As a continuation of our Vapor Intrusion Investigation (VII) series, it is vital to understand the residence / structure you are investigating prior to the collection of Indoor Air (IA) samples, and more importantly what may be stored and/or used by the occupants. For this, post we’ll take a quick look at a common household contaminant that could show up in your analysis…and leave the investigator scratching their head.  (As always, there is plenty of research, data, and guidance on this topic but the objective of this series is to simplify the discussion using typical and “hypothetical” scenarios).  

For this post, our objective is the collection of IA samples, and to identify whether a connection (or complete VI pathway) exists to the reported tetrachloroethylene (“PCE”) groundwater contamination nearby. The potential fears associated with the results of IA sampling include reduced property value and the impact on your kids’ health, so it’s understandable that some (if not most) homeowners are reluctant to follow-through, and allow such a test.  This is where experienced professionals usually excel…as they are typically able to effectively communicate and provide the sampling rationale with occupants, and conduct a thorough indoor air quality survey (or questionnaire) to identify potential background contaminants.    

Similar to prior posts, most technicians want to get in and get out, set up the required sampling canister, and not be hindered by having to complete a survey and inventory every potential indoor air contaminant. This can be time consuming, but there’s always value to being methodical.  

Start with the why: A poorly conducted indoor air survey will inhibit an investigator’s ability to assess whether sample results are “representative” of actual vapor intrusion conditions, or merely the result of background compounds or contaminants. As we’ve stressed in prior posts, this is why hiring that skilled practitioner is a good idea…as they’ll understand the value in spending the extra time completing a survey and product inventory, and also communicating with the occupant(s).    

Correlation of Results: Upon completion of a “properly” conducted IA sampling event, which included the collection of an ambient (outside) air sample, basement, first floor and second floor sample, numerous compounds were detected in the (EPA Method) TO-15 analyses including PCE.  PCE is the primary contaminant of concern in this scenario and was identified above action levels in a nearby groundwater monitoring well, and from a subsurface soil-gas sample collected in the basement.  With this information, it’s then up to the investigator to evaluate if the VII pathway is “complete.”  A quick look at the PCE data revealed the following:

• MW-1 (groundwater): 75(ug/L)
• Sub-Slab Soil Gas: 620 (ug/m3)
• Basement-Indoor Air: 0.6 (ug/m3)
• First Floor-Indoor Air: 10.2 (ug/m3)
• Second Floor-Indoor Air: 7.6 (ug/m3)
• Ambient (outside) Air: Not Detected.

The groundwater and sub-slab soil gas results displayed fairly high levels of PCE (which are likely above state action levels), but the indoor air results tell a different story. The expected highest concentrations of PCE would have been in the basement, not the first or second floors.  The first floor result is also potentially above an indoor air screening level.  At this point the experienced investigator would have to refer back to the completed building survey and product inventory to determine what potential background sources were present, and if the occupants followed the instructions that were provided (e.g. use of fireplaces, air fresheners, cleaning products, etc.).  IF the survey and inventory was completed properly, and IF the occupants were forthright, the answers will come quickly and potential follow-up activities and decisions (including any regulatory reporting) could be completed without delay.

For this scenario, no recent dry cleaned clothes were brought to the residence, no individuals worked at facilities where PCE may be used (and inadvertently brought home), and no interior cleaning products were used. However, the occupants indicated that they didn’t use air fresheners; but they frequently used various types of scented candles on both floors AND mistakenly used a scented candle on the first floor at the time of the sampling event.  Unbeknownst to some, scented candles may contain several organic compounds including (but not limited to) PCE, Formaldehyde, Acetaldehyde, Naphthalene, and Polycyclic Aromatic Hydrocarbons (PAHs).  Based on this information, and also due to elevated levels of Formaldehyde in the IA analyses, the logical conclusion in this scenario was to attribute the indoor PCE concentrations to the background contaminant, and not the nearby groundwater contamination.  More importantly, the Vapor Intrusion pathway was deemed incomplete, and mitigation was not unwarranted (using the state’s regulations and guidelines). 

Although mitigation is not warranted, staying abreast of remedial activities in the neighborhood, and the actions of responsible parties, would be advisable based on the contaminant concentrations in the groundwater and the sub-slab soil gas.  Re-testing may also be recommended if any changes occur in the residence that could complete the VI pathway (e.g. installation of a sump pit, french drain, etc.).  Additionally (and unofficially), providing some literature to the occupants on the long-term use of candles (and other indoor air contaminants including mothballs, nail polish, etc.) may also be a nice gesture!

In future posts for this VII series, we’ll take a look at some mitigation options, and elaborate on “effective communication techniques” with homeowners.  Stay tuned.  

We hope that you find these posts informative, and relatively useful, and your feedback is always welcome. For further information regarding the Vapor Intrusion Investigation process, please don't hesitate to contact us. tfrancis@cardinallsrp.com