MassDEP Revisiting TCE Sites

By Denise Kmetzo, DABT, Principal, Collaborative Risk Solutions LLC 

Trichloroethylene (TCE) is a chlorinated volatile organic compound present at many Massachusetts Contingency Plan (MCP) Sites.  In 2013, following a reassessment of TCE toxicity, the Massachusetts Department of Environmental Protection (MassDEP) announced that its research indicated that relatively low concentrations of TCE in indoor air could result in potential Imminent Hazard (IH) conditions.  MassDEP has since provided numerous documents related to indoor air TCE toxicity, assessment, and response actions, which are compiled on its website: http://www.mass.gov/eea/agencies/massdep/toxics/sources/trichloroethylene-tce.html 

As a result of its reassessment of TCE, MassDEP believes that the historically higher TCE GW-2 Standard used to close many sites may not be health-protective of indoor air exposures. The table below illustrates how GW-2 Standards for TCE have decreased over time:   

Date Range

GW-2 Standard

1993 - 2006

300 µg/L

2006 – 2014

30 µg/L

2014 –

5 µg/L

 

MassDEP is concerned that TCE in groundwater at a subset of sites closed with groundwater concentrations approaching the historic standard of 300 µg/L could be impacting indoor air to a degree that could result in an IH. Paul Locke, Assistant Commissioner of MassDEP’s Bureau of Waste Site Cleanup (BWSC), discussed MassDEP’s approach to these sites at the January 28, 2016, BWSC Advisory Committee Meeting, which can be viewed at this link: https://youtu.be/CVhyCx1NYZ8 

Mr. Locke announced that as part of a technical assistance public health effort, MassDEP had reviewed the files for sites with TCE contamination that were closed with an RAO prior to the 2014 changes to the MCP. MassDEP screened over 900 such sites, and prioritized approximately 200 sites with conditions that appeared to warrant some additional TCE investigation.  There was not a specific set of criteria that were applied to each site as a screening tool, but rather information was reviewed on a site-specific basis.  An example of a site prioritized for additional investigation is a site that was closed when the GW-2 Standard was 300 µg/L, at which shallow groundwater was contaminated with TCE at a concentration approaching 300 µg/L near an occupied building, and at which no soil gas or indoor air data was collected to further understand the potential for vapor intrusion. 

Historic GW-2 Standards were established prior to toxicity studies which formed the basis of the current IH thresholds.  How does the historic GW-2 Standard of 300 µg/L relate to an indoor air concentration?  If one uses the vapor intrusion model used by MassDEP to develop the current TCE GW-2 Standard, a groundwater concentration of 300 µg/L predicts an indoor air concentration of 45 µg/m3.  This value is well above the MassDEP IH thresholds of 6 µg/m3 (residential) and 24 µg/m3 (commercial) for pregnant women and those who may become pregnant.  The predicted value is also above the IH indoor air concentration of 20 µg/m3for all receptors under a residential exposure scenario, and the No Significant Risk threshold for typical residential and commercial indoor air exposures. The TCE GW-2 Standard was lowered in 2006 to 30 µg/L, based on an assumed indoor air concentration of 4.5 µg/m3, which is below the current IH threshold for all receptors.  Therefore, while MassDEP did not identify a lower-bound groundwater concentration for its review effort, it is unlikely that a site that met the 30 µg/L GW-2 Standard would be identified as a potential IH condition, unless a preferential pathway for vapors into indoor air (for example, through a sump or stone basement) is present. 

Mr. Locke stressed that MassDEP’s initiative is not an enforcement effort, and that MassDEP is not questioning the Standard of Practice at the time of site closure.  Rather, the effort reflects reassessment due to recent information regarding the potential hazards associated with exposure to TCE in pregnant women.  Mr. Locke stated, “For the record, DEP is not “re-opening closed TCE sites,” which implies revoking or invalidating the previous RAO.  I prefer “reviewing closed TCE sites” to see if the TCE contamination left behind (assumed appropriately left behind) might now be of concern.  This is not commentary on the work of the LSP, but an acknowledgement that new information about a chemical’s toxicity may precipitate additional work.” 

What Happens Next? 

MassDEP has prioritized the roughly 200 sites for further evaluation, and will contact property owners by telephone, followed by written communication.  MassDEP will not send out a mass mailing to all affected property owners, nor will it publish a list of the sites it has chosen for further evaluation.  Rather, property owners will be contacted in order of prioritization, and MassDEP will update the Searchable Sites database with correspondence as it occurs.  The LSP of Record will not be contacted initially; however, should the property owner request that their LSP be notified, then MassDEP may involve an LSP.  Mr. Locke expects that some property owners will opt to oversee additional investigations through their LSP, while others may require MassDEP assistance.  MassDEP expects that property owners will be willing to be accept additional data collection, and that additional groundwater, soil vapor and/or indoor air sampling will be recommended, based on site-specific information and the presence of pre-existing monitoring points. 

Should additional data identify a potential exposure of concern, MassDEP will treat the information like a new condition, and issue a new Release Tracking Number (RTN).  If additional data suggest that IH conditions are present, timely response actions would be triggered. 

Are you curious as to whether you or your client has a historic TCE Site that may be prioritized for further evaluation?  You certainly do not need to wait for a call from MassDEP.  A review of site documentation relative to the current understanding of vapor intrusion and TCE toxicity should help inform you of the potential for exposures of con