The baseline testing should include a range of water quality and microbiological parameters - especially with an open loop sysem.  The potential problems are not just because of corrosion, but also oxidation of dissolved minerals and potential for bacteria regrowth.  For geothermal systems - open loop we conduct the following

Field

pH, CO2, sulfur gas, conductivity,  oxidation- reducation potential and TDS - You can purchase relatively inexpansive test kits or probes.

Lab

pH, conductivity, alkalinity, iron, manganse, acidity, corrosion by-products, chloride, sulfate, total coliform, nuisance bacteria, standard plate count, sodium, potassium, and we calculate saturation index and other indices at multiple temperatures. 

Thanks

Brian Oram
http://www.water-research.net

tags: water quality, open loop systems, bacterial growth, slime coatings, chemical films

Great thread, timely discussion.  I'm experiencing similar reluctance to open-loop geothermal in my area.  It seems that the fear of the unknown is what's driving contractor's decisions to "not recommend" open-loops.  Potential poor water quality, low flow rates and a hesitancy to extract high volumes of water from the aquifer are the reasons I'm hearing.  Even when presented with water quality reports (including LSI index), contractors continue to fear scaling and equipment failure. 

On the other hand, there are numerous threads on this site pertaining to loop failures.  These failures are very involved, confusing, yet extremely fascinating due to the complexity of the malfunctions.

It seems to me that if you understand the limitations of the open-loop system (water quality and well volume), and do your research, an open-loop system would be embraced by the geo community as a great option. 

For those of you who have open-loop systems but have covered your backsides during construction and prepared for a closed-loop system, could you elaborate on what specific steps you took (both on the well-side and the mechanical side)?  Is a 6" open-loop well easily converted to a closed-loop well?

Thanks to all who have added to this discussion.

Dan

My sole hedge was to provide an extra 4" conduit beneath the slap to accommodate an extra loop line