Are tree roots clogging my well?

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Jefo

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The well was drilled in 2014. Very little water was encountered until the depth was past 800'. All at once, around 840 feet, the bit cracked into a water bearing fissure in the granite, and the compressed air was bringing up 200 gallons per minute - the driller almost got stuck in the mud. Static level was around 120 feet. The driller installed a high lift pump: 7.5 HP 18 gpm over 700' down. In addition to the static level and drawdown, water was lifted into the tanks 260' in elevation above the wellhead.

The motor failed in 2018, and replaced under warranty. I determined that the pump had been running in upthrust condition (excessive water flow). The new pump was a 4" Franklin "High Capacity" 45 gpm model, installed 550 feet down. I was a little disappointed that it took over 4 hours to fill the tanks (6200 gallons total). Based upon the performance specs of the pump, allowing for friction losses etc. the pumping level was 290', indicating a drawdown of 170'.

Two years later, the owner had a different installer replace the pump with a 35 gpm pump, because the production of the 45 gpm model had fallen off to only 12 gpm. To avoid the possibility of the higher lift pump sucking air, it was installed at 710 feet. That pump started out again pumping around 24 gpm, which indicated that drawdown had increased to 460'. Production of the well continued to decline. Earlier this year it was noted that it now took 8 hours to fill the tanks with no irrigation going on. The water table had slightly lowered - measured at 150'. Performance data of the pump indicates that the pumping level was now 660, indicating that the drawdown had increased to 510' with only half as much flow as two years ago.

The pump quit a month or so ago, and I was again hired to pull it up. I found that a splice failed due to excessive chafing against the tight 4" liner. I also found two large masses of roots. Each tightly woven mass of fine roots was the shape of the inside of the 4" liner (cylindrical), and 3 feet long. The first one encountered was 40 feet down, and the other was around 100 feet deeper. There is a large oak tree 50' away, but I am familiar with oak tree roots, and these are not oak. I believe, since there are 4 large Blue Gum (Eucalyptus) trees within 40 feet - the largest - over 80 feet tall is 20 feet from well, that it is eucalyptus roots I am looking at.

The pump finally emerged after pulling 710 feet of pipe. There are no signs of roots, or anything else, on the intake screen. I understand that the 4" thinwall PVC liner was installed solid down past 800 feet, with the bottom several pipe sections perforated by slitting with a Skilsaw before being glued together at the belled ends and lowered. There was no gravel added outside the liner. The 8" PVC well casing ends at the top of the bedrock, about 35 feet down, I am told.

Here is my question. Since the well production, expressed in terms of gallons per minute per 100 feet of drawdown, based upon my own measurements, the ranch foreman's reports, and pump specs; is less than 20% of what it was 4 years ago, and even then it was less than 60% of what the driller's report indicated that it should be, it is obvious that the slits in the liner are being gradually clogged or blocked. It it likely, or even possible, that Eucalyptus roots are reaching 800 feet down and interfering with water flow into the liner? Or would it be a buildup of sand in the absence of a gravel pack? Should I inject compressed air under 300 psi to the bottom (900' down) and see what blows out (and expect the owner to pay for the experiment)? Or should I recommend that the eucalyptus be felled, stumps removed, and reinstall the pump with a new motor and cross my fingers?
 

Reach4

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My search engine search says that eucalyptus roots are shallow. That does not make it true.
 

TJanak

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You would not have eucalyptus roots 800' deep. I do not believe the tree can build enough tension via transpiration to lift water that high, even with capillary action, adhesion, etc. working in it's favor. So it has no reason to send roots that deep. 40' is believable and 140' would be impressive, but nature often impresses us.
 
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