This is 30 year old data is from 10 wells in Maine measured over 3 weeks showing a variability of about 1/2 to double over 3 weeks. Of course this is Maine.
Your results are a lot greater. Getting a precise water sample takes a precise method for sure. In my last research I used a hose connection at the indoor well tank faucet routed into a 5 gallon bucket. I set volume low on the hose and when the there was enough water in the bottom of the bucket I placed hose into the sample vial under water and then capped it under water. Then repeated with a second vial. I got good precision between the two samples. But you said you also had good duplicate precision so that would indicate your method is good.

1 3,090 1,420 117%
2 21,200 12,400 71%
3 43,600 24,900 75%
4 66,400 18,900 251%
5 85,000 69,238 23%
6 99,200 40,781 143%
7 125,000 95,549 31%
8 128,000 107,196 19%
9 164,000 125,603 31%
10 1,080,000 758,760 42%

The last part of this post is the conclusion of my ground based exhaust study.

What I learned from reviewing all the original research done in early 1990's was the basis for exhausting above the roof occurred because Arthur Scott who I truly respected screwed up on his 1st EPA project of mitigating 40 homes in Pennsylvania. He aimed almost all the 40 system exhaust directly to the side of the building and half of the buildings failed the post mitigation radon test. The extremely high house he did direct away from the house passed the post test. Arthur corrected all those badly exhausted systems by mostly venting above the roof and EPA made the decision all systems needed to be vented above the roof. I got ahold of Bruce Henschel, the lead scientist who published the original EPA mitigation guides, and he told me his studies including a final wind tunnel test came to the conclusion that ground based system exhaust would work but by the time he finished his work the EPA had already set above roof venting as a requirement.

Although my study was on a single home the multiple CRM measurements for over two months confirmed that as long as the exhaust is straight out from the house as Bruce Henschel advised 30 years ago it is highly unlikely to raise the radon levels indoor. This is because of three factors.
1) There is no significant radon increase around the exhaust port, only in the air stream in front of the exhaust.
2) The area around the exhaust port is a very small fraction of the entire perimeter of a home.
3) If the wind blows the radon back towards the house, the dilution of the wind dramatically reduces the radon concentration.

Obviously some guidance needs to be included of how and where systems can be vented towards which the Canadian guidance goes not include. And further research is as always a good idea.

Here is the conclusion of my study. The entire study is on my website and due to be included in AARST papers this year after final review.

The results of the study indicate that radon system exhaust of about 234 pCi/l ( 8658 Bq/m3) vented at-grade directly away from the house produced on average radon levels around the exhaust location that never averaged greater than 1.5 pCi/l (74 Bq/m3) above the ambient radon levels. The average radon level beside the exhaust for the study was 0.5 pCi/l (18 Bq/m3) above ambient. When you consider that this portion of the exterior rim joist (about 1 meter) has slightly elevated radon as compared to the entire perimeter it appears from this study it is extremely unlikely that at-grade radon system exhaust could raise the indoor radon levels even if the exhaust concentration was four times or more higher. During the study no elevated indoor radon was measured that could be attributed to system exhaust except when a window directly above the exhaust was left open for four days with the system airflow of 40 CFM. During the open window test the indoor radon levels at the window was 0.4 pCi/l ( 15 Bq/m3) higher than another CRM twenty feet away. Lower exhaust rates did produce a higher though insignificant radon level to the side of the exhaust. Exhaust flow rates less than 20 CFM were not tested. Further studies should be considered with a building with significantly higher radon exhaust in combination with low flow rates and significant openings into the building during periods of strong stack effect.

Although the radon levels to the side of the exhaust were very low there was significantly elevated radon levels at one meter in direct line with the exhaust of about 7% to 16% of the exhaust concentration. The average at 2 meters dropped to less than 5% and at 3 meters to less than 2% and at four meters less than 1% of the exhaust concentration. One meter away at a 45 degree angle the concentration was less than 2.5% of the exhaust concentration. At 2 meters at a 45 degree angle it was less than 2% and at 3 meters at a 45 degree angle it was less than 1% of the exhaust concentration. This study indicates the location of grade level exhaust should not be direct towards any occupied location within 3 to 4 meters of the exhaust outlet in a area that is less than 45 degrees angled from the exhaust direction.

Thanks for all the comments Colin. It is obvious that the world needs to be more science based and at the same time open to new ideas. I have a tendency to test ideas and concepts myself to confirm or disprove their value or truth. Straight line discharge can send measurable but certainly dramatically reduced radon 20 feet from a adischarge as per my study in 2020. What was apparent in the study was very little radon accumulated around the discharge location which explains why Canadian side wall discharge works or at least appears to cause little or no re-entrainment.
Here is the link to the test which AARST will hopefully publish after some final reviews.

https://www.wpb-radon.com/At_Grade_Radon_Exhaust.html

Your diagnostics and careful sealing allowing 20 watt fans to work so well is a great example of measuring pfe post mitigation. The 1st step in my mind to getting to this place is to require mitigators to make post system PFE measurements. This is a tremendous way to make obvious you have over sized the fan or you need to do more thorough sealing or add more suction pits. You may have fixed a dozen homes in a development using the same fan but without checking the PFE it's more than likely they are either oversized if you also followed the guidance to seal the slab perimeter.

When my crews would come back from a job or jobs I always wanted to see what was the sub slab pressure, where did they take it and what was the u tube reading.
They would also regularly make PFE measurements before sealing using a test fan. They quickly learned that sealing even tiny perimeter cracks caused the far test hole to be 10 times stronger and sealing was a critical component not something to skip and use a larger fan to compensate.

Bill

Jeff. When you click the link it shows the entire state.
Are the only areas of concern the black outlined boxes with the green to red coloring? The rest of the state has no

Hi Henry
A common problem with post mitigation elevated radon is trying to locate a source when radon levels are only slightly above the guideline. Because the building is broken into individual rooms multiple CRM testing might be a good next stage. If you can spare 4 CRM's I would locate them in each of the main rooms for at least a day. To reduce the cost of that I have been working with one company Ecosense to develop a package of four radon monitors for the typical price of one CRM that you might consider getting. The package is called Ecotrackers and has four of the home style Radon Eye's that have been modified to go up to 255 pCi/l and can be programmed for 5 minute averages to use in sniffer mode or hourly averages to use as regular CRM's. Getting comparative measurements at the same time might clue you to which area is causing the elevation as all four units display their data on your phone at the same time using bluetooth. Or the home owner can also capture the data and email it to you if you leave the units for multiple days. Of course then you have to figure out why one area is higher. If the foundation walls are indeed poured then that usually rules them out as a source. Sometimes there are hidden abandoned utility pipes behind finished walls that have tripped me up for months until we found them because one room was higher radon than another. Good Hunting to you. Bill

Ryan asked about running a fan to reduce RDP without I assume changing the unattached fraction which I did not measure in this paper. I would think air agitation might actually cause more RDP to attach to air borne particles.

But the basic result of testing air movement and RDP levels or more relevant the Equilibrium ratio is fans as simple as a casablanca can reduce risk by reducing RDPs but the reduction in this case as we are not including filtration happens only where the air is being agitated .

So a good thing is a casablanca over your bed where you spend 8 hours a day. Here is the link to the tests I did to demonstrate that.

https://www.wpb-radon.com/pdf/RDP%20&%20Ventilation%20changes%2005.pdf

This is a complicated discussion because of all the variables which is likely the primary reason EPA does not recommend filtration for radon risk reduction. We have a slide in our training course that states radon decay products RDP are 20 times more deadly the radon atoms. So reducing the RDP seems like it would be the most prudent approach. I have measured very low WL (less than 5% equilibrium ratio) in an office building that had an air circulation rate of 5 to 10 times per hour. The health risk of radon in that building was very low even though the radon levels were above guidance levels. I did not measure unattached fraction so I can't factor in that affect. Filters on air handlers will also capture a percentage of the unattached but certainly not as efficiently as air borne particles and water molecules that the filter captures. The health risk from the unattached fraction has been stated by others to be 5 to 30 times more deadly than the attached fraction. If the breathable air has less particles the unattached fraction will rise. I would occasionally joke in my class that if you wanted to reduce your risk from radon,
smoke a cigar in your house and the unattached fraction will be greatly reduced.

So if the WL is reduced in half but the unattached fraction doubles than the health risk may not be reduced. The other compounding factor is the size of the particles and the thoroughness of the filtration. A stand alone air filter may be very effective if it is blowing filter air towards you but it may have very little effect on the other side of the room even though it may be reducing the number of particles in the air. All of these variables and the complicated cost to actually measure WL or even more so the unattached fraction lead the EPA to not recommend filtration as a radon risk reduction method.

As to the comment on using charcoal to gather radon it was tried years ago by a company that filtered air through a large carbon filter and then back flushed the carbon to the outside to try and remove the collected radon atoms. It could not capture enough radon and RDP to emit any significant amount of gamma and it was not able to back flush out the radon efficiently so it turned out to be impractical and expensive to operate.

Doug. Thanks for the reference. I don't think many people saw my 10 minuted allotted time at the last virtual radon conference about measuring ground based exhaust as the Canadians are allowed to do. When I looked into the research that both methods were based on I realized our exhaust at the roof requirement was based on research done in PA 30 years ago that was partially or primarily due to ground exhaust vented parallel to the siding. This lead to my extensive crm measurements of ground based exhaust at one house last summer. Being self funded research and requiring complete homeowner cooperation it of course had to be my own house so it is a one house study. Included is the link to the overview of the research and there is a link to the full paper on the web page.

https://www.wpb-radon.com/At_Grade_Radon_Exhaust.html

Yesterday a Consortium meeting included 18 people on the call for 2 hours. It is an amazing group willing to dedicate their valuable time often multiple times a month. After other issues were hashed about, time was given to discuss alarms and freeze ups one more time. Major parts of meetings have taken up this subject in the past so this is not a new subject or issue. Any radon company that has been in business for years knows of cases where homeowners were not aware their radon fans were dead for months if not years and they certainly know customers who have no idea how to read a u tube. This issue is of course nation wide.

After much discussion with Jesse Green and his consulting with a representative from one heat tape company that makes a product called FrostGuard to unfreeze gutters it appears to me that one solution for areas of frigid weather is to install a double box at all outside fan locations that includes a fan switch and a weatherproof outlet.

A heat tape could then be easily installed at the time of installation or at a later date. The heat tape could be given as an option on a contract for additional cost or included as standard equipment. Of course installed later would be an extra cost depending upon if the pipe is frozen but having offered it as an option on the original contract releaves responsibility for installing it for free.

The heat cable is available in different lengths and is 1/2" by 1/4". Tape incudes a 6 foot lead to a plug. A 3/4" hole could be drilled in the pipe above the fan. A fish cable could pull the tape to the top of the pipe where it is secured and looped down to give extra heat at the exhaust. The hole would sealed with silicone caulking. Replacing a worn out tape is straightforward assuming weather is above sub zero.

The tape uses 4 watts a foot at 65 degrees and 9 watts a foot at 0 degrees. The home owner has the option to unplug the tape to save electric cost. If the pipe does freeze solid I have no idea how long it would take to unfreeze a pipe already frozen once the tape is energized.

I think ithe issue is whether a company in a frigid climate is willing to add the expense of an outlet at the fan as standard equipment. This could be marketed as feature of your system that other companies don't provide. The heat cable then becomes a billable option installed during the installation or at a later date.

The same option could apply for fans in attics however insulating the pipe and fan in the attic assuming the pipe runs are short would be an option if an insulated roof pipe flashing is used. Heat tape used in the attic would likely be less expensive to install and the shortest length available would reduce electric cost.

Bill

When you get a tough one you can spend a month going back to a house multiple times trying to fine tune your existing system and or expand its reach when the main source is something overlooked like a pipe leading to soil. I had a house fail several years later after it initially passed. One finished room was slightly higher and one of the paneled walls seemed to also be higher. I finally removed the paneling and there was the old sewer pipe leading to the old septic field in the back yard. The owner then told me he had city sewer installed a few years ago. The guy who redid the plumbing and the guy who installed the paneling never bothered to stick a tennis ball or rag in the old sewer line! I don't know why it didn't smell.
One shot of expanding foam and system was fixed. It only took me 2 months to figure that out.

Mike Kitto mentioned thoron. Sime CRMs are sensitive to thoron and will include a percentage of the ambient thoron as radon. The Radon Eye RD200 has the shortest open path at the bottom to its chamber and thus includes a high percentage of thoron as radon in its result. If you use an RD200 for flux you must cover the open slots on the RD200 with poly tape. Thus reduces thoron response to about 5% but does not change the hour by hour radon result.

Randy
For the homeowner wanting to know the average radon level airthings and safety siren are fine. But for diagnostic measurements the Radon Eye RE200 is a great tool for mitigators and costs about the same. The RE200 sees 30 cph/pci/l. Compare that to the wave having about 1 cph/pci/l. Its sensitivity is so high it can give the 1st radon result in 13 minutes after plugging in and a new result every 10 minutes. The 1st result is about 75% of the actual level. In 33 minutes it is very close to actual level. You can buy 4 rd200s for less than than the cheapest professional monitor. On Amazon buy a few usb 5 volt to 12 volt dc 5.5mm plug cables. They are cheap. Now you can use any cell phone powerbank battery to make rd200 portable for 10 hours or more.
When you have a problem house. Put the 4 rd200s in all the suspect locations. 15 minutes later you have 4 simultanous results to compare. Only downside where I live is they only read to 100 pci/l so you blow them out at houses i work on.

If you leave them at the house you get hr by hr radon once downloaded to you phone.

Randy.
You can now purchase cheap gamma meters. Buy one and place it in the middle of the radios. They are slow to respond but will give a reading. If there is an elevatrd reading find a radio with highest gamma and test the flux.

Flux measurement with charcoal might give you a yes or no answer on the tile. You need two. One exposed on a cardboard box and one under double layers of 6 mil poly that is taped to the tile floor.
A much better method is to purchase a radon eye and a large metal mixing bowl. Seal radon eye under the metal bowl with poly tape. Leave on the floor for 24 hrs. You can also put a radio on the tile floor with radon eye and seal poly over it.

Bigger and bigger fans to fix problem houses is a rampant misconception among mitigators especially those who dont own or use a micromonometer. Of course there are cases where higher airflow is needed because sealing can't be done or soil is too porous. A micromonometer is your most critical instrument. We have to teach mitigators over and over, for gods sake please buy a micromonometer. With it you can measure the edge of the pressure field which is -0.001" or -0.1 Pa. I would guess each fan change you made changed u tube 20% greater. That means your previous vacuum readings are now -0.0012" or -0.12 Pa. That ain't much change.

What does work is adding another suction where micromonometer says there is no vacuum. That is always a better choice than the clueless mitigator simply installing a bigger fan and hoping it works.

My suspicion is your elevated readings are from a slab that butts up to the basement like a garage, front porch or family room slab. These adjoining slabs are often trapping radon that is bleeding into the basement.

The committee works for hours addressing issues of bad systems or problems like dead fans that owners have no clue about. When a new standard requirement to address these issues is written it may take the manufacturers and installers some time to find the best solutions but to demand the rule be removed because your systems are not functioning for a week or a month is not convincing and certainly not acceptable for the rest of the entire country. The alternate of having a radon monitor if it could be permanently part of the system is a definite consideration. The other is to talk to manufacturers about what would work better. I have been consulting with a manufacturer who will have different alarms available this spring including a battery one with a 4 day delay and a silent button as well as a plug in alarm that has a built in digital gauge that replaces the utube. Obviously solutions like insulated pipe or alarms with digital pressure gauges add system cost. I always tried to market these extra costs as examples of how my company did higher quality work than my competitors either as standard equipment or customer options if they were upgrades.

Andrew. As much as would like to think we don't have a bias, we all have them. You certainly have a bias as a mitigator and I have one as an instructor. Carolyn's point about a diverse mix in a consensus group is the exact reason it is this way to balance out these bias positions. When you spend time on these committees we all learn that we need to make concessions to our bias and do our best to work out solution for the majority if not the entire group.

From a point of view of reducing long term exposure which is what we are about, the inexpensive CRMs are truthfully the best choice as Doug has pointed out but that brings up the issue with long term reliability. Will these crms still be reasonably good indicators of elevated radon in 10 years? I have seen lots of u-tubes become stuck in their setting from dirt or bugs after 10 or 15 years but in general they do ok. The newest crms are only cell phone accessed so when the house gets sold there goes the crm. We would certainly consider the option of a crm that has a display that is permanently attached to a radon system. The issues with longevity with both alarms and crms does need to be considered.

Question: Has anyone had experience with homeowner crms drifting higher or lower over the years. I would assume the radon levels are low enough that their background counts don't grow significantly but I dont know that.

These are the outdoor magnehelics if no one has seen them before.
Radonaway sells the larger for about $78 plus you need the box and tubing. The other is a smaller mini-helic. Obar Systems in NJ sells this one for about $50 but it includes the mounting box and the tubing.
Remember that any clear or white tubing will degrade in sunlight. You need to use black tubing outdoors. The minihelic includes black tubing with the package.

100% outdoor piping and fan does present a problem and this would certainly be an issue with the alarm requirement. What we have done as a company is the following. For all commercial jobs and schools or in developments where there is a maintenance staff that must monitor the fans we always install the weatherproof 6X6 box with a magnehelic gauge outside. These types of installations typically include a fan cover both for appearance, protection from tampering and reduction in fan noise. The gauge gets installed above the cover and the vacuum tubing has minimal exposure to sunlight degradation. The material cost for this gauge is $100 but is easily included in the system cost when it is explained to the client the ease of checking the system operation from the outside. And it is a professional looking installation.
For typical residential installations our company like others has to be competitive. We however never install a u-tube outside. I do not agree with manufacturers selling outdoor accessories that implying a u-tube can be installed outside. All U-tube oil in sunlight changes to clear color and is very difficult to read plus bugs and water. Our alternative has been to install the u-tube and label inside on the drywall and route tubing to the outside piping below the fan. Obviously you have to consult with the owner where this is acceptable. This typically means we are deciding on the fan location based on where the u-tube can be acceptably installed indoors. With slab on grade systems you typically have lots of latitude as to where the actual suction hole can be installed.
For the alarm requirement the same design would need to be done that routes tubing from outside piping to the inside alarm and then split to the u-tube. We purchased black tubing for the outside because it is more sunlight resistant. Inside we transition to clear tubing for appearance.
I hope this helps.

Thanks everyone for relaying all these real life situations with long term system maintenance. It is clarifying the issues that I will present to the committee. I can completely understand the issues with audible alarms. Fortunately there are new alarms coming to the market. One manufacturer I recently spoke with is scheduled to have a plug in and a separate battery alarm in January that can be programed by the installer to have light and sound or just light. So there will be several choices for installers. The issue with homeowners not able to understand what the u-tube is or realize his fan is dead is very real. Homeowners we called to replace a dead fan often had no idea where the fan was. As an industry we need to address this. A blinking red light plus the u-tube may be the best option for a typical homeowner.

I assume that the battery alarm would be easier to install and thus a 1st choice for mitigators. However in reviewing the specifications for one model it listed the battery life as only 48 hours when the alarm was activated. This does not bode well for long term system operation. The standards committee should definitely consider these issues again.

I would also like to point out to this group that the different standard committee conference calls to review multiple issues are often 2 hours long with as many as 15 people on the call and literally calls are sometimes scheduled every 2 weeks. This is an incredible donation of time and effort to advance the quality of our entire industry. Committee members donation of their time needs to be recognized.

One last request.
I'm working on a research paper investigating ground based radon system exhaust dispersion and re-entrainment. If any of our good Canadian neighbors or US mitigators has had a radon system that appeared to re-entrain radon back into the house I would love to know the details. My direct email is wmbrodheadatgmaildotcom

As a standards committee member I have been involved in the discussions on both sides of the alarm issue. For myself the over riding reason for alarms is what I have seen and I'm sure every radon contractor has seen. When we go to replace a fan, we often notice there is a fan on the house next door and that fan is dead. We all know homeowners don't do the recommended re-test every two years. We also know that homeowners often have no idea what a u-tube is doing especially if they are new owners of a house with a radon system installed. If the auto industry had oil gauges instead of low oil warning lights there would be a lot of cars with blown engines. The average home owner needs at least a flashing light if the fan is dead and we need the oil gauge to determine how the fan is performing.

Every area of the country has different issues they must deal with when installing radon systems from the clay in Kansas soils to the Karst soil in Tennessee to the sand under the slabs in Florida and of course the freezing pipes in the North mid-west states. What would be really helpful for everyone on this list serve is to discuss solutions to each issue they face such as the outdoor gauges that were discussed in this string. By the way at Home Depot they sell a 6X6 electrical box that works nicely as a waterproof box to install a magnehelic gauge in using a 4.5 inch hole saw to cut a hole in the lid.

What I would love to know both for my mitigation class and for the Standards committee is what design features have any mitigators found that reduces pipe closures due to ice formation and what system designs increase the potential for ice freeze up.

1) Does foam core schedule pipe minimize freeze up?
2) Is freeze up more likely with 3" pipe or 4" pipe?
3) Have you observed more freeze with high flow (small u-tube difference) or low flow (large u-tube difference?

Bill