To continue with our Vapor Intrusion Investigation (VII) series, let’s do a quick comparison of two common leak-detection tests: Helium vs. Isopropyl Alcohol (IPA).  Short disclaimer: 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 “exterior” soil gas samples, and the debate is whether to conduct our “field” leak detection using helium (with a shroud, and He meters, etc.) or to just use IPA.  Conducting leak detection test in the field are often viewed as time consuming and not worth the effort, with the purpose to just to check the box on some regulatory Vapor Intrusion Guidance document.  Technicians want to get in and get out and not be hindered by some unimportant QA/QC methods…hurry, hurry, hurry.  But wait.  There’s value to being methodical, and doing a thorough job in the field and this needs to be stressed to new field team members…and even veteran technicians!  Now onto the comparison.

 Start with the why: Leakage in the soil gas sampling train (e.g. loose fittings, improper seals around sampling points, etc.) will draw in background compounds or contaminants and essentially generate results that are not “representative” of actual conditions. Hence the need to perform some measure of leak detection testing.

 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 conducting a proper leak test. They’ll also know which tests to avoid!

 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 is a vacant lot, is located next to a gasoline station (with leaking USTs), three (3) soil gas sampling points will be installed, target depths are roughly ten (10) below grade, and our driller or Geoprobe® costs (with supplies) are the same.

1.  Isopropyl Alcohol (IPA)Tracer- Leak Detection:

a.   Additional supplies: $25 +/-

b.   Additional field time (per Soil Gas Sampling Point): 5 minutes +/-  (15 minutes total)

1.  Helium Tracer- Leak Detection:

a.    Additional supplies: $200 +/-

b.   Additional field time (per Soil Gas Sampling Point): 15-30 minutes +/- (45-90 minutes total)

Overall, that’s not too much difference, right?  A few extra dollars for the Helium set-up and a little extra time; however, if you’re seeing leaks in the sampling train, and/or the bentonite you used to seal everything isn’t setting up quickly, then you need to add more valuable time to the process.  Time is money, but it pays to be methodical. Check your fittings, seals, helium meter, etc.   Here’s why:

1. The soil gas data when using a “properly” conducted helium tracer /leak detection produced results that (when thoroughly reviewed) appear representative.  An ambient air sample, collected concurrently with your soil gas samples, picked up numerous “common” compounds that are typical for your site’s location…none of which were detected in the soil gas which targeted a depth ten (10) feet below grade.  This is positive news as the data can be relied upon to make future decisions, especially if mitigation is warranted. 

Conversely; 

Assume that the few extra dollars for the helium set-up and likely extra time to conduct the leak detection test isn’t worth the effort (or in the budget), so you opt to use Isopropyl Alcohol.  It’s faster, easier, cheaper, and you know what you’re doing, so leaks shouldn’t be an issue. Faster and cheaper is always better, correct?  Let’s take a look at a potential outcome:

1. The soil gas data when using IPA as a tracer / leak detection method produced inconsistent results.  The TO-15 analysis displayed fairly high levels of IPA in the soil gas samples, and detections were also identified in that ambient air sample (which wasn’t surprising).  In addition, a few of the common ambient (or outside air) compounds were picked up in the soil gas analysis. But how can that be?  Everything looked good in the sampling train: all the fittings were tight (and not overtightened), the bentonite seals appeared okay, however, after reviewing the available data, too many discrepancies were identified and the levels of IPA were indicative of leakage “somewhere.”  The resultant decision was to repeat the sampling, which (as one could imagine) was a difficult discussion with the client.  Additional costs to re-sample including laboratory, driller, and labor costs:  $3,000-$4,500.   

The process identified above will typically take about one (1) day to complete in the field (using temporary probes) with the laboratory analysis being approximately (two) weeks.  The challenge is whether or not the sampling team and/or environmental professional is willing to budget a few hundred extra dollars to conduct a leak detection test using helium, and allot an extra hour or two to complete it effectively.  The risk of using IPA may be too significant if leaks are detected, and it’s too late to correct the issue. Now the cost and time to conduct a soil gas sampling program could double.  No client wants to hear that you have to re-do something on their dime, so when given a choice, opt to use a helium leak detection test or similar “field” test where leaks or other issues associated with a soil gas sampling event can be corrected prior to submitted samples to the laboratory.   

In future posts for this VII series, we’ll take a look at some common background contaminants, mitigation options, and 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