Hello Mr. Shepard –
As you know, concrete is not exactly the impervious material the casual homeowner would envision. The ordours associated with microbial activity are volatile gases, and not surprising, behave like gases. In much the same way that radon (a gas) enters a structure, all other soil gases will similarly enter the structure – there is no filter mechanism that selectively permits some gases but excludes others.
In one particular case, I was called in to find a strong and offensive “musty” odour in an hospital. The hospital administration had spent THOUSANDS of dollars trying to solve their “mould problem.” I arrived on site and using only my nose as my scientific detector quickly tracked the odour down to a main air supply line and thence to the handler. The supply fan was housed in the basement at the corner of the exterior foundation wall and drew air from the outside intake mounted on the roof. The pressure drop in the upstream side of the fan was something on the order of 1in WC. The concrete walls of the of the basement had normal hairline cracks. The negative pressure induced in the fan housing was sufficient to draw soil gas from the surrounding soils through the cracks. I identified the odour coming through the cracks … so that begged the question, what was the source of the odours in the soils?
I inspected the outside and found that approximately two meters from the foundation wall was a leaking steam line buried perhaps 90 cm. The soils surrounding the steam leak were awash with a prolific and impressive collection of microfauna and microflora all producing a soup of volatile compounds that were traveling through the porous soils into the fan housing, where the odours were being efficiently throughout the building.
Recommendation: Fix the steam leak.
My bill to fix the “mould problem:” About $275
Samples collected: Zero
Instruments needed: None
Time on scene: About 90 minutes
Lesson: Stick to the established: A source, a pathway, a susceptible recipient.
Caoimhín P. Connell
Forensic Industrial Hygienist
(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)