At a couple of sites, the initial sub-slab soil gas sample results were above action levels so additional sub-slab samples were collected several feet away. These new sampling results were averaged with the initial results to achieve a result that was below action levels. This result was then used as justification for avoiding indoor air sampling.

Considerations for Minimizing Audit Risks: For reasons similar to those stated in the violation above, and as MassDEP stated here, “Due to the dynamic nature of vapor migration, which may be subject to seasonal variation and intrusion via preferential migration pathways such as cracks and floor seams, averaging of soil gas samples may underestimate the potential for vapor infiltration into indoor air.” Consideration should be given to discrete sub-slab soil gas sample results in assessing migration, exposure, and risk.

Inadequate Assessment of System Efficacy:  One site was closed based on the results of one round of indoor air samples collected while the active sub-slab depressurization system was running, without the implementation of an AUL.  At other sites with passive sub-slab vapor mitigation systems, no indoor air samples were collected to assess the system efficacy or, in one case, four samples were collected.  However, the highest result (PCE > 6 ug/m3) was in January followed by lower results in the three summer samples.  The winter results were determined to be the result of new construction.  Follow-up samples in the winter, to confirm that opinion, were not collected. 

Considerations for Minimizing Audit Risks:
MassDEP stated that, besides determining the effectiveness of an active system when running, continued operation required “additional indoor air sampling or differential pressure measurements across the basement floor to demonstrate continued system effectiveness in controlling the source of VOCs to indoor air” in accordance with 310 CMR 40.1003(5)(a). The continued post-closure use of an active system to mitigate risk requires the implementation of an AUL and a method for monitoring the effectiveness of the system. Further, 310 CMR 40.0920 requires that such samples represent conservative estimates of exposure. In the case of soil gas intrusion into a building, the highest levels of impact are likely to occur during the winter months while the heating system is running. Collecting the majority of indoor air samples during the summer months is not considered a conservative representation of exposure. Consideration should be given to weighting the importance of indoor air sample events toward winter months.

Likewise, per 310 CMR 40.1025(2) under the new 2014 regulation changes, “Demonstration of the effectiveness of Active Exposure Pathway Mitigation Measure shall be made prior to the achievement of a Permanent Solution with Conditions and shall be based on the measurement of Exposure Point Concentrations representative of exposures for the Receptor(s) of concern during operation of the Active Exposure Pathway Mitigation Measure under normal operating conditions and over a period of time sufficient to account for temporal variability.

Given this, and the violations as noted above, consideration should be given to winter sampling prior to and after the implementation of an active sub-slab depressurization system used to mitigate receptor risks in support of a Permanent Solution.