I'm a first time poster, so please be gentle! I live right between the intracoastal waterway and the ocean in Central Florida and the distance between the two is only 1/3d of a mile. A couple of years ago, I installed a 3 ton geo unit in my house, using open loop, roughly 15 feet down, returning to the same depth. It has been working great. Since then, I got all my licenses and started a small business, GeoFlow. This last weekend I got a call from a coastal dweller in St.Augustine, with a very small piece of land, right next to a tidal river. The simplest solution would seem to be a shallow pair of wells to basically tap off the surficial water, which could easily go saline sometimes. It seems we're terribly afraid of salt water, but why? Ocean going boats use cupro-nickel heat exchangers to cool their engines. Is there any reason we can't just dig wells near the beach and enjoy the limitless supply of water? This is a very important question for me... because of where I live. So please give me considered opinions and sources. Many thanks Greenie
You can also look into stainless and/or titanium heat exchangers. Often what makes the most sense is the use a secondary isolation plate heat exchanger. You do have to be careful in pumping saltwater from coastal wells since infiltrating freshwater floats on saltwater according to the Ghyben-Herzberg equation. Pumping too much of either can move the interface inland which is why permitting can be a sticky issue in many coastal localities. -Adam Hydrogeologist
I would design the system to use salt water from the start, not deplete the fresh water due to pumping volume and get salt water later. Not at all familiar with your aquifers, but the way it works in my kneck of the woods is that the aquifers near the interface zone salt out at medium depths of the unconfined zone with fresh water "floating on the top". We currently have a large private club running on saltwater using fhp cupranickel that is 6 plus years old. we designed it that way from the beginning but still learned a lot we did not. If you choose to go down this road I wil share what we learned to help limit your warranty service. Eric
Thanks Eric and Adam Thank you both for your replies. I realize that the amount of surface fresh water is limited... but if you are putting back the same amount you take out, I don't really see any danger of depleting it... except in a very small radius around the supply well. The depression will presumably be filled by the mound over the return injection well. There is no evidence of any change in water in my home system over two years, and I'm only 100 feet from saline water, sucking from 14 feet below the surface. All that being said, I'm very interested in learning about your club which has been using salt water for 6 years successfully. To plan for that possibility seems like a really good idea. Once again, I'm REALLY grateful for your help. Robin Thomas robin@geoflowonline.com
Adam can better express the effects of relieving the pressuren in a fresh water aquifer allowing the intrusion of saltwater, which can not be reversed once it occurs. Project was a yact club, bay front approximately 60 yards from high tide line surrounded on 3 sides by tidal water. We drilled 2 eight inch supply wells and four 6inch return wells all to a depth of 60 feet. The supply wells produced in excess of 500gpm each, a result that was not anticipated. Projection was for around 150gpm each. All the wells yielded water that tested the same as the bay in regard to salinity. Pumping equipment used were franklin electric variable speed pumps 2 each producing 80gpm at 50psi. The lion share of the isues post install were on the hvac side. The use of poor quality materials in close proximity to salt air and water failed almost immediately. Odd galvonic corrosion was present around unit fittings and flow mwters. The most insiduous problem no one saw comming was the erosive effect of pumping water with that high of a salinity, it proved to be very abrasive to fittings. A program to replace the plumbing fittings with that abrasion in mind was undertaken in month 14 of operation. Changing 90 L's to two 45's ect. After all that was worked out it was smooth sailing with the exception of the locations frquency of lightning strikes which knock out control boxes for pumps. Electricians are still working to solve this riddle. The pumps used were also standard not special enviroment pumps. Hope this helps Eric
Thanks very much for your encouraging reply, Eric. It seems as though by sticking to HDPE hardware as much as possible, the worst pitfalls can be avoided. Were some of the failure points inside the heat exchanger? I hope to hear more from Adam about the potential depletion of the fresh water layer. Many Thanks again Robin
The only thing not effected by the salinity and electrolisis issues were the heat exchangers themselves. A true testament to cupranickele. Eric
