As a follow-up to our first Vapor Intrusion Investigation (VII) post, let’s take a quick look at the collection of Indoor Air (IA) samples. As discussed previously, there is plenty of research, data, and guidance on this topic but let’s simplify it. For this post, lets’ assume that Sub-Slab Soil Gas samples were already collected, and the laboratory has provided data. This is why hiring that skilled practitioner was a good idea…as they’ll know if the data obtained is representative, if it’s garbage, and how to effectively interpret what the results “mean.” *Demonstrating if there is a connection to that gas station next door is like connecting the dots, but hopefully the environmental professional you hire understands that that connector line may be crooked, diagonal, blocked, under water, in fractured bedrock…you get the picture (and maybe not as simple as you’d like).

For example: The station next door leaked gasoline into the groundwater, so the primary compounds to be on the lookout for would include Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX). There are some others that would likely turn up, but let’s focus on the primary players. To “connect the dots” or to evaluate the “pathway,” look to see if your Sub-Slab Soil Gas samples have detections of those BTEX compounds. If they do, and the results are above a regulatory screening level, you potentially need to go to the next step and collect Indoor Air samples. Your client won’t be thrilled, but let’s answer their question…“How much will it cost and how much longer will it take?”

Start with the why: Compounds were detected in Sub-Slab Soil Gas samples and the collection of Indoor air samples are necessary to assess if the vapor intrusion pathway is complete or incomplete. In laypersons speak: Gasoline vapors were identified below that basement slab, and you need to make sure they’re not getting into the house.

How much and how long will it take? Every Site is different, so let’s keep it simple again and assume that the Site in question contains a small house, is located next to that gasoline station (with leaking USTs), and you’ve already obtained the appropriate access from the property owner (and notified the regulatory agencies-if applicable). A typical approach is outlined as follows:

Review all available Sub-Slab Soil Gas data, and compare it to the product inventory collected during the initial walk-though (hopefully the investigator didn’t cut that initial corner). If those samples were collected properly, you probably shouldn’t see 1, 4 Dichlorobenzene (typically found in mothballs) in your results. If you see large detections of typical “Common Household” contaminants in your results, there was probably some leakage in the Sub-Slab Soil Gas sampling train (e.g. loose fittings, improper seal around sampling point, etc.). At that point, the investigator should decide if re-sampling is necessary. Don’t go to the next step (and collect Indoor Air samples) and don’t waste your clients’ time and money, if you can’t justify that your data is representative.
Assuming that all prior data is “useable,” Indoor Air sampling points should be identified. The number and locations should be based on professional judgment and in accordance with accepted guidance documents. Assume one (1) sample is needed from the basement, and one (1) from the first floor. Tip: Try to place the sample canisters in areas where they won’t be disturbed or knocked over.
Identify Ambient Air Sampling points. (This is a control sample to see if outside or ambient conditions are contributing to the quality of the indoor conditions.). Assume one (1) sample is needed and make sure you check the weather forecast.
Set-up and collect Indoor/Ambient Air samples (EPA Method TO-15). In most states, this generally takes about 24-hours for each, using certified-clean, 6-liter Summa Canisters. Collect / record the appropriate data (start and stop times, vacuum pressure, weather conditions, etc.) and submit to a certified Laboratory. Tip: Be extremely thorough and methodical; pre-arrange sample pick-up times with your client / homeowner in advance as you’ll need to return to the property the next day; don’t overtighten the Summa Canister regulators…that would be bad.
Assuming that standard analytical turnaround times are used, the data should be received in about two (2) weeks, at which time the investigator can review and compare the data to the appropriate screening levels.

So, after considering all of the above, the process identified above will typically take about three (3) to four (4) weeks and cost between $3,000 and $4,000. Additional costs should be considered if an Immediate Environmental Concern (IEC) is identified. In the next post for this VII series, we’ll dissect the data review component, as future mitigation (if necessary) will rely on it. Stay tuned.

For further information regarding the Vapor Intrusion Investigation process, please don't hesitate to contact us. tfrancis@cardinallsrp.com