Radon fan pulls water into sump pit

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  #1  
Old 01-22-10, 11:39 AM
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Radon fan pulls water into sump pit

Hopefully, this is the right forum for this.

I have a sump pit in one corner of my basement and a french drain system (black, corrugated piping with slits all the way around) with two pipes emptying into the sump pit. The house was new in 1999 and I had a radon system added in 2003 for which a 4-inch diameter hole was drilled into the sump lid and the lid was sealed. My sump pump has run constantly since the house was built. I am on my third pump already.

Last week, I noticed that when I turned the radon fan switch off, water stopped entering into the pit. The fact that water wasn't running into the pit is kind of odd in my case because in the past I've noticed water emptying into the pit 5 days after it last rained. Anyway, the sump pumps empties out of the house and into a pipe in the ground and theoretically into the sewer system. The water that enters the pit is very clear. I don't know if that is normal or not. But, I just tested this again last night (several days after I diagnosed the issue originally) as it hasn't rained for at least a week. When I turn the radon fan off, no water enters the pit. When I turn it on, it starts emptying into the pit at a pretty good rate (equivalent to a running faucet). To diagnose that it was coming in from the french drain pipes, I opened a small hole in the lid and put a mirror down there so as to not affect the suction of the fan much, but it was definitely entering from the french drain pipes. The more of the hole I covered up, the faster the water came in.

Other info:

The neighbor to the left of my house says his pump never runs but said the neighbor on the other side of him said his runs a lot.

There is an easement between my house and the house next to me (the one whose pump never runs). There is an open field behind my house with a sewer grate in the field to collect rainwater into the sewer system. I noticed some of the dirt around this has washed away so perhaps that is leaking.

When the guy installed the radon system, he put a little u-shaped, red-liquid filled meter on the pipe which measures the level of suction and noted that it was pretty high. Maybe that is due to the level of water in the french drain pipes. It has consistently stayed at about level 6 if that means anything to anyone.

Anyway, any input as to how I could find out why so much water enters my pit and why the radon fan pulls in water consistently would be appreciated.
 
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Old 01-22-10, 12:03 PM
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I have to be quick, but a couple of thoughts. When you turn off the radon fan, the system has been draining under that pressure and would take some time to recover. So leave the fan off for awhile to see if the water resumes flowing. Radon is not a deadly poison and if you left the fan off for a month you would be fine. Besides, radon does not flow through water and it soulds like you have more water than radon.

Next, have them install a much smaller radon fan. They can twest the levels, but my guess is you don't need as much pressure. In any case, the system needs to be re-engineered. I'll be back.

Bud
 
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Old 01-22-10, 03:46 PM
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Hi I'm Back, Not really a pro at this, but do have an interest. When the system was installed, do you remember the before and after readings for radon?

Your concern is that the vacuum from the radon fan is pulling water into the sump pit. If my memory is correct, that little u shaped tube with the red liquid is telling you the vacuum. The difference between the tall leg and the short leg on the u tube is the reading. If the difference is 1/2" then that is a static pressure (vacuum) of 1/2" water column. That's very low, but essentially would lift the water below your house something much less than 1/2". You can suck on a straw and pull the liquid up 1/2", but apply that same suction to the surface of a pond and you won't lift all of that water very much and the water under your home is essentially a small pond.

My guess will be, if you turn the system off, the next day you will see the same amount of water. That would simply indicate a high water table.

Conduct that test, then follow up with having the radon tested again, especially if you don't have before and after readings from the install.

Bud
 
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Old 01-23-10, 09:51 PM
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Thanks for the reply Bud. I appreciate your interest and help.

My radon reading in the basement before the radon system was installed was 18.4. It was 12 on the first and second floors. It was around 1 or so in the basement after the system was installed but I don't remember the exact number.

I shut the radon fan and pump off for about 12 hours today. When I turned the fan off, the flow stopped. I didn't hear any water for a few minutes so I left it off. I stopped back later tonight and didn't open the lid to check. I didn't hear water so I turned the fan back on and still didn't hear water. I had the sump pump unplugged so when I plugged it back in, it started pumping immediately and soon I heard water flowing back in. So, even though I didn't visually check the water flow, it must have leveled off once the sump pit filled to the level of the water table which is why I didn't hear water until the pump started pumping again and lowered the level of water in the pit.

When I turn the fan off, it stops, but I guess this test proves that the water did eventually start flowing back in since we didn't have any rain today. I guess the radon fan is raising the water table slightly?

The radon pressure gauge is at 0 when the fan is off. When on, the gauge reads at 5.5 to 6 which I measured to be about 13/16 to 7/8 of an inch above 0.

I'm still not sure why I have such a high water table. I bought a chlorine testing kit at Home Depot and am going to test the water in the pit to see if it has chlorine in it which would indicate some sort of water main leak. I am guessing it is just ground water but I saw someone suggest this test in another thread and thought it was worth running.

Is water that enters a sump pit generally clear? (Mine is)
 
  #5  
Old 01-24-10, 06:39 AM
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Surface water may be cloudy, but once it filters through a few feet of soil it will generally be clear.

I'm not sure how your u tube is set up, but the difference between the top of the short column and the tall column represents the lift pressure in inches of water column. I'm still not sure what the reading is, you indicate 7/8" above zero, but I don't know what zero is, or a scale reading of 5.5 or 6. But in either case it is contributing to the suction that brings water into your sump.

Surface drainage, testing for chlorine, gutters and leaders, and other water drainage issues should be revisited. I would also want to re-test the radon and see if a passive ventilation system will do the job. But that's me.

Is the landscaping around your property such that the basement floor level slopes to daylight somewhere. Often times a basement becomes a hole in the ground where all of the surrounding water gravitates. Simply giving it an outlet eliminates the problem. I'm guessing of course, so you sort it out.

Your test seems to indicate a high water table, so the radon pump is not entirely to blame.

Bud
 
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Old 02-08-10, 06:45 PM
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Hi,

I just stumbled across your post and agree with Bud and all assumptions made about the water table issue being high. The radon fan is just providing the extra nudge needed to pull it in to the sump, which really isn't a problem.

Your manometer reading indicates a properly sized radon fan for a drain tile system, if your device is similar to those commonly found with radon mitigation systems. Downsizing the fan probably wouldn't not be advisable with your high initial readings.

Val
 
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