Hmmm. I have a couple of university degrees. I assure you that any schmoe can get one. Or three.

How did you avoid the indoctrination?

Or did you?

It was a long time ago. In NJ. We Jersey guys have tougher minds and are more skeptical than most. Long live Chris Christie.

I assure you that any schmoe can get one. Or three.

That can be true. I guess it depends on which university you are talking about.

Rutgers. Rutgers College. Where the smart kids that can't afford Princeton go.

Probably not a good comparison. Princeton admissions rates run less than 10% while Rutgers is over 50%. Besides, "smart kids" go anywhere they want on scholarship. Although, I will agree that when you dig deeper down in the barrel it's more likely to find schools and programs that "any schmoe" can get through.

Not sure how it's organized now, but when I was there, Rutgers University was comprised of a number of "Colleges". For instance, Livingston College was for the athletes, Cook was the agricultural school, Douglas was the women's College, Rutgers College was the more elite Liberal Arts and Sciences College. But I think Ren's about to get p-o'ed at me again for hijacking the thread, so I'd best end here. Cheers!

Posted By Clark on 08 May 2010 12:05 AM
I installed the fan on the radon vent pipe running from the Form-A-Drain under the basement floor through the roof. After running the fan for 3 days, the radon dropped from 7 pCi/l to 1.5 pCi/l. Anything < 4 pCi/l is considered acceptable. I'm going to experiment to find what fan duty cycle is needed to maintain a safe radon level.

Many websites that discuss active sub-slab depressurization radon mitigation systems say to always leave the fan on.  No explanation given, but I suppose that one must maintain sub-slab depressurization to minimize the seepage of radon gas into the house.  Once inside, the gas is hard to get rid of.   My measured basement radon level with a passive radon stack was 7 pCi/L.  It dropped to 1.5 with a 167 CFM @ 0" WC 80 watt fan running continuously through a 4" vertical stack.  At 50% duty cycle (12 hours on, 12 hours off) the radon level increased to 5.0 pCi/L.  When I replaced the fan with a 134 CFM @ 0" WC which consumes 75% less electric energy (< 20 watts), the radon level dropped to 2.5 pCi/L when running continuously.

The lesson for me as relates operational cost:  Use the smallest fan that gets the radon level down to an acceptable level.  The question is:  Can one determine the required fan size a priori?

Technically, any radon level increases your cancer risk. So lower is always better (except for the energy usage). The better you can seal the under slab area, the less CFM you need.

so true about the need to seal under slab, especially in high radon areas. The Barrier works excellent for this as it has a 6 mil poly built in with self seaming taped edges as well as an insulator. To read more see www.barrett-inc.com/barrier.php

Not that this can help an existing building, but for those that are building in Radon Prone areas it may be a helpful product.


EnkaVent 6128 Radon Ventalation Mat:
http://www.colbond-usa.com/building-roofing-application/67-colbond-applications/building-roofing-applications-cat/radon-control-applications.html

All the technical data, etc is on the right side of the page.

I agree with jonr concerning the "safe" radon levels. I think that the incidence of lung cancer is thought to be roughly linear with radon concentration, so you should not think of 4 pC/l as a safe level, but rather low enough to pose acceptable risk, and a level usually achievable with adequate ventilation. Certainly the lower the better.

Is this Old Thread Revival Week?

An HRV or ERV system running at a reasonable duty cycle would do as much for mitigating risk at running a slab depressurization blower at similar power use, and a greater net benefit. If you don't have HRV/ERV, spending the money there makes more sense than going straight to slab depressurization. Even though it's somewhat more money, it provide far better overall health benefits.

Except that a reasonably well sealed slab needs far less blower power. Once radon is mixed in with the house air, you need to move many more CFM to get the same effect.

With the HRV it's more cfm, but at much lower impedance, not necessarily less overall power use. Retrofit sealing of the slab is always step #1 (which is I'm sure covered somewhere in the 6 pages of old thread, as is the HRV recommendations, etc.)

On the subject of radon sealing: http://www.aarst.org/proceedings/2010/03_EXPERIMENTAL_DETERMINATION_OF_THE_EFFECTIVENESS_OF_RADON_BARRIERS.pdf

If the slab is reasonably air tight, the bulk of the radon getting through the slab is via diffusion. Since a radon atom is somewhat bigger than a water molecule, it's a similar kind of vapor-pressure times area problem, and sub-slab depressurization has little effect on the diffusion unless it can pull dilution-air from the outdoors through the slab.

Posted By Dana1 on 24 Oct 2012 04:32 PM
...snip...
If the slab is reasonably air tight, the bulk of the radon getting through the slab is via diffusion. Since a radon atom is somewhat bigger than a water molecule, it's a similar kind of vapor-pressure times area problem, and sub-slab depressurization has little effect on the diffusion unless it can pull dilution-air from the outdoors through the slab.

I have a different impression of airflow using a radon remediation system fan. Rather than the main source of airflow being flow from the house through the slab, into the collection piping and then through the fan, I think of the air permeability of the soil as a significant source (http://www.hse.niordc.ir/uploads/86_106_Binder5.pdf). Our soil here is sand and rock, and I assume this soil has a high air permeability. Clay should be less when it is wet, but clay can open up large (compared to the interstitial spacing between soil particles) cracks when it is dry.

If the soil were not somewhat gas permeable, then radon would not be a problem in the first place.

Water molecules and mono-atomic gases like radon have a very small cross section compared to the di-atomic major components of air (N2 & O2).

Air-impermeable stone is often quite water & radon permeable- granite is a HUGE source of radon problems in homes.

Posted By Dana1 on 25 Oct 2012 02:52 PM
Water molecules and mono-atomic gases like radon have a very small cross section compared to the di-atomic major components of air (N2 & O2).

Air-impermeable stone is often quite water & radon permeable- granite is a HUGE source of radon problems in homes.

Radon does not have a very small cross section compared to nitrogen (N2) and oxygen (O2). From the CRC Handbook of Chemistry and Physics, the atomic and molecular diameters as determined from van der Waal's equation are: N2, 3.15 Angstroms; O2, 2.92 Angstroms; and Xe 4.02 Angstroms. Xenon is the largest atom listed, and it has a molecular weight of 131 compared to 226 for radon. Because of their relative placement on the periodic table, radon must have a larger cross section than xenon (http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Atomic-Sizes-911.html). Compare strontium to xenon in this reference, and note that radon is two levels further down the periodic table than strontium, has a molecular weight 2.6 times that of strontium, and therefore, is much larger.

So if a large atom like radon is diffusing through the soil to reach the slab, then air is even more easily diffusing through the soil. Therefore, some of the gas flowing through the radon remediation fan is likely flowing from the outside air and through the soil under the basement.

I stand corrected! (Knew I should have looked it up...) Thanks for taking the time!

Radon is only one row down the periodic from strontium, not two, and strontium is well to the left of in the row, radon on the far right, and as your reference states " Note how these radii decrease across and increase down the periodic table." For the lighter elements it would appear that row trumps column position for mono-atomic, but not covalent radii. In the case of strontium vs xenon, we only have a covalent radius for strontium- it's not a relevant means of estimating what the mono-atomic cross section radon might be, but yes, it's pretty clear mono-atomic radon gas will have a somewhat larger cross section that mono-atomic xenon, being one row down in the same column, and the molecular diameter of O2 is about the same as that of xenon, so yeah, radon is bigger than an O2 molecule (who knew? :-) )

The notion of "air tight" soil or stone different from "air permeable" at the molecular level. We tend to think of concrete as being air tight from a macroscopic air-barrier point of view, yet it's porous, and permeable to air. I doubt there is such a thing as an air-impermeable clay that is dramatically less permeable than granite, a known major source of radon. Liquid water is air & radon permeable too, which is why a high water table doesn't protect you from radon, nor would wet clay.

But most soil is indeed highly air-permeable, and yes the remediation fan is sucking outdoor air (and some indoor air), diluting the sub-slab radon concentration and changing the direction of air diffusion through the slab.