Conducting Critical Checks: Leak Check & Shut-In Check
These checks are the wildcards of the sampling process and should be addressed. Sampling vapor is different as you can’t see what you are sampling: An established operating procedure goes a long way to getting consistent data.
When done correctly and documented, the data user can have confidence in the reported results. When not performed or performed incorrectly without documentation, data quality can suffer. In an effort to assist in performing these checks, Alpha Analytical has created detailed demonstration videos on performing these Data Quality checks.
Helium Leak Check Procedure
The Helium Leak check procedure was first proposed in early guidance documents and published as an ASTM standard. Helium being a gas and that it is not detected in Method TO-15 makes it the perfect choice as indicator parameter. Other leak indicator compounds were proposed their common drawback is: If there is a leak, they can significantly impact the reported data.
The main challenge in the field using Helium is that it is relatively expensive to set up. It’s complicated to run. If done well, it provides confidence in sample integrity. Watch this video for detailed instructions on running a Helium Shroud test.
Water Dam Sub-Slab Sampling
An alternate method to check the integrity of this seal was developed using water to show a tight surface seal. “Water Dam”. If water is maintained around the surface seal during sampling, gas is not going to pass into the subsurface, to dilute the vapor sample causing a negative bias. Water Dam is not applicable in all situations. However, works well for sub-slab sampling where the slab is in good condition.
The water dam procedure is referenced in a number of guidance documents. View the video below for detailed steps for conducting water dam sub-slab sampling.
As always, contact me, Will Elcoate, with your questions at 800-624-9220 or email airtesting@alphalab.com.
