bluebiplane
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| 10/23/2009 12:13 PM |
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| My small town is drafting an alternative energy ordinance. Town's sole water supply is from a single source fractured rock aquifer. Wellhead protection zone encompasses town boundaries.
Are there any known concerns in the groundwater protection community (or other knowledgeable/professional entity) regarding groundwater/aquifer contamination via boreholes from vertical or diagonal (plastic pipe or DX copper) closed-loop geothermal systems?
Recommend any groundwater organizations to contact with same question?
Thanks in advance. |
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GTFLOWCENTER
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| 10/23/2009 12:52 PM |
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| In Iowa they do not allow methanol in vertical boreholes. You could check NGWA-national ground water association and also IHPA-Iowa Heat Pump Association. |
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waterpirate
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| 10/23/2009 2:59 PM |
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Typically what we run into is no drilling for any purpose within a well head protection zone. That being said other places allow drilling within the well head protection zone if the drilling stays above the source aquifer. I.E. municipal water producing zone is from 160 to 240, all loops terminate at 150.
The controversy surrounding copper pipe and dx applications is a mixed bag, some allow it some do not.
My personal and proffesional feeling is that the well head protection zone must be enforced for the greater good. I have had to tell more than one customer that if they could just move their project outside of the protection zone I would be happy to drill. |
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Eric Sackett
WeberWellDrilling.com |
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engineer
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| 10/23/2009 9:16 PM |
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That could be overkill. I grant that it is vital to protect potable groundwater, but geo provides a substantial benefit to the overall environment at minimal risk to groundwater. I'd want to be sure that the proposed protection zone is reasonable. Is all land within town borders a reasonable zone or merely the overcautious thinking of a small-minded, turf-guarding bureaucrat?
Is it sensible to sacrifice a technology providing substantial environmental benefit at the altar of a very minor risk?
Somewhere I read that geo discharge water is regarded as a "Class 5" no/ low risk discharge that basically ought to be allowed to be reinjected without restriction. That refers to open loop. There is always a small risk that some refrigerant and compressor oil and some other contaminants related to compressor failure would mix with groundwater if a heat exchanger failed. How big of a risk would that pose?
In the case of closed loop, a coax heat exchanger failure would introduce the above-listed contaminates into the loopfield and increase its pressure. My off-the cuff guess is that the pressure increase would not be sufficient to rupture the loopfield underground, so aquifer contamination would not occur. The system would fail and need substantial service, but the nasties would be removed above ground.
The foregoing is theory - does anyone have experience or data concerning a coax failure dumping a unit's refrigerant charge into the loopfield? |
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Without data, you only have an opinion. |
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waterpirate
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| 10/24/2009 5:06 AM |
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| You hit the nail on the head! Everyone wants to see some data, and there does not seem to be any yet. The drilling short loops example I gave had a specific thought in mind. It was to prevent salt water migration down to the fresh water bearing unit. A big risk to take with just grout, that does not play well with salt water. |
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Eric Sackett
WeberWellDrilling.com |
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Glen W
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| 11/10/2009 1:52 AM |
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| I guess I am luckily that our town gets its water from twenty miles away as our upper aquifer is already depleted, and the lower aquifer is at 1000 feet. Years ago when we were in aquaculture water was pumped from the lower aquifer and flood irrigated the crops which replenished the upper aquifer. Now they inject treated sewage into the aquifer. |
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joe.ami
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| 11/10/2009 6:28 AM |
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Posted By Glen W on 11/10/2009 1:52 AM
Now they inject treated sewage into the aquifer.
Yum....what could possibly go wrong there? I can see where millions of gallons of treatedd sewerage would be way more pallatable than a few gallons of methanol if something went wrong......
j |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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Down2Earth Geothermal
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| 11/11/2009 9:35 PM |
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The primary governing organization is USEPA which really hasn't had much to say to date. Their only open comment on DX is that the amount of oil contained is not appreciably more than in unregulated air-source heat pumps and that the refrigerants pose the same minimal environmental risk. They also have no Federal Maximum contaminant Levels (MCL) for Methanol since it quickly degrades in air, soil, and water (http://www.epa.gov/chemfact/f_methan.txt) Professionally, I believe that the real concern is ensuring that the boreholes are properly grouted for closed-loop geothermal installations--especially in aquifer protection areas.
Locally, Penn State has recently wrestled with this issue as the entire campus is within their groundwater protection zone and is underlain by a karst highly-transmissive, fractured carbonate aquifer. The result--rather than banning all drilling, is a permitting process that examines each request case by case and provides oversight to any drilling activities (including closed-loop geothermal borings). Their policy can be seen online under Section 33.22.00 at www.opp.psu.edu/planning-construction/design_and_construction_standards/division-33-utilities
-Adam
Hydrogeologist |
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Alex_in_FL
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| 11/13/2009 9:55 PM |
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The biggest danger is contamination from the boreholes not being grouted near the surface. Concerns about the methanol should be minor as it is readily biodegraded by bacteria. That said, propylene glycol is absolutely safe (it is a food additive) so if they might consider requiring this antifreeze - however it is more expensive.
Alex
Registered Environmental Manager
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