Infiltration and Geothermal Wells

[Yakman256]

Hey Guys

I have a project for a local college and they want to be as green as possible. They want to construct a new building but they want to infiltrate as much runoff as possible so I'm picking up the runoff from the building and a rather large area surrounding the building for infiltration and as a result, a rather large seepage bed (100' x 200' x 2.5' deep) has been designed in an area outside any tree disturbance. The campus is mostly wooded between the existing buildings and they are insistent that no trees be disturbed as a result of this project.

I'm currently ready to submit for final plan approval and the Architect has just recently indicated that the new building will require a geothermal well system. There is no where in close proximity to the new building where a well system could be installed without removing lots of trees. The architect wants to put the Geothermal system under the seepage bed. I told him that was a bad idea but aside from some possible compaction from the drilling equipment, I can any other reason no to do it.

Here's the question... Can anyone think of a reason not to allow a geothermal system under a seepage bed? I think its a bad idea but I'm not sure why.

Thanks

 

[oldestguy]

There are common rules in most areas that drinking water wells have to be more than "X" distance from waste disposal facilities, such as leaching fields. In this case how does anyone know that the wells might be used some day for drinking water and how does anyone know that the seepage fields won't be contaminated some how. There may already be some State rules about any well location no matter what the use.

 

[GeoPaveTraffic]

If you are doing a deep well geothermal system, I don't see any problems with having the well located in the same area as your infiltration field. I would located it on the edge closest to the building to reduce the potential for disturbing the field in the event of future maintenance.

Mike Lambert

 

[gbam]

Better consult the Water Resources Department for Aquifer protection requirements. At first, I would presume that you could contaminate the aquifer if your seepage area can enter into the well.

 

[Yakman256]

There is no danger of pollution of the aquifer. The college is serviced by public water and there is not any downstream water intake. There is a stream running just downhill of the project that is already impaired due to urban runoff.

My thought was that there has to be some maintenance associated with the geo-thermal system but I don't know if the actual wells would be affected.

 

[itdepends]

If it's a deep well geothermal system you're more likely to contaminate the aquifer with the water you're recirculating through the well then contaminate it with the infiltration field. How far down are you going to have to drill to get to your thermal source? Any idea how many wells are going to be put in? Any fracturing of the bed/hot rocks required?

I've only had a passing contact with this field- but I hope the architect isn't designing your geothermal well system.

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"

 

[Yakman256]

I'm unsure of the depth of the wells on this particular project at this time, but I have had wells on some of other projects in the area that have all been 400-500 feet deep and I'm assuming this system will be similar with 48 wells spaced at 15' o.c. Not sure about rock fracturing at this time. The geothermal system is usually designed by a mechanical contractor and the size and configuration will change a couple times before we get to the final design if things go like they have been in the past.

I asked if they could somehow install the geothermal wells around the existing trees and the answer was no, although I suspect they never consulted the mechanical contractor. I also asked if they could install the well system within the adjacent existing parking lot and the answer was also no.

I've floated the idea past the the Reviewing engineer to see what he says. If he says no then they'll have no other choice other than to have the system redesigned.

 

[beej67]

I thought geothermal wells were a closed loop. Are they not? If they're a closed loop, then what's the problem?

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[boo1]

They are typically closed loop.
Most commonly will be multi wells or trench and bury depending system design and size.

 

[racookpe1978]

If everything worked perfectly and never leaked or broke, you would not need safeguards or restraints or ponds or runoff protection.

The "pure water" in heat exchanger "closed loops" is not drinking water, but is almost always treated to reduce oxygen, salts, corrosion products, etc.