The well is being drilled for our geo system.  The design is for a standing column well (800 ft) plus a 10% (2.7 gpm) bleed to support 9 tons of heating load.

Problem: well driller is at 400 ft and can hardly continue due to hitting so much water along the way (100-200 gpm total).  They're talking about drilling another well or possibly adding to the bleed.

Does anyone have any experience with high-yield wells and the impact that has on the capacity of the well.  Can this large yield lessen the depth needed to support the load?  Are we better off drilling another well just to make sure we have enough capacity?  Anything else to take into consideration?

Thanks for any input.

Do you have a good place to dispose of the bleed water? Ie, any concerns about just increasing the bleed to make it a open loop/standing column hybrid or a closed loop/open loop hybrid?

Is the well producing 1-200gpm due to artesian pressure now? Or is the tooling on the drill fouling due to the presance of water? There are different solutions for each of these conditions. Has the driller talked to the system designer about it? They need to confab and come up with a game plan and then present to you.
hope this helps
Eric

One problem with large bleeds or pump/dump is that the state (MA) is really cracking down on these.  If your water fails any of the tests, then you can't dump the water.  Also, I think we'd have to go back to the state and get them to approve such a drastic change.  It took them 3 months to approve the original design.

We have very sandy soil and several acres, so we do have places to put the water if it comes to that.

I don't know the exact problem, but the driller said the pressure was too great to continue.  He said sometimes it eases off as you continue, but after only being able to drill 125' in a day and half, he has called it quits at 425', short of the 800 design.  He said the pressure just wasn't letting up.

The designer is on vacation this week, so I'm not sure what we're doing.  For now they're putting the shroud in this well, and, if the new design calls for it, they'll come back and add another well.

My main reason for asking the question in the first place was to see if anyone knew whether a large yield lessened the length of the column needed to cover the load.  I know the answer is probably a lot more complicated than yes/no, but I'm just looking for more understanding of the underground heat transfer process.

If would seem to me that if you have enough water, it's more like a pond loop.  But with a 6" hole down through these water sources, and the water being put back into the well, how much does new water mix with the old?  Is it very little unless you do a bleed?  I'm sure it depends on whether you are going through tiny pockets of water, or large pools of water.  Are underground aquifers rivers or just tiny cracks in the rocks?

Are there tests they can do to determine the thermal capacity of the well?  I know they can do a drawdown test to determine the gpm, but are there other factors that would point to the well's capacity to replenish the lost heat?  I suppose the best test would be monitoring the system in operation to see what happens?  We do have backup heat that could contribute the difference if it's not keeping up.  So we could try it and add another well later if needed, but I'm not sure if that adds more cost compared to doing it now.

One can do a test by adding or removing heat from the well and watching the effect on temperature - ie, it should support some number of BTU/hr at a given temperature delta. A typical designer may not be set up to do it though.

http://cedb.asce.org/cgi/WWWdisplay.cgi?264459

A pond is quite different in that there is much more water that is completely free to flow (convect).

The groundwater is present primarily in secondary porosity in the form of fractures in the igneous bedrock of MA and not "underground rivers". Flow in the borehole is generally minimal without the stress of some bleed-off or injection. You could test the well via a thermoconductivity test but it is unlikely to support your load as is. MASSDEP has definitely implemented some serious regulations in their new General Permit process: http://www.mass.gov/dep/water/laws/openf.pdf

You may be able to get a driller to come in with a different type of rig and/or tooling capable of dealing with the excess water and deepen your well. Another option to consider is discharging to a sewer/stormwater system as it may then not require the same permitting (only permission from said authority)--which is unfortunate. Still you may be able to modify your current permit to increase the bleed since the amount discharged is actually only a small part of the permit. Managing 2 SCW wells with bleed would be very difficult.

Lastly, you could look to convert to closed loop but it would require additional borehole for sure.

-Adam
Hydrogeologist

We installed our geo unit last spring.  We ran into the same problem.   We needed 10 gpm and 400' depth.  At 349' we had 2 gpm but 50' still to go.

At 350' we had a gyser come up.  The drillers could not continue as the water presure was greater than they could releive.  Our well is producing 150+ gpm.

We ended up puting in a 3" pitless addapter 8' down to releive the pressure, and took the water supply in at the 5' level.  Because we did not want to dump millions of gallons of water on the banking,  I had a 20' x 40'  bottomless concrete tank burried.  The excess water is piped into that tank and it has a 40' level spreader.  This way we leach as much water as possible back into the water table.  The rest that comes out of the level spreader, the banking can absorb it without any trouble.  The good news is I will never run out of water, and have a consant water supply for an irrigation system.  The bad news is the money I was going to use on installing solor panels went into the well.

One of the concerns we had was would the well take back the water we needed to pump back ( open loop system )  I only have a 3 ton unit, so we needed the well to take back 9 gpm.  Our other concern was the well water temp.  This is not an issue as the well pressure is so great any water pumped back into the well doesn't go down.  It is forced back up to the relief valve.  The water temp is a constant 49 degrees.  The well pump ( vari-speed) is sitting down at the 335' level.