To continue with the previous “How Much and How Long Will It Take?” posts, we’ll take a quick look at conducting Vapor intrusion Investigations (VII), and specifically two (2) initial phases of a VII (Building Survey and Sub-Slab Soil Gas Sampling). There is plenty of research, data, and guidance on this topic but let’s simplify it. Generally, a VII is conducted after some preliminary work (Phase I or II ESA, Preliminary Assessment, Groundwater Sampling, etc.) has already been completed at a specific site (or adjacent site), and the investigator “suspects” that harmful vapors emanating from the subsurface soil or groundwater are entering the indoor air of a structure. Skilled practitioners, using a multiple lines of evidence approach, know how to gather the data needed to “properly” assess whether a true issue is present (and if mitigation is needed). So...why conduct a VII and "How much will it cost and how long will it take?"
Start with the why: the purpose of a VII is to evaluate whether volatile chemicals are entering indoor air (or have the potential to enter indoor air). In laypersons speak: Is the air you breathe safe? This is what a properly conducted VII should hopefully answer.
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 structure that is less than 1,500 square feet, is located next to a gasoline station (with leaking USTs), and you’ve already obtained the appropriate access from the property owner (and notified the regulatory agencies-if applicable). Note: If you’re the homeowner, and an environmental professional tells you $500 and it will take 1-week to complete, seriously consider showing them the door within 15 minutes. Conversely, if you’re told that it’ll take 3-months and the costs will exceed $20k, tell them you never liked Cadillacs. Everything takes time and comes at a cost, but keep it simple, work methodically, and commit to the process. A typical approach is outlined as follows:
1. Review all available site data, complete a building survey and evaluate what (background) indoor contaminants may be present. Complete a product inventory (e.g. mothballs, ASTs, cleaning products, candles, etc.). Talk with the homeowner. Look at preferential pathways. Look at building structure, type and age. Slab-on-grade? Basement? Before any samples are even collected, this is the starting point and it needs to be done thoroughly. Don’t skimp here. It’ll cost you later if you do.
2. Identify Sub-Slab Soil Gas Sampling points. The number and locations should be based on professional judgment and in accordance with accepted guidance documents. Assume a minimum of two (2) are needed.
3. Install “temporary” soil gas probes below the slab, conduct appropriate leak testing (e.g. Helium tracer, etc.), and purge the lines. Spend the extra time ensuring a tight seal, and that tracer tests are accurate. It pays off later.
4. Collect sub-slab soil gas samples. In New Jersey, this generally takes about 5-minutes per location using certified-clean, 1-liter Summa Canisters. Collect / record the appropriate data (start and stop times, vacuum pressure, etc.) and submit to a certified Laboratory for (EPA Method TO-15) analysis.
5. 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, and (hopefully) determine if the VI pathway is complete or incomplete with a high degree of confidence.
So, after considering all of the above, a properly conduced VII of this nature will typically take about four (4) weeks, and cost between $3,500 and $5,000. Additional costs should be considered if indoor air and ambient air samples are collected concurrently with sub-slab soil gas samples. In the next post for this VII series, we’ll take a deeper look at the process, the collection of indoor air samples…and how a background contaminant source can throw a pretty good curveball. Stay tuned.
For further information regarding the Vapor Intrusion Investigation process, please don't hesitate to contact us. tfrancis@cardinallsrp.com