I have two problems, perhaps partly related.
Most serious is that the injection well was overflowing by the end of winter. Normal static level is about 25 feet down casing with about 8 foot rise when both units are running. When it overflowed I could see that there were a lot of bubbles, more than a pot at full boil.
My pump rate is 21 USgpm.
The bubbles were caused by pressure reducing valves (PRV's) that were installed downstream of each unit. When I cranked the PRV's wide open the bubbles stopped and then came back when I reset the PRV's. I did this several times and definitely isolated the bubbles to the PRV's.
I was told that the PRV's were necessary because the installers adjusted the flow rate through each unit to limit the leaving water temp to 38 degrees F so that there would be no risk of freezing the exchangers. This seems exactly incorrect to me since slowing down the flow would allow the unit to draw more heat from each gallon of water and thus reduce the leaving water temp. To prevent freezing you should speed up the flow so each gallon gives up less heat and the leaving water temp would be higher.
The bubbles air locked the well, at least part of the problem was solved by installing a pump down the injection well and pumping out for a while. Then going back to the main house pump in injection mode. A lot or air was discharged, quite violently, from the well. A few cycles of this and I solved most of the problem - the mound up is 2 or 3 feet higher than last summer.
I don't know if the remainder of the capacity loss is more air in the formation that I can't get out or possibly calcium or iron precititation partially plugging the limestone formation. I acid treated these wells after they were installed and that really increased the capacity so I can always do that again.
The wells are both open holes in limestone formations, no screens at all. Sometimes I get a small amount of sand plugging the filter in the basement but not much - about a tablespoon of sand once every 3 to 6 months. When I get the sand I just run the main pump on high to a pipe to the river for a few hours and the sand goes away for a few months. I may have to borrow a larger pump so I can over-pump the well to get rid of more of the sand. It's not the main problem anyway.
My biggest problem is iron bacteria infection. I have been getting red slime on the filter to the extent that I have to clean it every 2 to 4 weeks. I have also learned that the bubbles could have caused both iron and calcium to precipitate out of solution. The water tested high for calcium hardness and maxed the iron bacteria colony counts.
I have researched well disinfection both from local experts and internet googling. I learned that the infection usually comes back. I figure that is because the methods used for domestic water wells are not adequate, or more accurately not enough, for geothermal open-loops. Since we have been pumping for a year now the bacteria has been spread through the limestone formation between the wells. Testing shows a 4-inch drop at one well when pumping the other well and discharging to ground. This is a good dis- connection from the point of view of geothermal heating or cooling but any connection at all will lead to spreading the infection. So I figure that the reason the infections always return may be that you have to disinfect the whole flow path between the wells to get all of the bacteria. If you just disinfect each well then as soon as you go back to normal operation you will suck the bacteria that were out of range of the chlorine into the system and you are back at square one.
I am thinking of siphoning chlorine into the discharge pipe in the injection well for two weeks or so. This should get chlorine into the flow path between the wells and hopefully solve the problem once and for all. My concern is that I calculate the chlorine ampount as over $1500 for just 50 to 100 ppm, more for the higher concentrations.
Has anyone done any well disinfection? If so, was it successful and, if so, what did you do?